Water Words Glossary

A-HORIZON—The uppermost zone in the Soil Profile, from which soluble Salts and Colloids are leached, and in which organic matter has accumulated. Generally this represents the most fertile soil layer. Along with the B-Horizon, this layer constitutes part of the Zone of Eluviation.

A POSTERIORI CLASSIFICATION—A classification made based upon the results of experimentation.

A PRIORI CLASSIFICATION—A classification made prior to experimentation.

ABANDONED WATER RIGHT—A water right which has not been put to Beneficial Use for generally five or more years, in which the owner of the water right states that the water right will not be used, or takes such actions that would prevent the water from being beneficially used. Compare to Forfeited Water Right.

ABANDONED WELL—A well which is no longer used or a well removed from service; a well whose use has been permanently discontinued or which is in a state of such disrepair that it cannot be used for its intended purpose. Generally, abandoned wells will be filled with concrete or cement grout to protect groundwater from waste and contamination.

ABANDONMENT—Failure to put a water right to Beneficial Use for generally five or more years, in which the owner of the water right states that the water right will not be used, or takes such actions that would prevent the water from being beneficially used. Also see Abandoned Water Right.

ABANDONMENT OF A DAM—In a legal sense, abandonment is most precisely described as transfer of all rights, title and interest in a dam to the current property owner.

Abandonment may also involve the slow but resolute erosion of rights to a dam by non-use, physical destruction, lack of maintenance or intent of same. In this latter instance the final determination of legal abandonment can only be decided by the court holding jurisdiction.

ABIOSESTON—Nonliving components of the seston.

ABATEMENT—Reducing the degree or intensity of, or eliminating, pollution, as a water pollution abatement program.

ABIOTA—Those non-living factors which are present in and affect the characteristics of a given ecosystem.

ABIOTIC—Pertaining to any non- biological factor or influence, such as geological or meteorological characteristics.

ABLATION—(1) The process by which ice and snow waste away as a result of melting and/or evaporation. (2) The erosive processes by which a glacier is reduced.

ABSCISSA (Symbol X)—(Mathematics) The coordinate representing the position of a point along a line perpendicular to the y-axis (Ordinate) in a Plane Cartesian Coordinate System.

ABSCISSION—The dropping of leaves from a plant. Premature abscission in certain plant species frequently results from excessive exposure to certain air contaminants.

ABSOLUTE HUMIDITY—The actual weight of water vapor contained in a unit volume of the atmosphere, usually expressed in grams of water per kilogram of air. Compare to Relative Humidity.

ABSOLUTE TEMPERATURE (T)—A temperature expressed on the thermodynamic scale, measured from Absolute Zero, or 0 Kelvin (K), also equivalent to -273.15C or -459.67F.

ABSOLUTE ZERO—The zero value of thermodynamic temperature, or 0 Kelvin (K), also equivalent to -273.15 Celsius (C) on the Centigrade Temperature Scale or -459.67 Fahrenheit (F) on the Fahrenheit Temperature Scale.

ABSORBER—A material capable of taking in a substance, such as oil, as a sponge takes up water.

ABSORPTION—(1) The entrance of water into the soil or rocks by all natural processes, including the infiltration of precipitation or snowmelt, gravity flow of streams into the valley alluvium into sinkholes or other large openings, and the movement of atmospheric moisture. (2) The uptake of water or dissolved chemicals by a cell or an organism (as tree roots absorb dissolved nutrients in soil). (3) More generally, the process by which substances in gaseous, liquid, or solid form dissolve or mix with other substances. Not to be confused with Adsorption.

ABSORPTION LOSS—The loss of water by Infiltration or Seepage into the soil during the process of priming, i.e., during the initial irrigation of a field; generally expressed as flow volume per unit of time.

ABSORPTION TOWER—(Air Quality) An air pollution control device in which contaminated air is passed through a tower containing substances (packing) possessing large surface area. Water is passed over the packing material in a countercurrent fashion, i.e., in a direction opposite to the passage of the air, and the air contaminants are then absorbed into the liquid. Also referred to as Packed Tower, Spray Tower, or Tray Tower.

ABUTMENT (of a Dam)—The part of a valley side wall against which a dam is constructed. An artificial abutment is sometimes constructed as a concrete gravity section to take the thrust of an Arch Dam where there is no suitable natural abutment. Right and left abutments are designated as one looks downstream.

ABUTMENT SEEPAGE—Reservoir water that moves through seams or pores in the dam's natural Abutment material and exists as seepage.

ABYSSAL—Of or relating to the bottom waters of the ocean depth.

ABYSSAL DEPTH—In a limnological sense, that depth at which the water remains uniform in temperature, or is "stagnant".

ABYSSAL ZONE—The bottom of a deep ocean. Also see Bathyal Zone and Euphotic Zone.

ACCESS—The way for a person to enter a lake usually with a boat. Types of accesses include: easement access, funnel access, lake access and public access.

ACCLIMATIZATION—The physiological adjustment or adaptation by an organism to new physical and/or environmental conditions. With respect to water, it is frequently used in reference to the ability of a species to tolerate changes in water temperature, degradation of water quality, or increased levels of salinity.

ACCRETION—The slow addition to land by deposition of water-borne sediment. An increase in land along the shores of a body of water, as by Alluvial deposit. Accretion and alluvion are often used synonymously.

ACEC—Area of Critical Environmental Concern.

ACEQUIA—(Southwestern U.S.) An irrigation canal.

ACID—(1) Corrosive substances with pH of less than 7.0; acidity is caused by high concentrations of hydrogen ions. (2) Chemicals that release hydrogen ions (H+) in solution and produce hydronium ions (H3O+). Such solutions have a sour taste, neutralize bases, and conduct electricity. (3) Term applied to water with a pH of less than 7.0 on a pH scale of 0 to 14.

ACID AEROSOL—Airborne particles composed of sulfates (SOX), sulfuric acid (H2SO4), nitrates (NOX), and/or nitric acid (HNO3). Dry particle diameters are typically less than 1-2 microns. Also see Acid Deposition and Acid Fog.

ACID DEPOSITION—The introduction of acidic material to the ground or to surface waters. Involves a complex chemical and atmospheric phenomenon that occurs when emissions of sulfur and nitrogen compounds and other substances are transformed by chemical processes in the atmosphere, often far from the original sources, and then become deposited on the land or surface waters in either wet or dry forms. Wet Deposition (commonly referred to as Acid Rain or Acid Fog) results from precipitation as rain, snow, or fog. Dry Deposition results from particle fallout or acidic gases.

ACID FOG—Airborne water droplets containing sulfuric acid and/or nitric acid. Typical diameters are 3-30 microns. Also see Acid Deposition and Acid Aerosol.

ACID-FORMING MATERIAL—Material containing sulfide minerals or other materials, which if exposed to air, water, or weathering processes will form sulfuric acid that may create Acid Mine Drainage.

ACID LAKES— Lakes that have water with a pH less than 6 standard units.

ACID MINE DRAINAGE (AMD)—Acidic water that flows into streams from abandoned mines or piles of mining waste or tailings. The acid arises from the oxidation of iron sulfide compounds in the mines by air, dissolved oxygen in the water, and chemoautotrophs, which are bacteria that can use the iron sulfide as an energy source. Iron sulfide oxidation products include sulfuric acid, the presence of which has reduced or eliminated aquatic life in many streams in mining regions. Also see Open-Pit Mining and Yellowboy. Also referred to as Acid Mine Waste.

ACID NEUTRALIZING CAPACITY—A measure of the ability of water or soil to resist changes in pH.

ACID PRECIPITATION—Atmospheric deposition (rain, snow and dryfall) that is composed of the hydrolyzed by-products from oxidized halogen, nitrogen, and sulfur substances. Also see Acid Rain.

ACID RAIN—Rainfall with a pH of less than 7.0. One of the principle sources is the combining of rain (H2O) and sulfur dioxide (SO2), nitrous oxides (NOx), and carbon dioxide (CO2) emissions which are byproducts of the combustion of fossil fuels. These oxides react with the water vapor to form sulfuric (H2SO4), nitric (HNO3), and carbonic acids (H2CO3). Long-term deposition of these acids is linked to adverse effects on aquatic organisms and plant life in areas with poor neutralizing (buffering) capacity. Also see Acid Deposition.

ACIDIC—The condition of water or soil that contains a sufficient amount of acid substances to lower the pH below 7.0.

ACIDIFICATION—Raising the acidity (lowering the pH) of a fluid by adding an acid.

ACIDITY—A measure of how acid a solution may be. A solution with a pH of less than 7.0 is considered acidic. Solutions with a pH of less than 4.5 contain mineral acidity (due to strong inorganic acids), while a solution having a pH greater than 8.3 contains no acidity.

ACLs—Alternative Concentration Limits.

ACRE—A measure of area equal to 43,560 square feet (4,046.87 square meters). One square mile equals 640 acres, and is also referred to as a Section. An acre is slightly smaller in size than a football field.

ACREAGE—(1) An area of land or water measured in acres. (2)Number of acres.

ACRE-FEET (AF)—A unit commonly used for measuring the volume of water. See Acre-Foot.

ACRE-FOOT (AF)— A unit commonly used for measuring the volume of water; equal to the quantity of water required to cover one acre (43,560 square feet or 4,047 square meters) to a depth of 1 foot (0.30 meter) and equal to 43,560 cubic feet (1,234 cubic meters), or 325,851 gallons.

ACRE-INCH—The volume of water or solids that will cover one acre to a depth of one inch, equivalent to 3,630 cubic feet or 102.7 cubic meters.

ACTIVATED CARBON—A material produced by heating coal or wood in such a manner as to yield a porous structure, creating a very large internal surface area. Activated carbon is available in both powdered and granular forms, and is widely used to adsorb organic compounds from water and wastewater. It provides a means of removing tastes and odors from drinking water. Also see Granular Activated Carbon (GAC). Also referred to as Activated Charcoal.

ACTIVATED CARBON ADSORPTION—The process of pollutants moving out of water and attaching on to Activated Carbon.

ACTIVATED SLUDGE—The Floc produced in raw or settled wastewater due to the growth of bacteria and other organisms in the presence of Dissolved Oxygen. It is the product that results when primary effluent is mixed with bacteria-laden sludge and then agitated and aerated to promote biological treatment, speeding the breakdown of organic matter in raw sewage undergoing secondary waste treatment.

ACTIVATED SLUDGE PROCESS—A method of Secondary Wastewater Treatment in which the waste is treated by microorganisms in a well-aerated tank to degrade the organic material. A sedimentation tank is then used to remove the resultant sludge.

ACTIVE FAULT—A fault that has undergone movement in recent geologic time (the last 10,000 years) and may be subject to future movement. Also see Fault.

ACTIVE SOLAR WATER HEATER—A water heating system in which heat from the sun is absorbed by collectors and transferred by pumps to a storage unit. The heated fluid in the storage unit conveys its heat to the domestic hot water system of the house through a heat exchanger.

ACTIVE STORAGE CAPACITY—The total amount of usable reservoir capacity available for seasonal or cyclic water storage. It is gross reservoir capacity minus inactive storage capacity. More specifically, the volume of water in a reservoir below the maximum controllable level and above the minimum controllable level that can be released under gravity. In general, it is the volume of water between the outlet works and the spillway crest. In some instances, Minimum Pool operating constraints may prevent lowering the reservoir to the level of the outlet works, and the water below the minimum pool level is not considered to be in active storage.

ACTIVITY—The effective concentration of a chemical based on thermodynamic considerations. Activity and concentration have the same units and have the same value in very dilute solutions.

ACUTE—Designates an exposure to a dangerous substance or chemical in sufficient dosage to precipitate a severe reaction. Acute Exposure refers to such dosage levels received over a period of 24 hours or less. Longer-term exposures are referred to as Chronic Exposure.

ADAPTATION—Changes in an organism's structure or habits that allow it to adjust to its surroundings, which usually makes them more likely to survive and reproduce than their competitors.

ADENOSINE TRIPHOSPHATE (ATP)—An organic, phosphate-rich compound important in the transfer of energy in organisms. Its central role in living cells makes it an excellent indicator of the presence of living material in water. A measure of ATP therefore provides a sensitive and rapid estimate of Biomass. ATP is reported in micrograms per liter of the original water sample.

ADEQUATE-SIZE FARM—A farm with resources and productivity sufficient to generate enough income to (a) provide an acceptable level of family living; (b) pay current operating expenses and interest on loans; and (c) allow for capital growth to keep pace with technological growth.

ADHESION—Molecular attraction that holds the surfaces of two substances in contact, such as water and rock particles. Also, the attraction of water molecules to other materials as a result of hydrogen bonding.

ADIABATIC—Applies to a thermodynamic process during which no heat is added to or withdrawn from the body or system concerned. In the atmosphere, adiabatic changes of temperature occur only in consequence of compression or expansion accompanying an increase or decrease of atmospheric pressure. Thus, a descending body of air undergoes compression and adiabatic heating.

ADIABATIC LAPSE RATE—The theoretical rate at which the temperature of the air changes with altitude. The temperature change is due to the pressure drop and gas expansion only, and no heat is considered to be exchanged with the surrounding air through convection or mixing. The Dry Adiabatic Lapse Rate for air not saturated with water vapor is 0.98C per 100 meters (5.4F per 1,000 feet). The Wet Adiabatic Lapse Rate for air saturated with water vapor is about 0.60C per 100 meters (3.3F per 1,000 feet).

ADIABATIC PROCESS—A change involving no gain or loss of heat.

ADIT—A horizontal or nearly horizontal passage, driven from the surface, for the working or dewatering of a mine. Also referred to as Drift, Shaft, or Portal.

ADJUDICATION—Refers to a judicial process whereby water rights are determined or decreed by a court of law. A court proceeding to determine all rights to the use of water on a particular stream system or ground water basin.

ADMINISTERED GROUNDWATER BASIN—A groundwater basin (watershed, area, or sub-area) which, in the interest of public welfare, is monitored by an appropriate agency to insure adequate water resources for prescribed uses. Quite often, such basins will have Preferred Uses designated for future development to insure that the basin's Perennial Yield is not exceeded. Also referred to as Designated Groundwater Basin. Also see Designated Groundwater Basin [Nevada].

ADSORBATE—Any material adsorbed onto the surface of another.

ADSORBENT—Any material which adsorbs another on its surface.

ADSORBER—A solid or liquid that can hold molecules of another substance on its surface.

ADSORPTION—(1) The adherence of ions or molecules in solution to the surface of solids. (2) The adherence of a gas, liquid, or dissolved material on the surface of a solid. (3) The attraction and adhesion of a layer of ions from an aqueous solution to the solid mineral surfaces with which it is in contact. An example is the adsorption of organic materials by activated carbon. Not to be confused with Absorption.

ADVANCED TREATMENT—A level of wastewater treatment more stringent than secondary treatment; requires an 85 percent reduction in conventional pollutant concentration or a significant reduction in nonconventional pollutants.

ADVANCED WASTEWATER TREATMENT (AWT)—Any process which reduces the level of impurities in a wastewater below that attainable through conventional secondary or biological treatment. Includes the removal of nutrients such as phosphorus and nitrogen and a high percentage of suspended solids. Also see Tertiary Wastewater Treatment.

ADVANCE TIME—The time it takes for water to travel the length of an irrigation furrow.

ADVECTION—(1) The process by which solutes are transported by the bulk of flowing fluid such as the flowing ground water. (2) The horizontal transfer of heat energy by large-scale motions of the atmosphere.

ADVENTIVE— Non native plant. Recently introduced and starting to spread into new places.

AEDILE—An elected official of ancient Rome who was responsible for public works and games and who supervised markets, the grain supply, and the water supply.

AEOLIAN SOIL—Soil transported from one area to another by the wind.

AERATE—To supply or charge a liquid or body of water with a gas, as to expose a body of water to the circulation of air for purification. See Aerated Lagoon.

AERATED LAGOON—A holding and/or treatment pond that speeds up the natural process of biological decomposition of organic waste by stimulating the growth and activity of bacteria that degrade organic waste.

AERATION—Any active or passive process by which intimate contact between air and liquid is assured, generally by spraying liquid in the air, bubbling air through water, or mechanical agitation of the liquid to promote surface absorption of air.

AERATION TANK—A chamber used to inject air into water.

AERATION (UNSATURATED) ZONE—The zone between the land surface and the water table which characteristically contains liquid water under less than atmospheric pressure and water vapor and air or other gases at atmospheric pressure. The term Unsaturated Zone is now generally applied.

AERIAL— Occurring above water or land.

AEROBE—An organism which requires oxygen for its life processes.

AEROBIC—(1) Characterizing organisms able to live only in the presence of air or free oxygen, and conditions that exist only in the presence of air or free oxygen. Contrast with Anaerobic. (2) Process requiring oxygen.

AEROBIC BACTERIA—Single-celled, microscopic organisms that require oxygen to live and are partly responsible for the Aerobic Decomposition of organic wastes.

AEROBIC DECOMPOSITION—The biodegradation of materials by aerobic microorganisms resulting in the production of carbon dioxide, water, and other mineral products. Generally a faster process than Anaerobic Decomposition. Also see Aerobic Bacteria.

AEROBIC TREATMENT—The process by which microbes decompose complex organic compounds in the presence of oxygen and use the liberated energy for reproduction and growth. Such processes may include extended aeration, trickling filtration, and rotating biological contactors.

AERODYNAMIC—Refers to forces acting upon the soil or crop surface by moving air.

AEROPONICS—A technique for growing plants without soil or hydroponic media. The plants are held above a system that constantly mists the roots with nutrient-laden water. Also called Aeroculture.

AEROSOL—A suspension of liquid or solid particles in air or gas.

AESTHETICS (Lake)— Aesthetics are given consideration in the complete evaluation of lakes as a natural resource. The overall scenic attraction of the lake setting; natural beauty of shores and waters, or any unusual natural phenomena; the appeal of its wildlife and aquatic plants; desirable natural landscape for home sites on the shores are some of the matters considered under this heading.

AESTIVAL PONDS— Those ponds existing only in summer.

AF—Acre-Feet (or Acre-Foot).

AFFECTED PUBLIC—The people who live and/or work near a hazardous waste site or other source of pollutant emissions.

AFFLUENT (Lake)— A tributary or feeder stream. Streams receiving the run-off from the watershed and flowing into the lake are its affluents; analogous to the affluent of a river. The analogy can be very close where a lake has large inflowing and outflowing streams and is located in a valley or elongated basin. In usage, the term may have the same meaning as influent; although where the reference is to a single inflowing stream, the word influent appears to be the preferred one. See Influent and Inlet.

AFFLUENT (Stream)—A stream or river that flows into a larger one; a Tributary.

AFFORESTATION—The artificial establishment of forest crops by planting or sowing on land that has not previously, or recently, grown trees.

AFLOAT—Floating on water.

AFTERBAY—The tail race or reservoir of a hydroelectric power plant at the outlet of the turbines used to regulate the flow below the plant; may refer to a short stretch of stream or conduit, or to a pond or reservoir. Compare with Forebay.

AFY—Acre-Feet per Year.

AGE (of Groundwater)—An approximation of the time between the water's penetration of the land surface at one location and its later presence at another location.

AGENCY—A department of the government.

AGGLOMERATION—(Water Quality) The grouping of small suspended particles into larger particles that are more easily removed through filtration, skimming, or settling. Also see Coagulation.

AGGRADATION—(1) The build-up of sediments at the headwaters of a lake or reservoir or at a point where streamflow slows to the point that it will drop part or all of its sediment load. (2) Modification of the earth's surface in the direction of uniformity of grade or slope, by Deposition, as in a river bed.

AGGRADING—The building up of a stream channel which is flowing too slowly to carry its sediment load.

AGGRESSIVE WATER—Water which is soft and acidic and can corrode plumbing, piping, and appliances.

AGITATED PIT—A reservoir, pit, or pond that ordinarily is not stirred or aerated, but which is mixed just before emptying to suspend any settled solids.

AGITATOR/MIXER—(Water Quality) Blades or paddles that slowly rotate in a tank to facilitate the mixing of suspended material.

AGNPS— Agricultural Nonpoint Source Pollution Model.

AGP—Algae Growth Potential

AGRIBUSINESS—The sum of all operations involved in the production, storage, processing, and wholesale marketing of agricultural products.

AGRICULTURAL—Having to do with farming or farms.

AGRICULTURAL CAPABILITY— Determines, given the ideal state, what a given area of land is capable of producing in terms of agricultural production and output.

AGRICULTURAL DRAINAGE—(1) The process of directing excess water away from the root zones of plants by natural or artificial means, such as by using a system of pipes and drains placed below ground surface level. Also referred to as Subsurface Drainage. (2) The water drained away from irrigated farmland.

AGRICULTURAL ECONOMICS—The application of economic principles to the Agribusiness sector of the economy.

AGRICULTURAL LAND—Land in farms regularly used for agricultural production; all land devoted to crop or livestock enterprises, for example, farmstead lands, drainage and irrigation ditches, water supply, cropland, and grazing land.

AGRICULTURAL LEVEE—A levee that protects agricultural areas where the degree of protection is usually less than that of a flood control levee.

AGRICULTURAL POLLUTION—Liquid and solid wastes from all types of farming, including runoff from pesticides, fertilizers, and feedlots; erosion and dust from plowing; animal manure and carcasses; and crop residues and debris.

AGRICULTURAL RESTRUCTURING SCENARIO (ARS)—A term used to describe the sensitivity of agricultural water demand and farm marketing revenues to changes in certain cropping patterns.

AGRICULTURAL RUNOFF—The runoff into surface waters of herbicides, fungicides, insecticides, and the nitrate and phosphate components of fertilizers and animal wastes from agricultural land and operations. Considered a Non-Point Source (NPS) of water pollution.

AGRICULTURAL SUITABILITY— Determines how suitable a given area of land is, in it's present state, for agricultural purposes.

AGRICULTURAL USE—The use of any tract of land for the production of animal or vegetable life; uses include, but are not limited to, the pasturing, grazing, and watering of livestock and the cropping, cultivation, and harvesting of plants.

AGRICULTURAL WATER USE—Includes water used for irrigation and non-irrigation purposes. Irrigation water use includes the artificial application of water on lands to promote the growth of crops and pasture, or to maintain vegetative growth in recreational lands, parks, and golf courses. Non-irrigation water use includes water used for livestock, which includes water for stock watering, feedlots, and dairy operations, and fish farming and other farm needs.

AGRO-ECOSYSTEM—Land used for crops, pasture, and livestock; the adjacent uncultivated land that supports other vegetation and wildlife; and the associated atmosphere, the underlying soils, ground and surface waters, irrigation channels, and drainage networks.

AGROINDUSTRIAL—Of or relating to production (as of power for industry and water for irrigation) for both industrial and agricultural purposes.

AGROUND—Onto or on a shore, reef, or the bottom of a body of water.

AGUA— This Spanish word for water is occasionally used in Southwestern U. S. in names of bodies of water such as lakes and lagoons, as well as springs.

AIR—The colorless, odorless, tasteless, gaseous mixture that makes up the earth's Atmosphere. Four gases comprise 99.997 percent (by volume) of clean, dry, air: Nitrogen (78.084 percent); Oxygen (20.946 percent); Argon (0.934 percent); and Carbon Dioxide (0.033 percent). The remaining components include neon, helium, methane, krypton, nitrous oxide, hydrogen, xenon, and various organic vapors. Under normal conditions, air contains up to about 3 percent water vapor (by volume) and many solid, liquid, or gaseous contaminants introduced by human activities and natural causes such as wind erosion and the burning of fossil fuels.

AIR BINDING—A situation where air enters the filter media and harms both the filtration and backwash processes.

AIR-BOUND—Condition in a pipeline wherein air trapped in a summit prevents the free flow of the material in the pipeline.

AIR CURTAIN—A method for mechanical containment of oils spills in which air is bubbled through a perforated pipe, causing an upward water flow that retards the spreading of oil; also used as barriers to prevent fish from entering a polluted body of water.

AIR GAP—An open vertical gap or empty space that separates a drinking water supply to be protected from another water system in a treatment plant or other location. The open gap protects the drinking water from contamination by backflow or backsiphonage.

AIR HOLE—An opening in the frozen surface of a body of water.

AIR INJECTION—In groundwater management, the pumping of compressed air into the soil to move water in the Unsaturated Zone (Vadose Zone) down to the Saturated Zone (Phreatic Zone), or Water Table.

AIR LOCK—A bubble or pocket of air or vapor, as in a pipe, that stops the normal flow of fluid through the conducting part.

AIR MASS—A large body of air

AIR PADDING— Pumping dry air into a container to assist with the withdrawal of liquid or to force a liquefied gas such as chlorine out of the container.

AIR PHOTO— A photograph of the earth's surface taken from the air. It is usually a vertical view, and one of a series of photos taken from an aircraft flying a systematic pattern at a given altitude in order to obtain continuous photo coverage for mapping purposes (Terrain Geology Task Group 1994).

AIR POLLUTION— Process of making the air unclean, such as, burning wood or coal and putting its smoke into the atmosphere or gasoline burning in cars engine and expelling the by products out the exhaust pipe.

AIR STRIPPING—(Water Quality) A process for the removal of organic contaminants from groundwater. The groundwater flows downward inside a tower filled with materials (the packing) over a large surface area. Air is introduced at the bottom of the tower and is forced upward past the falling water. Individual organic contaminants are transferred from the water to the air, according to the gas and water equilibrium concentration values of each contaminant. Also referred to as Packed Tower Aeration.

AIR VENT (of a Dam)—A pipe designed to provide air to the outlet conduit to reduce turbulence and prevent negative pressures during the release of water. Extra air is usually necessary downstream of constrictions.

ALACHLOR—A herbicide, marketed under the trade name Lasso, listed by the U.S. Environmental Protection Agency (EPA) as a "probable human carcinogen" and found frequently in streams and rivers, particularly following floods and periods of heavy rain. Alachlor is used extensively for weed control in corn, cotton, and soybean fields.

ALDOSTERONE—A steroid hormone secreted by the adrenal cortex that regulates the salt and water balance in the human body.

ALFALFA VALVE—A screw-type valve placed on the end of a pipe to regulate the flow of water.

ALGAE— (1) Simple single-celled (phytoplankton), colonial, or multi-celled, mostly aquatic plants, containing chlorophyll and lacking roots, stems and leaves. Aquatic algae are microscopic plants that grow in sunlit water that contains phosphates, nitrates, and other nutrients. Algae, like all aquatic plants, add oxygen to the water and are important in the fish food chain. (2) Algae is either suspended in water (plankton) or attached to rocks and other substrates (periphyton). Their abundance, as measured by the amount of chlorophyll a (green pigment) in an open water sample, is commonly used to classify the trophic status of a lake. Algae are a essential part of the lake ecosystem and provides the food base for most lake organisms, including fish. Phytoplankton populations vary widely from day to day, as life cycles are short.

ALGAE BLUE GREEN— A group of largely microscopic, photosynthetic organisms with a bacterial structure (prokaryote), but containing chlorophyll a and a photosynthesis biochemistry unlike other bacteria but similar to that of other algae and higher plants. Alternative names are blue-green bacteria, cyanophytes, cyanobacteria, or, probably the most suitable, cyanoprokaryotes. Blue and red pigments, contained within them, give an often characteristic color.

ALGAE WASH— Shoreline drift composed mainly of filamentous algae. The plants are carried to the shore by wind and wave action and stranded at or near the limit of wave advance. The drift often accumulates in considerable quantity and can become highly obnoxious on beaches.

ALGAECIDE—One of a group of plant poisons used to kill filamentous algae and phytoplankton.

ALGAL BLOOM—Rapid growth of algae on the surface of lakes, streams, or ponds; stimulated by nutrient enrichment (or due to an increase in plant nutrients such as nitrates and phosphates). It is associated with Eutrophication and results in a deterioration in water quality. Also spelled Algae Bloom.

ALGAL GROWTH POTENTIAL (AGP)—The maximum algal dry weight biomass produced in a natural water sample under laboratory conditions. Expressed as milligrams (mg), dry weight per liter (l) of sample.

ALGAL GROWTH RATE—A measure of algal productivity in a body of water, the growth rate measures the mass of carbon used annually by algae per unit area of lake surface. The growth rate, typically referred to as Primary Productivity, is expressed as an index figure in grams of carbon per square meter per year, and indicates the state of Eutrophication of a body of water. Algal productivity is influenced by the quantities of nutrients that flow into, or fall onto, the lake each year and the number of days of sunshine. Another important factor is the mixing of the lake, which brings up to the surface where algae exist nutrients which have accumulated near the bottom of the lake.

ALGORITHM—A series of well-defined steps used in carrying out a specific process. May be in the form of a word description, an explanatory note, a diagram or labeled flow chart, or a series of mathematical equations.

ALKALI—Any strongly basic (high pH) substance capable of neutralizing an acid, such as soda, potash, etc., that is soluble in water and increases the pH of a solution greater than 7.0. Also refers to soluble salts in soil, surface water, or groundwater.

ALKALI LAKES— Those containing water very highly impregnated with alkalies. The "alkali" may be sodium carbonate or sodium sulfate and potassium carbonate but includes other alkaline compounds as well. Restricted to arid and semi-arid regions. See: Potash lakes and Soda lakes.

ALKALINE—Sometimes water or soils contain an amount of Alkali substances sufficient to raise the pH value above 7.0 and be harmful to the growth of crops. Generally, the term alkaline is applied to water with a pH greater than 7.4.

ALKALINITY—The capacity of water for neutralizing an acid solution. Alkalinity of natural waters is due primarily to the presence of hydroxides, bicarbonates, carbonates and occasionally borates, silicates and phosphates. It is expressed in units of milligrams per liter (mg/l) of CaCO3 (calcium carbonate) or as microequivalents per liter (µeq/l) 20 µeq/l = 1 mg/l of CaCO3. A solution having a pH below 4.5 contains no alkalinity. Low alkalinity is the main indicator of susceptibility to acid rain. Increasing alkalinity is often related to increased algal productivity. Lakes with watersheds that have sedimentary carbonate rocks are high in dissolved carbonates (hard-water lakes). Whereas lakes in granite or igneous rocks are low in dissolved carbonates (soft water lakes).

ALLELOPATHY— Production of substances by one organism that inhibit the growth, activity or reproduction of another.

ALLOCTHONOUS—Materials (e.g. organic matter and sediment) which enters a lake from atmosphere or drainage basin. See autochthonous.

ALLOCTHONOUS DETRITUS— Particulate matter originating outside, and carried into the lake.

ALLOGENIC—Exogenous, caused by external factors, such as a change in a habitat or environment caused by flooding. Contrast with Autogenic.

ALLOGENIC SUCCESSION—Predictable changes in plant and animal communities in which changes are caused by events external to the community, for example, fire, drought, floods, etc.

ALLUVIAL—An adjective referring to soil or earth material which has been deposited by running water, as in a riverbed, flood plain, or delta.

ALLUVIAL DAM LAKES— Numerous basins which are the sites of both existing and extinct lakes in the arid regions of western U. S. were formed by alluvial dams, especially by the coalescence of fans composed of detritus carried down by streams from opposite sides of valleys. In glaciated regions dams were formed in valleys by glacio-fluvial deposition during the Pleistocene; and barriers of various kinds, which impound water have been created in river flood plains by alluvial deposition. See Fluviatile lakes and Levee lakes.

ALLUVIAL FAN—A fan-shaped deposit of generally coarse material created where a stream flows out onto a gentle plain; a geomorphologic feature characterized by a cone or fan-shaped deposit of clay, silt, sand, gravel, and boulders that have been eroded from mountain slopes, transported by flood flows, and deposited on the valley floor.

ALLUVIAL FAN FLOODING—Flooding occurring on the surface of an Alluvial Fan or similar landform which originates at the apex and is characterized by high-velocity flows: active processes of erosion, sediment transport, deposition, and unpredictable flow paths.

ALLUVIAL LAND—Areas of unconsolidated alluvium, generally stratified and varying widely in texture, recently deposited by streams, and subject to frequent flooding.

ALLUVIAL VALLEY FLOOR—[Public Law 95-87, Section 701] (Legal) "The unconsolidated stream laid deposits where water availability is sufficient for subirrigation or flood irrigation. It does not include upland areas which are generally overlain by a thin veneer of colluvial deposits composed chiefly of debris from sheet erosion, deposits by unconcentrated runoff or slopewash, talus, or other mass movement accumulation and wind-blown deposits."

ALLUVION—(1) The flow of water against a shore or bank. Inundation by water; flood. (2) (Legal) The increasing of land area along a shore by deposited Alluvium or by the recession of water. (3) (Lake) In its legal meaning, alluvion is an accretion to land, made gradually, composed of detritus deposited by streams or of deposits accumulated by the action of waves and currents. On lakes, accretions are made: by alluvial deposition on the advancing front of a delta; by filling of shoreline lake bottom by erosion detritus carried by effluents, gullies and superficial surface run-off or rainwash; by shifting dune sand; and by waste disposal such as tailing from mine operations. Also natural accretions may be made to islands, bars and beaches of lakes. The deposits are realities, but whether or not, in specific instances, they constitute legal alluvion which involves land ownership is, ultimately, a matter for court decisions. See: Reliction

ALLUVIUM—A general term for deposits of clay, silt, sand, gravel, or other particulate material that has been deposited by a stream or other body of running water in a streambed, on a flood plain, on a delta, or at the base of a mountain. In lakes, alluvium is the sediments, or detrital matter carried by inflowing streams and deposited on lake bottoms. Also see Alluvion.

ALPENGLOW—A rosy glow that suffuses snow-covered mountain peaks at dawn or dusk on a clear day.

ALPINE—That portion of mountains above tree growth; or organisms living there. Alpine vegetation is dominated by shrubs, herbs, bryophytes, and lichens.

ALPINE DECREE [California and Nevada]—The Federal Court adjudication of the relative water rights on the Carson River which is the primary regulatory control of Carson River operations today. The decree is administered in the field by a watermaster appointed by the federal district court. The decree, initiated by the U.S. Department of the Interior on May 1, 1925 through U.S. v. Alpine Land and Reservoir Company, et al., to adjudicate water rights along the Carson River. The decree was finally entered 55 years later on October 28, 1980, making it the longest lawsuit undertaken by the federal government against private parties over water rights. The decree established the respective water rights (to surface water only) of the parties to the original lawsuit, both in California and Nevada to Carson River water. The decree did not make an interstate allocation of the Carson River between California and Nevada; it only quantified individual water rights. Neither state was a party to the decree. In addition to Carson River surface water rights, it also established the rights to reservoir storage in the high alpine reservoirs and confirmed the historical practice of operating the river on rotation, so that irrigators with more junior priorities could be served as long as possible. These upper alpine reservoirs were permitted to fill out of priority order, in accordance with historical practice. The decree also specifically recognized Riparian Water Rights in California (as distinguished from the quantified Appropriative Water Rights used in Nevada). For purposes of water distribution, the Carson River and its east and west forks, were divided into eight (8) segments and when the river went into regulation (i.e., there was not enough water in the Upper Carson River to serve the most junior priority) each segment of the river was to be administered autonomously. Duties of water were set forth for various locations according to Bench Land and Bottom Land designations. For lands in the Newlands Irrigation Project (i.e., below Lahontan Dam) in Churchill County near Fallon, the Alpine decree provided for an annual net consumptive use of surface water for irrigation of 2.99 acre-feet per acre and a maximum water duty of 4.5 acre-feet per acre for water-righted bench lands and 3.5 acre-feet per acre for water-righted bottom lands delivered to the land. For lands above the Newlands Project (i.e., above Lahontan Reservoir), the net consumptive water use was set at 2.5 acre-feet per acre with water duties of 4.5 acre-feet per acre diverted to the canal for bottom lands, 6.0 acre-feet per acre diverted to the canal for the alluvial fan lands and 9.0 acre-feet per acre diverted to the canal for the bench lands. This annual net consumptive use, or Crop Water Requirement, was based on the water duty of alfalfa as it is a dominant and the highest water-using crop grown in Nevada. While the Alpine Decree established water duties for bench and bottom lands throughout the Carson River Basin, it made no identification of those lands. The decree also granted landowners on the Newlands Project an Appurtenant Water Right for the patented lands, effectively transferring water rights to these land holders individually.

ALPINE LAKES— Lakes in any high mountain region, associated with snow, ice and a cold climate.

ALTERNATE CONCENTRATION LIMITS (ACLs)—One of the three types of standards that may be applied when a leak is detected at a treatment, storage, or disposal facility and groundwater compliance monitoring is required. ACLs are set by the U.S. Environmental Protection Agency (EPA) for specific hazardous waste constituents at levels that are designed to prevent a substantial hazard to human health or the environment. Groundwater compliance monitoring can use the following standards: (1) background concentrations, or the levels found in the area naturally; (2) specific values set by federal regulations in Title 40, Part 264.94, of the Code of Federal Regulations for eight metals and six pesticides and herbicides; or (3) alternative concentration limits.

ALTERNATIVE STABLE STATES —Potential existence of markedly different biological communities under the same external environmental conditions.

ALTITHERMAL—(Climatology) A period of time when it was much warmer than now, approximately 7,000-4,500 years before the present time. Also see Anathermal and Medithermal.

ALTITUDE—The vertical distance of a level, a point, or an object considered as a point, measured from Mean Sea Level (MSL).

ALTOCUMULUS CLOUD—A fleecy cloud, usually a rounded mass, but which can change radically and unexpectedly, producing intermediate forms, at an average height of 2.5 miles (4 kilometers). Also see Cloud.

ALTOSTRATUS CLOUD—A somewhat high level, blue to grayish blue cloud that forms a sheet or layer at an average height of 3.5 miles (5.6 kilometers). Also see Cloud.

ALUM—Common name for commercial-grade Aluminum Sulfate. Its chemical formula is generally denoted by Al2(SO4)3 12H2O (number of bound water molecules will vary from 12 to 18).

ALUM TREATMENT— Process of putting liquid alum (Aluminum Sulfate) into the lake water, to precipitate to a floc that settles through the water column removing fine particles to the sediment and building up a barrier layer to contain soluble phosphorus in the lake sediments.

ALUMINUM— A light, bluish white malleable and ductile metallic element found only in combinations. (Symbol Al).

ALUMINUM SULFATE—A white crystalline compound, Al2(SO4)3, used chiefly in paper making, water purification, sanitation, and tanning. See Alum.

AMBIENT WATER QUALITY STANDARDS—The allowable amount of materials, as a concentration of pollutants, in water. The standard is set to protect against anticipated adverse effects on human health or welfare, wildlife, or the environment, with a margin of safety in the case of human health. Also see Primary and Secondary Standards and 7Q10.

AMC—Antecedent Moisture Condition

AMD—Acid Mine Drainage

AMEBIC DYSENTERY—A disorder of the gastrointestinal tract caused by a protozoan parasite belonging to the genus Entamoeba histolytica. The disorder is commonly found in communities with poor sanitary conditions, particularly related to water and food storage and preparation. Infected individuals experience abdominal cramps, diarrhea, and blood and mucus in the feces. The parasite invades the liver in some cases.

AMENITIES—(Lake) Those features or aspects which produce a pleasurable effect, or have a sentimental value.

AMERICAN PUBLIC WORKS ASSOCIATION (APWA)—A national organization founded in 1894 and based in Chicago, Illinois of individuals and organizations involved in the management of municipal solid waste and in the design and operation of wastewater treatment plants.

AMERICAN SOCIETY OF CIVIL ENGINEERS (ASCE)—A professional organization in New York City founded in 1852 that supports the practice of, and research in, environmental engineering, hydrology, and water and wastewater treatment.

AMERICAN WATER WORKS ASSOCIATION (AWWA)—A national organization in Denver, Colorado, founded in 1881 of individuals involved in the design and operation of public water supplies and systems.

AMICTIC LAKE—A lake that does not experience mixing or turnover on a seasonal basis. Also see Dimictic Lake.

AMINO ACIDS —Components of proteins. They are soluble in water and contain an amino (NH2) group.

AMMONIA—A form of nitrogen found in organic materials, sewage, and many fertilizers. It is the first form of nitrogen released when organic matter decays. It can be used by most aquatic plants and is therefore an important nutrient. It converts rapidly to nitrate (NO3) if oxygen is present. The conversion rate is related to water temperature. Ammonia is toxic to fish at relatively low concentrations in pH-neutral or alkaline water. Under acid conditions, non-toxic ammonium ions (NH4+) form, but at high pH values the toxic ammonium hydroxide (NH4OH) occurs. The water quality standard for fish and aquatic life is 0.02 mg/l of NH4OH. At a pH of 7 and a temperature of 68 Deg. F (20 Deg. C), the ratio of ammonium ions to ammonium hydroxide is 250:1 at pH 8, the ratio is 26:1. Ammonia is an important aquatic plant nutrient because it is readily available.

AMMONIA STRIPPING—A process for the removal of ammonia from wastewater. The waste is first made alkaline to favor the NH3 form, and then aerated so that exchange between the water and the atmosphere is encouraged. Stripping towers are often used, with the waste trickling downward as air is forced upward through the tower.

AMMONIFICATION—The transformation of organic nitrogen to ammonia, generally by means of bacterial activity.

AMMONIUM SULFATE—A brownish-grey to white crystalline salt, (NH4)2SO4, used in fertilizers and water purification.

AMOEBA, also Ameba—A protozoan of the genus Amoeba or related genera, occurring in water and soil and as a parasite in other animals. An amoeba has no definite form and consists essentially of a mass of protoplasm containing one nucleus or more surrounded by a delicate, flexible outer membrane. It moves by means of pseudopods.

AMPHIBIAN—(1) A cold-blooded, smooth-skinned vertebrate of the class Amphibia, such as a frog or salamander, that characteristically hatches as an aquatic larva with gills. The larva then transforms into an adult having air-breathing lungs. (2) An animal capable of living both on land and in water.

AMPHIBIOTIC—Living in water during an early stage of development and on land during the adult stage.

AMPHIBIOUS—(Biology) (1) Living or able to live both on land and in water. (2) Able to operate both on land and in water.

AMPOULES—A sealed, liquid-filled tube which is broken to release or be filled with another fluid.

AMPROMETRIC TITRATION—A means to measure concentrations of certain substances in water using an electric current that flows during a chemical reaction. Also see Titration.

ANABAENA—Any of various freshwater algae of the genus anabaena that sometimes occur in drinking water and cause a bad taste and odor.

ANABRANCH—A diverging branch of a river which re-enters the main stream.

ANADROMOUS—Pertaining to fish that spend a part of their life cycle in the sea and return to freshwater streams to spawn, for example, salmon, steelhead, and shad. Contrast with Catadromous.

ANAEROBE—An organism that does not require oxygen to maintain its life processes.

ANAEROBIC—Characterizing organisms able to live and grow only where there is no air or free oxygen, and conditions that exist only in the absence of air or free oxygen.

ANAEROBIC BACTERIA— Bacteria that lives without oxygen.

ANAEROBIC DECOMPOSITION—The degradation of materials by Anaerobic microorganisms living beneath the ground or in oxygen-depleted water to form reduced compounds such as methane or hydrogen sulfide. Generally a slower process than Aerobic Decomposition.

ANAEROBIC DIGESTER—An airtight tank in which Anaerobic microorganisms decompose organic material and produce Biogas, mainly Methane. Sewage treatment plants often use anaerobic digesters to reduce the volume of Sludge produced in Primary and Secondary Treatment, and they sometimes use the methane as a heating fuel.

ANAEROBIC DIGESTION—The degradation of organic matter by microorganisms in the absence of oxygen, particularly as related to the treatment of sewage sludge. Sewage treatment plants often use anaerobic digesters to reduce the volume of sludge produced in primary and secondary treatment, and they sometimes use the resultant methane gas as a heating fuel.

ANALOG—A continuously variable electrical signal representing a measured quantity. For example, electrical signals such as current, voltage, frequency, or phase used to represent physical quantities such as water level, flow, and gate position.

ANALYTICAL MODEL—A model that provides approximate or exact solutions to simplified forms of the differential equations for water movement and solute transport. Such models generally require the use of complex calculations and the use of computers.

ANATHERMAL—(Climatology) The period preceding the Altithermal; the early Holocene epoch from about 10,000-7,000 years before the present. Also see Medithermal.

ANC — Acid Neutralizing Capacity.

ANCHOR—A series of methods used to secure a structure to its footings or foundation wall so that it will not be displaced by flood or wind forces.

ANCHOR ICE—Frazil ice that has collected on rocks on the stream bed. (Lake) Ice which extends down to and is attached, or frozen, to the lake bottom. Also, called Bottom Ice, Depth Ice, or Ground Ice.

ANEROID—Not using liquid.

ANGIOSPERMS (Angiospermea)—(Botanical) The vast majority of seed plants characterized as having ovules and seeds in a closed ovary. Along with the Gymnosperms (Gymnospermae), Angiosperms comprise a structurally superior class within the plant family Spermatophyta, or seed plants. Its two sub-classes consist of Monocotyledones and Dicotyledones. Also see Gymnosperms.

ANGLER-DAY—The time spent fishing by one person for any part of a day.

ANHYDRIDE—A chemical compound formed from another, often an acid, by the removal of water.

ANHYDROUS—Without water, especially water of crystallization; not hydrated (Dehydrated).

ANIMAL WASTE — The waste by products (manure and urine) produced by animals.

ANIMAL WASTE MANAGEMENT— A planned process of collection, storage and application of domestic animal waste to the land.

ANION—In an electrolyzed solution, the negatively charged particle, or ion, which travels to the anode and is therefore discharged, evolved, or deposited. Also, by extension, any negative ion. Anions are opposed to cations, which carry a positive charge. There must be equal amounts of positive and negative charged ions in any water sample. Following are the common anions in their order of decreasing concentration for most lakes: bicarbonate (HCO3-), Sulfate(SO4--), chloride (Cl-), carbonate (CO3--), nitrate (NO3-), Nitrite (NO2-), and phosphates (H2PO4-, HPO4--, and PO4-- ).

ANISOTROPY—(1) The condition of having different properties in different directions. (2) The condition under which one or more of the hydraulic properties of an aquifer vary according to the direction of the flow.

ANNUAL—(1) Measured by the year. (2) A plant that completes its life cycle in one year or one season. (Seed to: flowers, set seeds and dies)

ANNUAL FLOOD—The highest peak discharge of a stream in a Water Year.

ANNUAL FLOOD SERIES—A list of annual floods for a given period of time.

ANNUAL LOW-FLOW—The lowest flow occurring each year, usually the lowest average flow for periods of perhaps 3, 7, 15, 30, 60, 120, or 180 consecutive days.

ANNUAL TURNOVER—(1) Spring/fall turnover, mixing of the water in a lake, due to wind, annual cycle of air temperature, and heating from the sun.

ANNULAR — In the form of a ring.

ANNULAR SPACE—The space between two cylindrical objects, one of which surrounds the other, such as the space between the wall of the drilled hole and the casing, or between a permanent casing and the borehole.

ANNULUS—For a well, the space between the pipe and the outer wall (casing) of the borehole, which may be a pipe also (the well casing).

ANNULUS PRESSURE—The positive pressure maintained by a fluid introduced between the well piping and the outer wall (casing) of the borehole of an underground Injection Well providing an indication of the integrity of the well.

ANOXIA—The total deprivation of oxygen, as in bodies of water, lake sediments, or sewage.

ANOXIA, FUNCTIONAL—Although not well defined, generally refers to a body of water sufficiently deprived of oxygen to where Zooplankton and fish would not survive.

ANOXIC—(1) Denotes the absence of oxygen, as in a body of water. (2) Of, relating to, or affected with anoxia; greatly deficient in oxygen; oxygenless as with water.

ANSWERS— Areal Nonpoint Source Watershed Environmental Response Simulation.

ANTECEDENT MOISTURE—The degree of wetness of soil at the beginning of a runoff, determined by summation of weighted daily rainfall amounts for a period preceding the runoff.

ANTECEDENT MOISTURE CONDITION (AMC)—Soil moisture at the onset of a rainfall event. The U.S. Department of Agriculture, Natural Resources Conservation Service (NRCS), formerly the Soil Conservation Service (SCS), defines AMC in terms of total rainfall during the 5 days immediately preceding the rainfall event. Dry AMC conditions mean less than 1.4 inches, average is 1.4 to 2.1 inches, and wet is greater than 2.1 inches.

ANTECEDENT PRECIPITATION—Precipitation which occurred prior to a particular time over a specific area or Drainage Basin. Usually applied as a measure of moisture in the top layer of the soil which would affect runoff from additional rainfall. Also see Antecedent Precipitation Index (API).

ANTECEDENT PRECIPITATION INDEX (API)—An index of moisture stored in a basin before a storm, calculated as a weighted summation of past daily precipitation amounts. Also see Antecedent Precipitation.

ANTECEDENT SOIL WATER—Degree of wetness of a soil prior to irrigation or at the beginning of a runoff period, typically expressed as an index.

ANTECEDENT STREAMS—Antecedent streams are those in place before the rising of mountain chains. As the mountains rise, the streams cut through at the same rate and so maintain their positions.

ANTEDILUVIAN—(1) Extremely old and antiquated. (2) Occurring or belonging to the era before the Flood written about in the Bible. (Ecology) Used sometimes today to denote a public growth and water policy based on an area's natural ability to support population growth only through existing, readily available natural resources, i.e., water.

ANTHROPOGENIC—Involving the impact of man on nature; induced, caused, or altered by the presence and activities of man, as in water and air pollution.

ANTHROPOGENIC SITES — Sites modified by human activities to the extent that their initial physical properties (e.g. structures, cohesion, consolidation) have been drastically altered. (Terrain Geology Task Group 1994) Includes Spoil Heaps, Fill, Waste Water, or Archaeological Sites.

ANTICYCLONE—An area of relatively high pressure in which, in the northern hemisphere, the winds tend to blow spirally outward in a clockwise direction.

ANTIDEGRADATION POLICY (or Clause) —Rules or guidelines that are required of each state by federal regulations implementing the Clean Water Act (CWA), stating that existing water quality be maintained even if the current water quality in an area is higher than the minimum permitted as defined by federal ambient water quality standards. Some controlled degradation is permitted in support of economic development.

ANTIFREEZE—A substance, often a liquid such as ethylene glycol or alcohol, mixed with another liquid, such as water, to lower its freezing point.

ANTIFLUORIDATIONIST—One who is strongly opposed to the fluoridation of public water supplies.

ANTI-SEEPAGE COLLAR—A projecting collar, usually of concrete, built around the outside of a pipe, tunnel, or conduit, or conduit under or through an Embankment Dam to lengthen the seepage path along the outer surface of the conduit.

APEX—The highest point on an Alluvial Fan or similar landform below which the flow path of the major stream that formed the fan becomes unpredictable and Alluvial Fan Flooding can occur.

APHOTIC—Defined as without light (Dark zone). Of or relating to the region of a body of water that is not reached by sunlight and in which Photosynthesis is unable to occur. The Aphotic Zone of the ocean is the water deeper than about 800 meters (2,625 feet), beyond which no light penetrates. Aphotic zone is the zone in which most photosynthetic algae cannot survive, due to light deficiency. Contrast with Photic Zone.

APHOTIC ZONE—The zone in which most photosynthetic algae can not survive due to light deficiency.

APHYTAL— The plantless zone of a lake bottom. See: Profundal.

API—Antecedent Precipitation Index.

APM—Aquatic Plant Management

APOTHECARIES' MEASURE—A system of liquid volume measure used in pharmacy.

APPLICABLE or APPROPRIATE REQUIREMENTS (ARARs)—Any state or federal statute that pertains to the protection of human life and the environment in addressing specific conditions or use of a particular cleanup technology at a Superfund Site.

APPLICATION RATE—For irrigation, the rate at which water is applied per unit of land area, usually expressed in terms of inches per hour.

APPLICATION, WATER RIGHT—An official request for permission to develop a source of water or to change an existing water right; includes a description of the proposed project, a map of the project, and a legal description of the property involved. The application for a water right will typically consists of the following information:

[1] the total amount of water to be diverted or pumped; [2] the rate of flow (diversion); [3] the point of diversion or pumpage; [4] the point or place of use; [5] the manner of (beneficial) use; and [6] the period of use (continuous pumpage, seasonal diversion, etc.).

The application process is the first step in a process of obtaining a certificate of use or a Perfected Water Right. This process includes:

[1] the filing of the application, which establishes the priority date for appropriation purposes; [2] the permit which is issued by the State Engineer or other approving authority; [3] the proof of completion which is filed by the applicant; [4] the proof of beneficial use which is also filed by the applicant; and [5] the certificate or perfected water right which is issued by the State Engineer or other approving authority.

APPLIED WATER DEMAND—The quantity of water delivered to the intake of a city's water system or factory, the farm headgate, or a marsh or other wetland, either directly or by incidental drainage. For in-stream use, it is the portion of the stream flow dedicated to in-stream use or reserved under federal or state Wild and Scenic River Acts. Applied water includes the water that returns to groundwater, a stream, canal, or other supply source that can be reused or recycled and thus is not the same as Net Water Demand.

APPROPRIATE—To authorize the use of a quantity of water to an individual requesting it.

APPROPRIATED WATER—A quantity of water from a well, stream, river, reservoir, or other source reserved for a specific use and place of use under state water-right laws, statutes, or regulations.

APPROPRIATE TECHNOLOGY—The application of current scientific knowledge and technology in such a way so as to conform with existing economic, infrastructure, social, and cultural conditions and practices. By extension, the concept implies the implementation of low-technology solutions incorporating simplicity of design, use, and maintenance.

(PRIOR) APPROPRIATION DOCTRINE—The system for allocating water to private individuals used in most Western states. The doctrine of Prior Appropriation was in common use throughout the arid west as early settlers and miners began to develop the land. The prior appropriation doctrine is based on the concept of "First in Time, First in Right." The first person to take a quantity of water and put it to Beneficial Use has a higher priority of right than a subsequent user. Under drought conditions, higher priority users are satisfied before junior users receive water. Appropriative rights can be lost through nonuse; they can also be sold or transferred apart from the land. Contrasts with Riparian Water Rights.

APPROPRIATIVE WATER RIGHTS [Nevada]—Nevada's water law is based on statutes enacted in 1903 and 1905 and are founded on the principal of Prior Appropriation. Unlike some other states, Nevada has a statewide system for the administration of both ground water and surface water. Appropriative water rights are based on the concept of applying water to Beneficial Use and "First in Time, First in Right." Appropriative water rights can be lost through nonuse and they may be sold or transferred apart from the land. Due in large part to the relative scarcity of water in Nevada and numerous competing uses, Nevada has had a thriving market for water transfers for a number of years. A person in Nevada who desires to place water to beneficial use must file an application with the State Engineer to initiate the process of acquiring an appropriative water right. Also see Riparian Water Rights, Prescribed Water Rights, and Reserved Water Rights (Federal).

APPROXIMATE ORIGINAL CONTOUR—The surface configuration achieved by backfilling and grading of mined areas so that the reclaimed area, including any terracing or access roads, closely resembles the general surface configuration of the land prior to strip mining and blends into and complements the drainage pattern of the surrounding terrain.

APPURTENANT—(1) (Legal) A right, privilege, or property that is considered incident to the principal property for purposes such as passage of title, conveyance, or passage of title. (2) (Water-Related) A right to water that is incident to the ownership or possession of the land.

APPURTENANT STRUCTURES (of a Dam)—Auxiliary features of a dam such as an outlet, spillway, powerhouse, tunnel, etc.

APPURTENANT TO PLACE OF USE—A water right has several characteristics, one of which is the location of where the water will be put to beneficial use. An Appurtenant Water Right is a water right that belongs to the legal owner of the land described as the place of use on the water right.

APPURTENANT WATER RIGHT—A water right that is incident to the ownership or possession of land.

APRON—(1) A platform, as of planking, at the entrance to a dock. (2) A covering or structure along a shoreline for protection against erosion. A platform serving a similar purpose below a dam or in a sluiceway. (3) An area covered by sand and gravel deposited in the front of a glacial moraine.

APWA—American Public Works Association.

AQUA—Water; an Aqueous solution. A prefix meaning water, e.g., Aquaculture.

AQUACADE—(1) A water spectacle originated at Cleveland, Ohio, in 1937; (2) A water spectacle that consists usually of exhibitions of swimming and diving with musical accompaniment.

AQUACULTURE, also Aquiculture—The science, art, and business of cultivating marine or freshwater food fish or shellfish, such as oysters, clams, salmon, and trout, under controlled conditions for commercial purposes. Examples of aquaculture plant products include rice and cranberries.

AQUALUNG—Equipment used by a person to breath underwater.

AQUAMARSH—A water body in which the original open water is nearly or completely obscured by emergent, and floating aquatic vegetation. A stage in the evolution between open water and land marsh.

AQUANAUT—A person trained to live in underwater installations and conduct, assist in, or be a subject of scientific research. Also called Oceanaut.

AQUAPONICS—The culture of plants in water areas (which includes lakes) in contrast to cultivation of plants on land, or geoponics.

AQUARIUM—(1) A tank, bowl, or other water-filled enclosure in which living fish or other aquatic animals and plants are kept. (2) A place for the public exhibition of live aquatic animals and plants.

AQUARIUS—(1) A constellation in the equatorial region of the Southern Hemisphere near Pisces and Aquila also referred to as the Water Bearer. (2) The 11th sign of the zodiac in astrology.

AQUASOL—A water soil. Water is the medium in which the plants grow.

AQUATIC—(1) Consisting of, relating to, or being in water; living or growing in, on, or near the water. (2) Taking place in or on the water. (3) An organism that lives in, on, or near the water.

AQUATIC ALGAE—Microscopic plants that grow in sunlit water containing phosphates, nitrates, and other nutrients. Algae, like all aquatic plants, add oxygen to the water and are important in the fish food chain.

AQUATIC BIOLOGY—Field of biological study that deals with aquatic plants and animals.

AQUATIC ECOSYSTEM—The basic unit of aquatic organisms and nonliving environment they live in.

AQUATIC INVERTEBRATES—Aquatic animals without an internal skeletal structure such as insects, mollusks, and crayfish.

AQUATIC LIFE—All forms of living things found in water, ranging from bacteria to fish and rooted plants. Insect larva and zooplankton are also included.

AQUATIC MACROPHYTES—Macrophytes (large plants versus microscopic) that live completely or partially in water.

AQUATIC MACROPHYTES HARVESTING—The manual and mechanical cutting and collecting of aquatic plants from lakes.

AQUATIC MICROBIOLOGY—Study of microscopic plants and animals and their interrelationships.

AQUATIC PLANT MANAGEMENT—Steps taken to evaluate, establish a management plan, and do something to change the amount and types of aquatic plants in a lake.

AQUATIC WEEDS—A common, unsightly, troublesome aquatic (water) plant, that grows in abundance or out of place. See Water Weeds.

AQUEDUCT—(1) A pipe, conduit, or channel designed to transport water from a remote source, usually by gravity. (2) A bridge-like structure supporting a conduit or canal passing over a river or low ground.

AQUEOUS—(1) Relating to, similar to, containing, or dissolved in water; watery. (2) (Geology) Formed from matter deposited by water, as certain sedimentary rocks.

AQUI—A prefix for water, e.g., Aquifer.

AQUIC—A mostly reducing soil moisture regime nearly free of dissolved oxygen due to saturation by groundwater or its capillary fringe and occurring at periods when the soil temperature at 50 centimeters is above 5C (41F).

AQUICLUDE (Confining Bed)—A formation which, although porous and capable of absorbing water slowly, will not transmit water fast enough to furnish an appreciable supply for a well or spring. Aquicludes are characterized by very low values of "leakage" (the ratio of vertical Hydraulic Conductivity to thickness), so that they transmit only minor inter-aquifer flow and also have very low rates of yield from compressible storage. Therefore, they constitute boundaries of aquifer flow systems.

AQUICULTURE—See Aquaculture. Compare with Mariculture.

AQUIFER—A geologic formation, a group of formations, or a part of a formation that is water bearing. A geological formation or structure that stores or transmits water, or both, such as to wells and springs. Use of the term is usually restricted to those water-bearing structures capable of yielding water in sufficient quantity to constitute a usable supply.

AQUIFER, BASIN-FILL—An aquifer located in a basin surrounded by mountains and composed of sediments and debris shed from those mountains. Sediments are typically sand and gravel with some clay.

AQUIFER COMPACTION—Term used to describe the effects of emptying or overdrawing an aquifer; overdrafts tend to collapse the structure of the aquifer such that the original volume cannot be restored. May also be associated with a general Land Subsidence in the surrounding ground level as the result of such compaction.

AQUIFER, CONFINED—An aquifer which is bounded above and below by formations of impermeable or relatively impermeable material. An aquifer in which ground water is under pressure significantly greater than atmospheric and its upper limit is the bottom of a bed of distinctly lower hydraulic conductivity than that of the aquifer itself. See Artesian Aquifer.

AQUIFER, FRACTURED BEDROCK—An aquifer composed of solid rock, but where most water flows through cracks and fractures in the rock instead of through pore spaces. Flow through fractured rock is typically relatively fast.

AQUIFER, LEAKY (Semi-confined)—An aquifer overlaid and/or underlain by a thin semipervious layer through which flow into or out of the aquifer can take place.

AQUIFER, PERCHED—A groundwater unit, generally of moderate dimensions, that occurs whenever a groundwater body is separated from the main groundwater supply by a relatively impermeable stratum and by the Zone of Aeration above the main water body.

AQUIFER, SALINE/POOR QUALITY—An aquifer containing water that is high in total dissolved solids, and is unacceptable for use as drinking water.

AQUIFER, SANDSTONE—The type of aquifer supplying groundwater to large parts of the United States upper Middle West, Appalachia, and Texas. The water-bearing formation is often contained by shale strata, and the water has high levels of iron and magnesium.

AQUIFER SYSTEM—A body of permeable and relatively impermeable materials that functions regionally as a water-yielding unit. It comprises two or more permeable units separated at least locally by confining units (Aquitards) that impede ground-water movement but do not greatly affect the regional hydraulic continuity of the system. The permeable materials can include both saturated and unsaturated sections.

AQUIFER TEST—A test to determine hydrologic properties of an aquifer, involving the withdrawal of measured quantities of water from, or the addition of water to, a well and the measurement of resulting changes in head in the aquifer both during and after the period of discharge or addition (recharge).

AQUIFER, UNCONFINED—An Aquifer made up of loose material, such as sand or gravel, that has not undergone lithification (settling). In an unconfined aquifer the upper boundary is the top of the Zone of Saturation (water table).

AQUIFER, VOLCANIC ROCK—An aquifer composed of rock that originated from a volcano, such as basalt. This type of rock may or may not be very permeable.

AQUIFUSE—A formation that has no interconnected openings and hence cannot absorb or transmit water.

AQUITARD—A saturated, but poorly permeable bed that impedes ground-water movement and does not yield water freely to wells, but which may transmit appreciable water to or from adjacent aquifers and, where sufficiently thick, may constitute an important ground-water storage unit. Aquitards are characterized by values of leakance that may range from relatively low to relatively high. Aerial extensive aquitards of relatively low leakance may function regionally as boundaries of aquifer flow systems.

ARABLE LAND—Land capable of being cultivated and suitable for the production of crops. The (U.S. Department of the Interior) Bureau of Reclamation (USBR) defines arable land as: "Land which, in adequate units and when properly provided with the essential improvements of leveling, drainage, buildings, irrigation facilities and the like, will have a productive capacity, under sustained irrigation agriculture, sufficient to: meet all production expenses, including a reasonable return on investment; repay reasonable irrigation and improvement costs; and provide a satisfactory level of living for the farm family."

ARARs—Applicable, Relevant, Appropriate Requirements.

ARBORETUM—A collection of plants, trees, and shrubs grown for public exhibition, public enjoyment, recreation, education, or research.

ARBORICULTURE—The planting, care, and tending of trees and shrubs, individually or in small groups, for utilitarian purposes.

ARC VIEW—Desktop computer software program that allows viewing, manipulation, and printing of maps of lands and lakes. It allows for spatial analysis to help local land/lake use planning.

ARCH DAM—Curved masonry or concrete dam, convex in shape upstream, that depends on arch action for its stability; the load or water pressure is transferred by the arch to the Abutments. Also see Dam.

ARCH-GRAVITY STRUCTURE—A structure which derives its resistance to the pressure of water from both an arching effect and its own weight.

ARCHIMEDEAN SCREW—An ancient apparatus for raising water, consisting of either a spiral tube around an inclined axis or an inclined tube containing a tight-fitting, broad-threaded screw. Also referred to as Archimedes' Screw.

ARCTIC—Referring to the region of the earth between the North Pole and Arctic Circle.

ARCTIC TUNDRA—The grassland Biome characterized by permafrost (subsurface soil that remains frozen throughout the year).

ARE—A metric unit of land measure equal to 100 square meters or 1/100 Hectare (119.6 square yards). Also see Metric System.

AREA-CAPACITY CURVE—A graph showing the relation between the surface area of the water in a reservoir and the corresponding volume.

AREA FLOODED—Area of a floodplain that is flooded in a specific stream reach, watershed, or river basin; may be for a single flood event, but is usually expressed as an average, annual value based on the sum of areas from all individual flood events over a long period of time, such as 50 to 100 years, and adjusted to an average value.

AREA (SUB-AREA), HYDROGRAPHIC—Primarily these are sub-drainage systems, typically valleys, within a more comprehensive drainage basin. Hydrographic Areas (Valleys) may be further subdivided into Hydrographic Sub-Areas based on unique hydrologic characteristics (e.g., differences in surface flows) within a given valley or area.

AREA (SUB-AREA), HYDROGRAPHIC [Nevada]—Nevada's 14 major drainage Basins or Hydrographic Regions are divided further into 232 Hydrographic Areas (valleys) and 256 Hydrographic Areas and Hydrographic Sub-Areas as defined by the U.S. Geological Survey (USGS) and the Nevada Division of Water Resources, Department of Conservation and Natural Resources. See Basins [Nevada]. [A listing of these Hydrographic Areas and Sub-Areas is presented in Appendix A-1 (listed sequentially by Hydrographic Area number and Hydrographic Region/Basin), Appendix A-2 (listed alphabetically by Hydrographic Area and Sub-Area name), and Appendix A-3 (listed alphabetically by principal Nevada county(ies) in which located).]

AREA OF A LAKE—The space occupied by the water surface. The area of a lake, generally, is something that cannot be determined with great exactitude; often the figure given is an arbitrary one, and figures from different sources show considerable disagreements. This comes about, because some error is inherent in any of the procedures devised for determining area; because measurements may be made from hydrographic maps which differ in accuracy and detail, and in time at which the map was made. This latter becomes important where lakes fluctuate greatly in levels. Some differences may arise also where different mathematical procedures are followed in making measurements. Also, often arbitrary decisions must be made as to location of shore line, the inclusion or exclusion of islands, and boundaries between a lake and connecting water, all of which consequently affect the computed area. Area is usually expressed square miles and acres; or where the metric system is used in square kilometers and square meters.

AREA OF CRITICAL ENVIRONMENTAL CONCERN (ACEC)—An area on Public Lands where special management attention is required to protect and prevent irreparable damage to historic, cultural, or scenic values, fish and wildlife resources, or other natural systems or processes, or to protect people from natural hazards.

AREA OF INFLUENCE—The area surrounding a pumping or recharging well within which the water table or potentiometric surface has been changed due to the well's pumping or recharge.

AREA OF ORIGINS PROTECTION—State and federal laws, dating back to 1931, enacted to guarantee that the counties that contribute water to state and federal water projects will get priority for water when it is needed to match future growth. As yet, these statutes have not received close legal scrutiny by the courts.

AREA OF REVIEW—The area around an underground injection well that may be influenced adversely by fluid injection. Typically, the extent of this area may be calculated by using the specific gravity and rate of introduction of the injected fluids, the size, storage capacity, and hydraulic conductivity of the injection zone, and certain underground formation pressures.

AREA OF SHALLOW FLOODING—Designated Flood Zones AO and AH on a community's Flood Insurance Rate Map (FIRM) with a one percent or greater annual chance of flooding to an average depth of one to three feet where a clearly defined channel does not exist, where the path of flooding is unpredictable and where velocity flow may be evident. Such flooding is characterized by ponding or sheet flow. Also referred to as Sheet Flow Area.

AREA OF SPECIAL FLOOD-RELATED EROSION HAZARD—The land within a community which is most likely to be subject to experience flood-related erosion losses. The area may be designated as Zone E on the Flood Insurance Rate Map (FIRM). See Flood Zones.

ARGILLIC ALTERATION (ARGILLIZATION)—A form of Hydrothermal alteration in which certain minerals of rock are converted to clay minerals.

ARHIZOUS—Plant without roots.

ARID—A term applied to a climate or region where precipitation is so deficient in quantity, or occurs so infrequently, that crop production is impractical without irrigation.

ARIDIC—A soil moisture regime that has no moisture available for plants for more than half the cumulative time that the soil temperature at 19.7 inches (50 centimeters) is above 5C (41F) and has no period as long as 90 consecutive days when there is moisture for plants while the soil temperature at 50 centimeters is continuously above 8C (46.4F).

ARIDITY—The quality or state of being arid, dry, or barren.

ARITHMETIC GROWTH—(Statistics) A rate of increase (or decrease) by a constant amount per time period, for example a population increase of X persons per year, year after year. Compare to Exponential Growth and Sigmoid Growth.

ARITHMETIC MEAN—(Statistics) The sum of a set of observations divided by the number of observations. Also referred to as simply the Mean, or the Sample Mean. Compare to Mode and Median.

ARM—(1)An inlet of water (as from the sea). (2) (Lakes) A long and relatively narrow body of water extending inland from a main body. Usually the term arm is applied to a reach of water, greater in length and narrower than one called a bay, but often on maps no clear distinction exists between arm and bay: nor between arm and lobe.

ARMA—AutoRegressive Moving Average.

ARMORING—A facing layer (protective cover), or Rip Rap, consisting of very large stones placed to prevent erosion or the sloughing off of a structure or embankment. Also, a layer of large stones, broken rocks or boulders, or pre-cast blocks placed in random fashion on the upstream slope of an Embankment Dam, on a reservoir shore, or on the sides of a channel as a protection against waves, ice action, and flowing water. The term armoring generally refers only to very large rip rap.

(UNITED STATES) ARMY CORPS OF ENGINEERS (Corps or COE)—Originally formed in 1775 during the Revolutionary War by General George Washington as the engineering and construction arm of the Continental Army. Initially, the Corps of Engineers built fortifications and coastal batteries to strengthen the country's defenses and went on to found the Military Academy at West Point, help open the West, and to develop the nation's water resources. In its military role, the COE plans, designs, and supervises the construction of facilities to insure the combat readiness of the U.S. Army and Air Forces. In its civilian role, the COE has planned and executed national programs for navigation and commerce, flood control, water supply, hydroelectric power generation, recreation, conservation, and preservation of the environment. In a very general sense, the U.S. Army Corps of Engineers has a primary responsibility for water projects which protect property from potential flood damage, whereas the (U.S. Department of the Interior) Bureau of Reclamation (USBR) is responsible for primarily western water projects with respect to developing water sources for agriculture and commerce. In reality, however, quite often these federal agencies' project goals overlap with USBR's dams and reservoirs providing important flood protection and the COE's water projects—dams, locks, and canals—providing important water transportation linkages and benefits to commerce. [See Appendix C-2 for the U.S. Army Corps of Engineers' organizational structure and primary missions and objectives.]

ARRANGED DELIVERY—Operation of a water delivery system to meet predetermined needs, generally based on user water orders. Also referred to as Scheduled Delivery.

ARRASTRA—A crude drag-stone mill for pulverizing ores, especially those containing free gold or silver; frequently powered by falling water.

ARROYO—A water-carved channel or gully in an arid country which is usually rather small with steep banks and is dry much of the time due to infrequent rainfall and the shallowness of the cut, which does not penetrate below the level of permanent ground water.

ARS—Agricultural Research Service.

ARS—Agricultural Restructuring Scenario.

ARTESIAN—A commonly used expression, generally synonymous with Confined and referring to subsurface (ground) bodies of water which, due to underground drainage from higher elevations and confining layers of soil material above and below the water body (referred to as an Artesian Aquifer), result in underground water at pressures greater than atmospheric.

ARTESIAN AQUIFER—A commonly used expression, generally synonymous with (but a generally less favored term than) Confined Aquifer. An artesian aquifer is an aquifer which is bounded above and below by formations of impermeable or relatively impermeable material. An aquifer in which ground water is under pressure significantly greater than atmospheric and its upper limit is the bottom of a bed of distinctly lower hydraulic conductivity than that of the aquifer itself.

ARTESIAN PRESSURE—The pressure under which Artesian Water in an Artesian Aquifer is subjected, generally significantly greater than atmospheric.

ARTESIAN WATER—Ground water that is under pressure when tapped by a well and is able to rise above the level at which it is first encountered. It may or may not flow out at ground level. The pressure in such an aquifer commonly is called Artesian Pressure, and the formation containing artesian water is an Artesian Aquifer or Confined Aquifer.

ARTESIAN WELL—(1) A well bored down to the point, usually at great depth, at which the water pressure is so great that the water is forced out at the surface. The name is derived from the French region of Artois, where the oldest well in Europe was bored in 1126. (2) A well tapping a Confined or Artesian Aquifer in which the static water level stands above the top of the aquifer. The term is sometimes used to include all wells tapping confined water. Wells with water levels above the unconfined water table are said to have positive artesian head (pressure) and those with water level below the unconfined water table, negative artesian head. If the water level in an artesian well stands above the land surface, the well is a Flowing Artesian Well. If the water level in the well stands above the water table, it indicates that the artesian water can and probably does discharge to the unconfined water body.

ARTESIAN ZONE—A zone where water is confined in an aquifer under pressure so that the water will rise in the well casing or drilled hole above the bottom of the confining layer overlying the aquifer.

ARTICULATION—(of a lake) The ratio of area of inlets and bays to the total area of the lake.

ARTIFICIAL BEACH—A bathing beach created by removing peat or muck and subsequently filling with sand or fine gravel. Sand may also be spread over clay shore to create a more desirable beach. In a few instances sand is placed on a polyethylene (plastic) blanket which has been spread over soft bottom, but this kind of beach is not considered permanent. Groins are frequently constructed on the Great Lakes shoreline to trap shore drift thereby creating a beach.

ARTIFICIAL CIRCULATION—The mixing of lake water using an air bubble stream or other mechanical means rather or in addition to the wind mixing.

ARTIFICIAL LAKES, PONDS—Basins purposely excavated by man and filled with water by catchment from run-off, by pumping or diversion of natural water bodies. Definitely artificial are those ponds constructed for farm use, for receiving factory wastes, sewage, etc. However, there are degrees of artificiality. Bodies of water impounded by dams across rivers are artificial only to a degree as are lakes whose basins have been altered by dredging or filling or whose levels has been raised or lowered respectively by dams across outlets or by dredging outlets. A gravel pit or stone quarry is patently an artificial basin, but its filling with water, after abandonment, may be a natural process. Ponds occupying mine cave-in pits can hardly be accepted as natural geomorphological features, neither are they intentionally constructed and filled with water by man. Wherever man has made use of the water or occupied the adjacent land, he has modified natural lakes to some degree, and to that degree made them artificial.

ARTIFICIAL RECHARGE—The designed (as per man's activities as opposed to the natural or incidental) replenishment of ground water storage from surface water supplies such as irrigation or induced infiltration from streams or wells. There exist five (5) common techniques to effect artificial recharge of a groundwater basin:

[1] Water Spreading consisting of the basin method, stream-channel method, ditch method, and flooding method, all of which tend to divert surface water supplies to effect underground infiltration; [2] Recharge Pits designed to take advantage of permeable soil or rock formations; [3] Recharge Wells which work directly opposite of pumping wells, although they generally have limited scope and are better used for deep, confined aquifers; [4] Induced Recharge which results from pumping wells near surface supplies, thereby inducing higher discharge towards the well; and [5] Wastewater Disposal which includes the use of secondary treatment wastewater in combination with spreading techniques, recharge pits, and recharge wells to reintroduce the water into deep aquifers thereby both increasing the available groundwater supply and also further improving the quality of the wastewater.

Also referred to as Induced Recharge. Also see Natural Recharge, Incidental Recharge, Injection, and Perennial Yield.

ARTIFICIAL SUBSTRATE—A device placed in the water for a specified period of time that provides living spaces for a multiplicity of organisms; for example, glass slides, concrete blocks, multi-plate samplers, or rock baskets; used primarily to collect organisms in areas where the physical habitat is limiting or cannot be adequately sampled using conventional methods.

ASBESTOS—A mineral fiber that can pollute air or water and cause cancer or Asbestosis when inhaled. The U.S. Environmental Protection Agency (EPA) has banned or severely restricted its use in manufacturing and construction.

ASBESTOSIS—A disease associated with inhalation of Asbestos fibers. The disease makes breathing progressively more difficult and can be fatal.

ASC—Atmospheric Sciences Center (DRI).

ASCE—American Society of Civil Engineers.

ASEXUAL REPRODUCTION—Plants reproducing without the sexual process by fragmentation, turions, tubers, and/or other vegetative structures.

ASOS—Automated Surface Observing System (NWS/NOAA)

ASPECT—The compass direction toward which a sloping land area faces. The direction is measured downslope and normal to the contours of elevation.

ASPERSE—To sprinkle, especially with holy water.

ASSESSMENT REPORT—A comprehensive record of historical, existing and projected water quality conditions of a particular watershed.

ASSIGNMENT OF WATER—The transfer of a water right application or permit from one person to another. This can be done in conjunction with the sale of land.

ASSIMILATION—The ability of a body of water to purify itself of pollutants.

ASSIMILATIVE CAPACITY—(1) The ability of air, a natural body of water, or soil to effectively degrade and/or disperse chemical substances. If the rate of introduction of pollutants into the environment exceeds its assimilative capacity for these substances, then adverse effects may result to habitat and wildlife. (2) Its the ability of a lake to absorb nutrients or other potential pollutants without showing averse effects.

ASSOCIATION—(Lake) A voluntary union of riparians whose purpose is management or development, or use or conservation of riparian lands and lake surface. Their union may vary from a gentlemen's agreement or may be in the form of a profit or non-profit corporation.; In some instances the prospective buyer must become a member of the lake association prior to the purchase of frontage; continuous membership in the association becomes part of the purchase contract.

ASSOCIATION OF BOARDS OF CERTIFICATION—An international organization representing boards which certify the operators of waterworks and wastewater facilities.

ASTHENOSPHERE—The zone inside the earth beneath the Lithosphere constituting the source of Igneous rock (Magma).

ATHALASSOHALINE LAKE—A term used to describe a saline lake which is not of marine origin. In this respect athalassohaline lakes differ from lakes formed by the isolation of part of the ocean in as much as those lakes originating from evaporation of fresh water is the importance of bivalent ions such as calcium, magnesium, and sulfate relative to the dominance of two monovalent ions (sodium and chloride) in sea water. The different ionic ratios are important biologically because the osmotic strength of a solution at a given level of Total Dissolved Solids (TDS) changes with the valence of the dominant ions. The individual ion concentrations are also important in that some ions are more toxic to fish than others.

ATMOMETER—An instrument used to measure the rate of evaporation.

ATMOSPHERE—The gaseous layer covering the earth. The regions of the atmosphere are the Troposphere, Stratosphere, Mesosphere, Chemosphere, and the Thermosphere (which overlaps the Ionosphere and the Exosphere). The atmosphere is one of the four components, together with the Lithosphere, Hydrosphere, and Biosphere, that comprise the earth's ecosystem. Also see Air.

ATP—Adenosine TriPhosphate.

ATRAZINE—A herbicide listed by the U.S. Environmental Protection Agency (EPA) as a "possible human carcinogen" and found frequently in streams and rivers, particularly following floods and periods of heavy rain and runoff from agricultural lands. Atrazine is used extensively for weed control for corn, sorghum, and sugarcane. Along with another common farm herbicide, Cyanazine, atrazine concentrations can soar to levels much higher than federal standards during the peak growing season.

ATTACHED GROUND WATER—The portion or amount of alkali substances in the ground sufficient to raise the pH value above 7.0 or to be harmful to the growth of crops, a condition called alkaline.

ATTENUATION—(1) Generally, a term used to describe the slowing, modification, or diversion of the flow of water as with Detention and Retention. (2) (Water Quality) The process of diminishing contaminant concentrations in ground water, due to filtration, biodegradation, dilution, sorption, volatilization, and other processes. (3) The process where by the magnitude of an event is reduced, as the reduction and spreading out of the impact of a storms effect. Also see Natural Attenuation.

ATTERBERG LIMITS—The transition points between various states of soil consistency. The Atterberg Limits consist of: (1) the liquid limit (water content at which the soil passes from the liquid to the plastic state); (2) the plastic limit (water content at which the soil passes from the plastic to the semi-solid state); and (3) the shrinkage limit (water content at which the soil passes from the semi-solid to the solid state).

AUDUBON SOCIETY (NATIONAL)—A national environmental organization founded in 1905 and dedicated to the conservation and restoration of natural ecosystems with a focus on birds and other wildlife species for the benefit of humanity and the earth's biological diversity. Named after John James Audubon (1785-1851) who was one of the first American conservationists and who gained widespread recognition for his paintings of birds.

AUM—Animal Unit Month.

AUSTRAL—Southern as in southern pine forest. See Boreal.

AUTO-QI—Automated Q-ILLUDAS.

AUREOLE—(Astronomy) A faintly colored luminous ring appearing to surround a celestial body visible through a haze or thin cloud of water vapor, especially such a ring around the moon or sun, caused by the diffraction of light from suspended matter in the intervening medium. Also referred to as Corona.

AUTOCHTHONOUS—Pertaining to substances (organic matter from plankton), materials, or organisms originating within a particular waterway or lake and remaining in that waterway.

AUTOREGRESSION, or Autoregressive Process—(Statistics) A condition which exists whenever a lagged (i.e., prior period) value of the Dependent Variable, or the variable to be explained, appears as a regressor, that is, as an Explanatory Variable. The fundamental assumption is that future data values may be expressed as linear combinations of past observations. It is not uncommon in economics and other areas of scientific study for a variable to be influenced by its own behavior in prior periods. The problem with this equation (model) format is to insure that the lagged variable, represented below as Yt-1, is independent of the disturbance term, t. An example of a (first-order) autoregressive process, commonly termed AR(1), would be represented by:

Yt = ø1Yt-1 + ð + et

where the parameter ø1 < 1, and ð is the (constant, time insensitive) trend component, and et is the residual or disturbance term associated with each observation of Yt.

AUTOTROPHIC—Plants that produce their own nutrients. If photosynthetic and green then it contains chlorophyll.

AUTUMN TURNOVER—The mixing of the entire water mass of a lake in the autumn.

AUTUMNAL—Appearing or flowering in the fall.

AUXILIARY SPILLWAY—A dam spillway built to carry runoff in excess of that carried by the principal spillway; a secondary spillway designed to operate only during exceptionally large floods. Also referred to as Emergency Spillway. Also see Spillway.

AVAILABLE WATER—The portion of water in a soil that can be absorbed by plant roots, usually considered to be that water held in the soil against a tension of up to approximately 15 atmospheres.

AVAILABLE WATER HOLDING CAPACITY—The capacity of a soil to hold water in a form available to plants. Also, the amount of moisture held in the soil between field capacity, or about one-third atmosphere of tension, and the wilting coefficient, or about 15 atmospheres of tension.

AVALANCHE—A fall or slide of a large mass, as of snow or rock, down a mountainside.

AVERAGE ANNUAL FLOOD DAMAGES—The weighted average of all flood damages that would be expected to occur yearly under specified economic conditions and development. Such damages are computed on the basis of the expectancy in any one year of the amounts of damage that would result from floods throughout the full range of potential magnitude.

AVERAGE ANNUAL RECHARGE—The amount of water entering an aquifer on an average annual basis. In many, if not most, hydrologic conditions, "average" has little significance for planning purposes as there may exist so few "average" years in fact.

AVERAGE ANNUAL RUNOFF (YIELD)—The average of water-year (October 1-September 30) runoff or the supply of water produced by a given stream or water development project for a total period of record; measured in cubic feet per second or acre-feet.

AVERAGE DISCHARGE—In the annual series of the U.S. Geological Survey's (USGS) reports on surface-water supply, the arithmetic average of all complete water years of record whether or not they are consecutive. Average discharge is not published for less than 5 years of record. The term "average" is generally reserved for average of record and "mean" is used for averages of shorter periods, namely daily mean discharge.

AVERAGE WATER YEAR—A tern denoting the average annual hydrologic conditions based upon an extended or existing period of record. Because precipitation, runoff, and other hydrologic variables vary from year to year, planners typically project future scenarios based on hydrologic conditions that generally include average, wet (high-water), and drought (low-water) years.

AVERAGE YEAR WATER DEMAND—The demand for water under average hydrologic conditions for a defined level of development.

AVERAGE YEAR WATER SUPPLY—The average annual supply of a water development system over a long period. For a dedicated natural flow, it is the long-term average natural flow for wild and scenic rivers or it is Environmental Flows as required for an average year under specific agreements, water rights, court decisions, and congressional directives.

AVIGATIONAL TRESPASS—Persons using a float plane to gain access to a private lake without permission, trespass first on the air or avigational rights of the lake owners, then by landing on the surface of the lake, they commit simple trespass.

ÄVJA-GYTTJA—Lake bottom deposit composed largely of the remains of algae. See Gyttja.

AVOIRDUPOIS WEIGHT—The system in common use in English-speaking countries for weighing all commodities except precious stones, precious metals, and drugs. In it 16 drams (dr.) make 1 ounce (oz.), 16 ounces make 1 pound (lb.). The pound contains 7,000 grains (453.59 grams) and is equal to 1.2153 pounds troy (or, 1 lb.=14.5833 troy oz.). There are two avoirdupois tons, the long ton (2,240 pounds) and the short ton (2,000 pounds), of which the long ton is the customary one in Great Britain and the short ton is used in the United States. Also see Metric System.

AVULSION—(1) The sudden movement of soil from one property to another as a result of a flood or a shift in the course of a boundary stream. (2) A forcible separation or detachment; a sudden cutting off of land by flood, currents, or change in course of a body of water; especially one separating land from one person's property and joining it to another's.

AW—Applied Water

AWASH—Washed by the sea as level with or washed by waves. In such a position or way as to be covered with or as if with water.

AWT—Advanced Wastewater Treatment

AWWA—American Water Works Association.

AXIAL FLOW—Fluid flow in the same direction as the axis of symmetry of the duct, vessel, or tank.

AXIS (of a Dam)—The horizontal centerline of a dam in the longitudinal direction.

AZOTOBACTER—Any of various rod-shaped, nonpathogenic, nitrogen-fixing bacteria of the genus azotobacter, found in soil and water

B-HORIZON—The lower soil zone which is enriched by the deposition or precipitation of material from the overlying zone, or A-Horizon. Along with the A-horizon, constitutes part of the Zone of Eluviation.

BABBLE—to make a continuous low, murmuring sound, as flowing water.

BAC—see Biological Activated Carbon (BAC) Process.

BACKBAR CHANNEL—A channel formed behind a bar connected to the main channel but usually at a higher bed elevation than the man channel. Backbar channels may or may not contain flowing or standing water.

BACKFILL, or Backfilling—process of filling the notches carved in the earth from strip mining in order to restore the original slope. This is intended to reduce soil erosion and allow for the reestablishment of vegetation.

BACKFLOW—the backing up of water through a conduit or channel in the direction opposite to normal flow. A reverse flow condition created by a difference in water pressures that causes water to flow back into the distribution pipes of a drinking water supply from any source other than the intended one. Also referred to as Back Siphonage.

BACKGROUND—Value for a parameter that represents the conditions in a system prior to a given influence in space or time.

BACK PRESSURE—a pressure that can cause water to Backflow into the water supply when a user's waste water system is at a higher pressure than the public system.

BACKRUSH—the seaward return of water after the landward motion of a wave. Also referred to as Backwash.

BACKSET—An eddy or countercurrent in water.

BACKSHORE—The part of a shore between the Foreshore and the landward edge that is above high water except in the most severe storms.

BACK SIPHONAGE—A reverse flow condition created by a difference in water pressures that causes water to flow back into the distribution pipes of a drinking water supply from any source other than the intended one. Also referred to as Backflow.

BACK SWAMP—Marshy area of a flood plain at some distance from and lower than the banks of a river confined by natural levees.

BACKWASH—A backward flow or water, also referred to as Backrush. (Water Quality) The reversal of flow through a rapid sand filter to wash clogging material out of the filtering medium and reduce conditions causing loss of head (pressure).

BACKWASHING—In a wastewater or water treatment facility, the flow of clean water in a direction opposite (upward) to the normal flow of raw water through rapid sand filters in order to clean them.

BACKWATER—(1) A small, generally shallow body of water attached to the main channel, with little or no current of its own. (2) Water backed up or retarded in its course as compared with its normal or natural condition of flow. In Stream Gauging, a rise in Stage produced by a temporary obstruction such as ice or weeds, or by the flooding of the stream below. The difference between the observed stage and that indicated by the Stage-Discharge Relation, is reported as backwater.

BACKWATER CURVE—The longitudinal profile of the water surface in an open channel where the water surface is raised above its normal level by a natural or artificial obstruction. The term is sometimes used in a generic sense to denote all water surface profiles, or profiles where the water is flowing at depths greater than critical.

BACKWATER EFFECT—The rise in surface elevation of flowing water upstream from and as a result of an obstruction to flow. In stream gaging, a rise in stage produced by a temporary obstruction such as ice or weeds, or by the flooding of the stream below. The difference between the observed stage and that indicated by the stage-discharge relation is reported as backwater.

BACKWATER FLOODING—Flooding caused by a restriction or blocking of flow downstream. Examples include a narrowing of the channel, logjam, ice jam, high flow in a downstream confluence stream, or high tide blocking high river flows from entering estuaries.

BACKWATER POOLS—A pool type formed by an eddy along channel margins downstream from obstructions such as bars, rootwads, or boulders, or resulting from backflooding upstream from an obstructional blockage. Backwater pools are sometimes separated from the channel by sand or gravel bars.

BACTERIA (Singular: Bacterium)—Microscopic unicellular organisms, typically spherical, rod-like, or spiral and threadlike in shape, often clumped into colonies. Some bacteria cause disease, while others perform an essential role in nature in the recycling of materials, for example, decomposing organic matter into a form available for reuse by plants. Some forms of bacteria are used to stabilize organic wastes in wastewater treatment plants, oil spills, or other pollutants. Disease-causing forms of bacteria are termed "pathogenic." Some forms of bacteria harmful to man include:

[1] Total Coliform Bacteria—A particular group of bacteria that are used as indicators of possible sewage pollution. They are characterized as aerobic or facultative anaerobic, gram-negative, nonspore-forming, rod-shaped bacteria which ferment lactose with gas formation within 48 hours at 3C. In the laboratory these bacteria are defined as all the organisms that produce colonies with a golden-green metallic sheen within 24 hours when incubated at 35C plus or minus 1.0C on M-Endo medium (nutrient medium for bacterial growth). Their concentrations are expressed as numbers of colonies per 100 milliliter (ml)l of sample. [2] Fecal Coliform Bacteria—Bacteria that are present in the intestine or feces of warm-blooded animals. They are often used as indicators of the sanitary quality of the water. In the laboratory they are defined as all the organisms that produce blue colonies within 24 hours when incubated at 44.5C plus or minus 0.2C on M-FC medium (nutrient medium for bacterial growth). Their concentrations are expressed as numbers of colonies per 100 ml of sample. [3] Fecal Streptococcal Bacteria—Bacteria found also in the intestine of warm-blooded animals. Their presence in water is considered to verify fecal pollution. They are characterized as gram-positive, cocci bacteria which are capable of growth in brain-heart infusion broth. In the laboratory they are defined as all the organisms that produce colonies which produce red or pink colonies within 24 hours at 35C plus or minus 1.0C on KF-streptococcus medium (nutrient medium for bacterial growth). Their concentrations are expressed as numbers of colonies per 100 ml of sample.

BACTERIAL PLATE COUNT—A system used to quantify the number of bacteria in a sample of solid or liquid material by measuring the growth of bacterium into full colonies.

BACTERICIDAL—Able to kill bacteria.

BACTERIOSTATIC—A substance that inhibits bacterial growth but is not necessarily lethal.

BADLANDS—Barren land characterized by roughly eroded ridges, peaks, and mesas.

BADT—Best Available Demonstrated Technology.

BAFFLE—A flat board or plate, deflector, guide, or similar device constructed or placed in flowing water or slurry systems to cause more uniform flow velocities to absorb energy and to divert, guide, or agitate liquids.

BAG OF WATERS—The double-walled fluid-filled sac that encloses and protects the fetus in the womb and that breaks releasing its fluid during the birth process

BAIL—To remove water, as from the bottom of a boat or other vessel.

BAILER—An instrument such as a long pipe with a valve at the lower end used to extract a water sample from a groundwater well. Also used to remove slurry from the bottom or side of a well as it is being drilled.

BAJADA—A long outwash detrital (sedimentary) slope at the base of a mountain range.

BALANCED OPERATION—Operation of a canal system where the water supply exactly matches the total flow demand.

BALANCED GROUNDWATER SCENARIO (BGS)—A term referring to the development of a scenario exploring changes in cropping patterns such that long-term ground water withdrawals do not exceed long-term groundwater recharge rates. Also see Agricultural Restructuring Scenario (ARS), Ground Water Overdraft, and Ground Water Mining.

BALLAST—Heavy material, often seawater, placed in the hold of a ship to gain stability. Periodic discharges of this ballast water from oil tankers constitute a significant portion of the oil introduced into the oceans of the world each year.

BALL COCK—A self-regulating device controlling the supply of water in a tank, cistern, or toilet by means of a float connected to a valve that opens or closes with a change in water level.

BALL VALVE—A valve regulated by the position of a free-floating ball that moves in response to fluid or mechanical pressure.

BANK, and BANKS—The slope of land adjoining a body of water, especially adjoining a river, lake, or a channel. With respect to flowing waters, banks are either right or left as viewed facing in the direction of the flow. As Banks, a large elevated area of a sea floor.

BANK AND CHANNEL STABILIZATION—Implementation of structural features along a streambank to prevent or reduce bank erosion and channel degradation.

BANKFULL STAGE—The stage at which a stream first begins overflows its natural banks. More precisely, an established river stage at a given location along a river which is intended to represent the maximum safe water level that will not overflow the river banks or cause any significant damage within the river reach. Bankfull stage is a hydraulic term, whereas Flood Stage implies resultant damage.

BANKING (WATER)—See Water Banking.

BANK STORAGE—The water absorbed into the banks of a stream, lake, or reservoir, when the stage rises above the water table in the bank formations, then returns to the channel as effluent seepage when the stage falls below the water table. Bank storage may be returned in whole or in part as seepage back to the water body when the level of the surface water returns to a lower level.

BAPTISM—(1) A Christian sacrament marked by ritual use of water and admitting the recipient to the Christian community; (2) A non-Christian rite using water for ritual purification.

BAR—(1) An elongated landform generated by waves and currents, usually running parallel to the shore, composed predominantly of unconsolidated sand, gravel, stones, cobbles, or rubble and with water on two sides. (2) A unit of pressure equal to 106 dynes per cm2, 100 kilopascals, or 29.53 inches of mercury.

BAROTHERMOGRAPH—An instrument which records simultaneous barometric pressure and temperature on the same chart.

BAR RACKS—(Water Quality) The closely spaced rods, often in the form of a screen, that remove large solids from the wastewater entering a sewage treatment plant.

BARRAGE—An artificial obstruction, such as a dam or an irrigation channel, built in a watercourse to increase its depth or to divert its flow either for navigation or irrigation. Sometimes the purpose is to control peak flow for later release.

BARREL—(1) A measure of liquid volume (conventionally) equal to 42 U.S. gallons (34.9723 Imperial gallons), or 158.9873 liters. (2) Any of various units of volume or capacity. In the U.S. Customary System, it varies, as a liquid measure, from 31 to 42 U.S. gallons (approximately 120 to 159 liters) as established by law or usage.

BAR SCREEN—(Water Quality) In wastewater treatment, a device used to remove large solid materials.

BASALT—(Geology) A dark volcanic rock composed of microscopic grains of augite, feldspar, and olivine. Some basalts have many holes that give the rock a swiss-cheese-like appearance. As the lava cools, gases escape, leaving holes of different sizes.

BASALT AQUIFERS—Aquifers found in basalt rock in areas of past volcanic activity, particularly in the Pacific Northwest region of the United States and in Hawaii.

BASE—(1) Any of various typically water-soluble and bitter tasting compounds that in solution have a pH greater than 7, are capable of reacting with an acid to form a salt, and are molecules or ions able to take up a proton from an acid or able to give up an unshared pair of electrons to an acid. (2) Chemicals that release hydroxide ions (OH-) in solution. Such solutions have a soapy feel, neutralize acids, and conduct electricity.

BASE FLOOD (100-YEAR FLOOD)—The flood having a 1 percent average probability of being equaled or exceeded in a given year at a designated location. It may occur in any year or even in successive years if the hydrologic conditions are conducive for flooding. Also see Hundred-Year Flood, X-Year Flood, and X-Year Flood, Y-Duration Rain.

BASE FLOOD ELEVATION—The height in relation to mean sea level (MSL) expected to be reached by the waters of the base flood at pertinent points in the floodplain of Riverine areas.

BASE FLOODPLAIN—The floodplain that would be inundated by a one percent chance flood (100-Year Flood).

BASE FLOW—The fair-weather or sustained flow of streams; that part of stream discharge not attributable to direct runoff from precipitation, snowmelt, or a spring. Discharge entering streams channels as effluent from the groundwater reservoir. Also referred to as Groundwater Flow.

BASE LEVEL—The lowest level to which a land surface can be reduced by the action of running water.

BASELINE—The condition that would prevail if no action were taken.

BASELINE (DATA)—A quantitative level or value from which other data and observations of a comparable nature are referenced. Information accumulated concerning the state of a system, process, or activity before the initiation of actions that may result in changes.

BASE PERIOD—A period of time specified for the selection of data for analysis. The base period should be sufficiently long to contain data representative of the averages and deviations from the averages that must be expected in other periods of similar and greater length. For example, the U.S. Weather Bureau computes values of average, heavy, and light monthly precipitation from data observed during the base period of 1931-1960. For ground-water studies, the base period should both begin and end at the conclusion of a dry trend so that the difference between the amount of water in transit in the soil at the ends of the base period is minimal.

BASE RUNOFF—Sustained or fair weather runoff. In most streams, base runoff is composed largely of ground-water effluent. The term base flow is often used in the same sense as base runoff. However, the distinction is the same as that between streamflow and runoff. When the concept in the terms base flow and base runoff is that of the natural flow in a stream, base runoff is the more appropriate term.

BASE WIDTH—(1) The time interval between the beginning and end of the direct runoff produced by a storm. (2) The time period covered by a Unit Hydrograph.

BASIC—Describing a solution, sediment, or other material that has a pH greater than 7.0. see Alkaline

BASIC HYDROLOGIC DATA—Includes inventories of features of land and water that vary only from place to place (e.g., topographic and geologic maps), and records of processes that vary with both place and time (e.g., records of precipitation, streamflow, ground-water, and quality-of-water analyses). Basic Hydrologic Information is a broader term that includes surveys of the water resources of particular areas and a study of their physical and related economic processes, interrelations and mechanisms.

BASIN—(1) A geographic area drained by a single major stream; consists of a drainage system comprised of streams and often natural or man-made lakes. Also referred to as Drainage Basin, Watershed, or Hydrographic Region. (2) A naturally or artificially enclosed harbor for small craft, such as a yacht basin.

BASIN AND RANGE [Nevada]—A region of north-trending mountains ranges and valleys encompassing western Utah and essentially all of Nevada. This geologic territory includes virtually all of the Great Basin and extends south and east through Arizona, New Mexico, and Texas all the way into Mexico. The Basin and Range can be differentiated from its surrounding geologic regions by its uplifted and tilted ranges separated by broad elongated basins. The Great Basin forms a unique part of this geologic region in as much as this hydrologic area has no drainage to the ocean.

BASIN FILL—Unconsolidated material such as sand, gravel, and silt eroded from surrounding mountains and deposited in a valley.

BASIN LAG—(1) The time from the centroid (centermost point in time based on total period rainfall) of rainfall to the hydrograph peak. (2) The time from the centroid of rainfall to the centroid of the Unit Hydrograph.

BASIN MANAGEMENT (of Water)—Also referred to as Water or Watershed Management, it is the analysis, protection, development, operation, or maintenance of the land, vegetation, and water resources of a drainage basin for the conservation of all its resources for the benefit of man. Basin management for water production is concerned with the quality, quantity, and timing of the water which is produced.

BASIN YIELDS—The amount of water which will flow from a drainage or catchment area in a given storm.

BASINS [Nevada]—The U.S. Geological Survey (USGS) and the Nevada Division of Water Resources, Department of Conservation and Natural Resources, have divided the state into discrete hydrologic units for water planning and management purposes. These have been identified as 232 Hydrographic Areas (256 areas and sub-areas, combined) within 14 major Hydrographic Regions or Basins. These 14 Nevada Hydrographic Regions (Basins), along with the approximate surface areas, counties of coverage, and number of hydrographic areas and sub-areas are:

[1] Northwest Region—Covers 3,052 square miles (1,953,280 acres) of northern Washoe and Humboldt counties and encompasses 16 hydrographic areas; [2] Black Rock Desert Region—Covers 8,632 square miles (5,524,480 acres) of parts of Washoe, Humboldt, and Pershing counties and includes 17 valleys (hydrographic areas), two of which are divided into two sub-areas each; [3] Snake River Basin—Covers 5,230 square miles (3,347,200 acres) in parts of Elko and Humboldt counties to include eight hydrographic areas; [4] Humboldt River Basin—Covers over 16,843 square miles (10,779,520 acres) in parts of eight counties—Elko, White Pine, Eureka, Humboldt, Lander, Nye, Pershing, and Churchill—and the largest stream (Humboldt River) wholly within Nevada. This basin contains 34 hydrographic areas and one sub-area; [5] West Central Region—Covers 1,656 square miles (1,059,840 acres) and includes parts of Pershing, Lyon, and Churchill counties and comprises five hydrographic areas; [6] Truckee River Basin—Encompasses 2,300 square miles (1,472,000 acres) containing parts of Washoe, Pershing, Douglas, Carson City, and Storey counties comprising 12 hydrographic areas; [7] Western Region—Covers 602 square miles (385,280 acres) and is wholly contained in Washoe County and contains nine valleys (hydrographic areas) one of which is divided into two sub-areas and another divided into one sub-area; [8] Carson River Basin—Covers 3,634 square miles (2,325,760 acres) and includes parts of six counties—Douglas, Carson City, Lyon, Storey, Churchill, and Pershing—containing five hydrographic areas and one sub-area along the Carson River and its tributaries; [9] Walker River Basin—Covers 2,931 square miles (1,875,840 acres) of Mineral, Lyon, and Douglas counties (and a very small portion of Churchill County) including five hydrographic areas, one of which has been divided into three sub-areas; [10] Central Region—By far the largest hydrographic region in Nevada covering 46,783 square miles (29,941,120 acres) in 13 counties—Nye, Elko, White Pine, Lincoln, Clark, Humboldt, Pershing, Churchill, Lander, Eureka, Lyon, Mineral, and Esmeralda. This region includes 78 valleys (hydrographic areas), 10 of which are divided into two sub-areas and one into three sub-areas; [11] Great Salt Lake Basin—Covers 3,807 square miles (2,436,480 acres) of the easternmost portions of Elko, White Pine, and Lincoln counties. It consists of eight hydrographic areas, one of which is divided into four sub-areas; [12] Escalante Desert Basin—This basin covers a large area in Utah but only a very small part of it is in Lincoln County—106 square miles (67,480 acres)—and is made up of only one hydrographic area; [13] Colorado River Basin—Covers 12,376 square miles (7,920,640 acres) including parts of Clark, Lincoln, Nye, and White Pine counties and is divided into 27 hydrographic areas; [14] Death Valley Basin—Covers 2,593 square miles (1,659,520 acres) of Nye and Esmeralda counties including eight hydrographic areas, one of which has been divided into two sub-areas.

[A listing of Nevada's Hydrographic Areas and Sub-Areas is presented in Appendix A-1 (listed sequentially by Hydrographic Area number and Hydrographic Region/Basin), Appendix A-2 (listed alphabetically by Hydrographic Area and Sub-Area name), and Appendix A-3 (listed alphabetically by principal Nevada county(ies) in which located).]

BASS—Any of a number of North American fish found in streams and lakes. Bass are used for food.

BAT—Best Available Technology [Economically Achievable]

BATH—The act of soaking or cleansing a body, as in water or steam. Also, the water used for such cleansing.

BATHE—(1) To take a bath or go into the water for swimming or other recreation. (2) To become immersed in or as if in liquid; to seem to wash or pour over; suffuse.

BATHING WATER—Water in swimming pools or natural fresh or marine waters used for swimming.

BATHOLITH—A mass of Igneous rock that forms intrusively and can rise to the surface.

BATHOMETER—An instrument used to measure the depth of water.

BATHTUB—A large tub to bathe in.

BATHTUB EFFECT—The accumulation of Leachate in a landfill containing a good liner, but not equipped with a leachate collection and removal system.

BATHYAL ZONE—The ocean stratum beneath the Euphotic Zone and above the Abyssal Zone, or to the bottom of the Continental Shelf. The density of life in this zone depends on organic material settling from the euphotic zone and is generally inversely proportional to the depth.

BATHYMETRIC MAP—A map showing the depth (bottom contours) of water in lakes, streams, or oceans. Can be used to calculate lake volume.

BATHYMETRY—(1) The measurement of the depth of large bodies of water (oceans, seas, ponds and lakes). (2) The measurement of water depth at various places in a body of water. Also the information derived from such measurements.

BATHYSCAPHE—A free-diving, self-contained deep-sea research vessel consisting essentially of a large flotation hull with a crewed observation capsule fixed to its underside, capable of reaching depths of 10 kilometers (6.2 miles) or more.

BATHYSPHERE—A reinforced spherical deep-diving chamber in which persons are lowered by a cable to study the oceans. The bathysphere, limited to depths of about 900 meters (3,000 feet), has been supplanted by the safer and more navigable Bathyscaphe.

BATHYTHERMOGRAPH—An instrument designed to record water temperature as a function of depth.

BAUMÉ—Being, calibrated in accordance with, or according to either of two arbitrary hydrometer scales for liquids lighter than water or for liquids heavier than water that indicate specific gravity in degrees.

BAY—A part of a sea, reservoir, or lake, indenting the shoreline; a wide inlet not so large as a Gulf.

BAY-DELTA [California]—Refers to the region encompassing the Sacramento-San Joaquin river delta system forming a basically delta or triangular structure extending from south Sacramento in the north to below Stockton in the south to the San Francisco Bay in the west. The Bay-Delta is the largest remaining Estuarine system on the West Coast of the United States. The Bay-Delta contains approximately 738,000 total acres (1,153 square miles) interlaced with hundreds of miles of water waterways. Of this total area, 520,000 acres are in agriculture, 35,000 acres are contained in cities and towns, 50,000 acres are covered with water, and 133,000 acres remain undeveloped. The gross value of the Bay-Delta's agricultural production totals over $500 million per year. Deep water ship channels run through the Bay-Delta and connect both Sacramento and Stockton to the San Francisco Bay and the Pacific Ocean. As much of the Bay-Delta's land area is up to 21 feet below the water level, waters flowing throughout this system are controlled by over 1,100 miles of levees. Rivers flowing into the Bay-Delta include the Sacramento, San Joaquin, Mokelumne, Cosumnes, and Calaveras, which, along with their tributaries, carry 47 percent of California's total surface runoff. The Bay-Delta serves as the major collection point for the water that serves over two-thirds of California's total population. Along with associated pumping facilities, the Bay-Delta provides the source waters for a number of major water development projects to include the California Aqueduct, the Central Valley Project's Delta-Mendota Canal, the Contra Costa Canal, and the North and South Bay Aqueducts. Within the Bay-Delta system may be found extensive populations of fauna and flora to include 230 species of birds, 45 species of mammals, 52 species of fish, 25 species of reptiles and amphibians, and 150 species of flowering plants. Major Anadromous fish using the Bay-Delta include Salmon, Striped Bass, Steelhead Trout, American Shad, and Sturgeon. Also referred to as the Sacramento-San Joaquin Delta. Also see Central Valley Project (CVP) [California] and State Water Project (SWP) [California].

BAYESIAN INFERENCE—(Statistics) Bayes' theorem recognizes that a decision maker usually has some expectation (an a priori model) of what will occur even before acquiring information, and provides a procedure for using new evidence to produce a revised a posteriori estimate of probability. Also see Statistical Inference and Classical Inference.

BAYOU—In general, a creek, secondary watercourse, or minor river, tributary to another river or other body of water. A term regularly used in the lower Mississippi River basin and in the Gulf-coast region of the United States to denote a large stream or creek, or small river, characterized by a slow or imperceptible current through alluvial lowlands or swamps. May also refer to an estuarial creek or inlet on the Gulf coast; a small bay, open cove, or harbor; also, a lagoon, lake or bay, as in a sea marsh or among salt-marsh islands.

BCF—Bioconcentration Factor.

BCP—Bioconcentration Potential.

BCT—Best [conventional] Control Technology.

BEACH—A sloping landform on the shore of larger water bodies, generated by waves and currents and extending from the water to a distinct break in landform or substrate type (e.g., a foredune, cliff, or bank.)

BEACH EROSION—The carrying away of beach materials by wave action, tidal currents, or littoral currents, or by wind.

BEAD—A small, round object, especially a drop of moisture, as beads of sweat.

BEAUFORT'S SCALE—(Meteorology) A scale devised by Sir F. Beaufort, Royal Navy, in 1805, in which the strength of the wind is indicated by numbers from 0 to 12. The corresponding terms are: calm [0], light air [1], light breeze [2], gentle breeze [3], moderate breeze [4], fresh breeze [5], strong breeze [6], moderate gale [7], fresh gale [8], strong gale [9], whole gale [10], storm [11], hurricane [12]. Also see Wind Scale.

BED—(1) An underwater or intertidal area in which a particular organism is established in large numbers. (2) The bottom of a body of water, such as a stream. (Geology) A rock mass of large horizontal extent bounded, especially above, by physically different material (as in Bedrock).

BEDEW—To wet with or as if with Dew.

BED LOAD—Material in movement along a stream bottom, or, if wind is the moving agent, along the surface. Contrast with material carried in suspension or solution.

BED MATERIAL—The sediment mixture of which a streambed, lake, pond, reservoir, or estuary bottom is composed.

BEDROCK—(Geology) The solid rock beneath the soil (Zone of Aeration or Zone of Saturation) and superficial rock. A general term for solid rock that lies beneath soil, loose sediments, or other unconsolidated material.

BEHEADED STREAM—The lower section of a stream that has lost its upper portion through diversion or Stream Piracy.

BELL—A hollow, usually inverted vessel, such as one used for diving deep below the surface of a body of water.

BELT OF SOIL MOISTURE—Subdivision of the Zone of Aeration. Belt from which water may be used by plants or withdrawn by soil evaporation. Some of the water passes down into the intermediate belt, where it may be held by molecular attraction against the influence of gravity.

BENCH FLUME—A flume built on constructed benches or terraces along hillsides or around mountain slopes when the ground is too rough or too steep to permit the use of an excavated canal.

BENCH LAND (Soils)—A general term describing porous and coarse-textured (sandy-gravelly) well-drained soils, overlying a deep water table (if occurring), that exhibits relatively low water holding capacity and rapid infiltration of irrigation water.

BENCH LANDS [Nevada]—The U.S. Department of the Interior, Bureau of Reclamation criteria (revised 1992) has defined Bottom Land for Nevada's Newlands Irrigation Project, located in Churchill County, Nevada, as "those lands with a five-foot soil profile having a holding capacity equal to or exceeding 8 inches and/or a water table within 6 feet of the surface for a period equal to or exceeding 150 days. If neither of these factors apply, the land is designated as Bench Land." Lands classified as bench (or bottom) according to Bureau of Reclamation criteria, above, will be limited to maximum water deliveries (duty) in accordance to the provision of the Orr Ditch Decree and the Alpine Decree, which are identical in establishing water duties and establish the following limits: (1) Eligible lands designated as Bench Lands may receive a maximum of 4.5 acre-feet per acre per year (AF/acre/year); (2) eligible lands designated as Bottom Lands may receive a maximum of 3.5 acre-feet per acre per year (AF/acre/year).

BENCHMARK—Data used as a base for comparative purposes with comparable data.

BEND—The stream bends to the left just beyond that boat.

BENEFICIAL USE (of Water)—(1) The amount of water necessary when reasonable intelligence and diligence are used for a stated purpose. Most states recognize the following uses as beneficial:

[1] domestic and municipal uses; [2] industrial uses; [3] irrigation; [4] mining; [5] hydroelectric power; [6] navigation; [7] recreation; [8] stock raising; [9] public parks; [10] wildlife and game preserves.

(2) The cardinal principle of the (Prior) Appropriation Doctrine. A use of water that is, in general, productive of public benefit, and which promotes the peace, health, safety and welfare of the people of the State. A certificated water right is obtained by putting water to a beneficial use. The right may be lost if beneficial use is discontinued. A beneficial use of water is a use which is of benefit to the appropriator and to society as well. The term encompasses considerations of social and economic value and efficiency of use. In the past, most reasonably efficient uses of water for economic purposes have been considered beneficial. Usually, challenges have only been raised to wasteful use or use for some non-economic purpose, such as preserving in-stream values. Recent statutes in some states have expressly made the use of water for recreation, fish and wildlife purposes, or preservation of the environment a beneficial use. Also see Appropriative Water Rights.

BENEFIT-COST RATIO—The relationship of the economic benefits of an action to its total costs.

BENTHIC DEPOSITS—Bottom accumulations which may contain bottom-dwelling organisms and/or contaminants in a lake, harbor, or stream bed.

BENTHIC INVERTEBRATES—Aquatic animals without backbones that dwell on or in the bottom sediments of fresh or salt water. Examples are clams, crayfish, and a wide variety of worms.

BENTHIC ORGANISMS—Those organisms living at or near the bottom of a body of water.

BENTHIC REGION—The bottom of a body of water, supporting the Benthos.

BENTHIC ZONE—The bottom zone of a lake.

BENTHOS—All the plant and animals living on or closely associated with the bottom of a body of water (within or attached to the sediment of lakes, streams, and oceans). The phytobenthos includes the aquatic macrophytes and bottom-dwelling algae. The zoobenthos (benthic fauna) includes a variety of invertebrate animals, particularly larval forms and mollusks.

BENTONITE—A clay material that swells as it dries, filling gaps and sealing itself against a well casing. It is commonly used to seal abandoned dewatering wells at mines. Concrete, by contrast, shrinks as it cures, and can therefore leave gaps around a wellhead casing that can allow contaminated water from the surface to penetrated into the well.

BERG—A mass of floating or stationary ice; and Iceberg.

BERNOULLI EFFECT—The phenomenon of internal pressure reduction with increased stream velocity in a fluid. Named after Daniel Bernoulli.

BERNOULLI'S EQUATION—Under conditions of steady flow of water, the sum of the velocity head, the pressure head, and the head due to elevation at any given point is equal to the sum of these heads at any other point plus or minus the head losses between the points due to friction or other causes.

BERM—(1) A narrow ledge or path as at the top or bottom of a slope, stream bank, or along a beach. (2) (Dam) A horizontal step or bench in the upstream or downstream face of an Embankment Dam.

BEST AVAILABLE DEMONSTRATED TECHNOLOGY (BADT)—The level of effluent limitation technology required by the 1972 Clean Water Act (CWA) to be used in setting new source performance standards for new industrial direct dischargers of water pollutants.

BEST AVAILABLE TECHNOLOGY ECONOMICALLY ACHIEVABLE (BAT)—A national goal under the Water Pollution Control Act of 1972 (Public Law 92-500, commonly referred to as the Clean Water Act) which provides that industry shall use the best treatment technically and economically achievable for a category or class of point sources. Under this concept, pollution control will consider such factors as the age of the facilities and equipment involved, processes employed, engineering aspects of the control techniques, process changes, cost of the reductions, and environmental impacts other than water quality, including energy requirements.

BEST CONVENTIONAL CONTROL TECHNOLOGY (BCT) —The level of water pollution control technology required of existing dischargers for the treatment of conventional pollutants by the 1977 Clean Water Act (CWA).

BEST MANAGEMENT PRACTICES (BMP) —(1) Accepted methods for controlling Non-Point Source (NPS) Pollution as defined by the 1977 Clean Water Act (CWA); may include one or more conservation practices. Also refers to water conservation techniques of proven value. (2) State-of-the-art techniques and procedures used in an operation such as farming or waste disposal in order to minimize pollution or waste. See, for example, Best Management Practices (BMP)—Urban Water Use.

BEST MANAGEMENT PRACTICES (BMP)—URBAN WATER USE—Water conservation measures that generally meet one of two criteria: (1) Constitutes an established and generally accepted practice among water purveyors that provides for the more efficient use of existing water supplies or contributes towards the conservation of water; or (2) Practices which provide sufficient data to clearly indicate their value, are technically and economically reasonable, are environmentally and socially acceptable, are reasonably capable of being implemented by water purveyors and users, and for which significant conservation or conservation-related benefits can be achieved. See Appendix B-1, Best Management Practices—Urban Water Use, for a more complete itemization of BMPs and Potential BMPs.

BEST PRACTICABLE CONTROL TECHNOLOGY (BPT) —A national goal under the Water Pollution Control Act of 1972 (Public Law 92-500, or the Clean Water Act) which provides that industry shall use the best treatment practices practical, with due consideration to cost, age of the plant and equipment, and other factors.

BGS—Balanced Groundwater Scenario.

BIA—Bureau of Indian Affairs (USDI).

BIAS—An error in data gathering or analysis caused by faulty program design, mistakes on the part of personnel, or limitations imposed by available instrumentation or data sources.

BICARBONATE—(Water Quality) A compound containing the HCO3- group, for example, sodium bicarbonate (NaHCO3), which ionizes in solution (water) to produce HCO3-. Also see Carbonate and Carbonate Buffer System.

BIENNIAL PLANT—A plant that lives for two years, producing vegetative growth the first year, usually blooming and fruiting in the second year, and then dying.

BIFURCATE—Dividing structure which splits the flow of water.

BILGE WATER—Water that collects and stagnates in the bilge or bottom-most areas of a ship.

BILLABONG—(Australian) (1) A dead-end channel extending from the main stream of a river. (2) A streambed filled with water only in the rainy season. (3) A stagnant pool or backwater.

BILLION—One thousand times one million, 1,000,000,000

BILLOW—A large wave or swell of water.

BIMODAL DISTRIBUTION—(Statistics) A collection of observations with a large number of values centered (as in a Normal Distribution) around each of two points. For example, in a sampling of the heights of a population, the sample results would tend to be concentrated around an average heights for males and a second average height for females.

BIOACCUMULANTS—Substances that increase in concentration in living organisms as they take in contaminated air, water, or food because the substances are very slowly metabolized or excreted. Also see Biological Magnification.

BIOACCUMULATION—(1) The increase in concentration of a chemical in organisms that reside in environments contaminated with low concentrations of various organic compounds. Also used to describe the progressive increase in the amount of a chemical in an organism resulting from rates of absorption of a substance in excess of its metabolism and excretion. (2) Food chain is the sequence of algae being eaten by small aquatic animals (zooplankton) which in turn are eaten by small fish which are then eaten by larger fish and eventually by people or predators. Certain chemicals, such as PCBs mercury, and some pesticides, can be concentrated from very low levels in the water to toxic levels in animals through this process.

BIOASSAY—A method for quantitatively determining the concentration of a substance by its effects on the growth of a suitable animal, plant, or microorganism under controlled conditions.

BIOCHEMICAL OXIDATION—The process by which bacteria and other microorganisms feed on complex organic materials and decompose them. Self-purification of waterways and activated sludge and trickling filter wastewater treatment processes depend on this principle.

BIOCHEMICAL OXYGEN DEMAND (BOD)—(1) A measure of the amount of oxygen removed from aquatic environments by aerobic micro-organisms for their metabolic requirements. Measurement of BOD is used to determine the level of organic pollution of a stream or lake. The greater the BOD, the greater the degree of water pollution. (2) The amount of dissolved oxygen needed to break down organic materials to carbon dioxide, water, and minerals in a given volume of water at a certain temperature over a specified time period. Also, referred to as Biological Oxygen Demand (BOD).

BIOCHEMICAL OXYGEN DEMAND (BOD) LOADING —(Water Quality) The BOD content, commonly expressed in pounds/day, of wastewater passing into a waste treatment system or a body of water. The greater the BOD content, the greater the degree of pollution.

BIOCIDE—A chemical substance that kills living organisms. Typically used to include materials that can kill desirable as well as undesirable organisms.

BIOCLIMATIC ZONES—Also referred to as Biomes, these constitute the earth's ten zones differentiated by climate, soil, water, and plant and animal life. See Biome.

BIOCOENOSIS—A community of animal and plant life.

BIOCONCENTRATION—The increase in concentration of a chemical in an organism resulting from absorption levels exceeding the rate of metabolism and excretion.

BIOCONCENTRATION FACTOR (BCF)—Used to describe the accumulation of chemicals in aquatic organisms that live in contaminated environments. Also see Bioconcentration.

BIOCONCENTRATION POTENTIAL (BCP)—The maximum concentration of a chemical in an organism resulting from the rate of absorption equaling the rate of metabolism and excretion.

BIOCONVERSION—The conversion of organic materials, such as plant or animal waste, into usable products or energy sources by biological processes or agents, such as certain microorganisms.

BIODEGRADABLE—Capable of being decomposed by biological agents, especially bacteria. The property of a substance that permits it to be broken down by micro-organisms into simple, stable compounds such as carbon dioxide and water.

BIODEGRADATION—The metabolic breakdown of materials into simpler components by living organisms. A more specific form of Biotransformation.

BIODENITRIFICATION—The controlled use of microbes, usually bacteria, to reduce level of nitrates (NO3-) and thereby reclaim contaminated water or wastewater. The process consists of several stages to decompose the nitrates first into nitrites and then into nitrogen gas, N2. Upon entering the treatment process, sodium sulfite (Na2SO3) is added as a reducing agent to the wastewater to remove the oxygen from the water. To break down the nitrates, the bacteria must have a carbon food source and typically ethanol is added for the bacteria to feed on. In order to survive, however, the bacteria need oxygen which they obtain by breaking down the nitrate ions, first to nitrite and then to harmless nitrogen gas. Also referred to as Endogenous Respiration.

BIODISC—(Water Quality) A large rotating cylinder possessing surface features that allow for the growth of attached microorganisms. The cylinder revolves and contacts the wastewater along one side while the other side is exposed to air, thereby maximizing the oxygenation of the water and stimulating decomposition of dissolved or suspended organic material.

BIODIVERSITY—Refers to the variety and variability of life, including the complex relationships among microorganisms, insects, animals, and plants that decompose waste, cycle nutrients, and create the air that we breathe. Diversity can be defined as the number of different items and their relative frequencies. For biological diversity, these items are organized at many levels, ranging from complete Ecosystems to the biochemical structures that are the molecular basis of heredity. Thus, the term encompasses different ecosystems, species, and genes. It is generally accepted that human survival is dependent upon the conservation and preservation of this diversity of life forms. Typically five levels of biodiversity are recognized:

[1] Genes—Genetic diversity encompasses the variety of genetically coded characteristics of plant and animal populations; [2] Populations—Groups of individuals of a species that interbreed or interact socially in an area; [3] Species—The level at which most organisms are recognizable as distinct from all others; [4] Natural Communities—Groups of species that typically occur in recognizable units, such as redwood forests, coastal sage scrub, or oak woodlands. A natural community includes all the vegetation and animal life, and their interactions within that community; and [5] Ecosystems—A collection of natural communities. An ecosystem can be as small as a rotting log or a puddle of water, but current management efforts typically focus on larger landscape units, such as a mountain range, a river basin, or a watershed.

BIOFOULING—The gradual accumulation of waterborne organisms (as bacteria and protozoa) on the surfaces of engineering structures in water that contributes to corrosion of the structures and to a decrease in the efficiency of moving parts.

BIOGAS—Methane gas produced during the Anaerobic decomposition of the remains of plants or animal wastes by bacteria.

BIOGENIC—Used to describe changes in the environment resulting from the activities of living organisms.

BIOGEOCHEMICAL CYCLING—The flow of chemical substances to and from the major environmental reservoirs: Atmosphere, Hydrosphere, Lithosphere, and Biosphere. As chemicals move in the cycle, they often change chemical form, usually existing in a characteristic form in each reservoir. As an example, carbon (in the lithosphere) exists mainly as carbon dioxide in the atmosphere, carbonic acid, bicarbonate, or the carbonate ion when dissolved in water (hydrosphere), and as more complex organic compounds in animals and plants (biosphere).

BIOGEOCHEMISTRY—The study of the transformation and movement of chemical materials to and from the Lithosphere, the Atmosphere, the Hydrosphere, and the bodies of living organisms (the Biosphere).

BIOGEOGRAPHY—The study of the geographic distribution of organisms.

BIOINDICATOR—A living organism that denotes the presence of a specific environmental condition. For example, the presence of coliform bacteria identifies water that is contaminated with human fecal material.

BIOLOGICAL ACTIVATED CARBON (BAC) PROCESS—The combination of Ozonation and Granular Activated Carbon (GAC) for the removal of dissolved organics, particularly Dissolved Organic Carbon (DOC) from drinking water. This water treatment method has seen more widespread use in Europe primarily due to: (1) the generally poorer quality of surface waters there; (2) the greater concern and more stringent standards for chlorination byproducts; and (3) the strict aesthetic demand of European consumers. Also referred to as the Biologically Enhanced Activated Carbon Process.

BIOLOGICAL ADDITIVES—Cultures of bacteria, enzymes, or nutrients that are introduced into an oil discharge or other wastes to promote decomposition.

BIOLOGICAL COMMUNITY—All of the living things in a given environment.

BIOLOGICAL CONTROL—The direct human introduction of living organisms—predators, parasites, or pathogens—to eliminate or control undesirable species. The practice is usually considered an ecologically sound alternative to the application of chemical pesticides.

BIOLOGICAL DIVERSITY—The number and kinds of organisms per unit area of volume; the composition of species in a given area at a given time.

BIOLOGICAL MAGNIFICATION—Refers to the process whereby certain substances such as pesticides or heavy metals move up the food chain, work their way into rivers or lakes, and are eaten by aquatic organisms such as fish, which in turn are eaten by large birds, animals or humans. The substances become concentrated in tissues or internal organs as they move up the chain. Also see Bioaccumulants and Bioaccumulation.

BIOLOGICAL OPINION—A document which states the opinion of the U.S. Fish and Wildlife Service (USFWS) as to whether a federal action is likely to jeopardize the continued existence of a threatened or endangered species or result in the destruction or adverse modification of critical habitat.

BIOLOGICAL OXIDATION—Decomposition of complex organic materials by microorganisms. Occurs in the self-purification of water bodies and in activated sludge wastewater treatment processes.

BIOLOGICAL OXYGEN DEMAND (BOD)—(Water Quality) An indirect measure of the concentration of biologically degradable material present in organic wastes. It usually reflects the amount of oxygen consumed in five days by biological processes breaking down organic waste. Also see BOD5. Also referred to as Biochemical Oxygen Demand (BOD).

BIOLOGICAL PROCESSES—Processes characteristic of, ore resulting from, the activities of living organisms.

BIOLOGICAL TREATMENT—A treatment technology that uses bacteria to consume organic wastes.

BIOLOGICAL WASTEWATER TREATMENT—The use of bacteria to degrade and decompose organic materials in wastewater.

BIOLOGIST—Person who specialized or works in biology.

BIOLOGY—(1) The science of life and of living organisms, including their structure, function, growth, origin, evolution, and distribution. It includes Botany and Zoology and all their subdivisions. (2) The life processes or characteristic phenomena of a group or category of living organisms. (3) The plant and animal life of a specific area or region.

BIOMASS—(1) The total mass of living matter within a given unit of environmental area. (2) Plant material, vegetation, or agricultural waste used as a fuel or energy source. (3) The total quantity of plants and animals in a lake. Measured as organisms or dry matter per cubic meter, biomass indicates the degree of a lake system's eutrophication or productivity. Some methods of determining biomass in a sample include:

[1] Ash Mass—The mass or amount of residue present after the residue from the dry mass determination has been ashed in a muffle furnace at a temperature of 500C for 1 hour. The ash mass values of zooplankton and phytoplankton are expressed in grams per cubic meter (g/m3), and periphyton and benthic organisms in grams per square mile (g/mi2). [2] Dry Mass—The mass of residue present after drying in an oven at 105C for zooplankton and periphyton, until the mass remains unchanged. This mass represents the total organic matter, ash and sediment, in the sample. Dry-mass values are expressed in the same units as ash mass. [3] Organic Mass or Volatile Mass—Refers to the mass of a living substance as the difference between the dry mass and ash mass and represents the actual mass of the living matter. The organic mass is expressed in the same units as for the ash mass and dry mass. [4] Wet Mass—The mass of living matter plus contained water.

BIOMAT—(1) (Hydraulics) A term used in subsoil hydraulics to describe a clogging layer of typically densely packed decaying organic matter which impedes the downward flow of water. (2) (Water Quality) A restrictive layer that develops beneath the distribution lines of the Soil Absorption System (SAS) of Septic Tanks at the gravel-soil or bed-soil interface. As the Septic Tank Effluent (STE) is not suitable for direct discharge into surface waters or onto land surfaces because of the presence of biodegradable organics and high bacterial content that may include Pathogens, the effluent typically undergoes further purification by three processes: absorption, filtration, and microbiological decomposition. The biomat constitutes a clogging mat, Anaerobic in nature, characterized as a black slimy layer, and composed of accumulated suspended solids, minerals, bacterial cells, microorganism fragments, polysaccharides, and polyuronides. The biomat is extremely active biologically and helps ensure the conditions for optimal treatment of the effluent by restricting the infiltration rate into the soil, inducing unsaturated soil conditions and reducing the chances of high dispersion below the system. Biomats are also highly effective in removing bacterial and pathogens from the STE and can also detain viruses that can be present in the effluent. Also referred to as Biocrust, Clogging Mat, and Clogging Zone.

BIOME—A major regional or global Biotic community of plants and animals whose composition is determined by soil and the prevailing climate. The earth is characterized by ten Bioclimatic Zones or Biomes which consist of:

[1] Tundra—treeless areas between the icecap and the tree line of Arctic regions, having a permanently frozen subsoil and supporting low-growing vegetation such as lichens, mosses, and stunted shrubs. [2] Taiga—the Subarctic, evergreen coniferous forests of northern Eurasia located just south of the tundra and dominated by firs and spruces. [3] Temperate Forest—forested areas characterized by deciduous plants and moderate temperatures, weather, or climate. [4] Grassland—areas, such as a prairie or meadow, of grass or grass-like vegetation. [5] Savanna—flat grasslands of tropical or subtropical regions. [6] Desert—barren or desolate areas, especially dry, often sandy regions of little rainfall, extreme temperatures, and sparse vegetation. [7] Montane—cool, moist zones usually located near the timberline and usually dominated by evergreen trees. [8] Tropical Rain Forest —dense evergreen forests occupying a tropical region typically with an annual rainfall of at least 2.5 meters (100 inches). [9] Tropical Dry Forest —tropical or subtropical forests similar to tropical rain forests excepting that many of the plant species are deciduous and there exists a well-defined dry season. [10]Islands—land masses, especially ones smaller than a continent, entirely surrounded by water.

BIOMONITORING—The use of living organisms to test the suitability of an effluent for discharge into receiving waters or to test the quality of such receiving waters downstream from the discharge. Also see Bioassay.

BIOREMEDIATION—Simply, the use of biological techniques to clean up pollution. More specifically, the use of specialized, naturally-occurring micro-organisms with unique biological characteristics, appetites, and metabolisms as a form of waste cleanup. A critical underpinning of this process is the ability to economically generate a sufficient biomass of the appropriate microbes to accomplish in weeks or months what would normally take nature years to do. Typically, this is done either by applying a sufficient concentration of such microbes directly to the polluted area or by applying various concentrations of chemicals which, in turn, stimulate and foster the rapid growth of appropriate micro-organisms.

BIOSOLIDS—A nutrient-rich organic material resulting from the treatment of wastewater. Biosolids contain nitrogen and phosphorus along with other supplementary nutrients in smaller doses, such as potassium, sulfur, magnesium, calcium, copper and zinc. Soil that is lacking in these substances can be reclaimed with biosolids use. The application of biosolids to land improves soil properties and plant productivity, and reduces dependence on inorganic fertilizers. The terms biosolids, Sludge, and Sewage Sludge can be used interchangeably.

BIOSPHERE—In its broadest sense, the entire planetary ecosystem including all living organisms and those parts of the earth and its atmosphere in which living organisms exist or that are capable of supporting life, to include, in addition to the plant and animal species:

[1] Atmosphere—the gaseous layer covering the earth; [2] Lithosphere—the solid portion of the earth's crust and mantle; [3] Hydrosphere—that portion of the earth composed of liquid water; and

Also referred to as the Ecosphere. In a more restrictive sense, may also refer to only the living organisms on earth and not to their physical and chemical environments.

BIOTA—The plant (flora) and animal life (fauna) of a region or ecosystem, as in a stream or other body of water.

BIOTECHNOLOGY—The use of microorganisms, such as bacteria or yeasts, or biological substances, such as Enzymes, to perform specific industrial or manufacturing processes. Applications include the production of certain drugs, synthetic hormones, and bulk foodstuffs as well as the Bioconversion of organic waste and the use of genetically altered bacteria in the cleanup of oil spills and other hazardous materials.

BIOTIC—Pertaining (1) to life or living things, or caused by living organisms. (2) or to biological factors or influences, concerning biological activity.

BIOTIC COMMUNITY—A naturally occurring assemblage of plants and animals that live in the same environment and are mutually sustaining and interdependent. Also see Biome.

BIOTOWER—(Water Quality) A means of wastewater treatment in which the waste is allowed to fall through a tower packed with synthetic media, on which there is biological growth. Similar to a trickling filter in concept.

BIOTRANSFORMATION—Conversion of a substance into other compounds by organisms. A more general form of Biodegradation.

BITTERN—The bitter water solution of bromides, magnesium, and calcium salts remaining after sodium chloride is crystallized out of seawater.

BLACK ICE—A thin, nearly invisible coating of ice, as on the surface of a road or sidewalk, that is usually caused by freezing mist and is extremely hazardous.

BLACK SMOKER—A vent in a geologically active region of the sea floor from which issues superheated water laden with minerals (as sulfide precipitates).

BLACKWATER—Water that contains animal, human, or food wastes; wastewater from toilet, latrine, and agua privy flushing and sinks used for food preparation or disposal of chemical or chemical-biological ingredients. Compare to Greywater.

BLANCH—To scald or parboil in water or steam in order to remove the skin from, whiten, or stop enzymatic action in (as food for freezing).

BLANKET (of a Dam)—A portion of the physical structure of a dam designed to affect the dams hydrologic characteristics, particularly its seepage and strength characteristics. Types of dam blankets include:

[1] Drainage Blanket—A drainage layer placed directly over the dam's foundation material; [2] Grout Blanket—The injection of grout to consolidate a layer of the foundation, resulting in greater impermeability and/or strength; and [3] Upstream Blanket—An impervious layer placed on the reservoir floor upstream of a dam; in the case of an Embankment Dam, the blanket may be connected to the impermeable element in the dam itself.

BLANKET MIRES—See Peatland.

BLEAR—To dim with water or tears.

BLENDING—The mixing or combination of one water source with another, typically a finished source of water with raw water to reuse water while still satisfying water quality standards, for example, mixing of product water from a desalting plant with conventional water to obtain a desired dissolved solids content, or mixing brine effluents with sewage treatment plant effluents in order to reduce evaporation pond size.

BLINDS—Water samples containing a chemical of known concentration given a fictitious company name and slipped into the sample flow of the lab to test the impartiality of the lab staff.

BLM—Bureau of Land Management (USDI)

BLOOM—(1) In aquatic ecosystems, the rapid growth or proliferation of algae, usually visible to the naked eye, commonly referred to as Algal Bloom or Algae Bloom; often related to pollution, especially when pollutants accelerate growth. (2) Also a visible, colored area on the surface of bodies of water caused by excessive planktonic growth.

BLOWDOWN—The water drawn from boiler systems and cold water basins of cooling towers to prevent the buildup of solids.

BLOWHOLE—A hole in ice to which aquatic mammals, such as dolphins and seals, come to breathe.

BLOWOUT—A sudden escape of a confined gas or liquid, as from a well.

BLUE-GREEN ALGAE—A group of phytoplankton which often cause nuisance conditions in water, so called because they contain a blue pigment in addition to chlorophyll. Blue-green algae are often associated with problem blooms in lakes. Some produce chemicals toxic to other organisms, including humans. They often form floating scum as they die. Many can fix nitrogen (N2) from the air to provide their own nutrient.

BLUE WATER—The open sea.

BMP—See Best Management Practices (BMP) and Best Management Practices (BMP)—Urban Water Use.

BOAT—A small vessel used to travel on water.

BOATHOUSE—A building for storing boats.

BOB—To move up and down briefly or repeatedly, as in water.

BOD—See Biochemical Oxygen Demand (Biological Oxygen Demand).

BOD5—The amount of dissolved oxygen consumed in five days by biological processes breaking down organic matter. Also see Biological Oxygen Demand (BOD).

BODY FLUID—the total body water, contained principally in blood plasma and in intracellular and interstitial fluids. Also see Body Water Content.

BODY WATER CONTENT—That portion of the human body composed of water; expressed as a percentage of total body volume. Specifically, the human body is comprised of approximately 65-70 percent water: 67 percent of the water in the body is located within cells; 25 percent between cells; and the rest, about 8 percent, is located in the blood. If more than 8 percent of the body's water is lost, death will result.

BOG—A term frequently associated with Wetlands. A quagmire filled with decayed moss and other plant and vegetable matter; wet spongy ground, where a heavy body is apt to sink; a small, soggy marsh; a morass. (Ecology) A wet, overwhelmingly vegetative substratum which lacks drainage and where humic and other acids give rise to modifications of plant structure and function. Bogs depend primarily on precipitation for their water source, and are usually acidic and rich in plant residue with a conspicuous mat of living green moss. Only a restricted group of plants, mostly mycorrhizal (fungi, heaths, orchids, and saprophytes), can tolerate bog conditions. Also referred to as Peat Bog. Also see Peatland.

BOG HOLE—A hole containing soft mud or quicksand.

BOIL—To change from a liquid to a vapor by the application of heat till bubbles form and steam is given off. Also see Boiling Point.

BOILING POINT—The temperature at which the vapor pressure of a liquid is equal to the pressure exerted on the liquid. (Water) When the atmospheric pressure is 86 centimeters of mercury (sea level), the boiling point of water is, by definition, 100C (Celsius) or 212F (Fahrenheit). The boiling point decreases with elevation.

BOILING WATER REACTOR (BWR)—A nuclear reactor in which water, used as both coolant and moderator, is allowed to boil in the core. The resulting steam can be used directly to drive a turbine generating electric power.

BOILOFF—The vaporization of liquid.

BOLSON—An alluvium-floored basin, depression, or wide valley, mostly surrounded by mountains and drained by a system that has no surface outlet; an undrained basin. Bolson fill is the alluvial Detritus that fills a bolson; also commonly called bolson deposits.

BONG—A water pipe that consists of a bottle or a vertical tube partially filled with liquid and a smaller tube ending in a bowl, used often in smoking narcotic substances.

BOOM—A floating device used to contain oil on a body of water.

BORAX—A white crystalline compound that consists of a hydrated sodium borate Na2B4O710H2O, that occurs as a mineral or is prepared from other minerals, and that is used especially as a flux, cleansing agent, and water softener, as a preservative, and as a fireproofing agent.

BORDER DITCH—A ditch used as a border of an irrigated strip or plot, water being spread from one or both sides of the ditch along its entire length.

BORDER IRRIGATION—A surface method of irrigation by flooding between two confining border levees or dikes. Typically, these borders vary from 100 to 200 feet wide by 1,000 to 3,960 feet long.

BORE—A high, often dangerous wave caused by the surge of a flood tide upstream in a narrowing Estuary or by colliding tidal currents. Also referred to as an Eagre.

BOREAL FOREST—A northern forest, as in the boreal forest Biome, characterized by evergreen conifers and long winters. The boreal forest, also referred to as a Taiga, is found in the northern parts of North America, Europe, and Asia.

BOREHOLE—A hole bored or drilled in the earth, as an exploratory well; a small-diameter well drilled especially to obtain water.

BOTANY—The branch of Biology that studies plants, including their structure, function, growth, origin, evolution, and distribution.

BOTTLED WATER [General]—Water sold commercially generally for its health, therapeutic, or purity values. In the United States, bottled water is considered a food product and as such is regulated by the Food and Drug Administration (FDA). Beginning in May 1996, the FDA required all bottled waters to carry accurate labels: "spring water" must come from a spring; "mineral water" must carry a certain mineral content; "sterile" water must be processed to meet FDA standards for commercial sterility; and if water comes from municipal supplies, it must be labeled as such. See Bottled Water [Food and Drug Administration] and Bottled Water [Nevada].

BOTTLED WATER [Food and Drug Administration]—As defined by the FDA [Department of Health and Human Services, Federal Register, Part III, 21 CFR Part 165, Subpart B—Requirements for Specific Standardized Beverages, effective May 13, 1996] bottled water is water that is intended for human consumption and that is sealed in bottles or other containers with no added ingredients except that it may optionally contain safe and suitable anti-microbial agents. Fluoride may be optionally added within certain specified limitations. Bottled water may be named bottled water, drinking water, or alternatively one of the following terms may be used as appropriate:

[1] Artesian Water or Artesian Well Water—Water from a well tapping a confined aquifer in which the water level stands at some height above the tope of the aquifer. [2] Ground Water—Water from a subsurface saturated zone that is under a pressure equal to or greater than atmospheric pressure; ground water must not be under the direct influence of surface water. [3] Mineral Water—Water containing not less than 250 parts per million (ppm) total dissolved solids (TDS), coming from a source tapped at one or more bore holes or springs, originating from a geologically and physically protected underground water source; mineral water shall be distinguished from other types of water by its constant level and relative proportions of minerals and trace elements at the point of emergence from the source; no minerals may be added to this water. [4] Purified Water—Water that has been produced by distillation, deionization, reverse osmosis, or other suitable processes and that meets the definition of "purified water" in the United States Pharmacopeia. May also be called demineralized water, purified drinking water, or alternatively, based on the process used, deionized (drinking) water, distilled (drinking) water, reverse osmosis (drinking) water, etc. [5] Sparkling Bottled Water—Water that, after treatment and possible replacement of carbon dioxide, contains the same amount of carbon dioxide from the source that it had at emergence from the source. [6] Spring Water—Water derived from an underground formation from which water flows naturally to the surface of the earth; shall be collected only at the spring or through a bore hole tapping the underground formation feeding the spring. [7] Sterile or Sterilized Water—Water that meets the requirements under "Sterility Tests" in the United States Pharmacopeia. [8] Well Water—Water from a hole bored, drilled, or otherwise constructed in the ground which taps the water of an aquifer.

Other label statements for bottled water include "low mineral content" for TDS levels below 500 ppm, "high mineral content" for TDS levels above 1,500 ppm, or when the water comes from a community water system, it must be labeled "from a community water system," or, alternatively, "from a municipal source."

BOTTLED WATER [Nevada]—According to Nevada Administrative Code (NAC) Chapter 445A, "Bottled Water," effective November 1994, bottled water may be labeled and sold as:

[1] Distilled Water—Water that is demineralized by distillation and complies with the requirements for purified water set forth in the United States Pharmacopeia. [2] Drinking Water—Water that is filtered and disinfected by a process approved by the health authority. [3] Mineral Water—Water that is clearly distinguishable from other types of water by its specific content of minerals and trace elements which remain constant at the water's point of emergence; boreholes or springs from which mineral water is produced must originate from an underground source which is geologically and physically protected from contamination. [4] Natural Water—Water that is produced from a well (Natural Well Water) or an artesian well (Natural Artesian Water) and no minerals have been added or removed from the water; may be filtered and must be disinfected by a process approved by the health authority. [5] Purified Water—Water that is demineralized by distillation, deionization, or reverse osmosis and complies with the requirements for purified water set forth in the United States Pharmacopeia. [6] Spring Water—Water that is produced from a point at the surface where the water flows naturally from an underground formation or through a borehole adjacent to that point n a manner approved by the health authority. [7] Municipal Water—Water that is produced from a public water system; may be sold and labeled as distilled water, drinking water, purified water if it complies with specific filtration and disinfection requirements.

BOTTOM—(1) The deepest or lowest part, as the bottom of a well. (2) The solid surface under a body of water. (3) Often Bottoms: Low-lying alluvial land adjacent to a river, also referred to as bottomland. (4) (Nautical) The part of a ship's hull below the water line.

BOTTOMLAND, also Bottom Land (Soils)—A general term describing generally rich, loamy or fine-textured and poorly drained soils, overlying a shallow water table or possibly adjacent to a stream, lake or other body of water, that exhibits relatively good water holding capacity and slow to moderate infiltration of irrigation water; often associated with a river's floodplain.

BOTTOM LAND HARDWOODS—Forested freshwater Wetlands adjacent to rivers in the southeastern United States, especially valuable for wildlife breeding, nesting, and habitat.

BOTTOM LANDS [Nevada]—The U.S. Department of the Interior, Bureau of Reclamation (USBR) criteria (revised 1992) has defined Bottom Land for Nevada's Newlands Irrigation Project, located in Churchill County, Nevada, as "those lands with a five-foot soil profile having a holding capacity equal to or exceeding 8 inches and/or a water table within 6 feet of the surface for a period equal to or exceeding 150 days. If neither of these factors apply, the land is designated as Bench Land." Lands classified as bottom (or bench) according to USBR criteria, above, will be limited to maximum water deliveries (duty) in accordance to the provision of the Orr Ditch Decree and the Alpine Decree, which are identical in establishing water duties and establish the following limits: (1) Eligible lands designated as Bench Lands may receive a maximum of 4.5 acre-feet per acre per year (AF/acre/year); (2) eligible lands designated as Bottom Lands may receive a maximum of 3.5 acre-feet per acre per year (AF/acre/year).

BOTTOM MATERIAL—See Bed Material.

BOTTOM OUTLET—An opening at a low level from a reservoir generally used for emptying or for scouring sediment and sometimes for irrigation releases. Also referred to as Low-Level Outlet or Sluiceway.

BOULDER—Rock fragments larger than 60.4 cm (24 inches) in diameter.

BOUNDARY CONDITIONS—Flow conditions imposed at the ends of a pipeline or canal reach by various physical structures, which must be described mathematically to solve the general equation of flow for hydraulic transient computer models.

BOUNDARY LAYER—The layer of reduced velocity in fluids, such as air and water, that is immediately adjacent to the surface of a solid past which the fluid is flowing.

BOUND WATER—Water molecules that are held tightly to soil or other solids. This water is not easily removed by normal drying and is not available for other purposes such as plant growth.

BOURN, also Bourne—A stream, brook, or rivulet; in southern England, a winter stream of the chalk downs.

BP—Barometric Pressure.

BPI PAN—A circular evaporation pan, 6 feet in diameter and 2 feet deep, made of unpainted galvanized iron. The pan is buried in the ground so that about 4 inches of the rim extend above the surrounding ground and the water surface is maintained at about ground level. (BPI stands for Bureau of Plant Industry, USDA, which introduced this instrument.)

BPT—Best Practicable Control Technology.

BRACKISH—Having a somewhat salty taste, especially from containing a mixture of seawater and fresh water. Also see Brackish Water.

BRACKISH WATER—Generally, water containing dissolved minerals in amounts that exceed normally acceptable standards for municipal, domestic, and irrigation uses. Considerably less saline than sea water. Also, Marine and Estuarine waters with Mixohaline salinity (0.5 to 30 due to ocean salts). Water containing between 1,000-4,000 parts per million (PPM) Total Dissolved Solids (TDS). The term brackish water is frequently interchangeable with Saline Water. The term should not be applied to inland waters.

BRAIDED STREAM—A complex tangle of converging and diverging stream channels (Anabranches) separated by sand bars or islands. Characteristic of flood plains where the amount of debris is large in relation to the discharge.

BRAIDING (of River Channels)—Successive division and rejoining of riverflow with accompanying islands.

BRANCH—(1) A tributary of a river or other body of water. (2) A divergent section of a river, especially near the mouth.

BRANCH WATER—(Chiefly Southern United States) Plain water from a stream, especially when mixed with a liquor such as whiskey.

BRASH—A mass or pile of rubble, refuse, or fragments, as of stone, brush, or ice.

BRAWL—To flow noisily, as turbulent water.

BREACH—(1) A gap or rift, especially in or as if in a solid structure such as a dike or dam. (1) The breaking of waves or surf.

BREAK—(1) To emerge above the surface of the water. (2) (Geology) A marked change in topography such as a fault or deep valley.

BREAKER—(1) A small water cask. (2) A large foaming wave that breaks on rocky or sandy shores.

BREAKPOINT CHLORINATION—The addition of chlorine to water or wastewater until the chlorine demand has been satisfied and further additions result in a residual that is directly proportional to the amount added beyond the breakpoint.

BREAKTHROUGH—A crack or break in a filter bed that allows the passage of Floc or particulate matter through a filter. As a result, it will cause an increase in filter effluent Turbidity.

BREAKTHROUGH CURVE—A plot of relative concentration versus time, where relative concentration is defined as C/C0; the concentration at a point in the ground-water flow domain divided by the source concentration.

BREAKUP—The cracking and shifting of ice in rivers or harbors during the spring.

BREAKWATER—A barrier that protects a harbor or shore from the full impact of waves.

BREW—To prepare (as tea) by infusion in hot water.

BRIDGE—An over the lake, stream or river structure built so that people can get from one side to the other.

BRIM—The upper surface of a body of water.

BRINE—(1) Water saturated with or containing large amounts of a salt, especially of sodium chloride. According to U.S. Geologic Survey (USGS) classification, water classified as brine contains more than 35,000 ppm (parts per million) total dissolved solids (TDS) of salt; (2a) The water of a sea or an ocean; (2b) A large body of salt water. (3) The wastewater resulting from desalting. It is higher in dissolved solid content than feedwater or product water. Also see Saline Water.

BRINE DISPOSAL—Removing water that contains high concentrations of salt.

BRINE MUD—Waste material, often associated with well-drilling or mining, composed of mineral salts or other inorganic compounds.

BRINK—(1) The upper edge of a steep or vertical slope. (2) The margin of land bordering a body of water.

BRITISH THERMAL UNIT (BTU)—A unit of heat energy equal to the amount of heat required to raise the temperature of one pound of water one degree Fahrenheit. More precisely, the quantity of heat required to raise the temperature of one pound of water from 60F to 61F at a constant pressure of one atmosphere. Also, the quantity of heat equal to 1/180 of the heat required to raise the temperature of one pound of water from 32F (its freezing point) to 212F (its boiling point) at a constant pressure of one atmosphere. The British Thermal Unit is used when the measurement is in degrees Fahrenheit (F) on the Fahrenheit Scale and the Calorie is used when temperature is measured in degrees Celsius (C) on the Centigrade Scale.

BROAD-LEAVED DECIDUOUS—Woody Angiosperms (trees or shrubs) with relatively wide, flat leaves that are shed during the cold or dry season; e.g., black ash (Fraxinus nigra).

BROAD-LEAVED EVERGREEN—Woody Angiosperms (trees or shrubs) with relatively wide, flat leaves that generally remain green and are usually persistent for a year or more; e.g., red mangrove (Rhizophora mangle).

BROMIDE—A salt which naturally occurs in small quantities in sea water; a compound of bromine.

BROOK—A natural stream of water, smaller than a river or creek; especially a small stream or rivulet which breaks directly out of the ground, as from a spring or seep; also, a stream or torrent of similar size, produced by copious rainfall, melting snow and ice, etc.; a primary stream not formed by tributaries, though often fed below its source, as by rills or runlets; one of the smallest branches or ultimate ramifications of a drainage system.

BROWNIAN MOVEMENT—The constant, random, zigzag movement of small particles dispersed in a fluid medium, caused by collision with molecules of the fluid. Named after Robert Brown (1773-1858), the British botanist who first described it. Also referred to as Brownian Motion.

BSC—Biological Sciences Center. (DRI)

BTU—British Thermal Unit.

BUBBLE—(1) A thin, usually spherical or hemispherical film of liquid filled with air or gas, as a soap bubble. (2) A globular body of air or gas formed within a liquid, as air bubbles rising to the surface of a body of water.

BUBBLER—A drinking fountain from which a stream of water bubbles upward.

BUCKET—(1) A cylindrical vessel used for holding or carrying water or other liquids; a pail. (2) A receptacle on various machines, such as the compartments on a water wheel, used to gather and convey water.

BUDDLE—An inclined trough in which crushed ore is washed with running water to flush away impurities.

BUFFER—A solution which is resistant to pH changes, or a solution or liquid whose chemical makeup tends to neutralize acids or bases without a great change in pH. Surface waters and soils with chemical buffers are not as susceptible to acid deposition as those with poor buffering capacity.

BUFFER STRIPS—Strips of grass or other erosion-resisting vegetation between or below cultivated strips or fields. Also referred to as Buffer Zones.

BUFFER ZONE—A protective, neutral area between distinct environments.

BULK SEDIMENT ANALYSIS—Analysis of soil material or surface sediment deposits to determine the size and relative amounts of particles composing the material.

BULKHEAD—A low wall of stones, concrete, or piling built to protect a shore, or fills, from wave erosion.

BULKING SLUDGE—(Water Quality) Sludge that does not settle to the bottom of a clarifier, causing a rise in the level of suspended solids and biochemical oxygen demand in water leaving a wastewater treatment facility.

BUND—An embankment used especially in India to control the flow of water.

BUOY—(Nautical) A float, often having a bell or light, moored in water as a warning of danger or as a marker for a channel. Also, to keep afloat or aloft.

BUOYANCY—The tendency of a body to float or rise when submerged in a fluid.

BURAN—A violent windstorm of the Eurasian steppes, accompanied in summer by dust and in winter by snow.

BURBLE—(1) A gurgling or bubbling sound, as of running water. (2) A separation in the Boundary Layer of a fluid about a moving streamlined body, such as the wing of an airplane through air or the keel of a sailboat through water, causing a breakdown in the smooth flow of fluid and resulting in turbulence.

(UNITED STATES) BUREAU OF INDIAN AFFAIRS (BIA)—An agency of the U.S. Department of the Interior which has the primary responsibility for exercising the federal government's trust relationship with Indian tribes. The BIA was first established in 1824 in the War Department, then transferred to the Department of the Interior in 1849. The BIA has prime responsibility to provide services to Indian tribes and plays a central role in the settlement process of Indian water rights disputes. The BIA exercises prime trust responsibility in providing federal government protection for Indian resources and federal assistance in resource development and management. Quite often this responsibility complicates the Department of the Interior's other broad responsibilities to manage the use of lands and natural resources on public lands through its Bureau of Land Management (BLM) land use programs, its Bureau of Reclamation (USBR) water-related projects, and its U.S. Fish and Wildlife Service (USFWS) wildlife and habitat restoration programs, which may frequently come in conflict with the Bureau of Indian Affairs Indian water rights issues. [For example, in Nevada v. United States (463 U.S. 129{1983}), the United States Supreme Court held that the United States [Department of the Interior] could adequately represent more than one interest simultaneously, and so it is not subject to the same standards as a private trustee. In this case, the Court found that claims made by the United States on behalf of the Pyramid Lake Paiute Indian Tribe to protect fisheries should have been asserted in prior litigation. Nevertheless, the Court found the failure to do so was not a breach of its trust obligations to the tribe, even though the United States also had protected the competing interests of non-Indian irrigators.] Also see Negotiated Settlement and Truckee River Operating Agreement (TROA).

(UNITED STATES) BUREAU OF LAND MANAGEMENT (BLM)—An agency of the U.S. Department of the Interior responsible for the stewardship of the nation's public lands. The Bureau of Land Management is committed to the sustained management, protection, and improvement of these lands in a manner consistent with the needs of the American people. The BLM's management philosophy is based on the principles of multiple use and sustained yield of our nation's resources within a framework of environmental responsibility and scientific technology. The resources under the BLM's oversight include recreation, rangelands, timber, minerals, watersheds, fish and wildlife, wilderness, air, and scenic, scientific and cultural values. The BLM oversees the largest natural resource base in the federal government. This base includes 270 million acres of public lands ranging from old growth forests in the Pacific Northwest to sun drenched desert ecosystems in the Southwest to Arctic tundra in Alaska. The BLM also supervises mineral leasing and operations on an additional 300 million acres of federal mineral estate that underlie other surface ownerships. BLM managed public lands provide habitat for thousands of wildlife and plant species, including some 220 federally-listed threatened and endangered species and 1,200 species considered candidates for listing. The BLM manages over 169,000 miles of fish bearing streams and more than 50 million acres of forested lands. In addition, the BLM is caretaker of an estimated 4 million cultural properties, including 400 listed in the National Register of Historic Places. The BLM also manages more than 1.6 million acres of designated wilderness and 22.8 million acres of wilderness study areas. More than 46,500 wild horses and burros roam BLM land in the West. The BLM permits and manages various uses of the public lands, including grazing, mining, recreation, and timber operations. These activities traditionally have been managed on an individual basis. However, more recently the BLM's management efforts have shifted to a more comprehensive ecosystem basis of managing such lands to insure sustained benefits for future generations of Americans. The Bureau of Land Management has its headquarters office in Washington, D.C. There are an additional eleven state offices for managing resources in the western states of Alaska, Arizona, California, Idaho, Montana, Nevada, New Mexico, Oregon, Utah, and Wyoming. BLM resources for the Eastern United States are managed out of Springfield, Virginia. The BLM also supports a National Interagency Fire Center (NIFC) in Boise, Idaho as well as a public information service center (SC) in Denver, Colorado and a centralized employee training center in Phoenix, Arizona. In Nevada alone, the BLM manages some 48 million acres of public lands or approximately 67 percent of all lands in Nevada.

(UNITED STATES) BUREAU OF RECLAMATION (USBR)—An agency of the U.S. Department of the Interior responsible for many of the dam, reservoir, and irrigation projects in the Western United States. The USBR reclamation program was authorized by the Reclamation Act of 1902 which was initially intended to reclaim the arid and semiarid lands of the Western United States by conserving and supplying irrigation water to make them productive. Since that beginning, the USBR's mission has expanded considerably to include multipurpose water development by providing water for irrigation, hydroelectric power, water for homes, businesses and factories, outdoor recreation, flood control, fish and wildlife enhancement, improved water quality, river regulation and control, and other related uses of water. Currently the USBR administers some 322 storage dams, 14,490 miles of canals, 174 pumping plants, and 50 hydroelectric plants. USBR water irrigates 146,000 farms in the West, provides part or all the water needs on nearly 10 million acres, yielding enough food for 33 million people, and also provides 620 billion gallons of water a year of municipal and industrial use in western towns and cities. In terms of its original intent and broad governing guidelines, the U.S. Bureau of Reclamation is primarily responsible for water projects with respect to developing water sources for agriculture and commerce, while the U.S. Army Corps of Engineers (COE) has had primary responsibility for water projects which protect property from potential flood damage. In reality, however, quite often these federal agencies' project goals overlap with USBR's dams and reservoirs providing important flood protection and the COE's water projects—dams, locks, and canals—providing important water transportation linkages and benefits to commerce.

BURIED DRAIN—A covered drain usually made of clay, concrete, or plastic pipe installed beneath the ground surface at a planned grade and depth for conveyance of excess groundwater.

BURN—(Chiefly Scottish) (1) A brook; a rivulet. (2) Water, especially that used in brewing.

BUSHEL—(1) A unit of volume or capacity in the U.S. Customary System, used in dry measure and equal to 4 pecks, 2,150.42 cubic inches, or 35.24 liters. (2) A unit of volume or capacity in the British Imperial System, used in dry and liquid measure and equal to 2,219.36 cubic inches or 36.37 liters.

BUTT—A large cask especially for wine, beer, or water.

BUTTRESS DAM—A dam consisting of a watertight upstream face supported at intervals on the downstream side by a series of buttresses. Also see Dam.

BWR—Boiling Water Reactor.

BYPASS, also By-Pass—A pipe or channel used to conduct a liquid around another pipe or a fixture.

BYPASS SYSTEM—A structure in a dam that provides a route for fish to move through or around the dam without going through the turbines.

C-CELSIUS—Centigrade Temperature Scale

C-HORIZON—a layer of unconsolidated material, relatively little affected by the influence of organisms and presumed to be similar in chemical, physical, and mineralogical composition to the material from which at least a portion of the overlying Solum has developed.

CAA—Clean Air Act (EPA)

CABOTAGE—Trade or transport in coastal waters or airspace or between two points within a country.

CAISSON—(1) A watertight structure within which construction work is carried on under water. (2) A large box open at the top and one side, designed to fit against the side of a ship and used to repair damaged hulls under water. (3) A floating structure used to close off the entrance to a dock or canal lock. Also referred to as a Camel.

CALCAREOUS—Formed of calcium carbonate or magnesium carbonate by biological deposition or inorganic precipitation in sufficient quantities to effervesce carbon dioxide visibly when treated with cold 0.1 normal hydrochloric acid. Calcareous sands are usually formed of a mixture of fragments of mollusk shell, echinoderm spines and skeletal material, coral, foraminifera, and algal platelets.

CALCAREOUS FENS—Peatlands formed in areas of groundwater discharge, where cold, anoxic, mineral-rich water provides a specialized habitat for disproportionately large numbers of rare and endangered plants. Many of the plants found in calcareous fens are species which would be typical of more northern habitats. The health of such fens is inextricably linked to the presence of the upwelling groundwater. Also see Peat (Peatlands).

CALCINE—Heated to temperature of dissociation; for example, heat gypsum to the temperature where the water of crystallization is driven off.

CALCITE—(Geology) Calcium carbonate (CaCO3), with hexagonal crystallization, a mineral found in the form of limestone, chalk, and marble.

CALCIUM—(Ca++) The most abundant cation found in Wisconsin lakes. Its abundance is related to the presence of calcium-bearing minerals in the lake watershed. Reported as milligrams per liter (mg/l) as calcium carbonate (CaCO3), or milligrams per liter as calcium ion(Ca++).

CALCIUM CARBONATE—(CaCO3) The principal hardness and scale-causing compound in water. A white precipitate that forms in water lines, water heaters, and boilers in hard water areas; also known as scale. Also the principal chemical composition of Tufa, a calcareous and siliceous rock deposit of springs, lakes, or ground water.

CALCIUM CARBONATE TREATMENT—The adding of limestone (calcium carbonate) to an acid lake to raise the pH.

CALCIUM CHLORIDE—A white deliquescent compound, CaCl2, used chiefly as a drying agent, refrigerant, and preservative and for controlling dust and ice on roads.

CALCIUM HYDROXIDE—A white crystalline strong alkali Ca(OH)2 that is used especially to make mortar and plaster and to soften water.

CALCIUM NITRATE TREATMENT—A method of adding nitrate to lake sediments.

CALF—A large floating chunk of ice split off from a glacier, an iceberg, or a floe.

CALGON—Trademark product used for a water softener.

CALICHE—(1) A soil layer near the surface, more or less cemented by secondary carbonates of calcium or magnesium precipitated from the soil solution. It may occur as a soft, thin soil horizon, as a hard, thick bed just beneath the Solum, or as a surface layer exposed by erosion. (2) Alluvium cemented with sodium nitrate, chloride, and/or other soluble salts in the nitrate deposits of Chile and Peru. Also referred to as Hardpan.

CALIFORNIA DOCTRINE—A system of allocating water, first announced in California, which combines Riparian Rights and Appropriative Rights. A number of states have applied this doctrine at one time or another. However, most states have essentially abandoned the doctrine in favor of the Appropriation Doctrine, and it is primarily of historical significance. Also see Alpine Decree [California and Nevada].

CALIFORNIA ENVIRONMENTAL QUALITY ACT (CEQA)—The California equivalent of the federal National Environmental Policy Act (NEPA).

CALIFORNIA STATE WATER RESOURCES CONTROL BOARD (SWRCB)—See State Water Resources Control Board (SWRCB) [California].

CALIFORNIA WATER COMMISSION—See Department of Water Resources (DWR) [California].

CALM—A period or condition of freedom from storms, high winds, or rough activity of water.

CALORIE—(Abbreviation cal) (1) Basically, A unit of heat energy equal to the amount of heat needed to raise the temperature of one gram of water one degree Celsius (C). More precisely, any of several approximately equal units of heat, each measured as the quantity of heat required to raise the temperature of 1 gram of water by 1C from a standard initial temperature, especially from 3.98C (corresponding to the maximum density of water), 14.5C, or 19.5C, at 1 atmosphere pressure. Also referred to as the Gram Calorie and the Small Calorie. (2) The unit of heat equal to 1/100 the quantity of heat required to raise the temperature of 1 gram of water from 0C (its freezing point) to 100C (its boiling point) at 1 atmosphere pressure. Also referred to as the Mean Calorie. (3) The unit of heat equal to the amount of heat required to raise the temperature of 1 kilogram of water by 1C at 1 atmosphere pressure. Also referred to as the Kilocalorie, Kilogram Calorie, and Large Calorie. (4) A unit of energy-producing potential equal to this amount of heat that is contained in food and released upon oxidation by the body. Also referred to as the Nutritionist's Calorie. The calorie is used when temperature is measured in degrees Celsius (C) on the Centigrade Scale. The British Thermal Unit (BTU) is used when the measurement is in degrees Fahrenheit (F) on the Fahrenheit Scale.

CALVE—To break at an edge, sot that a portion separates. Used of a glacier or an iceberg.

CAMEL—A device used to raise sunken objects, consisting of a hollow structure that is submerged, attached tightly to the object, and pumped free of water. Also referred to as a Caisson.

CAMP SCAR—Camp sites on wilderness and primitive lakes are easily recognized from the water surface and air by their lighter tone and barren character. Landing beaches are cleared, ground cover is destroyed and large trees are dead or dying from soil compaction. Damage to the aesthetic image is frequently accentuated by blazes, temporary structures and bark stripping.

CANAL—A constructed open channel for transporting water.

CANAL, BOAT—A dredged canal between separate lakes or lakes and streams to provide convenient boat passage.

CANAL AUTOMATION—The implementation of a control system that upgrades the conventional method of canal system operation.

CANAL CHECK GATE STRUCTURE—A structure designed to control the water surface level and flow in a canal, maintaining a specified water depth or head on outlets or turnout structures. Most canal check structures have movable gates.

CANAL FREEBOARD—The amount of canal lining available above maximum design water depth.

CANAL POOL—Canal section between check structures

CANAL PRISM—The cross-sectional shape of a typical canal.

CANAL REACH—The segment of the main canal system consisting of a series of canal pools between major flow control structures.

CANAL SYSTEM OPERATION—Water transfer from its source to points of diversion for irrigation, municipal and industrial, fish and wildlife, and drainage purposes.

CANCELED WATER RIGHT—A water right that is invalidated due to the failure of the water right holder to comply with the terms and conditions of the permit. Also see Forfeited Water Right and Withdrawn Water Right.

CANDIDATE SPECIES—Plant or animal species designated by the Department of the Interior, U.S. Fish and Wildlife Service (USFWS) as candidates for potential future listing as an Endangered Species or Threatened Species pursuant to the Endangered Species Act (ESA) of 1973; plant or animal species that are candidates for designation as endangered (in danger of becoming extinct) or threatened (likely to become endangered).

CANOE— A light narrow boat made of bark, aluminum, or fiberglass. A paddle is used to steer and move it.

CANOE TRAIL—Connected lakes or closely associated lakes and streams used as canoe routes. Portages used in overland travel between water bodies and camp sites may be either marked or developed; (1) wilderness area canoe routes are long and provide no facilities, (2) primitive area canoe routes are of variable length and have developed portages and camp sites, (3) canoe routes in populated agricultural and forest areas may be quite short and have hotels, organized campgrounds and pick-up service.

CANOPY—The overhanging cover formed by leaves, needles, and branches of vegetation.

CANOPY CLOSURE—The degree of canopy cover relative to openings (Forestry Canada 1992). Class 1 has a cover of a few individuals, and class 9 has continuous canopy cover with no gaps.

CANYON, also Cañon—A narrow chasm with steep cliff walls, cut into the earth by running water; a gorge.

CAP—A layer of clay, or other impermeable material installed over the top of a closed landfill to prevent entry of rainwater and minimize Leachate.

CAPA (CRITICAL AQUIFER PROTECTION AREA)—As defined in the Safe Drinking Water Act (SDWA), is all or part of an area located within an area for which an application of designation as a sole or principal source aquifer (pursuant to Section 1424[e]) has been submitted and approved by the Administrator not later than 24 months after the date of enactment and which satisfies the criteria established by the Administrator; and all or part of an area that is within an aquifer designated as a Sole Source Aquifer (SSA), as of the date of the enactment of the Safe Drinking Water Act (SDWA) amendments of 1986, and for which an area wide ground-water protection plan has been approved under Section 208 of the Clean Water Act (CWA) prior to such enactment.

CAPACITIVE DEIONIZATION (CDI)—A relatively simple and straight forward electrochemical reaction process made unique and highly efficient through the development of a highly-porous material called carbon aerogel that absorbs huge volumes of ions. A single cube of carbon aerogel, one inch on a side, has an effective surface area of more than 20 million square inches. This unusually high surface area makes it possible to adsorb large numbers of ions. Water containing salt, heavy metals, or even radioactive isotopes is pumped through a series of electrochemical cells made from the aerogel, a material sometimes called "frozen smoke." Effluent water from the series of stacked cells is subsequently purified. The trapped ions can be released into a relatively small stream of "rinse" water typically comprising less than one percent of the total volume of produce water. Also see Deionization.

CAPACITY, FIELD or SOIL—The amount of water held in a soil sample after the excess gravitation water has drained away.

CAPACITY, GROSS RESERVOIR—The total amount of storage capacity available in a reservoir for all purposes from the streambed to the normal maximum operating level. It does not include surcharge, but does include dead storage.

CAPE—(1) A point or head of land projecting into a body of water. (2) A rounded projection, out into the water, and either high land or low land. For inland lakes, cape rarely appears on maps as a place name and also only infrequently in descriptions. Point and head according to present usage appears to be preferred to cape.

CAPILLARITY—(1) The property of tubes or earth-like particles with hair-like openings which, when immersed in fluid, raise (or depress) the fluid in the tubes above (or below) the surface of the fluid in which they are immersed. (2) The interaction between contacting surfaces of a liquid and a solid that distorts the liquid surface from a planar shape. Also referred to as Capillary Action or Capillary Attraction.

CAPILLARY ACTION—(1) The action by which water is drawn around soil particles because there is a stronger attraction between the soil particles and the water molecules themselves. (2) The movement of water within the interstices of a porous medium due to the forces of adhesion, cohesion, and surface tension acting in a liquid that is in contact with a solid. Synonymous with the terms Capillarity, Capillary Flow, and Capillary Migration.

CAPILLARY ATTRACTION—The force that results from greater adhesion of a liquid to a solid surface than internal cohesion of the liquid itself and that causes the liquid to be raised against a vertical surface, as water is in a clean glass tube. It is the force that allows a porous material like soil to soak up water from lower levels.

CAPILLARY FRINGE—(1) The zone at the bottom of the Zone of Aeration (Vadose Zone) where ground water is drawn upward by capillary force. (2) The zone immediately above the Zone of Saturation (or Groundwater Table) in which underground water is lifted against gravity by surface tension (Capillary Action) in passages of capillary size.

CAPILLARY PHENOMENA—A phenomenon of water movement caused by Capillarity.

CAPILLARY POTENTIAL—The work required to move a unit mass of water from the reference plane to any point in the soil column.

CAPILLARY RISE—The height above a free water surface to which water will rise by Capillary Action.

CAPILLARY WATER—(1) Water held in the soil above the Phreatic Surface by capillary forces; or soil water above hydroscopic moisture and below the field capacity. (2) A continuous film of water found around soil particles.

CAPILLARY ZONE—The soil area above the water table where water can rise up slightly through the cohesive force of Capillary Action.

CAPTURE—(1) Water withdrawn artificially from an aquifer is derived from a decrease in storage in the aquifer, a reduction in the previous discharge from the aquifer, an increase in the recharge, or a combination of these changes. The decrease in discharge from an aquifer plus the increase in recharge. Capture may occur in the form of decreases in the ground-water discharge into streams, lakes, and the ocean, or from decreases in that component of Evapotranspiration derived from the Zone of Saturation. (2) Diversion of the flow of water in the upper part of a stream by the headward growth of another stream.

CAPTURE ZONE—The zone around a well contributing water to the well; the area on the ground surface from which a well captures water.

CARBAMATES—A class of new-age pesticides that attack the nervous system of organisms.

CARBON—A nonmetallic element found in all organic substances and in some inorganic substances, as diamonds, coal, graphite, charcoal and lampblack.

CARBON ADSORPTION—(Water Quality) A treatment system that removes contaminants from ground water or surface water by forcing it through tanks containing activated carbon treated to attract the contaminants.

CARBON-CHLOROFORM EXTRACT (CCE)—A measurement of the organic content of a water. It consists of adsorbing the organic matter onto activated carbon, then extracting it with chloroform.

CARBON FILTRATION—(Water Quality) The passage of treated wastewater or domestic water supplies through activated charcoal in an effort to remove low concentrations of dissolved chemicals.

CARBON DIOXIDE—A colorless, odorless, nonpoisonous gas, CO2, that forms Carbonic Acid when dissolved in water. Carbon dioxide is typically produced during combustion and microbial decomposition. Because carbon dioxide absorbs infrared radiation, rising levels of carbon dioxide in the global atmosphere over the past century have prompted concerns about climatic change and more specifically the Greenhouse Effect.

CARBON POLISHING—(Water Quality) The removal of residual dissolved organic substances from wastewater by Adsorption on activated charcoal (granular activated carbon). A form of Tertiary Wastewater Treatment.

CARBON TREATMENT—(Water Quality) In a drinking water purification process, the removal of Colloids by Adsorption on Activated Charcoal. This step often improves the color, taste, and odor of drinking water. Also see Secondary Drinking Water Standards.

CARBONACEOUS BIOCHEMICAL OXYGEN DEMAND—The incubation of a sample of water or wastewater for a relatively short period of time in order to determine the Biochemical Oxygen Demand (BOD). The short incubation, usually 5 days, is sufficient to detect only the microbial utilization of carbon compounds. A longer incubation (15 to 20 days) would also detect the oxidation of inorganic nitrogenous compounds (ammonia and nitrite) and the subsequent demand for molecular oxygen by chemoautotrophic bacteria.

CARBONATE—(1) The collective term for the natural inorganic chemical compounds related to carbon dioxide that exist in natural waterways. (2) A sediment formed by the organic or inorganic precipitation from aqueous solution of carbonates of calcium, magnesium, or iron. The CO3-2 ion in the Carbonate Buffer System. Combined with one proton, it becomes Bicarbonate, HCO3- and with two protons, Carbonic Acid. The carbonate ion forms a solid precipitant when combined with dissolved ions of calcium or magnesium.

CARBONATE AQUIFER—An aquifer found in limestone and dolomite rocks. Carbonate aquifers typically produced hard water, that is, water containing relatively high levels of calcium and magnesium.

CARBONATE BUFFER SYSTEM—The most important buffer system in natural surface waters and wastewater treatment, consisting of a carbon dioxide, water, carbonic acid, Bicarbonate, and Carbonate ion equilibrium that resists changes in the water's pH. For example, if acid materials (hydrogen ions) are added to this buffer solution, the equilibrium is shifted and carbonate ions combine with the hydrogen ions to form bicarbonate. Subsequently, the bicarbonate then combines with hydrogen ions to form carbonic acid, which can dissociate into carbon dioxide and water. Thus the system pH is unaltered even though acid was introduced.

CARBONATE HARDNESS—Water hardness caused by the presence of Carbonate and Bicarbonate of calcium and magnesium. Also see Temporary Hardness.

CARBONATE ROCK—(Geology) A rock consisting chiefly of carbonate minerals, such as limestone and dolomite.

CARBONATED WATER—(1) Effervescent water, usually containing salts, charged under pressure with purified carbon dioxide gas, used as a beverage or mixer. Also referred to as soda water, club soda, or seltzer. (2) A solution of water, sodium bicarbonate, and acid.

CARBONATION, GROUNDWATER—The dissolving of carbon dioxide in surface water as it percolates through the ground. The carbon dioxide reacts with water to form carbonic acid, a weak acid that causes the water to have a slightly acidic pH.

CARBONIC ACID—A weak, unstable acid, H2CO3, present in solutions of carbon dioxide and water. The carbonic acid content of natural, unpolluted rainfall lowers its pH to about 5.6.

CARCINOGEN—A cancer-causing substance or agent.

CARCINOGENIC—Cancer causing.

CARLSON'S TROPHIC STATE INDEX (TSI)—A measure of Eutrophication of a body of water using a combination of measures of water transparency or turbidity (using Secchi Disk depth recordings), Chlorophyll-a concentrations, and total phosphorus levels. TSI measures range from a scale 20-80 and from Oligotrophic waters (maximum transparency, minimum chlorophyll-a, minimum phosphorus) through Mesotrophic, Eutrophic, to Hypereutrophic waters (minimum transparency, maximum chlorophyll-a, maximum phosphorus). Also referred to as the (Mean) Trophic State Index (TSI). Also see Total Inorganic Nitrogen (TIN) and Total Inorganic Phosphate (TIP).

CARNIVORE—An organism that feeds primarily on other animals.

CARNIVOROUS—Flesh eating organisms.

CARP—A fresh water fish that sometimes lives in schools in lakes. Sometimes used for food.

CARR, also CAR—(1) A pool; also, a Fen or a Bog. (2) The yellow or brown sediment of humate of iron in water flowing from a peaty bog.

CARRIAGE LOSSES (Water)—A term used to describe the operational losses associated with conveying water from its point of diversion to its point of use. These losses typically include spillage, seepage, evaporation, and phreatophyte usage along the water course, as applicable. Water rights applicants are entitled to water for transporting their entitlement to their proposed place(s) of use. Carriage losses are generally considered unavoidable, and are legally bearable so long as that extra water is used reasonably and economically in transporting the water to its destination.

CARRYING CAPACITY—(Biologic) The carrying capacity of a lake refers to its natural productivity. In relation to fish production, or other aquatic life, the numbers which the natural food supply, or pasturage, will support adequately.

CARRYING CAPACITY—(Commercial) The measure of the capacity of a lake for boating, skiing, bathing - recreational use in general - and residential occupation of the shore and shore border land without patent overcrowding, pollution and consequent danger to health and safety. Carrying capacity may be greatly limited if a single use is given priority; also it may be expanded if the surface area of the lake is zoned for particular uses and the time for use in each zone is specified. Some of the factors involved in determining carrying capacity: size, shape, depth, character and location of swimming areas and beaches, regulatory and zoning restrictions, season of year, accessibility (public or private), available services (boat liveries, marinas), level of pollution or smirchment, parking facilities, usable frontage and fish (abundance, species).

CARRYING CAPACITY—(Ecology) The maximum number and type of species which a particular habitat or environment can support without detrimental effects.

CARRYING CAPACITY—(Lake) The amount of human development that can occur in the lake's watershed without causing a significant change in its water quality.

CARRYING PLACES—Land portaged in navigation of lakes and streams, and legally a part of the navigation route.

CASCADE—A short, steep drop in stream bed elevation often marked by boulders and agitated white water.

CASCADE FLOW —Regulated flow through a series of flow control structures.

CASING—The steel conduit required to prevent waste and contamination of the ground water and to hold the formation open during the construction or use of the well. A tubular structure intended to be water tight installed in the excavated or drilled hole to maintain the well opening and, along with cementing, to confine the ground waters to their zones of origin and prevent the entrance of surface pollutants.

CASUAL WATER—A temporary accumulation of water not forming a regular hazard of a golf course.

CAT ICE—"Ice forming a thin shell from under which the water has receded." (Navigation Dictionary USHO, Bulletin 220, 1956) The term has some application to ice on lakes.

CATABOLISM—The biological breakdown of materials into their simpler components, i.e., decomposition. Performed by decomposer organisms, mainly bacteria and fungi.

CATADROMOUS—Used to describe fish that live in fresh water but migrate to marine waters to breed. Contrast with Anadromous.

CATALASE—A red crystalline enzyme that consists of a protein complex with hematin groups and catalyzes the decomposition of Hydrogen Peroxide into water and oxygen.

CATALYSIS—The action of a Catalyst, especially an increase in the rate of a chemical reaction.

CATALYST—A substance that alters the speed of a reaction, but does not change the form or amount of product. For example, Enzymes are biological catalysts, enhancing reactions within living organisms.

CATALYTIC CONVERTER—A reaction chamber typically containing a finely divided platinum-iridium Catalyst into which exhaust gases from an automotive engine are passed together with excess air so that carbon monoxide and hydrocarbon pollutants are oxidized to carbon dioxide and water.

CATALYZE—To modify, especially to increase, the rate of a chemical reaction by Catalysis or the action of a Catalyst.

CATAPHORESIS—The migration of charged colloidal particles (Colloids) or Molecules through a solution under the influence of an applied electric field usually provided by immersed electrodes. Also call Electrophoresis.

CATCH BASIN—A sieve-like device at the entrance to a sewer to stop matter that could possibly block up the sewer.

CATCHMENT—(1) The catching or collecting of water, especially rainfall. (2) A reservoir or other basin for catching water. (3) The water thus caught.

CATCHMENT AREA—(1) The intake area of an aquifer and all areas that contribute surface water to the intake area. (2) The areas tributary to a lake, stream, sewer, or drain. (3) A reservoir or basin developed for flood control or water management for livestock and/or wildlife. See also Drainage Area; Watershed. (4) The land (and including the streams, rivers, wetlands and lakes) from which water runs off to supply a particular location in a freshwater system. In North America, the term watershed is often used instead of catchment area. In the UK, watershed means the line separating two adjacent catchments.

CATCHMENT AREA (BASIN)—The area draining into a river, reservoir, or other body of water.

CATCHMENT BASIN—The entire area from which drainage is received by a river or a lake; most generally used in reference to surface runoff.

CATEGORICAL EXCLUSION—A class of actions which either individually or cumulatively would not have a significant effect on the human environment and therefore would not require preparation of an Environmental Assessment (EA) or an Environmental Impact Statement (EIS) under the National Environmental Policy Act (NEPA).

CATEGORICAL PRETREATMENT STANDARD—A technology-based effluent limitation for an industrial facility discharging into a municipal sewer system. Analogous in stringency to Best Available Technology (BAT) for direct dischargers.

CATEGORICAL VARIABLE—(Statistics) A qualitative variable created by classifying observations into categories. For example, a series of household incomes could be classified into the categorical variables low, medium, and high describing certain specific ranges of income levels. Many statistical techniques are inappropriate for the use of categorical variables. Also referred to as a Qualitative Variable. Contrast with Quantitative Variable.

CATFISH—A fish found in freshwater rivers and has long feelers around its mouth. Often used as food.

CATHOLE—A localism used by early settlers in southern Michigan for very small (usually less than an acre) shallow depressions or holes. The name presumably originated from the characteristic aquatic plant, the cattail, (Typha spp.). Later, the term came to be applied loosely to any shallow boggy or miry depression especially in the till clay plains. These depressions represented minor inequalities in the plains left by the ice sheet and were originally numerous but have been largely obliterated by land clearing and land drainage. The term cathole is also an old colloquialism for a hole or pond, in a stream, or swamp, frequented by catfish.

CATION—The positively charged particle or ion in an electrolyzed solution which travels to the cathode and is there discharged, evolved, or deposited. Also, by extension, any positive ion. The common cations present in lakes in normal order of decreasing concentrations follows: calcium (Ca++), magnesium (MG++), potassium (K+), sodium (Na+), ammonium (NH4+), ferric iron (FE+++), or ferrous iron (FE++), manganese (Mn++), and hydrogen (H+).

CATION EXCHANGE—A chemical process in which Cations of like charge are exchanged equally between a solid, such as zeolite, and a solution, such as water. The process is often used to soften water.

CATION EXCHANGE CAPACITY (CEC)—The total of exchangeable cations that a soil can adsorb; expressed in milliequivalents per 100 grams (g) of soil.

CAT'S-PAW, also Catspaw—A light breeze that ruffles small areas of a water surface.

CATTAIL—A tall, reedy marsh plant with brown furry fruiting spikes; an Emergent Plant.

CAUSEWAY—A raised roadway formed by filling across wet or marshy ground, or the surface of a lake from shore to shore.

CAUSTIC—Alkaline or basic.

CAVE-IN LAKES—Kettle lakes, sink lakes, thaw lakes, thermo-karst.

CAVENDISH, Henry (1731-1810)—A British chemist and physicist who discovered the properties of hydrogen and established that water was a compound of hydrogen and oxygen.

CAVERN—A large underground opening in rock (usually limestone) which occurred when some of the rock was dissolved by water. In some igneous (formed by volcanic action) rocks, caverns can be formed by large gas bubbles.

CAVITATION—(1) A process of erosion in a stream channel caused by sudden collapse of vapor bubbles against the channel wall. (2) The formation of cavities filled with air and water vapor due to internal pressure reduced below atmosphere. (3) The formation and collapse of gas pockets or bubbles on the blade of an impeller or the gate of a valve; collapse of these pockets or bubbles drives water with such force that it can cause pitting of the gate or valve surface.

CCE—Carbon - Chloroform Extract

CDI—Capacitive Deionization

CE-QUAL-ICM—Three-dimensional, time variable, integrated-compartment eutrophication model.

CE-QUAL-RIV—Hydrodynamic and water quality model for streams.

CE-QUAL-WZ—Two-dimensional, laterally averaged hydrodynamic and water quality model.

CEAM—Center for Exposure Assessment Modeling.

CEC—Cation Exchange Capacity

CELL—(Biology) The basic building block of all living matter. The cell of a living organism contains a high percentage of water.

CELLULAR—Made up of small compartments.

CELLULOSE—The fibrous part of plants used in making paper and textiles, which in turn may be made into building products.

CELSIUS [Temperature Scale] (C)—(1) Relating to, conforming to, or having the international thermometric scale on which the interval between the triple point of water and the boiling point of water is divided into 99.99 degrees with 0.01 representing the Triple Point and 100 the boiling point at one atmosphere of pressure; Abbreviation C; Compare to Centigrade [Temperature Scale]. The Celsius scale, which is identical to the centigrade scale, is named for the 18th-century Swedish astronomer Anders Celsius, who first proposed the use of a scale in which the interval between the freezing and boiling points of water is divided into 100 degrees. By international agreement, the term Celsius has officially replaced Centigrade. (2) Unit of measure for the Centigrade Temperature Scale of measuring temperature, as contrasted with the Fahrenheit unit of measure. The formula for converting a Celsius temperature to Fahrenheit temperature is °F = [9/5°C + 32]. Also see Temperature Scale.

CENOZOIC—Of, belonging to, or designating the latest era of geologic time, which includes the Tertiary Period and the Quaternary Period and is characterized by the formation of modern continents, glaciation, and the diversification of mammals, birds, and plants.

CENSUS—A complete counting, with classification, of a population or group at a particular point in time, as regards to some well-defined characteristic(s). Usually has governmental and economic and social connotations, e.g., the decennial census of the population; however, also used in a biological and environmental sense for plants, animals, and habitat.

CENSUS OF AGRICULTURE—A Census taken by the U.S. Department of Commerce, Bureau of the Census, every 5 years to include the number of farms, land in farms, crop acreage and production, irrigated acreage, farm spending, farm facilities and equipment, farm tenure, value of farm products sold, farm size, and other farm-related data.

CENSUS X-11 (Seasonal Adjustment) PROCESS—(Statistics) A seasonal adjustment process for decomposing time series data into its trend-level, seasonal index, trading day, and irregular components. It is primarily used to De-Seasonalize official government statistics for publication, but is arguably the most widely used and accepted seasonal adjusted process.

CENTER-PIVOT IRRIGATION—Automated sprinkler irrigation achieved by automatically rotating the sprinkler pipe or boom, supplying water to the sprinkler heads or nozzles, at a radius from the center of the field to be irrigated. Water is delivered to the center or pivot point of the system. The pipe is supported above the crop by towers at fixed spacing and propelled by pneumatic, mechanical, hydraulic, or electric power on wheels or skids in fixed circular paths at uniform angular speeds. Water is applied at a uniform rate by progressive increase of nozzle size from the pivot to the end of the line. The depth of water applied is determined by the rate of travel of the system. Single units are ordinarily about 1,250 to 1,300 feet long (381-397 meters) and irrigate approximately a 130-acre (52.7 hectare) circular area. Also see Irrigation Systems.

CENTIGRADE [Temperature Scale] (C)—Relating to, conforming to, or having a thermometric scale on which the interval between the freezing point of water and the boiling point of water is divided into 100 degrees with 0 representing the freezing point and 100 the boiling point at one atmosphere of pressure; Abbreviation C; Compare to Celsius [Temperature Scale]. The Centigrade scale is identical to the Celsius scale; however, by international agreement, the term Celsius has officially replaced Centigrade. Contrast with the Fahrenheit Temperature Scale, using degrees Fahrenheit (F), in which 32°F above the 0(°F) mark indicates the freezing point of water and 212°F indicates the boiling point of water (at sea level). Also see Temperature Scale.

CENTRAL VALLEY PROJECT (CVP) [California]—A multipurpose water project developed mainly by the U.S. Bureau of Reclamation (USBR), extending from the Cascade Range on the north to the semiarid but fertile plains of California's Kern River on the south. The state and federal portions of the Central Valley Project (CVP) encompass a number of dams, reservoirs, pumping facilities, canals, and aqueducts providing protection from saltwater intrusion into the Bay-Delta region (also referred to as the Sacramento-San Joaquin Delta), irrigation water for San Joaquin Valley farms, and municipal and industrial water for some of California's most populated urban areas. The construction of the CVP was approved by California voters in a 1933 referendum of the California Central Valley Project Act. Due to the effects of the Great Depression, the state was unable to construct the project at that time. Subsequently, portions of the CVP were authorized and constructed by the federal government. Other portions were later constructed by California after the Depression as part of the State Water Project (SWP), as authorized under the 1960 Burns-Porter Act. Principal facilities of the SWP include Oroville Dam, Delta Facilities, the California Aqueduct, and North and South Bay Aqueducts. Principle facilities of the federal CVP include Shasta, Trinity, Folsom, Friant, Clair Engle, Whiskeytown, and New Melones dams, Delta facilities, and the Delta Mendota Canal. Joint CVP/SWP facilities include San Luis Reservoir and Canal and various Delta facilities. Also see Bay-Delta [California].

CENTRALIZED CONTROL (Canal)—Control of a canal project from a central location by the watermaster.

CENTRALIZED HEADQUARTERS (Canal)— Control of a canal project from a central location generally by a master station, communications network, and one or more remote terminal units (RTUs).

CENTRIFUGAL PUMP—A device that converts mechanical energy to pressure or kinetic energy in a fluid by imparting centrifugal force on the fluid through a rapidly rotating impeller.

CENTRIFUGATION—(Water Quality) In water and wastewater treatment, a method used to remove liquid from sludge through use of centrifugal forces.

CEQA—See California Environmental Quality Act (CEQA).

CERCLA—See Comprehensive Environmental Response, Compensation, and Liability Act.

CERES—California Environmental Resources Evaluation System

CERTIFICATE OF WATER RIGHT—An official document which serves as evidence of a Perfected Water Right. Also see Application, Water Right.

CERTIFICATED WATER RIGHT—The right granted by a state water agency to use either surface or ground water. Also see Application, Water Right and Vested Water Right.

CERTIFICATED WATER RIGHT [Nevada]—The right to put surface or ground water to beneficial use that is identified by a recorded document issued by the Nevada State Engineer after satisfactory proof of "perfection of application" for a permitted water right has been filed in accordance with Nevada Revised Statues Chapter 533.

CERTIFIED WATER RIGHT—A state-issued document that serves as legal evidence that an approved application has been physically developed and the water put to beneficial use. The certificate establishes priority date, type of beneficial use, and the maximum amount of water that can be used. Before a water right can be certified, verification of the physical development must be provided to the state through a survey conducted by an approved water rights examiner. Even certified water rights are subject to occasional review to ensure continued beneficial use.

CESSPOOL—An underground catch basin for combined liquid and solid waste, such as household sewage, so designed as to retain the organic matter and solids but permitting the liquids to seep through the bottom and sides. Also see Septic Tanks.

CF—Cubic Feet (or Foot).

CFCs—Chlorofluorocarbons.

CFR—Code of Federal Regulations.

CFS (Cubic Foot per Second)—A unit of discharge for measurement of flowing liquid (usually water in a stream) equal to a flow of one cubic foot per second past a given section. A rate of flow equivalent to 448.83 gallons per minute. Also called Second-Foot.

CFS-DAY—The volume of water represented by a flow of 1 cubic foot per second for 24 hours. It equals 86,400 cubic feet, 1.983471 acre-feet, or 646,317 gallons.

CFSM (Cubic Feet per Second per Square Mile)—The average number of cubic feet of water per second flowing from each square mile of area drained by a stream, assuming that the runoff is distributed uniformly in time and area.

CHAIN OF LAKES—A number of lakes tied together by live connecting streams or natural channels.

CHALK—A mineral composed mainly of the calcareous shells of various marine microorganisms, but whose matrix consists of fine particles of calcium carbonate, some of which may have been chemically precipitated.

CHALYBEATE—Tasting like iron, as water from a mineral spring.

CHANNEL (LAKE)—In instances sub-lacustrine channels appear where a lake has been formed by the submergence of a valley, or the drowning of a river; the channels formed under subaerial conditions by stream cutting may remain unfilled by sediments, on the lake bottom. Channel is applied to a surface water way, either natural or artificial, which connects two lakes and provides for boat travel; to river distributaries and connecting water in a delta; and to trench-like excavations extended inland from a lake shoreline to provide water frontages and boat access for back lots.

CHANNEL (LAKE BASIN)—The deeper, narrow elogated or more sharply trenched part of a lake bottom.

CHANNEL (WATERCOURSE)—A natural stream that conveys water; a ditch or channel excavated for the flow of water. River, creek, run, branch, anabranch, and tributary are some of the terms used to describe natural channels, which may be single or braided. Canal, aqueduct, and floodway are some of the terms used to describe artificial (man-made) channels.

CHANNEL BANK—The sloping land bordering a channel. The bank has steeper slope than the bottom of the channel and is usually steeper than the land surrounding the channel.

CHANNEL CAPACITY—The maximum rate of flow that may occur in a stream without causing overbank flooding.

CHANNEL CONTROL—The condition under which the stage-discharge relation of a gaging station is governed by the slope, size, geometry, and roughness of the channel.

CHANNEL DENSITY—The ratio of the length of stream channels in a given basin to the area of the basin, expressed in feet per acre (meters per hectare).

CHANNEL INFLOW—Water which at any instant is flowing into the channel system from surface flow, subsurface flow, base flow, and rainfall directly on the channel.

CHANNEL LINING—Protection of the channel bottom and banks with concrete or Riprap.

CHANNEL MODIFICATION—The modification of the flow characteristics of a channel by clearing, excavation, realignment, lining, or other means to increase its capacity. Sometimes the term is used to connote Channel Stabilization.

CHANNEL REALIGNMENT—The construction of a new channel or a new alignment which may include the clearing, snagging, widening, and/or deepening of the existing channel.

CHANNEL STABILIZATION—Erosion prevention and stabilization of velocity distribution in a channel using jetties, drops, revetments, vegetation, and other measures.

CHANNEL STORAGE—The volume of water at a given time in the channel or over the flood plain of the streams in a drainage basin or river reach. Channel storage is sometimes significant during the progress of a flood event.

CHANNELED—Having one or more longitudinal grooves.

CHANNELIZATION—The artificial enlargement or realignment of a stream channel.

CHAOS THEORY—A modern development in mathematics and science that provides a framework for understanding irregular or erratic fluctuations in nature. Chaotic systems are found in many fields of science and engineering. Evidence of chaos occurs in models and experiments describing convection and mixing in fluids, in wave motion, in oscillating chemical reactions, and in electrical currents in semiconductors. It is also found in the dynamics of animal populations and attempts are being made to apply chaotic dynamics in the social sciences, such as the study of business cycles. A chaotic system is defined as one that shows "sensitivity to initial conditions." That is, any uncertainty in the initial state of the given system, no matter how small, will lead to rapidly growing errors in any effort to predict its future behavior. This "sensitivity to initial conditions" will make any long-term prediction of such phenomenon virtually impossible in reality. In other words, the system is chaotic and as such its behavior can be predicted only if the initial conditions are known to an infinite degree of accuracy, which is impossible. The possibility of chaos in a natural, or deterministic, system was first envisaged by the French mathematician Henri Poincare in the late 19th century. More recently, predictions have been made that the transition to chaotic turbulence in a moving fluid would take place at a well-defined critical value of the fluid's velocity (or some other important factor controlling the fluid's behavior). The term chaotic dynamics refers only to the evolution of a system in time. Chaotic systems, however, also often display spatial disorder—for example, in complicated fluid flows.

CHAPARRAL—A type of Biome with hot, dry summers and rainfall mainly in the winter months. Vegetation consists of shrubs, small evergreen trees, and sclerophyllous species. Chaparral communities are found around the Mediterranean Sea, in central and southern California, along coastal Chile, in southern Australia, and in southern Africa.

CHARA—Muskgrasses or stoneworts - An unusual type of algae that has a grown form resembling a higher plant, but a close look reveals each joint of the stem is a single cell with no connective tissue.

CHAROPHYTES—A group of green algae, visible to the naked eye, with a characteristic structure in which the 'stems' are very large single cells, from which whorls of similarly constructed branches emerge. Charophytes are anchored in sediments by branching cellular systems, not roots. They often deposit marl (calcium carbonate) giving them a rough texture and the common name of 'stoneworts', though not all do this. They also have a characteristic smell, which some people describe as 'garlicky'.

CHASM—Sometimes water filled, deep crack or opening in the earth's surface.

CHATTER MARK, also Chattermark —(Geology) One of a series of short scars made by glacial drift on a surface of bedrock.

CHECK DAM—A small dam constructed in a gully or other small watercourse to decrease the streamflow velocity, minimize channel erosion, promote deposition of sediment, and to divert water from a channel.

CHECK GATE—A gate located at a check structure used to control flow.

CHECK IRRIGATION—A method of irrigation in which an area is practically or entirely surrounded by earth ridges.

CHEMICAL—A substance made by chemistry. Oxidation is a chemical process in which iron combines with oxygen, commonly called rusting.

CHEMICAL EFFLUENTS—Non-natural liquids or emulsions discharged to a stream or lake.

CHEMICAL FEEDER—(Water Quality) A mechanical device for measuring quantities of chemical and applying them to a water at a preset rate.

CHEMICAL OXYGEN DEMAND (COD)—(Water Quality) A chemical measure of the amount of organic substances in water or wastewater. A strong oxidizing agent together with acid and heat are used to oxidize all carbon compounds in a water sample. Non-biodegradable and recalcitrant (slowly degrading) compounds, which are not detected by the test for Biochemical Oxygen Demand (BOD), are included in the analysis. The actual measurement involves a determination of the amount of oxidizing agent (typically, potassium dichromate) that is reduced during the reaction. Also see Total Carbon (TC) and Total Organic Carbon (TOC).

CHEMICAL PARAMETERS—The constituent chemicals found in a sample of a media, such as water.

CHEMICAL WEATHERING—The gradual decomposition of rock by exposure to rainwater, surface water, atmospheric oxygen, carbon dioxide and other gases in the atmosphere, as well as compounds secreted by organisms. Compare to Physical Weathering.

CHEMIGATION—Application of pesticides or fertilizers to farmlands through irrigation systems.

CHEMIST—A person who specializes or works in chemistry.

CHEMISTRY—The science of substances. It describes their characteristics, catalogs them and determines what happens when they are combine together and react.

CHEMOAUTOTROPH—An organism that utilizes oxidation of inorganic chemicals for its energy and carbon dioxide for cell growth. Also called a Chemosynthetic Autroph.

CHEMOCLINE—(1) The transition zone between layers in a Meromictic Lake. Here the density is usually controlled more with what is dissolved in the water than the temperature of a fluid. (2) The boundary between mixolimnion and monolimnion. The density gradient of a lake.

CHEMODYNAMICS—The study of the transport, conversion, and fate of chemical substances in air, water, or soil, including their movement from one medium to another.

CHEMOSPHERE—The region of the upper Atmosphere including the Mesosphere and upper Stratosphere in which various sunlight-driven chemical reactions occur.

CHEMOSYNTHESIS—The synthesis of carbohydrate from carbon dioxide and water using energy obtained from the chemical oxidation of simple inorganic compounds. This form of synthesis is limited to certain bacteria and fungi.

CHILILE—Inshore lake bottom.

CHIMNEY—A tall column of rock on the ocean floor that is formed by the precipitation of minerals from superheated water issuing from a vent in the earth's crust and rising through the column of rock. Also see Black Smoker.

CHINOOK—A downslope wind in which the air is warmed by adiabatic (gradual) heating. Such conditions describe a warm, dry southwest wind blowing from the sea onto the coast of Oregon and Washington in the winter and spring, as well as a warm, dry wind blowing down the eastern slope of the Rocky Mountains.

CHLORAMINES—Compounds containing nitrogen, hydrogen, and chlorine, formed by the reaction between hypochlorous acid (HOCl) and ammonia (NH3) and/or organic amines in water. The formation of chloramines in drinking water treatment extends the disinfecting power of chlorine. Also referred to as Combined Available Chlorine.

CHLORIDES—Negative chlorine ions, Cl-, found naturally in some surface waters and groundwaters and in high concentrations in seawater. Higher-than-normal chloride concentrations in fresh water, due to sodium chloride (table salt) that is used on foods and present in body wastes, can indicate sewage pollution. The use of highway deicing salts can also introduce chlorides to surface water or groundwater. Elevated groundwater chlorides in drinking water wells near coastlines may indicate Saltwater Intrusion.

CHLORINATED—(Water Quality) Describes water or wastewater that has been treated with either chlorine gas or a chlorine-containing compound.

CHLORINATED HYDROCARBONS—(Water Quality) Includes a class of persistent, broad-spectrum insecticides that linger in the environment and accumulate in the food chain. Among them are DDT, aldrin, diedrin, heptachlor, chlordane, lindane, endrine, mirex, hexachloride, and toxaphene.

CHLORINATION—The application of chlorine or one of its compounds to water or wastewater, often for disinfection or oxidation purposes.

CHLORINATOR—A device for adding a chlorine-containing gas or liquid to drinking water or wastewater.

CHLORINE—One of a group of elements classified as the halogens. Chlorine, Cl2, the most common halogen, is a greenish yellow gas with an irritating odor. Chlorine is very reactive; it forms salts with metals, forms acids when dissolved in water, and combines readily with hydrocarbons. Various forms of chlorine are used to disinfect water. Chlorine is produced by the electrolysis of brine (a concentrated salt solution). Atomic number 17; atomic weight 35.45; freezing point -100.98°C; boiling point -34.6°C; specific gravity 1.56 (-33.6°C).

CHLORINE BREAKPOINT—(Water Treatment) The point at which the chlorine dosage in a water treatment process has satisfied the Chlorine Demand. To eliminate the taste and odor associated with processed water, sufficient chlorine must be added to reach the breakpoint. Increasing the chlorine dose beyond the breakpoint produces a free chlorine residual, which is free to kill microorganisms. When chlorine is added to water, it first combines with constituents in the water such as iron, manganese, and nitrites. It is important to add enough chlorine to the water initially to ensure that these constituents are oxidized and to ensure that a residual is formed to react with the ammonia and organic matter in the water. Taste and odor problems result when chlorine dosages are either below the breakpoint, or well beyond the breakpoint.

CHLORINE-CONTACT CHAMBER—(Water Quality) In a wastewater treatment plant, a chamber in which effluent is disinfected by chlorine before it is discharged to the receiving waters.

CHLORINE DEMAND—(Water Quality) The amount of chlorine that must be added to purify drinking water; the amount of chlorine required to react with all dissolved and particulate materials and inorganic ammonia in the water.

CHLORINE RESIDUAL—The concentration of chlorine remaining in water or wastewater at the end of a specified contact period which will react chemically and biologically. May be present as either combined or free chlorine, or both.

CHLOROPHYLL—(1) The green pigments of plants. There are seven known types of chlorophyll, Chlorophyll a and Chlorophyll b are the two most common forms. A green photosynthetic coloring matter of plants found in chloroplasts and made up chiefly of a blue-black ester. (2) Major light gathering pigment of all photosynthetic organisms and is essential for the process of photosynthesis. The amount present in lake water depends on the amount of algae and is therefore used as an common indicator of water quality.

CHLOROPHYLL MAPPING—Showing the variation of chlorophyll over the surface of a water body on a map.

CHOLERA—An infectious waterborne disease that is characterized by severe diarrhea and its resultant dehydration and electrolyte imbalance. The disease is caused by bacteria belonging to the genus Vibrio. Outbreaks are associated with contamination of surface waters with human fecal material.

CHOLOPHYTE—Green algae, algae of the division Chlorophyta.

CHOP—A short, irregular motion of waves. Also, an area of choppy water, as on an ocean.

CHOTT, also Shott—(1) The depression surrounding a salt marsh or lake, especially in North Africa. (2) The bed of a dried salt marsh.

CHRESARD—Water present in the soil and available for plant absorption.

CHRONIC—Showing effects only over a long period of time, as in chronic toxicity.

CHRYSOPHYTE—Golden or yellow-green algae, algae of the division Chrysophyta.

CHUCKHOLE—A rough hole in pavement, made by wear and weathering, more commonly referred to as Pothole.

CHUTE, or CHUTE CUTOFF—As applied to stream flow, the term "chute" refers to a new route taken by a stream when its main flow is diverted to the inside of a bend, along a trough between low ridges formed by deposition on the inside of the bend where water velocities were reduced. Compare with Neck Cutoff.

CHUTE SPILLWAY—The overfall structure which allows water to drop rapidly through an open channel without causing erosion. Usually constructed near the edge of dams.

CIR—Consumptive Irrigation Requirement/Crop Irrigation Requirement.

CIRCULATE, or CIRCULATION—Movement or passage through a system of vessels, as water through pipes.

CIRCUMNEUTRAL—Term applied to water with a pH of 5.5 (acidic) to 7.4 (alkaline).

CIRQUE—A smallish, rounded depression with steeply sloping sides carved into the rock at the top of a ridge where a glacier has its head. After the period of glaciation ends, the cirque may contain a small remnant of the former glacier, or it may fill with water and become a lake. The term Tarn is also used to describe lakes that have formed in cirques.

CIRQUE BASIN—A half-amphitheater formed by alpine Glaciation with three steep sides. Usually found at upper ends of valleys and along ridges.

CIRQUE LAKE—A lake occupying a rock basin usually at the head of a valley in high mountain ranges.

CIRROCUMULUS CLOUDS—A high-altitude cloud composed of a series of small, regularly arranged cloudlets in the form of ripples or grains. Also see Cloud.

CIRROSTRATUS CLOUDS—A high-altitude, thin hazy cloud, usually covering the sky and often producing a halo effect. Also see Cloud.

CIRRUS CLOUDS—A principal cloud type found at high altitudes and composed of ice crystals collected into delicate wisps or patches. Also see Cloud.

CISTERN—An artificial reservoir or tank used for holding or storing water or other liquids. Typically a tank, often underground, used for storing rain water collected from a roof.

CLADOCERA—Water fleas. A group of crustaceans up to a few millimeters long, which either filter particles from water for food or grasp larger particles such as smaller animals. The best known genus is Daphnia.

CLAM—A mollusk with a hinged shell in two parts(bi-valve) and a soft body. An filter feeder in flowing fresh and salt waters.

CLAM-FLAT—(New England) A level stretch of soft tidal mud where clams burrow.

CLAMMY—(1) Disagreeably moist, sticky, and cold to the touch. (2) Damp and unpleasant.

CLARIFICATION—A process or combination of processes where the primary purpose is to reduce the concentration of suspended matter in a liquid.

CLARIFIER—A device or tank in which wastewater is held to allow the settling of particulate matter.

CLARITY—The transparency of a water column. Measured with a Secchi disc.

CLASS A PAN—The U.S. Weather Bureau evaporation pan is a cylindrical container fabricate of galvanized iron or monel metal with a depth of 10 inches and a diameter of 48 inches. The pan is placed on an open 2- X 4-inch wooden platform with the top of the pan about 41 cm (16 inches) above the soil surface. It is accurately leveled at a site that is nearly flat, well sodded, and free from obstructions. The pan is filled with water to a depth of eight inches, and periodic measurements are made of the changes of the water level with the aid of a hook gage set in the still well. When the water level drops to seven inches, the pan is refilled. Its average pan coefficient is about 0.7 for lake evaporation.

(INJECTION WELL) CLASSES—Classifications of the U.S. Environmental Protection Agency (EPA) that determine the permit requirements of an Injection Well. The following classes apply:

[1] Class I—A well into which liquid hazardous wastes or other fluids are pumped down, with the fluids being injected into an underground formation below the lowest underground source of drinking water that is within a one-quarter mile radius of the well; [2] Class II—A well used to dispose of fluids produced by oil and gas wells, to introduce fluids for enhanced oil recovery, or for liquid hydrocarbon storage; [3] Class III—A well used to pump fluids underground for mineral extraction; [4] Class IV—A well used to re-inject treated fluid from a superfund cleanup site into or above an underground formation within a one-quarter mile radius of the well; [5] Class V—Wells not included in Classes I-IV, mainly shallow industrial disposal wells or Recharge Wells.

CLASSICAL INFERENCE—(Statistics) Statistical inference is based on two basic premises: (1) The sample data constitute the only relevant information; and (2) The construction and assessment of the different procedures for inference are based on long-run behavior under essentially similar circumstances. Also see Statistical Inference and Bayesian Inference.

CLASSICAL LINEAR REGRESSION (CLR) MODEL—(Statistics) The standard for the Ordinary Least Squares (OLS), or Regression Analysis model. The CLR Model has five basic assumptions:

[1] Linearity—The dependent variable, or the variable to be explained or forecasted, can be calculated as a linear function of a specific set of independent, or explanatory variables; [2] Randomness of Disturbance Terms—The expected value of the disturbance term, that is the term showing the differences between the model's estimated values and the actual observed values, is zero; [3] Uncorrelated Disturbance Terms—The disturbance terms all have the same variance and are not correlated with each other (see Serial Correlation); [4] Data Conformity—The observations on the independent variable can be considered fixed in repeated samples, i.e., it is possible to repeat the sample with the same independent variables; [5] Sample Size and Selection—The number of observations is greater than the number of independent variables and that there are no linear relationships, i.e., no significant correlations, between the independent variables (see Multicollinearity).

CLASSIFICATION—(Soils)The systematic arrangement of soils into groups or categories on the basis of their characteristics. Broad groupings are made on the basis of general characteristics and subdivisions on the basis of more detailed differences in specific properties. Soil Taxonomy is the study of soil classification systems. (Lakes) Grouping by similar water quality. For a description of soil classifications, see Land Capability Classes.

CLASTIC—Pertaining to a rock or sediment composed principally of broken fragments that are derived from pre-existing rocks or minerals and that have been transported some distance from their places of origin.

CLAY—(1a) A fine-grained, firm earth material that is plastic when wet and hardens when heated, consisting primarily of hydrated silicates of aluminum and widely used in making bricks, tiles, and pottery; (1b) A hardening or non-hardening material having a consistency similar to clay and used for modeling. (2) (Geology) A sedimentary material with grains smaller than 0.2 millimeters in diameter. (3) Moist, sticky earth; mud.

CLAY LINER—A layer of clay soil that is added to the bottom and sides of a pit designed for use as a disposal site for potentially dangerous wastes. The clay prevents or reduces the migration of liquids from the disposal site.

CLAYBALLS—Both small and fairly large chunks of clay rounded by wave action. These are occasionally observed on Michigan beaches, especially a narrow strand bordered by steep clay banks of hard glacial till. Also known as mud balls, armored mud balls, pudding balls. Balls of a different origin, aggregates from clay in suspension or in a viscous state, are also sometimes formed in the beds of lakes and rivers.

CLAYBANKS (LAKESHORE)—Term applied to lake bluffs, or cliffs, composed almost entirely of till clay or glacial lacustrine clay.

CLAYPAN—(1) A dense, compact layer in the subsoil having a much higher clay content than the overlying material from which it is separated by a sharply defined boundary. Such layers are formed by the downward movement of clay or by synthesis of clay in place during soil formation. Claypans are usually hard when dry, and plastic and sticky when wet. They usually impede movement of water and air, and the growth of plant roots. (2) (Australian) A shallow depression in which water collects after rain. Also see Hardpan.

CLAYSEAL—A barrier constructed of impermeable clay that stops the flow of water or gas.

CLEAN (Water)—Water that is free from foreign matter or pollution; not infected; unadulterated.

CLEAN LAKES PROGRAM—Federal program evolved from Section 314 of the Clean Water Act.

CLEAN WATER ACT (CWA) [Public Law 92-500]—More formally referred to as the Federal Water Pollution Control Act, the Clean Water Act constitutes the basic federal water pollution control statute for the United States. Originally based on the Water Quality Act of 1965 which began setting water quality standards. The 1966 amendments to this act increased federal government funding for sewage treatment plants. Additional 1972 amendments established a goal of zero toxic discharges and "fishable" and "swimmable" surface waters. Enforceable provisions of the CWA include technology-based effluent standards for point sources of pollution, a state-run control program for nonpoint pollution sources, a construction grants program to build or upgrade municipal sewage treatment plants, a regulatory system for spills of oil and other hazardous wastes, and a Wetlands preservation program (Section 404).

CLEAN WATER ACT (CWA), SECTION 319—A federal grant program added by Congress to the CWA in 1987 and managed by the U.S. Environmental Protection Agency (EPA), Section 319 is specifically designed to develop and implement state Nonpoint Source (NPS) Pollution management programs, and to maximize the focus of such programs on a watershed or waterbasin basis with each state. Today, all 50 states and U.S. territories receive Section 319 grand funds and are encouraged to use the funding to conduct nonpoint source assessments and revise and strengthen their nonpoint source management programs.

CLEAN WATER STANDARDS (EPA)—Generally refers to any enforceable limitation, control, condition, prohibition, standard, or other requirement which is promulgated pursuant to the Federal Water Pollution Control Act (Clean Water Act) [Public Law 92-500] or contained in a permit issued to a discharger by the U.S. Environmental Protection Agency (EPA) or by a state under an approved program, as authorized by Section 402 of the Clean Water Act, or by local governments to ensure compliance with pretreatment regulations as required by Section 307 of the Clean Water Act.

CLEAR WELL—A reservoir containing potable water which has been previously treated before entering the distribution lines.

CLEPSYDRA—An ancient device that measured time by marking the regulated flow of water through a small opening. Also referred to as a Water Clock or Water Glass.

CLIFF—Steep, vertical or overhanging rock faces. Provide physical protection for wildlife and concentrate a variety of reptiles, birds and mammals into relatively small but stable environments.

CLIFF (LAKESHORE)—Often used interchangeably with bank and bluff, in technical descriptions cliff is preferred for the wave-cut nearly vertical acclivity or abrupt slope which borders the waterline, or marks the position of the present or former shore lines of lakes.

CLIMATE—The sum total of the meteorological elements that characterize the average and extreme conditions of the atmosphere over a long period of time at any one place or region of the earth's surface. The collective state of the atmosphere at a given place or over a given area within a specified period of time. Compare to Weather. Basic types of climates include:

[1] Continental—The climate characteristic of land areas separated from the moderating influences of oceans by distance, direction, or mountain barriers and marked by relatively large daily and seasonal fluctuations in temperature; [2] Oceanic—The climate characteristic of land lares near oceans which contribute to the humidity and at the same time have a moderating influence on temperature and the range of temperature variation.

CLIMATIC CYCLE—The periodic changes of climate, including a series of dry years following a series of years with heavy rainfall.

CLIMATIC YEAR—A period used in meteorological measurements. A continuous 12-month period during which a complete annual cycle occurs, arbitrarily selected for the presentation of data relative to hydrologic or meteorologic phenomena. The climatic year in the United States begins on October 1st and runs through September 30th. Similar to a Water Year.

CLIMATOLOGY, also Climatological—The science and study dealing with climate and climatic phenomena as exhibited by temperature, winds, and precipitation.

CLIMAX—The final stage of vegetation succession; a climax community reproduces itself and is in equilibrium with the existing environment.

CLOD—A compact, coherent mass of soil ranging in size from 5 to 10 millimeters (0.20 to 0.39 inch) to as much as 200 to 250 millimeters (7.87 to 9.84 inches) produced artificially, usually by the activity of man by plowing, digging, etc., especially when these operations are performed on soils that are either too wet or too dry for normal tillage operations.

CLOSED BASIN—A basin is considered closed with respect to surface flow if its topography prevents the occurrence of visible surface outflow. It is closed hydrologically if neither surface nor underground outflow can occur.

CLOSED-BASIN LAKE—A lake which has no outlet, from which water escapes only by evaporation.

CLOSED CANOPY—Forest trees dense enough that tree crowns fill or nearly fill the canopy layer.

CLOSED CONDUIT SYSTEM—A conveyance system where the flow of water is confined on all boundaries (i.e., pipe systems).

CLOSED-CYCLE COOLING—A process in which cooling water used in industrial processes or in the generation of electrical energy is not discharged into receiving streams, where direct discharge can have adverse effects, but is circulated through cooling towers, evaporators, ponds, or canals to allow the dissipation of the heat, and the water to be reused.

CLOSED DRAIN—Subsurface drain, tile, or perforated pipe that receives surface water through surface inlets.

CLOSED LAKES—Those that do not have an effluent in contrast to drainage lakes or open lakes which do have outlet streams. Closed lakes are common in arid and semi-arid regions where they usually contain saline or brackish water.

CLOSED-LOOP RECYCLING—Recycling or reusing wastewater for non-potable purposes in an enclosed process.

CLOSED WATER LOOP—A process in which decontaminated wastewater is not discharged into a receiving stream but is reused. Any water lost during the process through evaporation or binding with some material is replaced by makeup water. Contrast with Open Water Loop.

CLOSET—A water closet; a toilet.

CLOUD—A cloud is any concentration of gas, liquid droplets, or solid particles suspended as a distinct body in a gas or liquid. Generally, however, the term cloud is used to refer to the suspension of small ice or water particles in the Atmosphere. Cloud Formation—Clouds in the atmosphere form whenever the relative Humidity of an air mass, or parcel, reaches slightly more than 100 percent. This can occur for a number of reasons: the upward motion of air, which causes expansion and cooling; input of water from outside the parcel; or loss of heat by radiation. Among the major producers of the upward motion that results in clouds are the Low-Pressure systems with their cold, warm, and occluded Fronts; tropical disturbances such as Hurricanes, Cyclones, or Typhoons; and the lifting of air as it flows over hilly and mountainous terrain. The size of cloud droplets and ice crystals ranges from about 1 to 100 micrometers (4/100,000 to 4/1,000 in). Particles this small fall to the ground so slowly that they appear suspended in air, tending to move with the wind. The fall of larger particles, at much greater speeds, is called Precipitation. About 1 million cloud droplets, with an average radius of 10 micrometers (4/10,000 inch), are required to make a typical raindrop of 1 mm (4/100 inch). Cloud droplets can exist at temperatures below 0C (32F) and are then referred to as supercooled. When supercooled water and ice crystals occur at the same location, the ice grows at the expense of the water, and an ice cloud forms. This occurs because at a given temperature ice has a greater affinity than liquid water for water vapor. Cloud droplets and ice crystals first form on certain types of small particles of dust or other airborne materials. They are called condensation nuclei when water droplets are formed and ice nuclei when ice crystals result. The nuclei generally range in size from as small as 0.01 micrometer to about 1 micrometer (4/10,000,000 to 4/100,000 inch). The number of nuclei vary widely, depending on the source of the air mass in which the parcel is imbedded. The atmosphere over the ocean generally has the lowest number of nuclei, whereas polluted air has the highest. The more nuclei, and therefore the more water droplets or ice crystals, the slower the process of formation of precipitation-sized particles, because the competition for the available water is greater. Thus, although Rain often falls shortly after a cloud forms over the ocean, a much longer time is required over continental areas. Cloud Classification—Clouds are classed as warm if their temperature throughout is above 0C (32F) and cold if they extend to heights where temperatures are less than 0 C. Cold clouds containing both supercooled water and ice are defined as mixed clouds; clouds composed entirely of ice are said to be glaciated. Some cold clouds contain only supercooled water. These clouds are hazardous to aviation because the water, freezing on impact with an airplane, can cause ice to build up on the fuselage and wings. Clouds, defined in terms of their gross physical characteristics, can be classified as Stratiform or Cumuliform. Stratiform, or layered, clouds form when the upward motion is relatively uniform over an area, and cumuliform, or cottony, billowing clouds develop when upward and downward air currents are separated by fairly short distances. When clouds form at ground surface they are called Fog. Clouds that form in the middle Troposphere are called Altostratus and Altocumulus, and those in the upper troposphere are referred to as Cirrocumulus, Cirrostratus, or Cirrus. For those with bases in the lower troposphere, the terms Stratus and Cumulus are used. When precipitation is falling from these clouds, they are referred to with such terms as Nimbostratus or Cumulonimbus. Nimbostratus are the gray, leaden-sky clouds often produced by large-scale winter Cyclones in which precipitation is fairly steady and long-lasting. Cumulonimbus clouds, on the other hand, are associated with typical summertime Thunderstorms, in which rainfall is generally brief but heavy. A system of classifying clouds according to their physical characteristics has been devised by the World Meteorological Organization. Some of the more common cloud types are listed below:

[1] Cirrus—A high-altitude cloud composed of narrow bands or patches of thin, generally white, fleecy parts, typically at an average height of 7 miles (11.3 kilometers); [2] Cirrocumulus—A high-altitude cloud composed of a series of small, regularly arranged cloudlets in the form of ripples or grains, typically at an average height of 5 miles (8 kilometers); [3] Cirrostratus—A high-altitude, thin hazy cloud, usually covering the sky and often producing a halo effect, typically at an average height of 6 miles (9.7 kilometers); [4] Altostratus—A somewhat high level, blue to grayish blue cloud that forms a sheet or layer, typically at an average height of 3.5 miles (5.6 kilometers); [5] Altocumulus—A fleecy cloud, usually a rounded mass, but which can change radically and unexpectedly, producing intermediate forms, typically at an average height of 2.5 miles (4 kilometers); [6] Cumulonimbus—An extremely dense, vertically developed cumulus with a relatively hazy outline and a glaciated top extending to great heights, usually producing heavy rains, thunderstorms, or hailstorms, typically at an average height of 4 miles (6.4 kilometers); [7] Cumulus—A dense, white, fluffy, flat-based cloud with a multiple rounded top and a well-defined outline, usually formed by the ascent of thermally unstable air masses, typically at an average height of 2 miles (3.2 kilometers); [8] Nimbus/Nimbostratus—A rain cloud, especially a low dark layer of clouds precipitating continuous rain or snow, typically at an average height of .25 mile (.4 kilometer); [9] Stratus—A low-altitude cloud formation consisting of a horizontal layer of gray clouds, typically at an average height of .25 mile (.4 kilometer); [10] Stratocumulus—A low-lying cloud formation occurring in extensive horizontal layers with rounded summits, typically at an average height of 1 mile (1.6 kilometers).

CLOUDBURST—A sudden and extremely heavy downpour of rain that is small in areal extent, of short duration, and may be accompanied by lightening, thunder, and strong gusts of winds. Also, a torrential (hard) downpour of rain, which by its spottiness and relatively high intensity suggests the bursting and discharge of water from a cloud all at once.

CLOUD CHAMBER—A vessel containing air saturated with water vapor whose sudden expansion reveals the passage of an ionizing particle by a trail of visible droplets.

CLOUD MODIFICATION—Any process by which the natural course of development of a cloud is altered by artificial means. Also referred to as Weather Modification.

CLOUD SEEDING—A Weather Modification technique involving the injection of a substance into a cloud for the purpose of influencing the cloud's subsequent development. Ordinarily, this refers to the injection of a nucleating agent, which creates a nucleus around which precipitation will form. In common practice, cloud seeding involves the aerial release of silver iodide particles into convective clouds to create thunderstorms.

CLOUDY—(1) When the sky is covered with clouds. A cloudy sky makes for a dark and gray day. (2) Water is cloudy and not clear so we couldn't see the stream bottom.

CLR—Classical Linear Regression Model.

CLUSTER DEVELOPMENT—Placement of housing and other buildings of a development in groups to provide larger areas of open space between groups.

CNE—Curve Number Equation.

COAGULANT—(1) An agent that causes a liquid or sol to coagulate. (2) (Wastewater Treatment) A chemical compound, such as Alum (aluminum sulfate), used to produce coagulation.

COAGULANT AID—(Wastewater Treatment) Fine particles with high surface area and high specific gravity providing for increased particle collisions during the neutralization process in wastewater treatment plants. They also improve settling and strengthen flocs in the coagulation process. They are generally used in much smaller doses than the coagulant itself. For example, Sodium Bicarbonate increases the efficiency of coagulation and extends the pH range to a level at which Alum (aluminum sulfate), is effective.

COAGULATE—To cause the transformation of a liquid or sol, for example, into or as if into a soft, semisolid, or solid mass.

COAGULATION—The clumping of particles which results in the settling of impurities. It may be induced by coagulants such as lime, alum, and iron salts.

COAL SLURRY PIPELINE—A pipeline which transports pulverized coal suspended in liquid, usually water.

COAST—According to prevailing usage, the term is applied to land bordering seas. The shorelands of the Great Lakes are also called coasts.

COASTAL ZONE—Coastal waters and adjacent lands that exert a measurable influence on the uses of the seas and their resources and biota.

COASTAL ZONE MANAGEMENT ACT (CZMA)—A 1972 federal law, amended in 1980, that provides guidance and financial assistance to voluntary state and local coastal management programs. Goals of the program include the protection of natural resources and the management of land development in coastal areas, along shorelines, and on shorelands (extending inland as far as a strong influence on the shore is expected). The state programs established under the CZMA vary widely in their approach and application.

COASTLINE—The shape or outline of a coast.

COBBLE—Rock fragments 7.6 cm (3 inches) to 25.4 cm (10 inches) in diameter.

COBBLESTONE PAVEMENT—See Boulder Pavement.

COD—See Chemical Oxygen Demand.

COD—See Cone of Depression.

CODE OF FEDERAL REGULATIONS (CFR)—The annual compilation of all current regulations that have been issued in final form by any federal regulatory agency. The publication is organized by subject titles. Environmental regulations are covered under Title 40, Protection of the Environment.

CO-DOMINANT—Two or more plant species providing about equal areal cover which in combination control the environment.

COE—Corps of Engineers

COEFFICIENT TERM—(Statistics) The weight applied to one of the Independent (or Exogenous) Variables in the best prediction of the Dependent (or Endogenous) Variable. It is interpreted as the slope of the relation between the independent variable and the dependent variable, or the change in the dependent variable for a unit change in the independent variable.

COEFFICIENT OF DETERMINATION (R2)—(Statistics) A common measure of the "Goodness of Fit" in Regression Analysis used to assess the degree of causation between two variables or between one or more independent variables and a single dependent variable. The coefficient of determination is equivalent to the square of the Correlation Coefficient and reflects the percent of variation in the dependent (explained) variable that is explained by the variations in the independent (explanatory) variable(s). The value of the coefficient of determination various between 0 (0 percent) and 1 (100 percent) with higher numbers representing better explanatory powers of a model in explaining the trends in historical data.

COEFFICIENT OF DISCHARGE—The ratio of the observed to theoretical discharge.

COEFFICIENT OF LINEAR EXTENSIBILITY—The ratio of the difference between the moist and dry lengths of a Clod to its dry length. The measurement correlates with the volume change of a soil upon wetting and drying.

COEFFICIENT OF MECHANICAL DIFFUSION—The rate at which solutes are mechanically mixed during Advective Transport, caused by the velocity variations at the microscopic level.

COEFFICIENT OF MOLECULAR DIFFUSION—(1) The rate at which solutes are transported at the microscopic level due to variations in the solute concentrations within the fluid phases. (2) The rate of dispersion of a chemical caused by the kinetic activity of the ionic or molecular constituents. Also referred to as the Diffusion Coefficient. See Molecular Diffusion.

COEFFICIENT OF ROUGHNESS—Factor in fluid flow determination expressing the character of a surface and its fractional resistance to flow. Also referred to as Roughness Coefficient.

COEFFICIENT OF RUNOFF—Factor in the rational runoff formula expressing the ratio of peak runoff rate to rainfall intensity.

COEFFICIENT OF STORAGE—The volume of water an aquifer releases from or takes into storage per unit surface area of the aquifer per unit change in head.

COEFFICIENT OF TRANSMISSIVITY (t)—The rate at which water of the prevailing kinematic viscosity is transmitted through a unit width of the aquifer under a unit Hydraulic Gradient. It is equal to an integration of the hydraulic conductivities across the saturated part of the aquifer perpendicular to the flow paths. Also, the rate at which water is transmitted through a unit width of an aquifer under a unit hydraulic gradient. Transmissivity values are given in gallons per minute through a vertical section of an aquifer 1 foot wide and extending the full saturated height of an aquifer under a hydraulic gradient of one in the English Engineering System; in the Standard International System, transmissivity is given in cubic meters per day through a vertical section of an aquifer 1 meter wide and extending the full saturated height of an aquifer under hydraulic gradient of one. It is a function of properties of the liquid, the porous media, and the thickness of the porous media. Also see Transmissivity.

COEFFICIENT OF VARIATION, or VARIABILITY—The Standard Deviation of a statistic expressed as a fraction of the mean or a percentage.

COEFFICIENT OF VISCOSITY—The degree to which a fluid resists flow under an applied force, measured by the tangential friction force per unit area divided by the velocity gradient under conditions of streamline flow.

COFFERDAM—A temporary watertight enclosure that is pumped dry to expose the bottom of a body of water so that construction, as of piers, a dam, and bridge footings, may be undertaken. Also, a watertight chamber attached to the side of a ship to facilitate repairs below the water line. A Diversion Cofferdam prevents all downstream flow by diverting the flow of a river into a pipe, channel, or tunnel. Also see Dam, Caisson and Camel.

COHESION—A molecular attraction by which the particles of a body are united throughout the mass whether like of unlike. Compare to Adhesion.

COI—Cone of Influence.

COLD VAPOR—A method to test water for the presence of mercury.

COLD-WATER—Lacking modern plumbing or heating facilities, as a cold-water residence.

COLDWATER FISH—A fish that requires relatively cool water for survival. While the optimum temperature varies by species, most are found in water where temperatures are 20C (68F) or less.

COLIFORM (BACTERIA)—A group of organisms (Colon bacilli) usually found in the colons of all warm blooded animals and humans; non-pathogenic microorganisms used in testing water to indicate the presence of pathogenic bacteria. The presence of coliform bacteria in water is an indicator of possible pollution by fecal material. Generally reported as colonies per 100 milliliters (ml) of sample.

COLIFORM INDEX—An index of the bacteriological quality of water, based on a count of the numbers of coliform bacteria.

COLLECTION SITE—A stream, lake, reservoir, or other body of water fed by water drained from a watershed.

COLLECTOR SEWERS—Pipes used to collect and carry wastewater from individual sources to an interceptor sewer that will carry it to a treatment facility.

COLLECTOR SYSTEM—Conveys water from several individual sources such as groundwater wells and drains and surface inlet drains for rainstorm and snowmelt runoff to a single point of diversion. The collector system is associated with projects that increase water supply and decrease flood damage.

COLLECTOR WELL—A well located near a surface water supply used to lower the water table and thereby induce infiltration of surface water through the bed of the water body to the well.

COLLOIDAL SUSPENSION—Suspension in water of particles so finely divided that they will not settle under the action of gravity, but will diffuse, even in quiet water, under the random impulses of Brownian Movement. Particles typically range in size from about one micron (0.000001 millimeter) to about one millimicron; however, there is no distinct differentiation by particle size between true Suspension and colloidal suspension or between colloidal suspension and Solution.

COLLOIDS—Quantities of extremely small particles, typically 0.0001 to 1 micron in size, and small enough to remain suspended in a fluid medium without settling to the bottom. Substances that, when apparently dissolved in water or other liquid, diffuse not at all or very slowly through a membrane and show other special properties, as lack of pronounced effect on the freezing point or vapor pressure of the solvent. Colloids represent intermediate substances between a true dissolved particle and a suspended solid, which will settle out of solution.

COLLUVIAL MATERIAL—(Geology) Material consisting of Alluvium in part and also containing angular fragments of the original rocks. Typically found at the bottom or on the lower slopes of a hill.

COLLUVIUM—A general term used to describe loose and incoherent deposits of rock moved downslope by gravitational force in the form of soil Creep, slides, and local wash. Also see Colluvial Material.

COLON BACILLUS—(Microbiology) A rod-shaped bacterium, especially Escherichia coli (E. coli), a normal, generally nonpathogenic commensal found in all vertebrate intestinal tracts, but which can be virulent, causing diarrhea and other dysenteric symptoms. Its presence in water is an indicator of fecal contamination.

COLONIZATION—(Biology) As applied to vegetation, the invasion of a disturbed area; annual plants are often colonizing species.

COLOR—(1) Measured in units that relate to a standard. A yellow-brown natural color is associated with lakes or rivers receiving wetland drainage. The average color value for Wisconsin lakes is 39 units, with the color of state lakes ranging from zero to 320 units. Color also affects light penetration and therefore the depth at which plants can grow. (2) One control of light transmission through water. High color values in many lakes result from the decomposition of vegetation, which gives the water a brown, tea-like color. Determined by a comparison with standardized colored-glass discs and reported in platinum-cobalt (Pt-Co) units.

COLOR (OF LAKE WATERS)—An effect of light penetration, radiation absorption and reflection. Related to: transparency and depth of water;type of lake bottom and matter held in solution; suspension or floating. Blues and greens are commonly observed in clear water lakes with clean bottoms of sand, rock or marl. Often, the blue tints are in deeper water and greens in shallower sections. Greens are often due to large populations of blue green and green algae in suspension or on the lake bottom. Yellows may be due to certain species of algae and to diatoms in large populations, and in certain types of lakes yellows have been attributed to sulfur bacteria. Pale yellows, yellow brown and coffee color or "black," can be produced by large quantities of dissolved humic substances and by particulate organic matter in suspension. Reds may be a reflection of the pigment color of certain algae; and may be caused by the presence of certain micro-crustaceans and other zooplankton; the "blood lakes" of central Europe are attributed to the presence of the microorganism Euglena sanguinea. Lake waters may be variously colored by suspended particulate inorganic matter especially that which is clayey or colloidal in nature. Some glacial lakes may be milky because of "glacial flour" in suspension, and the shallow water of marl lakes is often milky. Some colors are reflections of yellow sands on shallow bottoms, or from the black of organic sediments; or the blue of the sky. Colors vary with the weather, the time of day and the season. The words white and black have been used to describe lake waters. White has been applied where the water is merely colorless, and sometimes where it is milky from grey or white particulate matter in suspension. Black may be due to: large amounts of humic matter in solution, such as that in water flowing from some kinds of bogs; reflection of black bottoms; the dull appearance of some waters when the sky is heavily overcast. Unusual colors may be produced by pollution from industrial wastes.

COLORADO RIVER COMMISSION [Nevada]—An agency of the State of Nevada consisting of seven members, to include four members appointed by the Governor and three members from the Southern Nevada Water Authority Board of Directors. The Colorado River Commission has broad statutory authority to establish policies for the management of Nevada's allocation of power and water resources from the Colorado River and for the development of designated land in Southern Nevada.

COLORADO RIVER COMPACT—An agreement entered into on November 24, 1922 and ratified by the legislatures of the seven states within the Colorado River Basin—Arizona, California, Colorado, Nevada, New Mexico, Utah, and Wyoming—agreeing to the general allocation of the waters of the Colorado River. The compact divided the Colorado River Basin into an Upper Basin and a Lower Basin, with the division point established at Lees Ferry, a point in the mainstream of the Colorado River approximately 30 river miles south of the Utah-Arizona boundary. The Upper Basin was defined to include those parts of the states of Arizona, Colorado, New Mexico, Utah, and Wyoming within and from which waters naturally drain into the Colorado River system above Lees Ferry, and all parts of these states that are not part of the river's drainage system but may benefit from water diverted from the system above Lees Ferry. The Lower Basin was defined to include those parts of the states of Arizona, California, Nevada, New Mexico, and Utah within and from which waters naturally drain into the Colorado River system below Lees Ferry, and all parts of these states that are not part of the river's drainage system but may benefit from water diverted from the system below Lees Ferry. The compact did not apportion water to any state; however, it did apportion to each upper and lower basin the exclusive, beneficial consumptive use of 7,500,000 acre-feet of water per year from the Colorado River system in perpetuity. Further, the compact gave to the Lower Basin the right to increase its annual beneficial consumptive use of such water by 1,000,000 acre-feet. This compact cleared the way for federal legislation for the construction of Hoover Dam. Subsequently, the Upper Basin states entered into the Upper Colorado River Basin Compact on October 11, 1948 which provided Arizona to use 50,000 acre-feet of water per year from the upper Colorado River system and apportioned the remaining water to the Upper Basin states according to the following percentages: Colorado, 51.75 percent; New Mexico, 11.25 percent; Utah, 23 percent; and Wyoming, 14 percent. The Lower Basin states could not come to an agreement on apportionment on their own, and in October 1962, the U.S. Supreme Court ruled that of the first 7,500,000 acre-feet of mainstream water in the Lower Basin, California is entitled to 4,400,000 acre-feet (58.67 percent), Arizona to 2,800,000 acre-feet (37.33 percent), and Nevada to 300,000 acre-feet (4.00 percent).

COLVIN ALGORITHM—A canal flow control structure technique that operates the gates based on the rate of deviation of the water surface level from the setpoint.

COMBINED AVAILABLE CHLORINE—Concentration of chlorine which is combined with ammonia as chloramine or as other chloro-derivatives yet is still available to oxidize organic matter.

COMBINED RESIDUAL CHLORINATION—(Water Quality) The drinking water treatment method that involves the addition of chlorine to water at levels sufficient to produce, in combination with ammonia and/or organic amines, a Combine Available Chlorine residual. This chlorine residual maintains the treatment's disinfecting power throughout the water distribution system. Another approach to water chlorination is Breakpoint Chlorination.

COMBINED SEWER OVERFLOW (CSO)—(Water Quality) The condition that occurs when a Combined Sewer System (CSS) that is already loaded with wastewater experiences an influx of stormwater runoff from a heavy rain or melting snows. This causes the sewers to overload and excess stormwater and wastewater to discharge directly into receiving streams through overflow ports without treatment.

COMBINED SEWER SYSTEM (CSS)—A sewage system that carries both sanitary sewage and storm water runoff. During dry weather, combined sewers carry all wastewater for treatment. During storm events, part of the load may be intercepted to prevent overloading of the processing facility. In this case, the untreated portion is frequently allowed to enter the receiving stream. Also see Combined Sewer Overflow.

COMET—A celestial body, observed only in that part of its orbit that is relatively close to the sun, having a head consisting of a solid nucleus surrounded by a nebulous coma up to 2.4 million kilometers (1.5 million miles) in diameter and an elongated, curved vapor tail arising from the coma when sufficiently close to the sun. Comets are thought to consist primarily of ammonia, methane, carbon dioxide, and water.

COMMERCIAL FRONTAGE (LAKE)—Riparian lands zoned for commercial use.

COMMERCIAL WATER USE—Water for motels, hotels, restaurants, office buildings, and other commercial facilities and institutions, both civilian and military. The water may be obtained from a public supply or may be self supplied. Also see Public Water Supply System and Self-Supplied Water.

COMMISSION—A group of persons choosen to do or oversee certain work.

COMMITTEE—A group of persons chosen to complete certain work.

COMMUNITY—(1) A naturally occurring, distinctive group of different organisms which inhabit a common environment, interact with each other, and are relatively independent of other groups. (2) A group of people who participate in a social and economic network of statistically significant frequency and within the cultural and geographic boundaries of the network.

COMMUNITY BEACH—Beach dedicated for the semi-exclusive use of a definite subdivision. Property owners in the subdivision may use the beach, but others are excluded. This riparian right should be properly defined on the deed of each lot. The actual ownership of the community beach may be vested in an association or each separate lot owner may be vested with a riparian interest.

COMMUNITY WATER SYSTEM—A public water system with 15 or more connections and serving 25 or more year-round residents and thus is subject to the U.S. Environmental Protection Agency (EPA) regulations enforcing the Safe Drinking Water Act (SDWA).

COMPACT, WATER—An agreement between states, ratified by Congress, providing for the division and apportionment of waters of an interstate river or other body of water.

COMPACTION—A physical change in soil properties that result in an increase in soli bulk density and a decrease in Porosity. The packing together of soil particles by forces exerted at the soil surface, resulting in increased soil density.

COMPENSATION LEVEL—The level in a body of water, usually occurring at the depth of 1 percent light penetration, which forms the lower boundary of the Zone of Net Metabolic Production. Also see Metabolism.

COMPENSATION POINT—The point under water at which plant photosynthesis just equals plant respiration. The water depth defines the lower boundary, where photosynthesis takes place, of the Euphotic Zone. Also referred to as the Compensation Level.

COMPLETE TREATMENT—A method of treating water that consists of the addition of coagulant chemicals, flash mixing, coagulation-flocculation, sedimentation, and filtration. Also referred to as Conventional Filtration.

COMPLETED TEST—(Water Quality) The third, and last, part of the examination of water for the presence of bacteria of fecal origin. Cultures that are scored as positive in the earlier steps of the analysis (Presumptive Test and Confirmed Test) are subjected to a verification by inoculating appropriate media (eosin methylene blue agar plates) and performing a gram-positive/gram-negative stain on isolated colonies.

COMPLETION—Sealing off access of undesirable water to the well bore by proper casing and/or cementing procedures.

COMPLIANCE CYCLE—(Water Quality) The 9-year calendar year cycle, beginning January 1, 1993, during which public water systems must monitor. Each cycle consists of three 3-year compliance periods.

COMPLIANCE MONITORING—(Water Quality) Collection and evaluation of data, including self-monitoring reports, and verification to show whether pollutant concentrations and loads contained in permitted discharges are in compliance with the limits and conditions specified in the permit.

COMPLIANCE SCHEDULE—(Water Quality) A negotiated agreement between a pollution source and a government agency that specifies dates and procedures by which a source will reduce emissions and, thereby, comply with a regulation.

COMPLY (EPA)—A term used to indicate compliance or adherence with Clean Water Standards, specifically with respect to a schedule or plan ordered or approved by a court of competent jurisdiction, the U.S. Environmental Protection Agency (EPA), or a water pollution control agency in accordance with the requirements of the Federal Water Pollution Control Act (Clean Water Act) [Public Law 92-500] and regulations issued pursuant thereto.

COMPOSITE SAMPLE—(Water Quality) A representative water or wastewater sample made up of individual smaller samples taken at periodic intervals and composited into one representative sample for analysis.

COMPOST—A mixture that consists largely of decayed organic matter, used for fertilizing and conditioning land.

COMPOUND—A substance composed of separate elements, ingredients, or parts. Water is a compound consisting of hydrogen and oxygen, chemical symbol H2O.

COMPREHENSIVE ENVIRONMENTAL RESPONSE, COMPENSATION, AND LIABILITY ACT (CERCLA)—Also referred to as the Superfund Law, this statute, originally enacted in 1980 and substantially modified in 1986, establishes the U.S. Environmental Protection Agency's (EPA) authority for emergency response and cleanup of hazardous substances that have been spilled, improperly disposed of, or released into the environment. The primary responsibility for response and cleanup is on the generators or disposers of the hazardous substances, with a backup federal response using a trust fund provision.

COMPREHENSIVE PLAN—(Natural Resource) A plan for water and related land resources development, that does consider all economic and social factors and provides the greatest overall benefits to the region as a whole.

COMPUTER APPLICATIONS—Computer programs written to perform certain tasks, such as word processing, mapping, etc.

COMPUTER MODELLING—Representing a system using mathematical equations and measured values.

COMPUTER PROGRAMS—Code used by the computer to accomplish a task.

CONCENTRATE—To make a solution or mixture less dilute, as by removing water from a solution.

CONCENTRATION—The amount of Solute present in proportion to the total Solution. More specifically, a measure of the average density of pollutants or other constituents, usually specified in terms of mass per unit volume of water or other Solvent (e.g., milligrams per liter) or in terms of relative volume of solute per unit volume of water (e.g., parts per million).

CONCENTRATION TIME—The period of time required for storm runoff to flow from the most remote point of a catchment or drainage area to the outlet or point under consideration. Concentration time varies with depth of flow and channel condition.

CONCENTRATION UNITS—Express the amount of a chemical dissolved in water. The most common ways chemical data is expressed is in milligrams per liter (mg/l) and micrograms per liter (ug/l). One milligram per liter is equal to one part per million (ppm). To convert micrograms per liter (ug/l) to milligrams per liter (mg/l), divide by 1000 (e.g. 30 ug/l = 0.03 ug/l). To convert milligrams per liter (mg/l) to micrograms per liter (ug/l), multiply by 1000 (e.g. 0.5 mg/l=500 ug/l). Microequivalents per liter (ueq/l) is also sometimes used, especially for alkalinity; it is calculated by dividing the weight of the compound by 1000 and then dividing that number into the milligrams per liter.

CONCORDANT FLOWS—Flows at different points in a river system that have the same Recurrence Interval, or the same frequency of occurrence. It is most often applied to flood-flows.

CONCRETE—A mixture of water, cement, sand, and pebbles. The hydration of cement and drying of concrete causes it to become very hard.

CONCRETE-GRAVITY STRUCTURE—A type of concrete structure in which resistance to overturning is provided only by its own weight.

CONDEMNATION—Taking private property for public use, with compensation to the owner, under the right of Eminent Domain.

CONDENSATE—A product of Condensation.

CONDENSATION—(1) (Physics) The process by which a gas or vapor changes to a liquid or solid; also the liquid or solid so formed. (2) (Chemistry) A chemical reaction in which water or another simple substance is released by the combination of two or more molecules. The opposite of Evaporation. In meteorological usage, this term is applied only to the transformation from vapor to liquid.

CONDENSE—(1) To cause a gas or vapor to change to a liquid. (2) To remove water from a substance, as from milk, for example.

CONDITIONAL WATER PERMIT—An authorization for the permittee to construct any facilities (such as a well and irrigation system) and to begin utilization of the water. A water right and a water permit are not the same thing. Also see Water Right.

CONDUCTANCE—A rapid method of estimating the dissolved solids content of a water supply by determining the capacity of a water sample to carry an electrical current.

CONDUCTIVITY—(1)A measure of the ability of a solution to carry an electrical current. (2)Measures water's ability to conduct an electric current or the total ionic concentration of water. Conductivity is reported in micromhos per centimeter (umhos/cm) and is directly related to the total dissolved inorganic chemicals in the water. Values are commonly two times the water hardness unless the water is receiving high concentrations of contaminants introduced by humans. A conductivity meter tests the flow of electrons through the water which is heightened in the presence of electrolytes (total dissolved solids). see Specific Conductance.

CONDUCTOR CASING—The temporary or permanent steel casing used in the upper portion of the borehole to prevent collapse of the formation during the construction of the well or to conduct the gravel pack to the perforated or screened areas of the casing.

CONDUIT—(1) A natural or artificial channel through which fluids may be conveyed. (2) (Dam) A closed channel for conveying discharge through, under, or around a dam.

CONE OF DEPRESSION (COD)/CONE OF INFLUENCE (COI)—A cone-like depression of the water table or other piezometric surface that has the shape of an inverted cone and is formed in the vicinity of a well by withdrawal of water. The surface area included in the cone is known as the area of influence of the well. Also referred to as the Pumping Cone and the Cone of Drawdown.

CONFIDENCE LIMITS—(Statistics) Bounds of statistical probability, e.g., 95 percent, 98 percent, 99 percent, etc., established as part of the testing criteria. The confidence limits express the statistical probability associated with the acceptance of an econometric model's results.

CONFINED AQUIFER—An aquifer which is bounded above and below by formations of impermeable or relatively impermeable material. An aquifer in which ground water is under pressure significantly greater than atmospheric and its upper limit is the bottom of a bed of distinctly lower hydraulic conductivity than that of the aquifer itself. See Artesian Aquifer.

CONFINED GROUND WATER—A body of ground water covered by material so impervious as to sever the hydraulic connection with overlying ground water except at the intake or recharge area. Confined water moves in pressure conduits due to the difference in head between intake and discharge areas of the confined water body.

CONFINED WATER (ARTESIAN)—Water under artesian pressure. Water that is not confined is said to be under water table conditions.

CONFINING BED—A body of "impermeable" material stratigraphically adjacent to one or more aquifers. It may lie above or below the aquifer. In nature its hydraulic conductivity may actually range from nearly zero to some value distinctly lower than that of the aquifer. In some literature, the term confining bed has now supplanted the terms Aquiclude, Aquitard, and Aquifuge. Also referred to as Confining Layer.

CONFINING UNIT—A hydrogeologic unit of relatively impermeable material, bounding one or more aquifers. This is a general term that has replaced Aquitard, Aquifuge, and Aquiclude and is synonymous with Confining Bed.

CONFIRMED TEST—(Water Quality) The second stage in the examination of water for the presence of bacteria of fecal origin. Cultures that are positive on the first portion of the testing procedure (the Presumptive Test) are inoculated into tubes of brilliant green lactose bile broth and examined for fermentation when incubated at 35C (95F) for 48 hours. If fermentation is present, a third stage, the Completed Test, is performed.

CONFLICTING USES (OF LAKE)—Uses that act to the detriment of other users. Technically, conflicts of use may exist only between riparians because all acts of others would be in the realm of trespass.

CONFLUENCE—(1) The act of flowing together; the meeting or junction of two or more streams or rivers; also, the place where these streams meet. (2) The stream or body of water formed by the junction of two or more streams or rivers; a combined flood.

CONFLUENT GROWTH—(Water Quality) A continuous bacterial growth covering all or part of the filtration area of a membrane filter in which the bacteria colonies are not discrete. In coliform testing, abundant or overflowing bacterial growth which makes accurate measurement difficult or impossible.

CONFOUNDING VARIABLE—(Statistics) A variable which is associated with two or more observed variables and which directly affects the relationship between the observed variables. Often causal relationships are attributed to the observed variables when, in fact, it is the confounding variable that is the true causal factor. By holding the behavior of the confounding variable constant, the relationship between the two observed variables is no longer evident. Also see Secondary (Indirect) Association.

CONIFER—A tree belonging to the order Coniferae with cones and leaves of needle shape or "scalelike."

CONIFEROUS—Pertaining to Conifers, which bear woody cones containing naked seeds.

CONJUNCTIVE MANAGEMENT—The integrated management and use of two or more water resources, such as a (ground water) aquifer and a surface water body.

CONJUNCTIVE OPERATION—The operation of a ground water basin in combination with a surface water storage and conveyance system. Water is stored in the ground water basin for later use by intentionally recharging the basin during years of above-normal water supply.

CONJUNCTIVE (WATER) USE—The combined use of surface and ground water systems and sources to optimize resource use and prevent or minimize adverse effects of using a single source.

CONNATE WATER—Water that was trapped in the interstices of a sedimentary or extrusive igneous rock at the time of its deposition. It is usually highly mineralized and frequently saline.

CONNECTING STREAM—A stream connecting a lake with another lake or stream.

CONNECTOR SYSTEM—Conveys water from a single source to a different location typically without intermediate collection of diversions. The connector system is associated with regulation reservoirs and intakes to pumping plants or powerplants.

CONSENT DECREE—(Environmental) A legal document approved by a judge, that formalizes an agreement reached between the U.S. Environmental Protection Agency (EPA) and a Potentially Responsible Party (PRP) or parties through which the PRP will conduct all or part of a cleanup action at a Superfund Site, cease or correct actions or processes that are polluting the environment, or otherwise comply with EPA initiated regulatory enforcement actions to resolve the contamination at the Superfund site involved. The consent decree describes the actions the PRP will take and may be subject to a public comment period.

CONSEQUENT ISLAND—An original island. An elevation in the lake basin which remained above the water surface at the time of the formation of the lake. Also called a residual island.

CONSEQUENT LAKE—Lake existing in a depression representing the original inequality in a new land surface. The ponds and lakes in depressions on the recently uplifted plains of sedimentation bordering the Atlantic Coast and forming a part of the Coastal Plain of the Southeastern US are consequent. Also called newland lakes. Lakes in a plain of glacial deposition may also be consequent.

CONSEQUENT STREAM—A stream following a course that is a direct consequence of the original slope of the surface on which it developed.

CONSERVATION—(1) Increasing the efficiency of energy use, water use, production, or distribution. (2) The careful and organized management and use of natural resource, for example, the controlled use and systematic protection of natural resources, such as forests, soil, and water systems in accordance with principles that assure their optimum long-term economic and social benefits. Also, preservation of such resources from loss, damage, or neglect.

CONSERVATION DISTRICT—A public organization crated under state-enabling law as a special purpose district to develop and carry out a program of soil, water, and related resource conservation, use, and development within its boundaries. In the United States, such districts are usually a subdivision of state government with a local governing body and are frequently called a soil conservation district or a soil and water conservation district.

CONSERVATION EASEMENT—An agreement negotiated on privately owned lands to preserve open space or protect certain natural resources.

CONSERVATION EDUCATION—A comprehensive concept that spans curricula from kindergarten through adult, post-graduate programs and links the subject to natural resource conservation, stressing the characteristics and interrelationships in management and use of our natural resources that will result in knowledgeable citizenry with attitudes of responsibility toward the conservation of those natural resources.

CONSERVATION PLAN—A collection of material containing land user information requested for making decisions regarding the conservation of soil, water, and related plant and animal resources, along with necessary habitat, for all or part of an operating unit.

CONSERVATION PRACTICE—A technique or measure used to meet a specific need in planning and carrying out soil and water conservation programs for which standards and specifications have been developed.

CONSERVATION STANDARDS—Standards for various types of soils and land uses, including criteria, techniques, and methods for the control of erosion and sediment and impacts on plant and animal species and necessary habitat resulting from land disturbing activities.

CONSERVATION STORAGE—The portion of water stored in a reservoir that can be later released for useful purposes such as municipal water supply, power, or irrigation. Conservation storage is the volume of water stored between dead reservoir storage and flood control storage.

CONSERVATION TILLAGE—A level of reduced tillage combined with one or more soil and water conservation practices designed to reduce loss of soil or water relative to conventional tillage. Such activities often take the form of non-inversion tillage that retains productive amounts of residue mulch on the surface.

CONSERVATIVE SUBSTANCES—Non- interacting substances, undergoing no kinetic reactions; chloride and sodium are approximate examples.

CONSOLIDATED AQUIFER—An aquifer made up of consolidated rock that has undergone solidification or lithification.

CONSOLIDATED FORMATION—Geological formations which occur naturally and have been turned to stone. The term is sometimes used interchangeably with the word Bedrock. It includes rock such as basalt, rhyolite, sandstone, limestone and shale. Typically, these formations will stand at the edges of a bore hole without caving.

CONSOLIDATION—(Soil Mechanics) Adjustment of a soil in response to increased load; involves squeezing of water from the pores and a decrease in void ratio (pore space). Frequently the geologic term Compaction is used instead.

CONSOLIDATION GROUTING (of a Dam)—The injection of grout to consolidate a layer of the foundation, resulting in greater impermeability and/or strength. Also referred to as Blanket Grouting. Also see Blanket (of a Dam).

CONSOLUTE—Of or relating to liquid substances that are capable of being mixed in all proportions.

CONSTANT HEAD ORIFICE TURNOUT (Canal)—A calibrated structure containing an adjustable orifice gate and a gate downstream to control a constant head differential across the orifice gate to divert and measure water from a main irrigation canal to a distributing canal.

CONSTANT VOLUME OPERATION METHOD (Canal)—A canal operation that maintains a relatively constant water volume in each canal pool.

CONSTITUENTS—Any of the chemical substances found in water. Typically, measurements of such constituents in sampled drinking water may consist of Total Dissolved Solids (TDS), Hardness (concentrations of Calcium and Magnesium, specifically), Sodium, Potassium, Sulfate, Chloride, Nitrate, Alkalinity, Bicarbonate, Carbonate, Fluoride, Arsenic, Iron, Manganese, Copper, Zinc, Barium, Boron, Silica, as well as other physical characteristics and properties such as water color, turbidity, pH, and electro-conductivity (EC). [As an example of constituents and their acceptable levels for drinking water, see Appendix D-5, Nevada Drinking Water Standards.]

CONSTRUCTED WETLANDS—(1) Wetlands constructed by man either as part of a Wetland Banking, Wetland Clumping (Aggregation), or Wetland Mitigation program, or to achieve some other environmental preservation or restoration program. (2) (Water Quality) Wetlands constructed specifically for the purpose of treating waste water effluent before re-entering a stream or other body of water or being allowed to percolate into the groundwater. Also see Lagoon.

CONSTRUCTION—The process of building.

CONSTRUCTION JOINT (of a Dam)—The interface between two successive placings or pours of concrete in a dam's structure where a bond, and not a permanent separation, is intended.

CONSUMABLE WATER SUPPLY—That amount of river water available for consumption at a given point on the river after existing prior water rights have been met.

CONSUMERS—Organisms that obtain their energy by eating other organisms; generally divided into primary consumers (herbivores), secondary consumers (carnivores), and microconsumers (decomposers).

CONSUMPTION, DOMESTIC—The quantity or quantity per capita (person) of water consumed in a municipality or district for domestic uses during a given period, usually one day. Domestic consumption is generally considered to include all uses included in "municipal use of water," in addition to the quantity of water wasted, lost, or otherwise unaccounted for. Also see Consumption, Municipal; Municipal Use of Water.

CONSUMPTION, INDUSTRIAL—The quantity of water consumed in a municipality or district for mechanical, trade, and manufacturing uses during a given period, usually one day.

CONSUMPTION, MUNICIPAL—The quantity of water consumed through use in developed urban areas. Also see Consumption, Domestic; Consumptive Use.

CONSUMPTIVE IRRIGATION REQUIREMENT (CIR)—The quantity of irrigation water, exclusive of precipitation, stored soil moisture, or ground water, that is required consumptively for crop production.

CONSUMPTIVE USE (LAKE WATERS)—Implies withdrawal of water for such purposes as irrigation, power generation and industrial, municipal and domestic water supplies. Destructive use, such as for waste disposal or as a carrier for sewage, is considered consumptive. Nonconsumptive uses (those that do not reduce the supply) are: recreational, bathing, fishing, boating and hunting, navigable waterways and for aquaculture.

CONSUMPTIVE WASTE—Water that returns to the atmosphere without providing benefit to humans.

CONSUMPTIVE WATER USE—(1) A use which lessens the amount of water available for another use (e.g., water that is used for development and growth of plant tissue or consumed by humans or animals). (2) The portion of water withdrawn from a surface or groundwater source that is consumed for a particular use (e.g., irrigation, domestic needs, and industry), and does not return to its original source or another body of water. The terms Consumptive Use and Nonconsumptive Use are traditionally associated with water rights and water use studies, but they are not completely definitive. No typical consumptive use is 100 percent efficient; there is always some return flow associated with such use either in the form of a return to surface flows or as a ground water recharge. Nor are typically nonconsumptive uses of water entirely nonconsumptive. There are evaporation losses, for instance, associated with maintaining a reservoir at a specified elevation to support fish, recreation, or hydropower, and there are conveyance losses associated with maintaining a minimum streamflow in a river, diversion canal, or irrigation ditch.

CONSUMPTIVE WATER USE, IRRIGATION—The quantity of water that is absorbed by the crop and transpired or used directly in the building of plant tissue, together with that evaporated from the cropped area. Does not include runoff or deep percolation in support of the Crop Leaching Requirement.

CONSUMPTIVE WATER USE, NET—The consumptive use decreased by the estimated contribution by rainfall toward the production of irrigated crops. Net consumptive use is sometimes referred to as the Crop Irrigation Requirement.

CONSUMPTIVE WATER USE REQUIREMENT (CROP)—The annual irrigation consumptive use expressed in feet or acre-feet per acre.

CONTACT RECREATION (Water)—Recreational activities involving a significant risk of ingestion of water, including wading by children, swimming, water skiing, diving and surfing.

CONTACT STABILIZATION—A modification of the Activated Sludge Process wherein a contact basin provides for the rapid adsorption of the waste. A separate tank is provided for stabilization of the solids before they are reintroduced into the raw wastewater flow.

CONTAMINANT—(Water Quality) In a broad sense any physical, chemical, biological, or radiological substance or matter in water. In more restricted usage, a substance in water of public health or welfare concern. Also, an undesirable substance not normally present, or an usually high concentration of a naturally-occurring substance, in water, soil, or other environmental medium.

CONTAMINATE—To make impure or unclean by contact or mixture.

CONTAMINATION (WATER)—Impairment of the quality of water sources by sewage, industrial waste, or other matters to a degree which creates a hazard to public health. Also, the degradation of the natural quality of water as a result of man's activities. There is no implication of any specific limits, since the degree of permissible contamination depends upon the intended end use, or uses, of the water. See Pollution.

CONTENTS (STORAGE)—The volume of water in a reservoir. Unless otherwise indicated, reservoir content is computed on the basis of a level pool and does not include bank storage.

CONTINENTAL DIVIDE—A drainage divide separating the rivers which flow toward opposite sides of a continent.

CONTINENTAL DIVIDE [United States]—A ridge of the Rocky Mountains forming the North American watershed that separates rivers flowing in an easterly direction from those flowing in a westerly direction.

CONTINENTAL DRIFT—The theory that continents slowly shift their positions as a result of currents in the molten rocks of the earth's mantle.

CONTINENTAL SHELF—The submerged shelf of land that slopes gradually from the exposed edge of a continent for a variable distance to the point where the steeper descent (the Continental Slope) to the ocean bottom begins, commonly at a depth of about 600 feet (183 meters).

CONTINUITY EQUATION—The relation, based on the conservation of mass, that equates the Volumetric Flow Rate, Q, of an incompressible fluid in a duct or pipe to the product of the fluid velocity, V, and the cross-sectional area, A, of the duct or pipe, by

Q = VA

If the area, A, increases, then the velocity, V, must decrease, and conversely. The equation is also applied to liquid flow through a system, stating that the flow in, Qin, flow out, Qout, and the change in the storage volume for a given time must be in balance, or

Qin — Qout = Change in Storage Volume

CONTINUOUS DELIVERY—A method of delivering water to the farm headgate from an irrigation conveyance system on a continuous basis, as opposed to a demand delivery where flows are delivered on a rotational time schedule and/or upon demand.

CONTINUOUS DISCHARGE—A routine release to the environment that occurs without interruption, except for infrequent shutdowns for maintenance, process changes, etc.

CONTINUOUS RECORDER (GAGE)—A device which measures stream flow levels on a continual basis.

CONTINUOUS SAMPLE—A flow of water from a particular place in a plant to the location where samples are collected for testing. May be used to obtain Grab Samples or Composite Samples.

CONTOUR—A line on a map that indicates a line of equal elevation on the land or water in feet over mean sea level. A line of equal thickness of water depth, soil or sediment thickness, or geologic structure thickness.

CONTOUR DITCH—An irrigation ditch laid out approximately on the contour, or elevation of the land.

CONTOUR FLOODING—Irrigation method resulting in flooding fields from Contour Ditches.

CONTOUR-FURROW IRRIGATION—The application of irrigation water in furrows that run across the slope with a forward grade in the furrows.

CONTOUR FURROWS—Furrows plowed approximately on the contour on pasture and rangeland to prevent runoff and increase infiltration; also, furrows laid out approximately on the contour for irrigation purposes.

CONTOUR PLOWING—A soil tilling technique that follows the shape of the land to minimize erosion.

CONTOUR STRIP FARMING—A kind of contour farming in which row crops are planted in strips, between alternating strips of close-growing, erosion-resistant forage crops.

CONTOUR TRENCHING—Development of water storage Detention or Retention Facilities along the contour by excavation and placement of soils as an embankment along the downstream side. Intervals vary with precipitation, slope, and soil.

CONTRACT (USBR)—Any repayment or water service contract between the United States and a district providing for the payment of construction charges to the federal government, including normal operation, maintenance, and replacement costs pursuant to federal reclamation law. All water service and repayment contracts are considered contracts even if the contract does not specifically identify that portion of the payment which is to be attributed to operation and maintenance and that which is to be attributed to construction.

CONTRACT RATE (USBR)— The repayment or water service rate set forth in a contract to be paid by a district to the federal government.

CONTRAIL—A visible trail of streaks of condensed water vapor or ice crystals sometimes forming in the wake of an aircraft. Also referred to as Vapor Trail.

CONTRIBUTING AREA—That portion of a watershed which contributes to measured runoff under normal conditions.

CONTROL—A natural constriction of the channel, a long reach of the channel, a stretch of rapids, or an artificial structure downstream from a Gaging Station that determines the Stage-Discharge Relation at the gage. A control may be complete or partial. A complete control exists where the stage-discharge relation at a gaging station is entirely independent of fluctuations in stage downstream from the control. A partial control exists where downstream fluctuations have some effect upon the stage-discharge relation at a gaging station. A control, either partial or complete, may also be shifting. Most natural controls are shifting to a degree, but a shifting control exists where the stage-discharge relation experiences frequent changes owing to impermanent bed or banks.

CONTROL DAM—A dam or structure with gates to control the discharge from the upstream reservoir or lake.

CONTROL POINTS (Horizontal and Vertical)—Small monuments that are securely embedded in the surface of a dam and used to detect any movement with respect to Permanent Monuments placed away from the dam itself.

CONTROL SCHEME (Canal)—The collection of methods and algorithms brought together to accomplish control of a canal system.

CONTROL STRUCTURE (LAKE LEVEL)—Dam, dike, pump or any structure built for the purpose of controlling the water level of a lake or pond.

CONTROL SYSTEM (Canal)—An arrangement of electronic, electrical, and mechanical components that commands or directs the regulation of a canal system.

CONTROLLED DRAINAGE—(Irrigation) Regulation of the water table to maintain the water level at a depth favorable for optimum crop growth.

CONTROLLED VOLUME OPERATION METHOD (Canal)—An operation in which the volume of water within a canal reach between two check structures is controlled in a rescribed manner for time variable inflows and outflows such as off-peak pumping or canal-side deliveries.

CONVECTION—(1) (Physics) Heat transfer in a gas or liquid by the circulation of currents from one region to another; also fluid motion caused by an external force such as gravity. (2) (Meteorology) The phenomenon occurring where large masses of warm air, heated by contact with a warm land surface and usually containing appreciable amounts of moisture, rise upward from the surface of the earth.

CONVECTIVE CLOUDS—Clouds generated by the rising of air over a relatively warm land mass.

CONVECTIVE PRECIPITATION—Precipitation resulting from vertical movement of moisture-laden air, which upon rising, cools and precipitates its moisture.

CONVECTIVE TRANSPORT—The component of movement of heat or mass induced by thermal gradients in ground water. Also see Advection.

CONVENTIONAL ACTIVATED SLUDGE—A process in which influent and recycled sludge enter at the head of the aeration tank.

CONVENTIONAL METHOD (Canal)—Where operations personnel (ditchrider and watermaster) control the canal system onsite. Labor-saving devices and machinery may be used to assist in the control of the canal facilities.

CONVENTIONAL SYSTEMS—(Water Quality) Systems that have been traditionally used to collect municipal wastewater in gravity sewers and convey it to a central primary or secondary treatment plant prior to discharge to surface waters.

CONVENTIONAL TILLING—Tillage operations considered standard for a specific location and crop and that tend to bury the crop residues; usually considered as a base for determining the cost effectiveness of control practices.

CONVENTIONAL WATER—A natural freshwater supply as opposed to desalted or brackish water.

CONVEYANCE LOSS—Water that is lost in transit from a pipe, canal, conduit, or ditch by leakage, seepage, evaporation, or evapotranspiration. Generally, these conveyance losses are not available for further use; however, leakage from an irrigation ditch, for example, may percolate to a ground-water source and be available for further use.

COOLANT—An agent, such as water, that produces cooling as by drawing off heat by circulating through an engine or by bathing a mechanical part.

COOLING POND—Usually a man-made water body used by power plants or large industrial plants that enables the facility to recirculate once-through cooling water. The water levels in the pond are usually maintained by rainfall or augmented by pumping (withdrawal) water from another source. Also see Cooling Water and Once-Through Cooling Water.

COOLING TOWER—A large tower or stack that is used for heat exchange of once-through cooling water generated by steam condensers. Hot water from the plant is sprayed in the tower and exchanges heat with the passing air. The water is then collected at the bottom of the tower and used again. A small amount of water is lost (consumed) through evaporation in this process. Also see Cooling Water and Once-Through Cooling Water.

COOLING WATER—Water used for cooling purposes by electric generators, steam condensers, large machinery or products at industrial plants, and nuclear reactors. Water used for cooling purposes can be either fresh or saline and may be used only once or recirculated multiple times. Also see Cooling Pond and Once-Through Cooling Water.

COOLING WATER CONSUMPTION (POWER)—The cooling water which is lost to the atmosphere, caused primarily by evaporation due to the temperature rise in the cooling water as it passes through the condenser. The amount of consumption (loss) is dependent on the type of cooling employed—Once-Through Cooling Water, Cooling Pond, or Cooling Tower.

COOLING WATER LOAD—The waste heat energy dissipated in the cooling water.

COOLING WATER REQUIRED (POWER)—The amount of water needed to pass through the condensing unit in order to condense the steam to water.

COORDINATED RESOURCE MANAGEMENT AND PLANNING—A planning process used by the U.S. Department of the Interior, Bureau of Land Management (BLM) that includes public users, interest groups, agencies and affected individuals in the decision-making process before on-the-ground implementation of an activity plan.

COORDINATED RESOURCE PLAN—A conservation plan including privately-owned land and public land.

COPEPODITES—The penultimate five, out of a total of twelve, life history stages of copepods.

COPEPODS—Group of crustaceans more diverse in the sea than freshwaters. Some species filter particles for food, others grasp larger particles such as smaller animals. The life history comprises six successively larger naupliar and then five copepodite stages before the sexually reproducing adults are formed as the twelfth stage.

CO-PERMITTEE—A permittee to a NPDES permit that is only responsible for permit conditions relating to the discharge for which it is operator.

CORE—(Geology) The central portion of the earth below the Mantle, beginning at a depth of about 2,900 kilometers (1,800 miles) and probably consisting of iron and nickel. It is made up of a liquid outer core and a solid inner core.

CORE WALL (of a Dam)—A wall built of impervious material, usually concrete or asphaltic concrete, in the body of an Embankment Dam to prevent leakage.

CORIOLIS EFFECT—(Climatology and Oceanography) The Coriolis effect, named for French physicist Gaspard Coriolis (1792-1843), is an imaginary force that appears to be exerted on an object moving within a rotation system. The apparent force is simply the acceleration of the object caused by the rotation. This effect may seen on a large scale in the movement of winds and ocean currents on the rotating earth. It dominates weather patterns, producing the counterclockwise flow observed around low-pressure zones in the Northern Hemisphere and the clockwise flow around such zones in the Southern Hemisphere. This effect is also responsible for the rotation of water funnels in the drains of tubs and water basins; the funnels will rotate counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere. Along the equator, there will be no such rotation.

CORMIX—Cornell Mixing Zone Expert System.

CORN SNOW—Snow that has melted and refrozen into a rough, granular surface.

CORONA—(Astronomy) A faintly colored luminous ring appearing to surround a celestial body visible through a haze or thin cloud of water vapor, especially such a ring around the moon or sun, caused by the diffraction of light from suspended matter in the intervening medium. Also referred to as Aureole.

(U.S. ARMY) CORPS OF ENGINEERS (COE)—See (United States) Army Corps of Engineers (COE). [See Appendix C-2 for the U.S. Army Corps of Engineers' organizational structure and primary missions and objectives.]

CORRASION—The wearing away of earth materials through the cutting, scraping, scratching, and scouring effects of solid material carried by water or air.

CORRELATION—(Statistics) A statistical means to measure the degree of "coincidence of change" between two variables, producing a value of variance termed the Correlation Coefficient. In strict correlation analysis, no inference of causation, i.e., one variable being "explained" by the variations of another, is made. Therefore, high correlations do not provide for an inference of causality; one must use previous information that the two sampled variables are indeed related to one another. The concept of the Coefficient of Determination, on the other hand, used as a common measure of "Goodness of Fit" in Regression Analysis, is used to assess the degree of causation between two variables or between one or more independent variables and a single dependent variable. The coefficient of determination is equivalent to the square of the correlation coefficient and reflects the percent of change in the dependent (explained) variable that is explained by the variations in the independent (explanatory) variable.

CORRELATION COEFFICIENT (R)—(Statistics) A measure of the coincidence of change between two variables. The use of the correlation coefficient makes no inference as to causation, i.e., one variable causing changes to occur in another; it only represents a measure of the simultaneous behavior between two variables which either are related or are being affected similarly by a third variable. The value of the correlation coefficient will vary between -1.00 (-100 percent) and +1.00 (+100 percent) with higher numbers representing stronger levels of coincidence of changes. Positive correlation coefficients denote that the two series evidence changes in the same direction while negative correlation coefficients reflect an inverse relationship between changes in one series and another.

CORRELATIVE ESTIMATE—A discharge or stream flow estimate determined by Correlation, or comparisons to other, possibly influencing factors, e.g., rainfall, snowpack, levels of upstream lakes and reservoirs, etc. A correlative estimate represents a likely value of the discharge or flow for any particular period—commonly a month—according to a specified method of analysis and the explanatory variables chosen.

CORRELATIVE (WATER) RIGHTS—Certain rights of land owners over a common ground water basin are coequal, or correlative, so that any one owner cannot take more than his share even if the rights of others are impaired. Where a source of water does not provide enough for all users, the water is reapportioned on the basis of prior water rights held by each user.

CORROSIVE—A substance that deteriorates material, such as pipe, through electrochemical processes.

CORRUGATION IRRIGATION—Spreading water by directing it into small channels across the field. Also referred to as Furrow Irrigation.

COSMETIC SOLUTION—Acting upon symptoms or given conditions without correcting the actual cause of the symptoms or conditions.

COST-BENEFIT ANALYSIS (CBA)—Analysis technique which compares the cost of a project with the benefits derived from it. Expressed as a ratio of benefits to costs. Ratios greater than 1.0 are deemed to be cost-effective. The determination of costs and benefits to be included in the analysis can be a contentious issue, particularly for public goods and the monetization of natural resources.

COTTAGE-WATER RATIO—The ratio between the number of shoreland cottages or lake homes (whose owners or occupants have access to the water) and the area (expressed in acres) of the lake surface.

COULEE—(1) (Western U.S.) A deep gulch or ravine with sloping sides, often dry in summer. (2) (Louisiana and Southern Mississippi) A streambed, often dry according to the season; a small stream, bayou, or canal. (3) (Upper Midwest) A valley with hills or either side. (4) (Geology) A stream of molten lava; a sheet of solidified lava.

COULOIR—A deep mountain gorge or gully.

COUPON TEST—A method of determining the rate of corrosion or scale formation by placing metal strips (or coupons) of a known weight in the pipe.

COURSE (WATER)—The route or path taken by flowing water, such as a stream or river.

COVARIANCE—(Statistics) A measure of the linear association between two variables. If both variables are always above and below their means at the same time, the covariance is said to be positive. If one variable is above its mean when the other variable is below its mean and vice versa, the covariance is said to be negative. The value of the covariance is dependent upon the units in which each variable is measured whereas the Correlation Coefficient is a measure of this association which has been normalized and is therefore "unit free."

COVE—A small sheltered inlet, creek, or bay; a recess in the shore.

COVER—(1) Vegetation or other material providing protection to a surface. (2) The area covered by live above-ground parts of plants.

COVER CROP—A close-growing crop grown primarily for the purpose of protecting and improving soil between periods of regular crop production or between trees and vines in orchards and vineyards.

CP—Cultural Practices.

CPI—Consumer Price Index.

CRADLE—A supporting structure shaped to fit the conduit it supports.

CRANBERRY—A sour, red berry grown on low bushes in bogs and swamps. Used to make jelly, juice and sauce.

CRANBERRY BOG—A bog dominated by this mat-forming evergreen shrub; common in eastern North America. Most commercial operations require planting and some form of water level control for frost protection and to facilitate harvesting.

CRATER LAKE—A lake formed in a crater. Caldera are basins formed by the collapse of magma in the vents of volcanoes. Maars are volcanic basins formed by single explosive eruptions. Depressions in the earth's surface made by impact of falling meteors are also called craters, although the existence of only a few crater lakes of this origin has been clearly established.

CRAYFISH—Freshwater crustacean smaller than a lobster. Also called crawfish.

CREAMS—Chemicals, Runoff and Erosion from Agricultural Management Systems.

CREEK—A small stream of water which serves as the natural drainage course for a drainage basin; a flowing rivulet or stream of water normally smaller than a river and larger than a brook. The term is often relative according to size and locality. Some creeks in a humid region would be called rivers if they occurred in an arid area.

CREEP—Slow mass movement of soil and soil material down relatively steep slopes, primarily under the influence of gravity but facilitated by saturation with water and by alternate freezing and thawing.

CREEPER—A grappling device for dragging bodies of water, such as lakes or rivers.

CREOSOTE—Chemical used in wood preserving operations and produced by distillation of tar, including Polycyclic Aromatic Hydrocarbons and Polynuclear Aromatic Hydrocarbons (PAHs and PNAs). Contaminating sediments, soils, and surface water, creosotes may cause skin ulcerations and cancer with prolonged exposure.

CREST—(1) The top of a dam, dike, or spillway, which water must reach before passing over the structure; in international usage it refers to the crown of an overflow section of a dam. (2) The summit or highest point of a wave. (3) The highest elevation reached by flood waters flowing in a channel as in Crest Stage or Flood Stage.

CREST GAGE—An instrument used to obtain a record of flood crests at sites where recording gages are not installed.

CREST GATE—A temporary or movable gate installed on top of a spillway crest to provide additional storage or prevent flow over the crest.

CREST LENGTH—The length of the top or crest of a dam, including the length of the spillway, powerhouse, navigation lock, fish pass, etc., where these structures form part of the length of a dam. If detached from a dam, these structures would not be included in the crest length.

CREST STAGE—The highest value of river Stage (or streamflow) attained in a flood.

CREST WIDTH (or Top Thickness)—The thickness or width of a dam at the level of the top (crest) of the dam. In general, the term "thickness" is used for Gravity and Arch Dams and the term "width" is used for other dams.

CREVASSE—(1) A deep crack or fissure, especially in a glacier. (2) A break in the levee of a river, dike, or similar structure. Also see Levee.

CRIB DAM—A barrier or form of Gravity Dam constructed of timber forming bays, boxes, cribs, crossed timbers, gabions or cells that are filled with earth, stone or heavy material. Also see Dam.

CRICK—(Inland Northern U.S. and Western U.S.) Variant of Creek.

CRITERIA—Water quality conditions which are to be met in order to support and protect desired uses.

CRITERIA, TESTING (R2, t-Statistic, and F-Statistic)—(Statistics) In criteria testing of the appropriateness of a econometric forecast model's structure (Specification), certain testing criteria are used most frequently. Specifically, the Coefficient of Determination, R2, is used as an overall measure of the "goodness of fit," the t-Statistic, is used as a measure of the appropriateness of individual explanatory variables, and the F-Statistic, is used as a measure of the appropriateness of the inclusion or exclusion of a set of explanatory variables simultaneously. Also see Model and Regression Analysis.

CRITERIA, WHPA—Conceptual standards that form the basis for Wellhead Protection Area (WHPA) delineation. WHPA criteria can include distance, drawdown, time of travel, assimilative capacity, and flow boundaries. See Wellhead Protection Area (WHPA) and Wellhead Protection (Program).

CRITICAL—(Chemistry and Physics) Of or relating to the value of a measurement, such as temperature, at which an abrupt change in a quality, property, or state occurs. For example, a critical temperature of water is 100C (212F), its boiling point at standard atmospheric pressure.

CRITICAL AQUIFER PROTECTION AREA (CAPA)—As defined in the Safe Drinking Water Act (SDWA), is all or part of an area located within an area for which an application of designation as a sole or principal source aquifer (pursuant to Section 1424[e]) has been submitted and approved by the Administrator not later than 24 months after the date of enactment and which satisfies the criteria established by the Administrator; and all or part of an area that is within an aquifer designated as a sole source aquifer (SSA), as of the date of the enactment of the Safe Drinking Water Act Amendments of 1986, and for which an areawide ground-water protection plan has been approved under Section 208 of the Clean Water Act (CWA) prior to such enactment.

CRITICAL AREA—An area that, because of its size, location, condition, or importance, must be treated with special consideration because of inherent site factors and difficulty of management. Also, a severely eroded, sediment-producing area that requires special management to establish and maintain vegetation to stabilize the soil.

CRITICAL (GROUND WATER) AREA—An area that has certain ground water problems, such as declining water levels due, for example, to the use of underground water that approaches or exceeds the current recharge rate. These designated areas are usually limited in their development and use.

CRITICAL DEPTH—The depth of water flowing in an open channel or conduit under conditions of critical flow at which specific energy is a minimum for a given discharge.

CRITICAL DRY PERIOD—As a general definition, describes a series of water-deficient years, usually a historical period, in which a full reservoir storage system at the beginning is drawn down to minimum storage at the end without any spill.

CRITICAL DRY YEAR—A dry year in which the full commitments for a dependable water supply cannot be met and deficiencies are imposed on water deliveries.

CRITICAL FLOW—(1) The flow conditions at which the discharge is a maximum for a given specific energy, or at which the specific energy is a minimum for a given discharge. (2) In reference to Reynolds' critical velocities, the point at which the flow changes from streamline or non-turbulent to turbulent.

CRITICAL HABITAT—The area of land, water, and airspace required for normal needs and survival (e.g., forage, reproduction, or cover) of a plant or animal species.

CRITICAL LOW-FLOW—Low flow conditions below which some standards (Criteria) do not apply. The impacts of permitted discharges are typically analyzed at critical low-flow.

CRITICAL POINT—(1) (Physics) The temperature and pressure at which the liquid and gaseous phases of a pure stable substance become identical. Also referred to as the Critical State. (2) (Water Quality) The location downstream from a waste discharge at which the dissolved oxygen of the water is at its lowest. Also referred to as the Critical Reach.

CRITICAL REACH—The point in the receiving stream below a discharge point at which the lowest dissolved oxygen level is reached and recovery begins. Also referred to as the Critical Point.

CRITICAL SLOPE—That slope that will sustain a given discharge at uniform, Critical Depth in a given channel.

CRITICAL VELOCITY—Velocity at which a given discharge changes from tranquil to rapid flow; that velocity in open channels for which the specific energy (the sum of the depth and velocity head) is a minimum for a given discharge.

CRITICAL WILDLIFE HABITAT—Habitat that is vital to the health and maintenance of one or a variety of species based on habitat features such as nesting sites, denning sites, food sources, breeding grounds, etc.

CROP—(1) Plants, seeds, flowers and root tubers that are grown to be used as food or to be sold for profit. (2)Total amount of plants of one type harvested.

CROP COEFFICIENT—The ratio of evapotranspiration occurring with a specific crop at a specific stage of growth to potential evapotranspiration at that time.

CROP CONSUMPTIVE USE (Crop Requirement)—Often called Evapotranspiration. The amount of water used by vegetative growth of a given area by transpiration and that evaporated from adjacent soil or intercepted precipitation on the plant foliage in any specified time (acre-feet/acre).

CROP IRRIGATION REQUIREMENT— The amount of irrigation water in acre-feet per acre required by the crop; it is the difference between Crop Consumptive Use, or Crop Requirement, and the effective precipitation for plant growth. To this amount the following items, as applicable, are added: (1) irrigation applied prior to crop growth; (2) water required for leaching; (3) miscellaneous requirements of germination, frost protection, plant cooling, etc.; and (4) the decrease in soil moisture should be subtracted.

CROPLAND—Land currently tilled, including cropland harvested, land on which crops have failed, summer fallowed land, idle cropland, cropland planted in cover crops or soil improvement crops not harvested or pastured, rotation pasture, and cropland being prepared for crops, or newly seeded cropland. Cropland also includes land planted in vegetables and fruits, including those grown on farms for home use. All cultivated (tame) hay is included as cropland. Wild hay is excluded from cropland and included in pasture and range.

CROP REQUIREMENT— See Crop Consumptive Use.

CROP ROTATION—A pattern of changing the crops grown in a specific field from year to year in order to control pests and maintain soil fertility.

CROP SUBSIDY—A price support paid to farmers by the government.

CROSS CONNECTION—A physical connection through which a supply of potable water could become contaminated. May include any actual or potential connection between a drinking water system and an unapproved water supply or other source of contamination.

CROSS-SECTIONAL ANALYSIS—(Statistics) Observations or characteristics of a variable analyzed without respect to variations due to time. Cross-sectional econometric models provide information on the behavior of a variable due to external factors. Contrast with Time-Series Analysis.

CRP—Conservation Reserve Program. US Department of Agriculture program that provides incentives and assistance to farmers and ranchers for establishing conservation practices. It encourages farmers to plant permanent covers of grass and trees on land that is subject to erosion, where vegetation can improve water quality or provide food and habitat for wildlife.

CRUD—(Sports) Heavy, sticky snow that is unsuitable for skiing.

CRUSTACEA—One of several jointed-legged groups of animals that comprise the Arthopoda. Crustaceans have no particular set body pattern, as do the insects and spiders, often form a shell or carapace rich in calcium and are predominantly aquatic. They include the water fleas, copepods and mysids.

CRUSTACEAN—A fresh and salt water animal that has a hard shell. Such as a skud, shrimp, or lobster.

CRYOLOGY—The science of the physical aspects of snow, ice, hail, sleet, and other forms of water produced by temperatures below 0C (32F).

CRYOSCOPE—An instrument used to measure the freezing point of a liquid.

CRYPTO OOCYST—The hard shell in which the parasite, Cryptosporidium parvum, resides. This hard shell protects the parasite in the environment and remains viable for up to six months. This shell also protects the protozoa from chlorine disinfection treatment.

CRYPTODEPRESSION (LAKE)—Lake basin whose deep parts are below sea level.

CRYPTOMONADS—A group of brown colored flagellate algae, very common in the phytoplankton.

CRYPTOPHYTE—Algae of variable pigment concentrations, with various other unusual features. Algae of the division Cryptophyta.

CRYPTOSPORIDIOSIS—A disease of the intestinal tract caused by the parasite Cryptosporidium parvum. Common symptoms include stomach cramps and diarrhea.

CRYPTOSPORIDIUM PARVUM—A parasite often found in the intestines of livestock which contaminates water when the animal feces interact with a water source. Literally, cryptosporidium means "mystery spore," and the parasite was not recognized as a human pathogen until 1976. In healthy individuals, infection may result in an acute diarrheal illness lasting for 2-3 weeks. In immuno-suppressed individuals (e.g., AIDs patients, children, elderly), Cryptosporidiosis, the disease from infection by the parasite, may be life-threatening. While much needs to be learned about the infectious level of crypto, studies have indicated that it takes five to ten cysts to make someone sick. Of particular concern to health officials and public drinking water supplies is that the most widely used agent to disinfect tap water—chlorine—does not kill the parasite. Also, the laboratory tests used to detect crypto are time-consuming, laborious, and expensive. As an additional complication in the detection process, there are several varieties of crypto, but only one—Cryptosporidium parvum—is infectious to humans. Also, laboratory tests cannot determine whether a Crypto Oocyst, the hard shell that protects the protozoa, is alive or dead. Currently, the only effective treatment for water supplies is through filtration (crypto oocysts are only 3 to 7 microns in size) and the use of ozone gas rather than chlorine. As of January 1997, the U.S. Environmental Protection Agency (EPA), through the Information Collection Rule (ICR), has required that all public water supply systems serving more than 100,000 connections to monitor for cryptosporidium.

CSO—See Combined Sewer Overflow.

CSS—Combined Sewer System.

CSTR—Continuously Stirred Tank Reactor.

CU—Catalog Unit.

CUBIC FEET PER SECOND (CFS)—A unit expressing rate of discharge, typically used in measuring streamflow. One cubic foot per second is equal to the discharge of a stream having a cross section of 1 square foot and flowing at an average velocity of 1 foot per second. It also equals a rate of approximately 7.48 gallons per second, 448.83 gallons per minute. 1.9835 acre-feet per day, or 723.97 acre-feet per year.

CUBIC FEET PER SECOND DAY (CFS-DAY)—The volume of water represented by a flow of one cubic foot per second for 24 hours. It equals 86,400 cubic feet, 1.983471 acre-feet, or 646,317 gallons.

CUCKING STOOL—A chair formerly used for punishing offenders (as dishonest tradesmen) by public exposure or ducking in water.

CULTIVAR—Plant form originating from under cultivation.

CULTURAL EUTROPHICATION—Accelerated eutrophication (generally enrichment by nutrients) that occurs as a result of human activities in the watershed that increase nutrient loads in runoff water that drains into lakes.

CULTURAL LANDSCAPE—Man-made features of a region reflecting land-use patterns, population distribution, and other activities of man that have altered the natural landscape.

CULVERT—A transverse drain or waterway under a road, railroad, canal, or other obstruction.

CULVERT DAM—When culverts are constructed under roads that cross over the effluent (outlet) stream of a lake, they may be laid at a higher level than the original stream bed. When installed in this fashion, they act as low head dams and may raise the level of the entire lake. The culvert acts as an outlet when the water rises to its level.

CUMULATIVE IMPACT—The environmental impacts of a proposed action in combination with the impacts of other past, existing and proposed actions. Each increment from each action may not be noticeable but cumulative impacts may be noticeable when all increments are considered together.

CUMULATIVE INFILTRATION—The summation of the depth of water absorbed by a soil in a specified elapsed time in reference to the time of initial water application.

CUMULONIMBUS CLOUDS—A principal cloud type; the ultimate stage of development of Cumulus clouds. Cumulonimbus clouds are very dense and very tall, commonly 5 to 10 miles in diameter, and sometimes reaching heights of 12 miles or more. The upper portion is at least partly composed of ice crystals, and it often takes the form of an anvil or vast plume. The base of the cloud is invariably dark and is often accompanied by low, ragged clouds. Also commonly called Thundercloud, Thunderhead, Thunderstorm. Also see Cloud.

CUMULUS CLOUDS—A principal cloud type characterized by vertical development; usually isolated with a dark, nearly horizontal base and upper parts resembling domes or towers and usually formed by the ascent of thermally unstable air masses. Also see Cloud.

CUNETTE—A longitudinal channel constructed along the center and lowest part of a channel or through a detention or retention facility and intended to carry low flows. Also referred to as a Trickle Channel.

CURB STOP—A water service shutoff valve located in a water service pipe near the curb and between the water main and the building.

CURL—A hollow arch of water formed when the crest of a breaking wave spills forward.

CURRENT—(1) The portion of a stream or body of water which is moving with a velocity much greater than the average of the rest of the water. The progress of the water is principally concentrated in the current. (2) The swiftest part of a stream; (3) A tidal or nontidal movement of lake or ocean water; (4) Flow marked by force or strength; (5) Currents of various types and names have been recognized: littoral, longshore, undertow, rip, density, convection, turbidity, eddies, stream.

CURRENT CANAL—The current caused by an influent (inlet) or effluent (outlet) stream may effectively limit the growth of aquatic plants and create canal-like openings through weed beds.

CURRENT METER—An instrument for measuring the velocity of water flowing in a stream, open channel, or conduit by ascertaining the speed at which elements of the flowing water rotate a vane or series of cups.

CUSP, BEACH—Triangular deposit of sand, or other current drift, spaced along a shore. Size and configuration is apparently controlled by the magnitude and direction of wave action or current forces. Cusps are transient under some conditions, formed by storm waves and erased by a succeeding storm, but under other conditions are fairly long and relatively permanent features.

CUSPATE FORELAND—Formation consisting of a V-bar and a foreland created from the joining of two spits in a lake. The space between the enclosing sides may be water; or the foreland may be a complex of beach deposits which are cuspate in form.

CUT AND BUILT TERRACE—See Wave Built Terrace or Littoral Shelf.

CUTBACK IRRIGATION—Water applied at a faster rate at the beginning of the irrigation period and then reduced or cutback to a lesser rate, usually one-half the initial rate or that amount to balance with the intake rate.

CUTICLE—Waxy protective layer on the surface of a leaf or stem.

CUTOFF, also Cut-Off—(1) (Hydraulics) The new and shorter channel formed either naturally or artificially when a stream cuts through the neck of a bank or oxbow. (2) (Dam) An impervious construction or material which reduces seepage or prevents it from passing through the foundation material of a dam structure.

CUTOFF TRENCH (of a Dam)—An excavation later to be filled with impervious material to form a Cutoff. Sometimes used incorrectly to describe the cutoff itself.

CUTOFF WALL (of a Dam)—A wall of impervious material (e.g., concrete, asphaltic concrete, steel sheet piling) built into the foundation of a dam to reduce or prevent seepage under the dam.

CUTWATER—(1) (Nautical) The forward part of a ship's prow. (2) The wedge-shaped end of a bridge pier, designed to divide the current and break up ice floes.

CVP—Central Valley Project (State of California).

CWA—Clean Water Act (EPA).

CYANAZINE—A herbicide listed by the U.S. Environmental Protection Agency (EPA) as a "possible human carcinogen" and found frequently in streams and rivers, particularly following floods and periods of heavy rain and runoff from agricultural lands. Cyanazine is used extensively for weed control for corn, sorghum, and sugarcane. Along with another common farm herbicide, Atrazine, Cyanazine concentrations can soar to levels much higher than federal standards during the peak growing season.

CYANOBACTERIA—See Blue-green Algae.

CYANOPHYTE—Blue green algae, algae of the division Cyanophyta actually a set of pigmented bacteria.

CYCLE—(Statistics) A periodic, repetitive fluctuation in time series data from either a constant mean or trend line. Typically, the oscillations of a cycle will be greater than one year in length. Cycles within a year are termed Seasonality.

CYCLE OF EROSION—A qualitative description of river valleys and regions passing through the stages of youth, maturity, and old age with respect to the amount of erosion that has been effected.

CYCLONE—(Meteorology) An atmospheric system characterized by the rapid, inward circulation of air masses about a low-pressure center, usually accompanied by stormy, often destructive, weather. Cyclones circulate counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere. Also see Typhoon and Coriolis Effect.

CYCLONIC PRECIPITATION—Precipitation which results from the lifting of air converging into a low-pressure area, or Cyclone.

CYPRESS KNEES—Part of a cypress tree's root system that juts out of the ground, extending above the high water mark.

CYPRESS PONDS—Ponds or lakes characterized by growths of cypress (Taxodium spp.).

CYPRESS SWAMP—A wetland environment common throughout the southeastern United States in which cypress trees are a dominant species.

CYPRIERE—In Louisiana, a cypress swamp. Cypress swamps generally are permanently water covered areas.

CZMA—Coastal Zone Management Act (EPA).

DABBLE—To bob forward and under in shallow water so as to feed off the bottom.

DAILY FLOOD PEAK—The maximum mean daily discharge occurring in a stream during a given flood event.

DAILY TEMPERATURE RANGE—The difference between the highest and lowest temperatures recorded on a particular day.

DAM—A structure of earth, rock, or concrete designed to form a basin and hold water back to make a pond, lake, or reservoir. A barrier built, usually across a watercourse, for impounding or diverting the flow of water. General types of dams include:

[1] Arch Dam—Curved masonry or concrete dam, convex in shape upstream, that depends on arch action for its stability; the load or water pressure is transferred by the arch to the Abutments. [2] Buttress Dam—A dam consisting of a watertight upstream face supported at intervals on the downstream side by a series of buttresses. [3] Cofferdam—A temporary watertight enclosure that is pumped dry to expose the bottom of a body of water so that construction, as of piers, a dam, and bridge footings, may be undertaken. A "diversion cofferdam" prevents all downstream flow by diverting the flow of a river into a pipe, channel, or tunnel. [4] Crib Dam—A barrier or form of Gravity Dam constructed of timber forming bays, boxes, cribs, crossed timbers, gabions or cells that are filled with earth, stone or heavy material. [5] Embankment Dam—A dam structure constructed of fill material, usually earth or rock, placed with sloping sides and usually with a length greater than its height. Types of embankment dams include: Earthfill or Earth Dam—A dam in which more than 50 percent of the total volume is formed of compacted fine-grained material obtained from a borrow area (i.e., excavation pit); Fill Dam—Any dam constructed of excavated natural materials or of industrial waste materials; Homogeneous Earthfill Dam—A dam constructed of similar earth material throughout, except for the possible inclusion of internal drains or drainage blankets; distinguished from a Zoned Earthfill Dam; Hydraulic Fill Dam—A dam constructed of materials, often dredged, that are conveyed and placed by suspension in flowing water; Rockfill Dam—A dam in which more than 50 percent of the total volume is comprised of compacted or dumped pervious natural or crushed rock; Rolled Fill Dam—A dam of earth or rock in which the material is placed in layers and compacted by using rollers or rolling equipment; and Zoned Embankment Dam—A dam which is composed of zones of selected materials having different degrees of porosity, permeability, and density. [6] Gravity Dam—A dam constructed of concrete and/or masonry that relies on its weight for stability. [7] Masonry Dam—A dam constructed mainly of stone, brick, or concrete blocks that may or may not be joined with mortar. A dam having only a masonry facing should not be referred to as a masonry dam. [8] Weir—A dam in a river to stop and raise the water, for the purpose of conducting it to a mill, forming a fishpond, or the like. When uncontrolled, the weir is termed a fixed-crest weir. Other types of weirs include broad-crested, sharp-crested, drowned, and submerged.

DAMAGE-FREQUENCY CURVE—A graph showing the flood damages and their probabilities of occurrence. The total area under the curve represents the annual damage.

DAMAGES PREVENTED—The difference between the amount of damages without a particular water project and the damages with the project in place.

DAMP—Slightly wet; somewhat moist or wet.

DAP—(1) To dip lightly or quickly into water, as a bird does. (2) To skip or bounce, especially over the surface of water.

DARCY'S LAW—An empirically derived equation for the flow of fluids through porous media. It is based on the assumption that flow is laminar and inertia can be neglected, and states that velocity of flow is directly proportional to Hydraulic Gradient. For groundwater, this is equivalent to the velocity being equal to the product of the hydraulic gradient and the effective subsoil conductivity or permeability. See Specific Discharge (Specific Flux).

DATA—In its strictest sense, data may be defined only as the raw numbers (or descriptions, in the case of qualitative data), either in Time-Series format (data covering observations over specific periods of time), Cross-Sectional format (data consisting of a number of observations taken at a specific point in time or about a specific event or phenomenon), or a combination of these two. Also see Information.

DATA BANK—A well-defined collection of data, usually of the same general type, which can be accessed by a computer and may readily be used for further analysis, presentation, and forecasting. Also referred to as a Data Base.

DATA, CROSS-SECTIONAL—(Statistics) Data which describe the activities or behavior of individual persons, firms, or other units at a given point in time.

DATA MANAGEMENT—The act, process, or means by which data is managed. This may include the compilation, storage, safe-guarding, listing, organization, extraction, retrieval, manipulation, and dissemination of data. In its strictest sense, data may be defined only as the raw numbers for numeric or quantitative data (or descriptions, in the case of qualitative data), either in time-series format (data covering observations over specific periods of time), cross-sectional format (data consisting of a number of observations taken at a specific point in time or about a specific event or phenomenon without regard to its behavior over time), or a combination of these two. Information, on the other hand, deals more specifically with the manipulation, re-organization, analysis, graphing, charting, and presentation of data for specific management and decision-making purposes. Also see Information Management.

DATA, PRIMARY—Typically, data acquired by direct interaction, such as direct observation through measurements, tabulation, or surveys. Contrast with Secondary Data.

DATA, SECONDARY—Typically, data acquired from published sources as opposed to data acquired from direct observation or measurement such as a survey. Contrast with Primary Data.

DATA, TIME-SERIES—(Statistics) Data which describe the movement of a variable over time, e.g., monthly, quarterly, annually.

DATUM—Any numerical or geometric quantity or set of such quantities that may serve as a reference or base for other, comparable quantities. For example, Mean Sea Level (MSL) is the datum used on most topographic maps. However, most river gages use an arbitrary elevation above the National Geodetic Vertical Datum (NGVD) of 1929 for use as a zero datum (e.g., datum equals 3412.6 feet above NGVD of 1929). Datums are always chosen so there will never be negative stages.

DDT (DICHLORODIPHENYLTRICHLOROETHANE)—A colorless odorless water-insoluble crystalline insecticide C14H9Cl5 that tends to accumulate in ecosystems and has toxic effects on many vertebrates. DDT was used extensively prior to 1972 at which time the U.S. Environmental Protection Agency (EPA) banned its production and distribution. Although banned from usage for a number of years, the inert nature of such toxic chemicals and their low biodegradability (15-year half-life) allow them to exist in soils, river sediment, and plants and animals for many years.

DEAD END—The end of a water main which is not connected to other parts of the distribution system.

DEAD STORAGE—The volume of water in a reservoir stored below the lowest outlet or operating level.

DEAD TIME—The time required for the response to a change of input to a system to reach the location of a sensor (i.e., the time for a control initiated surge wave to travel from an upstream control check gate to a downstream sensor in a canal.)

DEAD ZONE [Gulf of Mexico]—(Ecology) A term referring to an extensive area, recorded to be as large as 7,000 square miles [July 1995], that develops every summer at the bottom of the Gulf of Mexico. The area consists of a lifeless area devoid of oxygen that results from an ecological chain reaction precipitated by fertilizers, sewage, and runoff that flows from the Mississippi River. While many sources contribute to this phenomenon, the primary nutrient cause consists of fertilizer runoff from agriculture in the Mississippi River Basin.

DEBACLE—(1) The breaking up of ice in a river. (2) A violent flood.

DEBOUCH—To emerge; issue, as a river into which a large stream debouches.

DEBOUCHURE—An opening or mouth, as of a river or stream.

DEBRIS—Any material, including floating or submerged trash, suspended sediment, or bed load, moved by a flowing stream.

DEBRIS BASINS—Storage for sediment and floating material provided by a dam with spillway above channel grade, by excavation below grade, or both. Water retention is not an intended function of the structure.

DEBRIS DAM—A barrier built across a stream channel to retain rock, sand, gravel, silt, or other material.

DEBRIS FLOW—A moving mass of rock fragments, soil, and mud with more than one-half of the material being larger than sand size.

DEBRIS GUARD—A screen or grate at the intake of a channel, drainage, or pump structure for the purpose of stopping debris.

DECANT—To draw off the upper layer of liquid after the heaviest material (a solid or other liquid) has settled.

DECAY—The disintegration of organic materials into simpler forms, or into their original elements, by action of bacteria, fungi, or other microorganisms.

DECHLORINATE—To remove Chlorine from water.

DECHLORINATION—The partial or complete reduction of residual chlorine in a liquid by any chemical or physical process. Commonly used dechlorinating agents include activated carbon and sulfur dioxide.

DECIDUOUS (PLANT)—(Botanical) (1) Plants characterized by a specific growth and dormancy cycle, with certain parts falling at the end of the growing period, as leaves, fruits, etc., or after anthesis, as the petals of many flowers. (2) Plants having leaves of this type. As contrasted with Evergreen which remains verdant throughout the year.

DECIDUOUS STAND—A plant community where Deciduous trees or shrubs represent more than 50 percent of the total areal coverage of trees or shrubs.

DECLARED UNDERGROUND WATER BASIN—An area of a state designated in some states by their respective State Engineers to be underlain by a ground water source having reasonably ascertainable boundaries. By such a designation, the State Engineer assumes jurisdiction over the appropriation and use of ground water from the source. May not be applicable in states which already claim regulatory rights over both surface and ground waters.

DECOMPOSER—Any of various organisms (as many bacteria and fungi) that feed on and break down organic substances (such as dead plants and animals).

DECOMPOSITION—The breakdown of matter by bacteria and fungi, changing the chemical makeup and physical appearance of materials.

DECORATIVE WATER FEATURE—Any manmade stream, fountain, waterfall, or other such water feature that contains water that flows or is sprayed into the air, constructed for decorative, scenic, or landscape purposes.

DECREED RIGHTS (WATER)—Water rights determined by court decree.

DEDICATED NATURAL FLOW—River flows dedicated to environmental use. Also see Environmental Flows.

DEDICATIONS (Water)—A controversial water rights policy that involves a trade-off in which a user can begin pumping groundwater in exchange for a guarantee to buy and retire a like amount of surface water in the future. Critics of the policy argue that dedications are often difficult to enforce and can lead to overuse of groundwater when a user fails to fulfill on the guarantee.

DEEP CARBONATE AQUIFER [Nevada]—An aquifer within the Great Basin which is comprised of a thick sequence of carbonate rock, generally lying below basin fill deposits.

DEEP-DRAFT HARBOR—A harbor designed to accommodate commercial cargo vessels having drafts greater than 15 feet (4.6 meters).

DEEP-LAVA THEORY—(Geophysics and Climatology) A theory first espoused by a geophysicist from the University of Hawaii whose research found a strong Correlation between periodic patterns of undersea volcanoes (and related seismic activity) within what is known as the East Pacific Rise and the onset of El Niño, a phenomenon characterized by a warming of surface waters in the eastern Pacific Ocean near the Equator. While the causes surrounding the arrival of the El Niño effect are complex and not fully understood, it is generally recognized that the event is accompanied by a stall in the trade winds that normally blow from west to east across the southern Pacific. The Deep-Lava Theory postulates that heated seawater (from increased undersea lava flow activity) weakens a normally high-pressure area in the eastern Pacific. This, in turn, reduces air pressure and slows the trade winds. Subsequently, warm water in the western Pacific is released, along with warm unstable air above it, by the absence of the trade winds, thereby producing the El Niño effect along the western coast of South America, along with changes to other weather patterns elsewhere. For example, also see Hurricane Forecasting.

DEEP PERCOLATION (LOSS)—Water that percolates below the lower limit of the Root Zone of plants into a ground water aquifer and cannot be used by plants.

DEEP SEEPAGE (LOSSES)—That portion of applied irrigation water that, in excess of the leaching requirement, passes through the rooting zone and is subsequently unavailable for crop use.

DEEP-WATER—Of, relating to, or carried on in waters of a relatively great depth, for example, a deep-water port or a deep-water drilling for oil; Of, relating to, or characterized by water of considerable depth, especially water able to accommodate oceangoing vessels.

DEEPWATER HABITATS—(Ecology) In conjunction with Wetlands, Deepwater Habitats constitute the spectrum of an ecological classification system to better understand and describe the characteristics and values of all types of land and to wisely and effectively manage such ecosystems. Deepwater habitats are permanently flooded lands lying below the deepwater boundary of wetlands. Deepwater habitats include environments where surface water is permanent and often deep, so that water, rather than air, is the principal medium within which the dominant organisms live, whether or not they are attached to the substrate. As in wetlands, the dominant plants are hydrophytes; however, the substrates are considered nonsoil because the water is too deep to support emergent vegetation. While wetlands and deepwater habitats are defined separately, both must be considered in an ecological approach to classification. The deepwater habitat/wetland classification includes five major Systems:

[1] Marine [2] Estuarine [3] Riverine [4] Lacustrine [5] Palustrine

The first four of these classifications include both wetland and deepwater habitats, but the Palustrine Wetlands System includes only wetland habitats. Also see Wetlands and Wetlands, Palustrine. [See Appendix W-3 for an explanation of the Wetland and Deepwater Habitat Classification System.]

DEEP WELL—A well whose pumping head is too great to permit use of a suction pump.

DEEP-WELL DISPOSAL—Transfer of liquid wastewater to underground strata; usually limited to biologically or chemically stable wastes.

DEEP-WELL INJECTION—Deposition of raw or treated, filtered hazardous waste by pumping it into deep wells, where it is contained in the pores of permeable subsurface rock.

DEFLOCCULATE—To cause the particles of the disperse phase of a colloidal system to become suspended in the dispersion medium.

DEFLOCCULATING AGENT—A material added to a suspension to prevent settling.

DEFLUORIDATION—(Water Quality) A process by which the level of fluoride in a water is reduced to prevent mottling of teeth or fluorosis in consumers. Either activated alumina or bone charcoal is used in the process.

DEFOG—To remove condensed water vapor from a surface.

DEFROST—(1) To remove ice or frost from. (2) To cause to thaw.

DEGASIFICATION—A water treatment process that removes dissolved gases from the water.

DEGRADATION (River Beds or Stream Channels)—The general lowering of the streambed by erosive processes, such as scouring by flowing water. The removal of channel bed materials and downcutting of natural stream channels. Such erosion may initiate degradation of tributary channels, causing damage similar to that due to gully erosion and valley trenching.

DEGREE DAY—The difference, expressed in degrees, between the mean temperature for a given day and a reference temperature (usually 0°C).

DEGREE OF PROTECTION—The amount of protection that a flood control measure is designed for, i.e., 100-year, as determined by engineering feasibility, economic criteria, and social, environmental, and other considerations.

DEHUMIDIFY—To remove atmospheric moisture from.

DEHYDRATASE—(Biochemistry) An Enzyme that catalyzes the removal of oxygen and hydrogen from organic compounds in the form of water.

DEHYDRATE—(1) To remove bound water or hydrogen and oxygen from (a chemical compound) in the proportion in which they form water. (2) To remove water from (as foods). (3) To remove water from; make Anhydrous. (4) To Lose water or moisture; become dry.

DEHYDRATION—(1) The process of removing water from a substance or compound. (2) Excessive loss of water from the body or from an organ or a body part, as from illness or fluid deprivation.

DEHYDRATOR—(1) A substance, such as sulfuric acid, that removes water. (2) A container or an engineered system designed to remove water from substances such as absorbents or food.

DEICE—To make or keep free of ice; melt ice from.

DEICER—(1) A device used on an aircraft to keep the wings and propellers free from ice or to remove ice after it has formed. (2) A compound, such as ethylene glycol, used to prevent the formation of ice, as on windshields.

DEIONIZATION—The removal of all charged atoms or molecules from some material such as water. For example, the removal of salt from water involves the removal of sodium ions (Na+) and chloride ions (Cl-). The process commonly employs one resin that attracts all positive ions and another resin to capture all negative ions. Also see Capacitive Deionization.

DEIONIZE—To remove ions from water by Ion Exchange. See Deionization.

DEIONIZED WATER—Water that has been passed through resins that remove all ions. Also see Deionization.

DELAY TIME—Duration of time for contamination or water to move from point of concern to the well; analogous to time-of-travel.

DELEGATED STATE—A state (or other governmental entity such as a tribal government) that has received authority from the U.S. Environmental Protection Agency (EPA) to administer an environmental regulatory program in lieu of a federal counterpart. As used in connection with National Pollutant Discharge Elimination System (NPDES), Underground Injection Control (UIC), and Public Water System (PWS) programs, the term does not connote any transfer of federal authority to a state. Also see Primacy.

DELINEATION—The process of deciding where something, for example, the boundaries of a Wetland, begins and ends.

DELIQUESCE—(1) To melt away; to disappear as if by melting. (2) (Chemistry) To dissolve and become liquid by absorbing moisture from the air.

DELIQUESCENCE—The process whereby substances absorb water from the air, and eventually form solutions.

DELIVERY—(Irrigation) The release of water from turnouts to water users.

DELIVERY BOX—An irrigation structure for diverting water from a canal to a farm unit, often including measuring devices.

DELIVERY CONCEPT—The mode of making deliveries with respect to time; types are rotation, scheduled, or demand deliver concepts.

DELIVERY FLEXIBILITY—The flexibility that water users have in requesting delivery changes and the ability of the canal system to accommodate the request.

DELIVERY/RELEASE—The amount of water delivered to the point of use and the amount released after use; the difference between these amounts is usually the same as the Consumptive Use.

DELIVERY SYSTEM—A system which conveys water from a single source, such as a storage reservoir, to a number of individual points of use. The delivery system is a common classification. It is associated with irrigation, municipal and industrial use, and fish and wildlife canal systems.

DELTA—(1) An alluvial deposit made of rock particles (sediment and debris) dropped by a stream as it enters a body of water. (2) A plain underlain by an assemblage of sediments that accumulate where a stream flows into a body of standing water where its velocity and transporting power are suddenly reduced. Originally so named because many deltas are roughly triangular in plan, like the Greek letter delta (^), with the apex pointing upstream.

DELUGE—(1) A great flood. (2) A heavy downpour.

DEMAND (Water)—Maximum water use under a specified condition.

DEMAND DELIVERY—A method of irrigation water delivery whereby the project delivers water to the headgate upon farm irrigator demand; usually is associated with high head (cfs) delivery rates. Unrestricted use of the available water supply with limitations only on maximum flow rate and total allotment.

DEMAND MANAGEMENT ALTERNATIVES—Water management programs that reduce the demand for water, such as water conservation, drought rationing, rate incentive programs, public awareness and education, drought landscaping, etc.

DEMERSAL—(1) Dwelling at or near the bottom of a body of water, such as demersal fish. (2) Sinking to or deposited near the bottom of a body of water, such as demersal fish eggs.

DEMINERALIZATION, also Demineralize—The act or treatment process that removes dissolved minerals or mineral salts from a liquid, such as water.

DEMINERALIZED WATER—Water which has been passed through a mixed-bed ion exchanger to remove soluble ionic impurities. Nonelectrolytes and Colloids are not removed from water so treated. Also referred to as Deionized Water.

DEMOGRAPHICS—Relating to the statistical study of human populations to include such characteristics and factors as population counts, births, deaths, migration, sex, age, and related statistics.

DEMOGRAPHY—The statistical science dealing with the distribution, density, vital statistics, and other related characteristics of population. Demographics is the adjective describing the various characteristics of a population.

DENDRITIC—A drainage pattern in which tributaries branch irregularly in all directions from and at almost any angle to a larger stream. From an aerial view, it resembles the branching pattern of trees.

DENDROCHRONOLOGY—Dating an object by means of tree rings.

DENITRIFICATION—The removal of nitrate ions (NO3-) from soil or water; involves the Anaerobic biological reduction of nitrate to nitrogen gas. The process reduces desirable fertility of an agricultural field or the extent of undesirable aquatic weed production in aquatic environments. Also see Denitrifying Bacteria.

DENITRIFYING BACTERIA—Bacteria in soil or water that are capable of anaerobic respiration, using the nitrate ion as a substitute for molecular oxygen during their metabolism. The nitrate is reduced to nitrogen gas (N2), which is lost to the atmosphere during the process.

DENIZEN—(Ecology) An animal or a plant naturalized in a region.

DENSITY—(1) Matter measured as mass per unit volume expressed in pounds per gallon (lb/gal), pounds per cubic foot (lb/ft3), and kilograms per cubic meter (kg/m3). The mass of quantity of a substance per unit volume. (2) (Biology) The number per unit area of individuals of any given species at any given time. A term used synonymously with Population Density.

DENSITY CURRENT—A flow of water maintained by gravity through a large body of water, such as a reservoir or lake, which retains its identity because of a difference in density.

DENSITY STRATIFICATION—The arrangement of water masses into separate, distinct horizontal layers as a result of differences in density. Such differences may be caused by differences in temperature or dissolved and suspended solids. Also see Thermal Stratification.

DEOXYGENATE—To remove dissolved oxygen from a liquid, such as water.

DEPARTMENT OF CONSERVATION AND NATURAL RESOURCES [Nevada]—The mission of the Department is to conserve, protect, manage, and enhance the Nevada's natural resources in order to provide the highest quality of life for Nevada's citizens and visitors. The Department consists of nine divisions and/or agencies which include:

[1] Division of Conservation Districts—Regulates the activities of the state's locally elected conservation districts which work for the conservation and proper development of the state's renewable natural resources by providing services to individual landowners and coordination with other public and private agencies. [2] Division of Environmental Protection (DEP)—Responsible for the administration and enforcement of all environmental statutes and regulations; issues permits, monitors for air and water pollution and inspects solid and hazardous waste management. The Division consists of the Bureau of Air Quality, the Bureau of Water Pollution Control, Bureau of Mining Regulation and Reclamation, Bureau of Water Quality Planning, Bureau of Corrective Actions, Bureau of Waste Management, and the Bureau of Federal Facilities. The State Environmental Commission is also part of the Division and is responsible for adopting necessary environmental rules, regulations and plans authorized by statute. [See Appendix E-3 for a more complete description of DEP's functional responsibilities.] [3] Division of Forestry—Manages and coordinates all forestry, nursery, endangered plant species and watershed resource activities on certain public and private lands; responsible for protecting structural and natural resources through fire protection, prevention and suppression. The Division also conducts the Forestry Conservation Camps Program which coordinates and supervises the outside work performed by inmates residing in Department of Prison conservation camps. [4] Division of State Lands—Acquires, holds, and disposes of all state lands and interests in lands; provides technical land-use planning assistance, training, and information to local units of government or other agencies; develops policies and plans for the use of lands under federal management and represents the state in its dealings with the federal land management agencies. [5] Division of State Parks—Plans, develops, and maintains a system of parks and recreational areas for the use and enjoyment of residents and visitors. The Division also preserves areas of scenic, historic, and scientific significance in Nevada. [6] Division of Water Planning—Provides technical, financial and economic assistance to government agencies and individual citizens concerning regional and local water supplies; develops and implements a statewide water resource management plan and policy initiatives on a watershed basis; conducts hydrologic, climatologic, and socioeconomic data collection, research, modeling, forecasting and data analysis; develops and implements water resource public information and education programs; provides technical and financial assistance and outreach programs to assist local governments, watershed planning groups, and other agencies with respect to water resource matters; and develops and implements a statewide water conservation program. [7] Division of Water Resources—Responsible for protecting the health and safety of Nevada citizens through the appropriation of public waters. Other responsibilities include the adjudication of claims of vested water rights; distribution of water in accordance with court decrees; review of water availability for new major construction and housing projects; review of the construction and operation of dams; appropriation of geothermal resources; licensing of well drillers and water right surveyors; review of flood control projects; maintenance of water resource data and records; and providing technical assistance to government boards, offices, and agencies. [8] Division of Wildlife—Preserves, protects, manages and restores wildlife and its habitat within the state for aesthetic, scientific, recreational and economic benefits; tasked with promoting safety for persons and property in the operation of equipment and boating vessels [9] Natural Heritage Program—Serves as a centralized repository containing detailed information on sensitive (threatened and endangered) species of animals, plants, and communities; provides information on biology, habitats, locations, population and conservation status, and management needs.

(UNITED STATES) DEPARTMENT OF THE INTERIOR (USDI)—Originally established by Congress in 1849 as the executive department of the United States government, the USDI's function has changed from that of performing housekeeping duties for the federal government to its present role as custodian of the nation's natural resources. As the nation's principal conservation agency, the USDI has the responsibility of protecting and conserving the country's land, water, minerals, fish, and wildlife; of promoting the wise use of all these natural resources; of maintaining national parks and recreation areas; and of preserving historic places. It also provides for the welfare of American Indian reservation communities and of inhabitants of island territories under U.S. administration. As of 1988 the USDI managed more than 220 million hectares (550 million acres, or 850,000 square miles) of federal resource lands; about 340 units of the national park system; 70 fish hatcheries, and 442 National Wildlife Refuges (NWF); and numerous reclamation dams that provide water, electricity, and recreation. The USDI also constructs irrigation works, enforces mine safety laws, makes geological surveys and prepares maps, conducts mineral research, and administers wild and scenic rivers as well as national and regional trails. The USDI is currently in charge of the Bureau of Indian Affairs (BIA), the U.S. Fish and Wildlife Service (USFWS), the National Park Service (NPS), and the U.S. Geological Survey (USGS). It also oversees the Bureau of Mines, which is responsible for ensuring that the nation has adequate mineral supplies and for overseeing and evaluating all aspects of minerals research; the U.S. Bureau of Land Management (BLM), which manages public lands and their resources; the U.S. Bureau of Reclamation (USBR), which assists local governments in reclaiming arid lands in western states and provides programs for hydro-electric power generation, flood control, and river regulation; the Minerals Management Service, which deals with leasable minerals on the Outer Continental Shelf and ensures efficient recovery of mineral resources; and the Office of Surface Mining Reclamation and Enforcement, which helps to protect the environment from adverse effects of mining operations. Other agencies under the USDI's jurisdiction include the Office of Small and Disadvantaged Business Utilization and the Office of Territorial and International Affairs.

DEPARTMENT OF WATER RESOURCES (DWR) [California]—The California state agency within The Resources Agency that is responsible for long-term water planning, operation of the State Water Project, and state water conservation programs. The basic goal of the DWR is to ensure that California's needs for water supplies, water-related recreation, fish and wildlife, hydroelectric power, prevention of damage and loss of life from floods and dam failure, and water-related environmental enhancements are met; and to ensure that the manner in which these needs are fulfilled is consistent with public desires and attitudes concerning environmental and social considerations. The California Water Commission, also within The Resources Agency, serves as a policy advisory body to the Director of the DWR on matters within the department's jurisdiction and coordinates state and local views on federal appropriations for water projects in California. The commission also conducts public hearings and investigations statewide for the department and provides an open forum for interested citizens to voice on water development issues. The California State Water Resources Control Board (SWRCB), located within the California Environmental Protection Agency, is assigned the responsibility to protect water quality and allocate water rights.

DEPAUPERATE—(Biology) An area poor in species quantities and/or diversity; an aquatic sample showing few life forms. Impoverished habitat.

DEPENDABLE SUPPLY—That water which can be expected to be available at a time and place with the quality demanded; sometimes the amount of water available is at a stated percentage of time.

DEPENDABLE YIELD—The maximum annual supply of a given water development that is expected to be available on demand, with the understanding that lower yields will occur in accordance with a predetermined schedule or probability. More frequently referred to as Firm Yield.

DEPLETION—The water consumed within a service area or no longer available as a source of supply; that part of a withdrawal that has been evaporated, transpired, incorporated into crops or products, consumed by man or livestock, or otherwise removed. For agriculture and wetlands, it is the Evapotranspiration of Applied Water (ETAW) (and Evapotranspiration (ET) of flooded wetlands) plus irrecoverable losses. For urban water use, it is the ETAW (water applied to landscaping or home gardens), sewage effluent that flows to a salt sink, and incidental ET losses. For instream use, it is the amount of dedicated flow that proceeds to a salt sink and is not available for reuse.

DEPLETION (GROUND WATER)—The withdrawal of water from a ground water source at a rate greater than its rate of recharge, usually over an extended period of several years.

DEPLETION (STREAMFLOW)—The amount of water that flows into a valley, or onto a particular land area, minus the water that flows out of the valley or off from the particular land area.

DEPLETION (WATER)—That portion of the water supply that is consumptively used.

DEPLETION CURVE—(Hydraulics) A graphical representation of water depletion from storage-stream channels, surface soil, and groundwater. A depletion curve can be drawn for base flow, direct runoff, or total flow.

DEPOSIT—Something dropped or left behind by moving water, as sand or mud.

DEPOSITING SUBSTRATES—Bottom areas where solids are being actively deposited; often occurring in the vicinity of effluent discharges.

DEPOSITION—The accumulation of material dropped because of a slackening movement of the transporting medium, e.g., water or wind. Also, the transition of a substance from the vapor phase directly to the solid phase, without passing through an intermediate liquid phase, also referred to as Sublimation.

DEPRESSION STORAGE—Water contained in natural depressions in the land surface, such as puddles.

DEPTH, often Depths—A deep art of place, as the ocean depths.

DEPTH-AREA-DURATION ANALYSIS—Determination of the maximum amounts of precipitation within various durations over areas of various sizes; used to predict flood events.

DEPTH FINDER—An instrument used to measure the depth of water, especially by radar or ultrasound.

DEPTH OF RUNOFF—The total runoff from a drainage basin divided by its area. For convenience in comparing runoff with precipitation, depth of runoff is usually expressed in inches during a given period of time over the drainage area expressed in inches per square mile.

DEPTH SOUNDER—An ultrasonic instrument used to measure the depth of water under a ship.

DEPURATION—A process during which an organism, such as an oyster or clam, eliminates dangerous chemicals or microorganisms when placed in uncontaminated water.

DERELICT—(Legal) Land left dry by a permanent recession of the water line.

DERELICTION—(Legal) (1) A gaining of land by the permanent recession of the water line. (2) The land so gained. Also see Reliction and Doctrine of Reliction.

DESALINATION, or Desalinization—To remove salts and other chemicals, as from sea water or soil, for example. Usually used with respect to the salt contained in water. Also referred to as Desalting.

DESALINIZE—See Desalination or Desalinization.

DESALTING—The term used to refer to any process by which the dissolved solids content of saline water or seawater is reduced. Also known as Desalination, Desalinization, or Saline Water Conversion.

DE-SEASONALIZATION—(Statistics) A process which removes the seasonal effects from time series data. One way to determine if a de-seasonalization transformation of the data is necessary is to examine the autocorrelations. If, for monthly data, the twelfth autocorrelation is abnormally high, or for quarterly data, the fourth autocorrelation abnormally high, then the data is seasonal in nature and requires de-seasonalization before attempting to fit a model to its behavior. More frequently referred to as Seasonal Adjustment (S.A.). Also see Seasonal Adjustment, Seasonal Adjustment Factors, Seasonal Factors, and Seasonality.

DESERT—A barren or desolate area, especially one characterized by dry, often sandy conditions of little rainfall, typically less than 10 inches of rain per year, extreme temperatures, and sparse vegetation. Also see Biome.

DESERTIFICATION—The transformation of arable or habitable land to desert, as by a change in climate or destructive land use. The term is generally applied to the production of artificial deserts where people have intensified the problems caused by droughts through overgrazing marginal land, repeated burning of natural vegetation, intensive farming of arid land, aggressive removal of trees, and prolonged irrigation of arid land for agricultural use.

DESERT RESEARCH INSTITUTE (DRI) [Nevada]—The Desert Research Institute was created in 1959 by an act of the Nevada Legislature as a unit of the University of Nevada. When the University of Nevada System was formed in 1968, DRI became an autonomous, nonprofit division of this system. Since that time DRI has grown to be one of the world's largest multi-disciplinary environmental research organizations focusing on arid lands. The DRI operates from statewide facilities in Las Vegas, Reno, Stead, Laughlin, and Boulder City. The DRI's activities are directed from five research centers representing the Geosphere (Quaternary Sciences Center), Hydrosphere (Water Resources Center), Biosphere (Biological Sciences Center), and Atmosphere (Atmospheric Sciences Center and Energy and Environmental Engineering Center). Multi-disciplinary teams drawn from these centers are assembled to address basic and applied research problems on a project-by-project basis. Listed below are the DRI's five research centers and their primary mission statement:

[1] Atmospheric Sciences Center (ASC)—The ASC is a nationally recognized leader in the field of atmospheric sciences. The ASC's mission is to improve the fundamental understanding of the earth's atmosphere, particularly as it relates to the weather and to the climate of arid regions. The ASC is the home of the strongest atmospheric modification research program in the United States. [2] Biological Sciences Center (BSC)—The BSC focuses on plant and soil biology from an ecological perspective. The BSC's mission is to improve the fundamental understanding of the earth's biosphere, thereby providing the knowledge needed to effectively manage biological resources important to the future use and habitation of the earth. [3] Energy and Environmental Engineering Center (EEEC)—The EEEC largely conducts air resources research. The EEEC's mission is to conduct high-quality research to understand current and future human impacts on the environment, especially air quality, an the technology that can be applied to mitigate these impacts. [4] Quaternary Sciences Center (QSC)—The QSC is one of approximately 15 Quaternary research programs worldwide. The QSC's mission is to improve the fundamental understanding of past climates and associated environmental responses and human adaptations to climate change during the Quaternary Period (covering the last 1.8 million years). V [5] Water Resources Center (WRC)—The WRC is the largest water research group focused on arid lands in the United States. The WRC's mission to improve the fundamental understanding and knowledge of hydrologic systems, with special emphasis on arid lands, for more effective management of hydrologic resources.

[See Appendix D-6 for a more complete listing of the DRI's major laboratories operated and the principal skills and activities supported.]

DESERT NATIONAL WILDLIFE REFUGE (NWR) [Nevada]—One of the nine National Wildlife Refuges (NWR) located in the State of Nevada, the Desert NWR was established in 1936 and covers 1,588,459 acres (2,482 square miles) of the diverse Mohave Desert in southern Nevada and is the largest National Wildlife Refuge in the 48 contiguous United States. The Desert NWR's most important objective is the perpetuation of the desert bighorn sheep and its habitat. The refuge contains six major mountain ranges, the highest rising from a 2,500 foot elevation valley floor to nearly 10,000 feet. The dry climate and varying elevations provide varied plant life with creosote bush and white bursage dominant in the lower elevations, Mojave yucca and cactus dominant in the mid-elevations, blackbrush and Joshua trees prevalent near 6,000 feet, and single-leaf pinyon and Utah juniper become prominent at 6,000 feet. From 7,000-9,000 feet Ponderosa pine and white fir become dominant and near 10,000 feet the only remaining tree is the bristlecone pine. Throughout this area the big sagebrush is the most common shrub. Within this refuge, and in stark contrast to the typical habitat and wildlife prevalent throughout the refuge, are the numerous and diverse plant and animal communities at Corn Creek. Here springs turn the desert into an oasis attracting over 200 species of birds alone. Also see National Wildlife Refuge (NWR) System and National Wildlife Refuges (NWR) [Nevada].

DESICCANT—A substance, such as calcium oxide or silica gel, that has a high affinity for water and is used as a drying agent.

DESICCATE—(1) To dry out thoroughly. (2) To preserve (foods) by removing moisture.

DESICCATION—(1) Loss of water from pore spaces of sediments through compaction or through evaporation caused by exposure to air. (2) (Geology) Used to refer to a long period of time between Pluvial (wet) episodes.

DESICCATION CRACKS—Surface fractures that can result from the drying of soil or porous sedimentary rock.

DESIGN CAPACITY—The average daily flow that a water or wastewater treatment plant or other facility is designed to accommodate.

DESIGN FLOOD—The flood magnitude selected for use as a criterion in designing flood control works. The largest flood that a given project is designed to pass safely. In dam design and construction, the reservoir inflow-outflow hydrograph used to estimate the spillway discharge capacity requirements and corresponding maximum surcharge elevation in the reservoir.

DESIGN FLOW—The average flow of wastewater that a treatment facility is built to process efficiently, commonly expressed in millions of gallons per day (MGD).

DESIGN RUNOFF RATE—In irrigation, the maximum runoff rate expected over a given period of time.

DESIGNATED FLOODWAY—The channel of a stream and the portion of the adjoining floodplain designated by a regulatory agency to be kept free of further development to provide for unobstructed passage of flood flows.

DESIGNATED GROUNDWATER BASIN—A basin where permitted ground water rights approach or exceed the estimated average annual recharge and the water resources are being depleted or require additional administration. Under such conditions, a state's water officials will so designate a groundwater basin and, in the interest of public welfare, declare Preferred Uses (e.g., municipal and industrial, domestic, agriculture, etc.). Also referred to as Administered Groundwater Basin.

DESIGNATED GROUNDWATER BASIN [Nevada]—In the interest of public welfare, the Nevada State Engineer, Division of Water Resources, Department of Conservation and Natural Resources, is authorized by statute (Nevada Revised Statute 534.120) and directed to designate a ground water basin and declare Preferred Uses within such designated basin. The State Engineer has additional authority in the administration of the water resources within a designated ground water basin. [A listing of Nevada's designated Hydrographic Areas and Hydrographic Sub-Areas is presented in Appendix D-1 (listed sequentially by Hydrographic Area number and Hydrographic Region/Basin), Appendix D-2 (listed alphabetically by Hydrographic Area and Sub-Area name), and Appendix D-3 (listed alphabetically by principal Nevada county(ies) in which located).]

DESIGNATED USES—Those water uses identified in state water quality standards that must be achieved and maintained as required under the Clean Water Act (CWA). Such uses may include cold water fisheries, public water supply, irrigation, recreation, minimum stream flows, etc.

DESIGNATED WATERSHEDS—Watershed areas that have been set aside as sources of municipal water or other similar purposes would be included in this category. Other uses are either modified or excluded.

DESIGNER BUGS—A popular term for Microbes developed through Biotechnology that can degrade specific toxic chemicals at their source in toxic waste dumps, in ground water, or on the land surface. May also be useful in cleaning (decomposing) oil spills.

DESILTING AREA—An area of grass, shrubs, or other vegetation used for inducing the deposition of silt and other debris from flowing water. Typically located above a stock tank, pond, field, or other area needing protection from sediment accumulation.

DESORPTION—The removal of a substance adsorbed to the surface of an adsorbent. Also see Sorption, which is the reverse process.

DESTRATIFICATION—Vertical mixing within a lake or reservoir to totally or partially eliminate separate layers of temperature, plant, or animal life.

DETACHMENT—The removal of transportable fragments of soil material from a soil mass by an eroding agent, usually falling raindrops, running water, or wind. Through this process, soil particles or aggregates are made ready for transport, the first stage in soil erosion.

DETECTABLE LEAK RATE—The smallest leak (from a storage tank), expressed in terms of gallons or liters per hour, that a test can reliably discern with a certain probability of detection or false alarm.

DETECTION CRITERION—A predetermined rule to ascertain whether a tank is leaking or not. Most volumetric tests use a threshold value as the detection criterion. Also see Volumetric Tank Tests.

DETECTION MONITORING PROGRAM—Groundwater monitoring at the boundary of a treatment, storage, or disposal facility (the point of compliance) to detect any contamination caused by leaks from the hazardous waste at the facility. The materials for which the samples must be analyzed (the indicator parameters/constituents) are specified in the facility permit.

DETENTION DAM—A dam constructed for the purpose of temporary storage of streamflow or surface runoff and for releasing the stored water at controlled rates.

DETENTION BASIN—A relatively small storage lagoon for slowing stormwater runoff, generally filled with water for only a short period of time after a heavy rainfall. Also see Retention Basin.

DETENTION FACILITY—A surface water runoff storage facility that is normally dry but is designed to hold (detain) surface water temporarily during and immediately after a runoff event. Examples of detentional facilities are: natural swales provided with crosswise earthen berms to serve as control structures, constructed or natural surface depressions, subsurface tanks or reservoirs, rooftop storage, and infiltration or filtration basins. Also see Retention Facility.

DETENTION STORAGE—The volume of water, other than depression storage, existing on the land surface as flowing water which has not yet reached the channel.

DETENTION STRUCTURE (DAM)—A structure constructed for the temporary storage of floodflows where the opening for release is of a fixed capacity and not manually operated.

DETENTION TIME—(1) The theoretical calculated time required for a small amount of water to pass through a tank at a given rate of flow. (2) The actual time that a small amount of water is in a settling basin, flocculating basin, or rapid-mix chamber. (3) In storage reservoirs, the length of time water will be held before being used.

DETERGENT—Synthetic washing agent that helps to remove dirt and oil. Some contain compounds which kill useful bacteria and encourage algae growth when they are in wastewater that reaches receiving waters.

DETERMINISTIC PROCESS—(Statistics) An analytical and forecasting technique which assumes that the future can be predicted exactly from its past. Consequently, it is assumed that the data series to be forecasted contains all the information necessary to predict its future behavior. A deterministic process or relationship is assumed to be "exact", and therefore assumes no presence of a Disturbance (or Error) Term. The simplest form of this process is commonly termed an AutoRegressive Moving Average (ARMA) Process, or Box-Jenkins, which involves regressing a series on itself and using solely the historical patterns contained in the data to formulate forecasts. As a naive method, such a process does not include the capability to incorporate external "shocks" or other influences which may have an effect on the future behavior of a series. Such a technique is typically used only for well-behaved data showing typically predictable repetitive cycles and patterns. Contrast with Stochastic Process.

DETRITAL—(Geology) Clastic; rock and minerals occurring in sedimentary rocks that were derived from pre-existing igneous, sedimentary, or metamorphic rocks.

DETRITUS—(1) The heavier mineral debris moved by natural water courses, usually in the form of Bed Load. (2) The sand, grit, and other coarse material removed by differential sedimentation in a relatively short period of detention.

DEUTERIUM OXIDE—An isotopic form of water with composition D2O, isolated for use as a moderator in certain nuclear reactors. Also referred to as Heavy Water. Also see Heavy Water Moderated Reactor and Light Water Reactor (LWR).

DEVIATION, STANDARD—(Statistics) A measure of the average variation of a series of observations or items of a population about their mean. In a normally distributed set of observations the interval of the mean plus or minus one standard deviation includes about two-thirds of the observations.

DEW—The droplets of water condensed from air, usually at night, onto cool surfaces.

DEWATER, and Dewatering—(1) To remove water from a waste produce or streambed, for example. (2) The extraction of a portion of the water present in sludge or slurry, producing a dewatered product which is easier to handle. (3) (Mining) The removal of ground water in conjunction with mining operations, particularly open-pit mining when the excavation has penetrated below the ground-water table. Such operations may include extensive ground-water removal and, if extensive enough and if not re-injected into the groundwater, these discharges may alter surface water (stream) flows and lead to the creation of lakes and wetland areas. As such water removals only last so long as the mine is in operation, eventually surface water impacts, if present, will be eliminated, consequently jeopardizing surface water uses, such as irrigation, livestock, wildlife, or riparian habitat that may have become dependent upon the continuation of these temporary flows. Also, when the mine dewatering operations cease, the remaining open pit will eventually begin to fill up with ground water, resulting in significantly increased evaporation from ground water reservoirs.

DEW POINT—The temperature at which a gas or vapor condenses to form a liquid; the point at which dew begins to form.

DIADROMOUS—Relating to a fish that migrates between salt and fresh waters.

DIASTROPHIC—(Geology) Pertaining to processes by which the earth's crust is deformed, producing continents, oceans, basins, mountains, and other Geophysical features. Also see Orogenic and Tectonic.

DIATOM—Any of the microscopic unicellular or colonial algae constituting the class Bacillarieae. They have a silicified cell wall, which persists as a skeleton after death and forms kieselguhr (loose or porous diatomite). Diatoms occur abundantly in fresh and salt waters, in soil, and as fossils. They form a large part of the Plankton.

DIATOMA—A small genus of fresh-water diatoms typifying the family Diatomaceae. They sometimes cause aromatic or disagreeable odors in water.

DIATOMACEOUS EARTH—A yellow, white or light-gray material composed of the siliceous shells of Diatoms (fossilized diatoms) and used in water filtration to filter out solid waste in wastewater treatment plants; also used as an active ingredient in some powdered pesticides. Also referred to as Diatomite.

DIATOMITE—See Diatomaceous Earth.

DIFFUSED AIR—(Water Quality) A type of aeration that forces oxygen into sewage by pumping air through perforated pipes inside a holding tank.

DIFFUSION—The movement of a substance from an area of high concentration to an area of low concentration. Turbulent diffusion results from atmospheric motions diffusing water, vapor, heat, and other gaseous components by exchanging parcels called eddies between regions in space in apparent random fashion.

DIFFUSION COEFFICIENT—(1) The rate at which solutes are transported at the microscopic level due to variations in the solute concentrations within the fluid phases. (2) The rate of dispersion of a chemical caused by the kinetic activity of the ionic or molecular constituents. Also referred to as the Coefficient of Molecular Diffusion. See Molecular Diffusion.

DIFFUSIVITY, SOIL WATER—The hydraulic conductivity divided by the differential water capacity, or the flux of water per unit gradient of moisture content in the absence of other force fields.

DIGESTER—(Water Quality) In a Wastewater Treatment Plant, a closed tank that decreases the volume of solids and stabilizes raw sludge by bacterial action.

DIGESTER GAS—The gas produced as a result of the microbial decomposition of particulate organic matter under Anaerobic conditions. Methane and hydrogen are major components.

DIGESTION—(General) The biochemical decomposition of organic matter, resulting in partial gasification, liquefaction, and mineralization of pollutants. (Water Quality) In wastewater treatment, the biological decomposition of organic matter in sludge.

DIKE—(1) (Engineering) An embankment to confine or control water, especially one built along the banks of a river to prevent overflow of lowlands; a levee. (2) A low wall that can act as a barrier to prevent a spill from spreading. (3) (Geology) A tabular body of igneous (formed by volcanic action) rock that cuts across the structure of adjacent rocks or cuts massive rocks.

DILUENT—A substance used to dilute a solution or suspension.

DILUTE—To make thinner or less concentrated by adding a liquid such as water.

DILUTION—The reduction of the concentration of a substance in air or water.

DILUTION FACTOR—The extent to which the concentration of some solution or suspension has been lowered through the addition of a Diluent.

DILUTION RATIO—(Water Quality) The ratio of the volume of water in a stream to the volume of incoming waste. The capacity of a stream to assimilate waste is reflected in the dilution ratio.

DILUVIAL, also Diluvian—Of, relating to, or produced by a flood.

DIMICTIC LAKE (or Reservoir)—A stratified lake or reservoir that experiences two periods of full mixing or (Fall and Spring) Overturns annually. The water in lakes layer in response to differences in the temperatures of surface and deep waters. The surface water will be warmer because of radiant heating by the sun, and the bottom water will be cooler and therefore denser. The waters in these two layers (termed the Epilimnion on the surface and Hypolimnion on the bottom) are separated by a boundary referred to as the Thermocline. This layering is disrupted in response to variation in air temperature associated with changes in the seasons of the year. As the epilimnion cools, it sinks, mixing the water within the lake. Contrast with Meromictic Lake.

DIOXIN—Any of several carcinogenic or teratogenic heterocyclic hydrocarbons that occur as impurities in petroleum-derived herbicides and through over-use or runoff may threaten both surface and groundwater supplies. Dioxin has been linked to cancer, damage to the immune system, and other serious health conditions. It is also produced in paper mills when chlorine is mixed with wood pulp to brighten paper. Dioxin ends up in the mills' wastewater, which is then discharged into rivers.

DIP—To plunge briefly into a liquid, as in order to wet, coat, or saturate. Synonymous with Dunk.

DIPPER—One that dips, especially a container for taking up water.

DIQUAT—A strong, non-persistent, yellow, crystalline herbicide, C12H12Br2N2, used to control water weeds.

DIRECT DISCHARGER—A municipal or industrial facility which introduces pollution through a defined conveyance or system such as outlet pipes; a point source.

DIRECT FILTRATION—(Water Quality) A method of treating water which consists of the addition of coagulant chemicals, flash mixing, coagulation, minimal flocculation, and filtration. Sedimentation is not used in this process.

DIRECT PRECIPITATION—Water that falls directly into a lake or stream without passing through any land phase of the runoff cycle.

DIRECT RUNOFF—The runoff entering stream channels most immediately after rainfall or snowmelt. It consists of surface runoff plus interflow and forms the bulk of the Hydrograph of a flood. Direct runoff plus Base Runoff compose the entire flood hydrograph.

DIRECT WATER USES—Uses of water that are apparent, for example, washing, bathing, cooking, etc.

DISASTER AREA—An area that officially qualifies for emergency governmental aid as a result of a catastrophe, such as an earthquake or a flood.

DISCHARGE (HYDROLOGIC)—In its simplest concept, discharge means outflow and is used as a measure of the rate at which a volume of water passes a given point. Therefore, the use of this term is not restricted as to course or location, and it can be used to describe the flow of water from a pipe or a drainage basin. With reference to groundwater, the process by which groundwater leaves the Zone of Saturation via Evaporation, Evapotranspiration, or by flow to the surface through springs and seeps. The data in the reports of the U.S. Geological Survey (USGS) on surface water represent the total fluids measured. Thus, the terms discharge, streamflow, and runoff represent water with the solids dissolved in it and the sediment mixed with it. Of these terms, discharge is the most comprehensive. The discharge of drainage basins is distinguished as follows:

[1] Yield—The total water runout or "water crop" and includes runoff plus underflow; [2] Runoff—That part of water yield that appears in streams; and [3] Streamflow—The actual flow in streams, whether or not subject to regulation or underflow.

Each of these terms can be reported in total volumes (e.g., acre-feet) or time-related rates of flow (e.g., cubic feet per second or acre-feet per year).

DISCHARGE AREA—(1) An area in which ground water is discharged to the land surface, surface water, or atmosphere. (2) An area in which there are upward components of hydraulic head in the aquifer. Ground water is flowing toward the surface in a discharge area and may escape as a spring, seep, or base flow, or by evaporation and transpiration.

DISCHARGE, AVERAGE—The arithmetic average of the annual discharges for all complete water years of record whether or not they are consecutive. The term average is generally reserved for average of record and mean is used for averages of shorter periods; namely, daily mean discharge.

DISCHARGE COEFFICIENT—(Hydraulics) The ratio of actual rate of flow to the theoretical rate of flow through orifices, weirs, or other hydraulic structures.

DISCHARGE CURVE—A curve that expresses the relation between the discharge of a stream or open conduit at a given location and the stage or elevation of the liquid surface at or near that location. Also called Rating Curve and Discharge Rating Curve.

DISCHARGE FORMULA—(Hydraulics) A formula used to calculate the rate of flow of fluid in a conduit or through an opening. For a steady flow discharge,

Q = A V

where Q is the rate of flow, A is the cross-sectional area, and V is the mean velocity. Common units are cubic feet per second.

DISCHARGE MEASUREMENT—Total discharge is equal to the cross-sectional area of the water in a channel or pipe times its average velocity.

DISCHARGE PERIOD—The period of time during which effluent is discharged.

DISCHARGE PERMIT—A permit issued by the state to discharge effluent into waters of the state.

DISCHARGE POINT—A location at which effluent is released into a receiving stream or body of water.

DISCHARGE PROBABILITY RELATIONSHIP—A graph of annual instantaneous peak discharge (or other hydrologic quantity) on the vertical axis, versus probability and/or recurrence interval on the horizontal axis. The graph provides a means of estimating the flow that will be reached or exceeded in a given year at a specified probability, or a means of estimating the probability that a specified discharge will be reached or exceeded in a given year.

DISCHARGE, SEDIMENT—The rate at which sediment passes a section of a stream or the quantity of sediment, as measured by dry weight or by volume, that is discharged in a given time.

DISCHARGE VELOCITY—An apparent velocity, calculated by Darcy's Law, which represents the flow rate at which water would move through an aquifer if the aquifer were an open conduit. Also referred to as Specific Discharge.

DISCOUNT RATE—The interest rate used in evaluating water (and other) projects to calculate the present value of future benefits and future costs or to convert benefits and costs to a common time basis (e.g., current dollars).

DISEMBOGUE—To discharge or pour fourth; to flow out or empty, as water from a channel.

DISINFECTANT—A chemical or physical process that kills pathogenic organisms in water. Chlorine is often used to disinfect sewage treatment effluent, water supplies, wells, and swimming pools.

DISINFECTANT AND DISINFECTION BY-PRODUCT RULE (D/DBP)—The rule promulgated by the U.S. Environmental Protection Agency (EPA) that would require water suppliers to reduce the levels of Disinfection By-Products found in treated drinking water. State 1 of the rule has been delayed until at least the year 2000 with State 2 following in 2003.

DISINFECTANT BY-PRODUCT—A compound formed by the reaction of a Disinfectant such as Chlorine with organic material in the water supply. See Disinfection By-Products.

DISINFECTANT TIME—The time it takes water to move from the point of Disinfectant application (or the previous point of residual disinfectant measurement) to a point before or at the point where the residual disinfectant is measured.

DISINFECTION—(Water Quality) The process of killing a large portion of microorganisms in or on a substance, but not bacterial spores. The primary of disinfection in water and wastewater treatment is to kill or render harmless microbiological organisms that cause disease. At the present time Chlorination is the most important disinfection option for drinking water treatment for the foreseeable future; however, other viable disinfection processes include Ozonation and Ultraviolet Radiation (UV).

DISINFECTION BY-PRODUCTS—Chemicals which are formed when a disinfectant such as Chlorine is added to water that contains organic matter, usually from decaying plant or animal material. Such by-products are suspected to be human Carcinogens. One typical such disinfection by-product for which the U.S. Environmental Protection Agency (EPA) has established Maximum Contaminant Levels (MCLs) as part of its enforcement of the Safe Drinking Water Act (SDWA) are total Trihalomethanes (TTHMs).

DISPERSANT—A chemical agent used to break up concentrations of organic material such as spilled oil on a water surface.

DISPERSION—The spreading and mixing of chemical constituents in both surface and ground waters caused by diffusion and mixing due to microscopic variations in densities and velocities.

DISPERSION COEFFICIENT—A measure of the spreading of a flowing substance due to the nature of the porous medium (and specific substance or fluid properties), with interconnected channels distributed at random in all directions. Also equals the sum of the Coefficient of Mechanical Dispersion and the Coefficient of Molecular Diffusion in a porous medium.

DISPERSIVITY—A property of a porous medium (and the specific substance or fluid) that determines the dispersion characteristics of the contaminant in that medium by relating the components of pore velocity to the Dispersion Coefficient.

DISPLACEMENT—(Geology) The distance by which portions of the same geological layer are offset from each other by a fault.

DISPLACEMENT TON—(Nautical) A unit for measuring the displacement of a ship afloat, equivalent to one long ton or about one cubic meter of salt water.

DISPOSAL—The transference of unwanted material, such as wastes, to a new entity, a new place, or a new form.

DISPOSAL FIELD—Area used for spreading liquid effluent for separation of wastes from water, degradation of impurities, and improvement of drainage waters. Also referred to as Infiltration Field or Septic Tank Absorption Field.

DISPOSAL POND—A small, usually diked, enclosure that is open to the atmosphere and into which a liquid waste is discharged. Also see Lagoon.

DISPOSAL SYSTEM—A system for the disposing of wastes, either by surface or underground methods; includes sewer systems, treatment works, disposal wells, and other systems.

DISPOSAL WELL—A deep well used for the disposal of liquid wastes.

DISSOLUBLE—That can be dissolved, e.g., dissoluble airborne pollutants brought back to the earth as rain.

DISSOLVE—A condition where solid particles mix, molecule by molecule, with a liquid and appear to become part of the liquid.

DISSOLVED LOAD—All the material transported by a stream or river in solution, as contrasted with Bed Load and Suspended Load.

DISSOLVED ORGANIC CARBON (DOC)—A measure of the organic compounds that are dissolved in water. In the analytical test for DOC, a water sample is first filtered to remove particulate material, and the organic compounds that pass through the filter are chemically converted to carbon dioxide, which is then measured to compute the amount of organic material dissolved in the water.

DISSOLVED ORGANIC COMPOUNDS—Carbon substances dissolved in water.

DISSOLVED OXYGEN (DO)—The amount of free (not chemically combined) oxygen dissolved in water, wastewater, or other liquid, usually expressed in milligrams per liter, parts per million, or percent of saturation. Adequate concentrations of dissolved oxygen are necessary for the life of fish and other aquatic organisms and the prevention of offensive odors. Dissolved oxygen levels are considered the most important and commonly employed measurement of water quality and indicator of a water body's ability to support desirable aquatic life. The ideal dissolved oxygen level for fish is between 7 and 9 milligrams per liter (mg/l); most fish cannot survive at levels below 3 mg/l of dissolved oxygen. Secondary and advanced wastewater treatment techniques are generally designed to ensure adequate dissolved oxygen in waste-receiving waters.

DISSOLVED SOLIDS—The dissolved mineral constituents or chemical compounds in water or solution; they form the residue that remains after evaporation and drying. Excessive amounts of dissolved solids make water unfit to drink or use in industrial processes.

DISSOLVED SOLIDS CONCENTRATION—For water this concentration is determined either analytically by the "residue-on-evaporation" method, or mathematically by totaling the concentrations of individual constituents reported in a comprehensive chemical analysis.

DISTILLATE—A liquid condensed from vapor in Distillation.

DISTILLATION—The separation of different substances in a solution by boiling off those of a lower boiling point first. For example, water can be distilled and the steam condensed back into a liquid that is almost pure water. The impurities (minerals) remain in the concentrated residue. In waste treatment, distillation consists of heating the effluent and then removing the vapor or steam. When the steam is returned to a liquid, it is almost pure (distilled) water. The pollutants remain in the concentrated residue.

DISTILLED WATER (DW)—Water that has been purified by the Distillation process. Water that contains various chemicals or ions in solution is heated to boiling and the water vapor is condensed. The process leaves behind various inorganic ions and results in a water that is free of dissolved salts.

DISTRIBUTARY—A diverging stream which does not return to the main stream, but discharges into another stream or the ocean. Also refers to conduits that take water from a main canal for delivery to a farm. See Distributary Channel or Stream.

DISTRIBUTARY CHANNEL (or Stream)—A river branch that flows away from a main stream and does not rejoin it. Characteristic of Deltas and Alluvial Fans.

DISTRIBUTION (of Water)—The management of water which allows water users to receive the amount of water to which they are entitled by law and as supply permits.

DISTRIBUTION COEFFICIENT—The quantity of a solute absorbed per unit weight of a solid divided by the quantity dissolved in water per unit volume of water.

DISTRIBUTION GRAPH (DISTRIBUTION HYDROGRAPH)—A Unit Hydrograph of direct runoff modified to show the portion of the volume of runoff that occurs during successive equal units of time.

DISTRIBUTION SYSTEM—(Irrigation) (1) System of ditches and their appurtenances which convey irrigation water from the main canal to the farm units; diverse water from the main canal-side turnout to individual water users or to other smaller distribution systems. (2) Any system that distributes water within a farm.

DISTRIBUTION UNIFORMITY (DU)—(1) Generally, a term used to describe how evenly water is applied on a field and therefore a practical method for measuring the performance of an irrigation system. The concept of distribution uniformity constitutes one of the limiting factors on a system's Irrigation Efficiency (I.E.). (2) Also, a ratio used to measure the infiltration of irrigation water through a given soil profile. More specifically, the ratio of the average low-quarter depth of irrigation to the average depth of irrigation, for the entire farm field, expressed as a percent. Typically, a DU of between 80 and 90 percent is considered very good.

DISTRICT (USBR)—An entity that has a contract with the U.S. Bureau of Reclamation (USBR) for the delivery of irrigation water. Such entities include, but are not limited to: canal companies, conservancy districts, ditch companies, irrigation and drainage districts, irrigation companies, irrigation districts, reclamation districts, service districts, storage districts, water districts, and water users associations.

DISTURBED AREA—(Geology) Area where vegetation, topsoil, or overburden has been removed, or where topsoil, spoil, and processed waste has been placed.

DITCH—A long narrow trench or furrow dug in the ground, as for irrigation, drainage, or a boundary line.

DITCH RIDERS—Individuals responsible for operating structures and distribute water internally within an irrigation project. Canal system operations personnel. The person or persons responsible for controlling the canal system based on the flow schedule established by the Watermaster.

DIVE—To plunge, especially headfirst, into water.

DIVERGENCE—A meteorological condition characterized by the uniform expansion in volume of a mass of air over a region, usually accompanied by fair dry weather.

DIVERGENT PLATE BOUNDARY—In the theory of Plate Tectonics, a boundary between two plates that make up the crust of the earth. The boundary is characterized by a chasm between the two plates, filled with molten rock from within the earth.

DIVERSION—The transfer of water from a stream, lake, aquifer, or other source of water by a canal, pipe, well, or other conduit to another watercourse or to the land, as in the case of an irrigation system. Also, a turning aside or alteration of the natural course of a flow of water, normally considered physically to leave the natural channel. In some states, this can be a consumptive use direct from a stream, such as by livestock watering. In other states, a diversion must consist of such actions as taking water through a canal or conduit.

DIVERSION CHANNEL—(1) An artificial channel constructed around a town or other point of high potential flood damages to divert floodwater from the main channel to minimize flood damages. (2) A channel carrying water from a diversion dam.

DIVERSION DAM (and DIKE)—A barrier built to divert part or all of the water from a stream into a different course. The diversion dam is commonly constructed on a natural river channel and is designed to check or elevate the water level for diversion into a main canal system. Also referred to as Diversion Cofferdam.

DIVERSION RATE—A rate of water flow (cfs) diverted into a canal or through a farm headgate.

DIVERSITY INDEX—A numerical expression of the evenness of distribution of aquatic organisms. Several different formulae are in current use for its calculations.

DIVERTIBLE WATER SUPPLY—Includes that amount of water consumptively used and that water which returns to the river system. Since return flow becomes available for subsequent diversion and reuse, the total divertible supply is greater than the available supply.

DIVIDE—An imaginary line indicating the limits of a subbasin, subwatershed, or watershed; the boundary line along a topographic ridge or high point which separates two adjacent drainage basins. Also referred to as Ridge Lines.

DIVING REFLEX—A reflexive response to diving in many aquatic mammals and birds, characterized by physiological changes that decrease oxygen consumption, such as slowed heart rate and decreased blood flow to the abdominal organs and muscles, until breathing resumes. Though less pronounced, the reflex also occurs in certain nonaquatic animals, including human beings, upon submersion in water.

DIVINING ROD—A forked branch or stick that is believed to indicate subterranean water or minerals by bending downward when held over a source. Also see Douse (also Dowse).

DIVISION BOX—(Irrigation) A structure used to divide and direct the flow of water between two or more irrigation ditches.

(STATE) DIVISION OF HEALTH [Nevada]—An agency within the Department of Human Resources, State of Nevada, whose primary water-related mandate (Nevada Revised Statutes 445.361) is "to provide water which is safe for drinking and other domestic purposes and thereby promote the public health and welfare." The Division serves as the primacy agency for the Public Water System Supervision Program (PWSSP) as authorized under the federal Safe Drinking Water Act (SDWA) [Public Law 93-523] and its amendments. The Division implements State Board of Health regulations which address drinking water monitoring and quality, public water system construction, and public water system operator certification. To accomplish its tasks, the Division consists of a number of Boards and Bureaus, to include:

[1] State Board of Health—Advises the Health Division Administrator on matters relating to public health and welfare. [2] State Health Officer—Primary state adviser on matters pertaining to medical health; oversees the activities of the Bureau of Laboratory Services, Bureau of Community Health Services, Bureau of Family Health Services, Bureau of Disease Control and Intervention Services, and the Bureau of Health Planning. [3] Bureau of Health Protection Services—Provides for safe drinking water, health engineering, sanitation (food, dairy, drugs and cosmetics), and radiological health matters. [4] Bureau of Laboratory Services—Microbiology lab, chemistry lab, research and testing on community water systems. [5] Bureau of Community Health Services—Family planning, community health nursing, and clinic services. [6] Bureau of Family Health Services—Genetics, special children's clinic, children's dental services, newborn screening, and health promotion and education. [7] Bureau of Health Planning—State health plan, primary care development center, state center for health statistics, tobacco control initiative. [8] Bureau of Disease Control and Intervention Services—Programs dealing with surveillance, immunization, TB control. [9] Bureau of Licensure and Certification—Programs dealing with health facilities, laboratory personnel certification, emergency medical services and trauma. [10] Bureau of Administrative Services—Fiscal management, personnel, affirmative action, legal services, vital records, and cancer registry.

DO—See Dissolved Oxygen (DO).

DOC—See Dissolved Organic Carbon (DOC).

DOCK—(1) The area of water between two piers or alongside a pier that receives a ship for loading, unloading, or repairs. (2) A pier; a wharf. (3) Often docks: A group of piers on a commercial waterfront that serve as a general landing area for ships or boats.

DOCKYARD—An area, often bordering a body of water, with facilities for building, repairing, or dry-docking ships.

DOCTRINE OF RELICTION [Nevada]—In a Nevada Supreme Court ruling (State Engineer v. Cowles Bros., 86 Nev. 872, 1964) it was held that the lands so exposed by Reliction, i.e., those lands exposed by the recession of a body of water, should belong to the adjoining land owners. This held true even for those lands exposed by the recession of a navigable body of water, whose bed is owned by the State of Nevada (e.g., Winnemucca Lake). Also see Dereliction.

DOLDRUMS—(1) A region of the ocean near the equator, characterized by calm, light winds, or squalls. (2) The weather conditions characteristic of these regions of the ocean.

DOLLOP—A small quantity or splash of a liquid.

DOLOS—A concrete protective unit used to dissipate wave energy thus preventing damages to breakwaters and jetties. Units may vary in size and weight depending on design wave parameters.

DOMESTIC CONSUMPTION—Water used for household purposes such as washing, food preparation, toilets and showers. It is the quantity, or quantity per capita (person), of water consumed in a municipality or district for domestic uses or purposes during a given period. It sometimes encompasses all uses, including the quantity wasted, lost, or otherwise unaccounted for.

DOMESTIC SEWAGE—Wastewater and solid waste that is characteristic of the flow from toilets, sinks, showers, and tubs in a household. Also referred to as Domestic Waste.

DOMESTIC WASTEWATER FACILITY—Refers to those facilities that receive or dispose of wastewater derived principally from residential dwellings, business or commercial buildings, institutions, and the like. May also include some wastewater derived from industrial facilities. Also referred to as Municipal Wastewater Facility.

DOMESTIC WATER—Water supplied to individual dwellings and other land uses which is suitable for drinking.

DOMESTIC WATER USE—Water used normally for residential purposes, including household use, personal hygiene, drinking, washing clothes and dishes, flushing toilets, watering of domestic animals, and outside uses such as car washing, swimming pools, and for lawns, gardens, trees and shrubs. The water may be obtained from a public supply or may be self supplied. Also referred to as Residential Water Use. Also see Public Water Supply System and Self-Supplied Water.

DOUBLE CROPPING—The practice of producing two or more crops consecutively on the same parcel of land during a 12-month period. Also referred to as Multi-Cropping.

DOUCHE—A stream of water, often containing medicinal or cleansing agents, that is applied to a body part or cavity for hygienic or therapeutic purposes.

DOUSE, also Dowse—(1) To plunge into liquid; to immerse and wet thoroughly. (2) To use a Divining Rod to search for underground water or minerals, as in Dowsing.

DOWNFALL—A fall of rain or snow, especially a heavy or unexpected one.

DOWNGRADIENT—The direction that groundwater flows; similar to "downstream" for surface water flows.

DOWNGRADIENT WELL—One or more monitoring wells placed to sample groundwater that has passed beneath a facility with the potential to release chemical contaminants into the ground. Results of testing downgradient well water are compared with data from an Upgradient Well to determine whether the facility may be contaminating the groundwater.

DOWNPOUR—A heavy fall of rain.

DOWNSTREAM—In the direction of the current of a stream.

DOWNSTREAM CONTROL—(Irrigation) Control structure adjustments which are based on information from downstream; the required information is measured by a sensor located downstream or based on the downstream water schedule established by the Watermaster. DOWNSTREAM SLOPE (of a Dam)—The slope or face of the dam away from the reservoir water, which, for Embankment Dams, requires some form of protection such as grass to protect it from the erosive effects of rain and surface flows.

DOWNSTREAM TOE OF DAM—The junction of the downstream face of a dam with the ground surface. For and Embankment Dam the junction of the upstream face with the ground surface is the upstream toe.

DOWSER—(1) A person who uses a Divining Rod to search for underground water or minerals. (2) A divining rod.

DRAFT—(1) The act of drawing or removing water from a tank or reservoir. (2) The water which is drawn or removed. (3) (Nautical) The depth of a vessel's keel below the water line, especially when loaded.

DRAG—To search or sweep the bottom of a body of water, as with a grappling hook or dragnet.

DRAIN—(1) To draw of (a liquid) by a gradual process. (2) A buried pipe or other conduit (closed drain) for the conveyance of surplus groundwater. (3) A ditch (open drain) for carrying off surplus surface water or groundwater. (4) A system to control water tables near the ground surface to maintain levels at or below specified depths.

DRAINAGE—(1) The removal of excess surface water or groundwater from land by means of surface or subsurface drains. (2) Improving the productivity of agricultural land by removing excess water from the soil by such means as ditches or subsurface drainage tiles (pipes). (3) Soil characteristics that affect natural drainage.

DRAINAGE AREA (of a Stream at a Specified Location)—That area, measured in a horizontal plane, enclosed by a topographic (drainage) divide from which direct surface runoff from precipitation normally drains by gravity into the stream above the specified point.

DRAINAGE BASIN—Part of the surface of the earth that is occupied by a drainage system, which consists of a surface stream or a body of impounded surface water together with all tributary surface streams and bodies of impounded surface water. The term is used synonymously with Watershed, River Basin, or Catchment.

DRAINAGE CLASS, SOILS—The relative terms used to describe natural drainage and corresponding types of soils are as follows:

[1] Excessive—Excessively drained soils are commonly very porous and rapidly permeable, and have low water-holding capacity; [2] Somewhat Excessive—Somewhat excessively drained soils are also very permeable and are free from mottling throughout their profile; [3] Good—Well drained soils that are nearly free of mottling and are commonly of intermediate texture; [4] Moderately Good—Moderately well drained soils that commonly have a slowly permeable layer in or immediately beneath the solum. They have uniform color in the surface layers and upper subsoil, and mottling in the lower subsoils and substrata; [5] Somewhat Poor—Somewhat poorly drained soils are wet for significant periods, but not all the time. They commonly have a slowly permeable layer in their profile, a high water table, additions through seepage, or a combination of these conditions; [6] Poor—Poorly drained soils are wet for long periods of time. They are light gray and generally are mottled from the surface downward, although mottling may be absent or nearly so in some soils.

DRAINAGE COEFFICIENT—Design rate at which water is to be removed from a drainage area.

DRAINAGE DENSITY—(1) The relative density of natural drainage channels in a given area, obtained by dividing the total length of the stream channels by the area. (2) The length of all channels above those of a specified Stream Order per unit of Drainage Area.

DRAINAGE DISTRICT—A special purpose district created under state law to finance, construct, operate, and maintain a drainage system involving a group of land holdings.

DRAINAGE DIVIDE—The line of highest elevations which separates adjoining drainage basins.

DRAINAGE FIELD DITCH—A shallow graded ditch for collecting excess water within a field, usually constructed with flat side slopes for ease of crossing.

DRAINAGE FLOODING—Ponding of water at or near the point where it fell due to improper or limited drainage.

DRAINAGE LATERAL—A side ditch or conduit which contributes water to a drainage main.

DRAINAGE LAYER (or Blanket)—(Dam) A layer of permeable material in a dam to relieve pore pressure or to facilitate drainage of fill material.

DRAINAGE MAIN—A natural or artificial ditch or conduit for moving water off the land.

DRAINAGE WATER—The water which has been collected by a drainage system. It may come from surface water or from water passing through the soil. It may be of a quality suitable for reuse or it may be of no further economic use.

DRAINAGE WELL—(Irrigation) A vertical opening to a permeable substation into which surface and subsurface water is channeled. A well drilled to carry excess water off agricultural fields. Because they act as a funnel from the surface to the groundwater below, drainage wells can contribute to groundwater pollution.

DRAIN FIELD—A network of buried piping or tubing where the fluid is discharged to the ground through seepage. Most common use is with septic tanks, but can also be used for domestic or industrial wastewater disposal after other treatment methods.

DRAINPIPE—A pipe for carrying off water or sewage.

DRAINS (of a Dam)—A vertical well or borehole, usually downstream of impervious cores, grout curtains, or cutoffs, designed to collect and direct seepage through or under a dam to reduce uplift pressure under or within the dam. A line of such wells forms a drainage curtain. Also referred to as Relief Wells.

DRAW—To cause to flow forth as a pump drawing water.

DRAWDOWN—(1) The act, process, or result of depleting, as a liquid or body of water as in the lowering of the water surface level due to release of water from a reservoir. (2) The magnitude of lowering of the surface of a body of water or of its piezometric surface as a result of withdrawal of the release of water therefrom. (3) The decline of water below the static level during pumping. (4) (Water Table) The lowering of the elevation of the Groundwater Table, usually from pumping wells, but can occur naturally during periods of prolonged drought. At the well, it is the vertical distance between the static and the pumping level.

DREDGE—To clean, deepen, or widen with a mechanical scoop. See Dredging.

DREDGING—A method for deepening streams, swamps, or other waters by scraping and removing solid materials from the bottom. Such actions can disturb the Ecosystem and cause silting that kills aquatic life. Dredging of contaminated muds can expose Biota to heavy metals and other toxic substances. Dredging activities may be subject to regulation under Section 404 of the Clean Water Act (CWA).

DREG—The sediment in a liquid; lees. Often used in the plural.

DRENCH—To wet through and through; soak.

DRI [Nevada]—See Desert Research Institute (DRI) [Nevada].

DRIBBLE—To flow or fall in drops or an unsteady stream; trickle.

DRIBLET—A tiny falling drop of liquid.

DRIFT—To be carried along by currents of air or water.

DRIFTAGE—(1) (Nautical) Deviation from a set course caused by drifting. (2) Matter that has been carried along or deposited by air or water currents.

DRIFT ORGANISMS—Benthic organisms temporarily suspended in the water and carried downstream by the current.

DRILLER'S WELL LOG—A log kept at the time of drilling showing the depth, thickness, character of the different strata penetrated, location of water-bearing strata, depth, size, and character of casing installed.

DRILLING MUD—A mixture of clay, water, and other materials, often bentonite clay and barite, commonly used in drilling with a rotary drill rig. The mud is pumped down the drill pipe and through a drill bit and back up to the surface between the drill pipe and the walls of the hole. The mud helps lubricate and cool the drill bit as well as carry the cuttings to the surface. The mud also stabilizes the hole. Also referred to as Drilling Fluid.

DRINK—(1) To take into the mouth and swallow a liquid such as water. (2) To take in or soak up; absorb.

DRINKABLE—Suitable or fit for drinking; Potable.

DRINKING WATER—A term used synonymously with Potable Water, and refers to water that meets federal drinking water standards of the Safe Drinking Water Act [SDWA] (Public Law 93-523) as well as state and local water quality standards and is considered safe for human consumption. Freshwater that exceeds established standards for chloride content and dissolved solids limits is often referred to as slightly saline, brackish, or nonpotable water and is either diluted with fresher water or treated through a desalination process to meet drinking-water standards for public supply.

DRINKING WATER EQUIVALENT LEVEL—Protective level of exposure related to potentially non-carcinogenic effects of chemicals that are also known to cause cancer.

DRINKING WATER STANDARDS—Drinking water standards established by state agencies, the U.S. Public Health Service, and the U.S. Environmental Protection Agency (EPA) for drinking water throughout the United States. [See Appendix S-1 for regulated contaminants and Appendix S-2 for proposed contaminants to be regulated by the Safe Drinking Water Act [SDWA] (Public Law 93-523)]

DRINKING WATER STANDARDS [Nevada]—The primary objective of Nevada's drinking water standards is to assure safe water for human consumption. To this end, the Nevada Department of Human Resources, Health Division—Consumer Health Protection has established statewide primary and secondary drinking water standards at least as rigorous as those required by the U.S. Environmental Protection Agency (EPA). Primary Drinking Water Standards limit contaminants (constituents) which may affect consumer health. Secondary Drinking Water Standards were developed to deal with the aesthetic qualities of drinking water. [Appendix D-5, Nevada Drinking Water Standards, presents a listing of Nevada's current primary and secondary drinking water quality standards.]

DRINKING WATER SUPPLY—Water provided for use in households. The most common sources are from surface supplies (rivers, lakes, and reservoirs) or subsurface supplies (aquifers). The distribution of water to households is regulated under the Safe Drinking Water Act (SDWA) of 1974, as amended.

DRIP—To fall in drops; to shed drops; to ooze or become saturated with or as if with liquid.

DRIP IRRIGATION—A planned irrigation system in which water is applied directly to the Root Zone of plants by means of applicators (orifices, emitters, porous tubing, perforated pipe, etc.) operated under low pressure. The applicators may be placed on or below the surface of the ground. Also see Irrigation Systems.

DRIP (TRICKLE) SOIL ABSORPTION SYSTEM—A shallow slow rate pressure-dosed system used for land application of treated wastewater, particularly under soil conditions unsuitable for normal septic tanks and gravity-fed soil absorption systems. In agriculture, drip soil irrigation systems irrigate crops by means of a network of shallow underground pipes fed by a pump. Such a system conserves water used in crop irrigation by applying it at a controlled rate in the root zone, minimizing evaporation and percolation losses. In the drip soil absorption system, the filtered effluent is delivered via supply lines to a subsurface drip field consisting of parallel rows of polyethylene tubing, known as dripper lines. Emitters are installed along these tubes to uniformly distribute and control the flow of effluent. The key to the effective operation of drip soil absorption systems is the slow and controlled rate at which it applies effluent over a large surface area, allowing relatively shallow placement of the dripper lines and long-term use without risk of saturating soils. This allows such systems to be effectively used for subsurface irrigation of trees, shrubs, and gardens in arid regions. Also see Septic Tank Soil Absorption System (ST-SAS).

DRIZZLE—Rather uniform precipitation consisting exclusively of minute and very numerous drops of water less than 0.02 inches (0.51 mm) in diameter, which seem to float in and follow even the slightest motion of the air. Poor visibility during drizzle, which frequently occurs simultaneously with fog, distinguishes it from light rain.

DROP—The quantity of fluid which falls in one spherical mass; a liquid globule; often, a teardrop, raindrop, dewdrop, etc. The size of a drop varies with the specific gravity and viscosity of the liquid and also with the conditions under which it is formed.

DROP-INLET SPILLWAY—Overfall structure in which the water drops through a vertical riser connected to a discharge conduit.

DROP SPILLWAY—An overfall structure in which water drops over a vertical wall onto a protected apron at a lower elevation.

DROPLET—A small airborne liquid particle that is larger than liquid aerosol and therefore settles out of the atmosphere relatively quickly.

DROPPER—A small tube with a suction bulb at one end for drawing in a liquid and releasing it in drops.

DROPS—Structures to reduce or control water velocity within an irrigation ditch or canal by lowering the water abruptly from one level to a lower level.

DROP SPILLWAY—An overfall structure in which water drops over a vertical wall onto a protected apron at a lower elevation.

DROP STRUCTURE—A structure for dropping water to a lower level and dissipating its surplus energy. A drop may be vertical or inclined.

DROUGHT—There is no universally accepted quantitative definition of drought. Generally, the term is applied to periods of less than average or normal precipitation over a certain period of time sufficiently prolonged to cause a serious hydrological imbalance resulting in biological losses (impact flora and fauna ecosystems) and/or economic losses (affecting man). In a less precise sense, it can also signify nature's failure to fulfill the water wants and needs of man.

DROUGHT CONDITION—Hydrologic conditions during a defined Drought period during which rainfall and runoff are much less than average.

DROUGHT PERIOD—The period of time over which Drought Conditions exist.

DROUGHT RESERVE WATER —Generally, water reserved in upstream reservoirs for release for downstream purposes, e.g., municipal and industrial, agriculture, recreational, etc. Often provisions will be made such that drought reserve water will convert to Fish Credit Water if snowpack water content or runoff is deemed sufficient by a stipulated date.

DROUGHT YEAR SUPPLY—The average annual supply of a water development system during a defined Drought Period. For dedicated natural flow, it is the average flows or levels for specific drought water years for specific streams or bodies of water, or it is the Environmental Flows as required under specific agreements, water rights, court decisions, and congressional directives.

DROWN—(1) To kill by submerging and suffocating in water or another liquid. (2) To drench thoroughly or cover with or as if with a liquid.

DRUMLIN—An elongated hill or ridge of Glacial Drift.

DRY—(1) Free from liquid or moisture. (2) Having or characterized by little or no rain, as a dry climate. (3) Marked by the absence of natural or normal moisture, as a dry month. (4) Not under water, as dry land. (5) Having all the water or liquid drained away, evaporated, or exhausted, as a dry river.

DRY ADIABATIC LAPSE RATE—The Adiabatic Lapse Rate for air not saturated with water vapor, or 0.98°C per 100 meters rise (5.4°F per 1,000 feet), expressed as:

ðd = -dT/dz

where:

dT is the change in air temperature; dz is the change in altitude; and ðd is the dry adiabatic lapse rate.

Compare to Wet Adiabatic Lapse Rate.

DRY DAM—A dam that has an outlet positioned so that essentially all stored water will be drained from the reservoir by gravity. The reservoir will normally be dry. Permanent storage is not involved, and the detention reservoir can be used for other purposes (farming, grazing, recreation) between flood periods.

DRY DEPOSITION—The introduction of acidic material to the ground or to surface waters by the settling of particles containing sulfate or nitrate salts. Compare to Wet Deposition.

DRY DOCK—(Nautical) A large dock in the form of a basin from which the water can be emptied or pumped, used for building or repairing a ship below its water line.

DRY FARMING—A type of farming practiced in arid areas without irrigation by planting drought-resistant crops and maintaining a fine surface tilth or mulch that protects the natural moisture of the soil from evaporation. Also referred to as Dryland Farming.

DRY HYDRANTS—A siphon buried beneath the water line that enables fire crews to draw, or "draft" water from ponds or other bodies of water located nearby. Such devices are used in more remote locations and are typically used only for interim purposes until a more consistent supply may be obtained to fight a fire.

DRY ICE—Solid carbon dioxide that sublimates at -78.5°C (-110°F) and is used primarily as a coolant.

DRYING OFF—The process of reducing moisture to induce dormancy or a rest period in plants.

DRYLAND FARMING—The practice of crop production without irrigation in semiarid regions usually by using moisture-conserving farming techniques. Also referred to as Dry Farming.

DRY PROOFING—A flood-proofing method used to design and construct buildings so as to prevent the entrance of floodwaters.

DRY WASH—A defined drainage channel in arid regions that is dry except following a major storm or heavy spring snowmelt.

DRYLAND (FARMING)—Non-irrigated cropland. See Dry Farming.

DUAL-DISTRIBUTION PIPING—A water distribution system that uses one set of pipes for the distribution of potable water and a separate set for the distribution of Reclaimed Water.

DUAL MEDIA FILTRATION—A system using two layers of dissimilar media, such as anthracite and sand.

DUCKING STOOL—A seat attached to a plank and formerly used to plunge culprits tied to it into water.

DUCKWEED—Any of various small, free-floating, stemless aquatic flowering plants of the genus Lemna. Particularly useful in filtering Constituents and Contaminants out of water.

DUCT—An often enclosed passage or channel for conveying a substance, especially a liquid or gas.

DUFF—A general, non-specific term referring to the more or less firm organic layer on top of mineral soil, consisting of fallen vegetative matter in the process of decomposition, including everything from litter on the surface to pure humus.

DUNE—A mound or ridge of sand piled up by wind.

DUNE POND ("Lake")—A lake occupying a basin formed as a result of the blocking of the mouth of a stream by sand dunes migrating along the shore.

DUNE SWALE—A low place among sand dunes, typically moister and often having distinctive vegetation differing from the surrounding sand environment.

DUNK—To plunge into liquid; immerse as in to submerge oneself briefly in water. Synonymous with Dip.

DUPLICATES—(Water Quality) Two separate samples with separate containers taken at the same time at the same location.

DURALUMIN—An alloy of aluminum that contains copper, manganese, magnesium, iron, and silicon and is resistant to corrosion by acids and sea water. The term was originally a trademark.

DURATION CURVE—A graph representing the percentage of time during which the value of a given parameter (e.g., water level, discharge, etc.) is equaled or exceeded.

DURIPAN—A subsurface (soil) horizon that is cemented by silica.

DUTY (of Water)—The total volume of irrigation water required for irrigation in order to mature a particular type of crop. In stating the duty, the crop, and usually the location of the land in question, as well as the type of soil, should be specified. It also includes consumptive use, evaporation and seepage from on-farm ditches and canals, and the water that is eventually returned to streams by percolation and surface runoff. Also see Alpine Decree [Nevada], Orr Ditch Decree [Nevada], Bench Lands [Nevada], and Bottom Lands [Nevada] for additional information and examples of specific water duties.

DUSTING—A light sprinkling as of snow.

DYNAMIC EQUILIBRIUM—A condition of which the amount of recharge to an aquifer equals the amount of natural discharge.

DYNAMIC HEAD—(Irrigation) The total of the following factors: (1) the total static head, including suction lift; (2) friction head in the discharge pipeline; (3) head losses in fittings, elbows, and valves; and (4) pressure required to operate lateral lines.

DYSENTERY—A disorder of the gastrointestinal tract characterized by severe diarrhea with blood and pus in the feces. The disease frequently results from an infection by bacteria belonging to the genus Shigella.

DYSTROPHIC—(Ecology) Characterized by having brownish acidic waters, a high concentration of humic matter, and a small plant population. Typically used to describe a lake or pond.

DYSTROPHIC LAKE—A lake characterized by a lack of nutrients, and often having a low pH (acidic) and a high humus content. Plant and animal life are typically sparse, and the water has a high oxygen demand. This stage follows the Eutrophic Phase in the life cycle of a lake

E. COLI (ESCHERICHIA COLI)—A bacterial species which inhabits the intestinal tract of man and other warm-blooded animals. Although it poses no threat to human health, its presence in drinking water does indicate the presence of other, more dangerous bacteria. Also see Bacteria.

EAGRE—A high, often dangerous wave caused by the surge of a flood tide upstream in a narrowing Estuary or by colliding tidal currents. Also referred to as a Bore.

EARLY SERAL CONDITION—Synonymous with poor ecological conditions.

EARTHFILL DAM—A dam the main section of which is composed principally of earth, gravel, sand, silt, and clay. Also referred to as Earth Dam. Also see Embankment Dam.

EASEMENT—A legal instrument enabling the giving, selling, or taking or certain land or water rights without transfer of title, such as for the passage of utility lines. An affirmative easement gives the owner of the easement the right to use the land for a stated purpose. A negative easement is an agreement with a private property owner to limit the development of his land in specific ways.

EBB—(1) Ebb Tide. (2) To fall back from the Flood Stage.

EBB TIDE—That period of tide between a high water and the succeeding low water; falling tide. Also see Tides.

ECHARD—Soil water not available for absorption by plants.

ECHO SOUNDER—A device for measuring the depth of water or the depth of an object below the surface by sending pressure waves down from the surface and recording the time until the echo returns from the bottom.

ECOLOGICAL IMPACT—The effect that a man-made or natural activity has on living organisms and their non-living (abiotic) environment.

ECOLOGICAL INDICATOR—An individual species or a defined assemblage of organisms that serves as a gauge of the condition of the environment. The term is a collective term for response, exposure, habitat, and stressor indicators. For example, the bacterium Escherichia coli indicates the presence of sewage in water, and the mussel, Mytilus edulis lives in polluted waters.

ECOLOGICAL RISK ASSESSMENT—The application of a formal framework, analytical process, or model to estimate the effects of human actions on a natural resource and to interpret the significance of those effects in light of the uncertainties identified in each component of the assessment process. Such analysis includes initial hazard identification, exposure and dose-response assessments, and risk characteristics.

ECOLOGICAL SUCCESSION—An orderly, directional and therefore predictable process of development that involves changes in species structure and community processes over time. It results from a modification of the physical environment by the community and culminates in a stabilized ecosystem in which maximum biomass and symbiotic functions are maintained.

ECOLOGY—The study of the inter-relationships of living things to one another and to the environment.

ECONOMETRIC MODEL BUILDING—(Statistics) An iterative process for developing a model beginning with some information about the form and structure of the problem and with relevant data. The model building process typically follows a sequence of inter-related steps to include:

[1] Problem Identification and Data Selection—Data is selected, compilation, screened, and analyzed, and the various series tested based on hypotheses of probable causation; [2] Model Identification (or Specification)—Selection of a general model structure is made based on the nature of the data and the types of outputs desired. Some of these include, for example, a simple single mathematical equation, or multiple (sequential) equations, statistically-based univariate (deterministic) autoregressive functions, multivariate analysis, simple ordinary least squares (OLS) regression, multiple regression, simultaneous equation, etc.; [3] Estimation (Model Fitting)—Based on the selection of a model structure, the data is used to best describe the behavior of the variable under observation, e.g., stream flows, reservoir levels, runoff, economic output, employment, consumer spending, etc.; [4] Model Testing (and Refinement, as Necessary)—The model's structure and variables chosen are then validated by applying the data and observing forecast errors with respect to know (sample) values; [5] Forecasting—Based upon the ability of the model to accurately "fit" or predict historical values, the model is used to forecast beyond the last data point as prescribed by scenarios under analysis.

Also see Econometrics, Regression Analysis, Stochastic Process, and Deterministic Process.

ECONOMETRICS—(Statistics) The application of statistical and mathematical methods to the analysis of economic data, with a purpose of giving empirical content to economic theories and verifying them or refuting them. Also see Econometric Model Building, Regression Analysis, Stochastic Process, and Deterministic Process.

ECOSPHERE—The mantle of earth and troposphere inhabited by living organisms; the "bio-bubble" that contains life on earth, in surface waters, and in the air. Also see Biosphere.

ECOSYSTEM—A community of animals, plants, and bacteria, and its interrelated physical and chemical environment. An ecosystem can be as small as a rotting log or a puddle of water, but current management efforts typically focus on larger landscape units, such as a mountain range, a river basin, or a watershed. Also see Biodiversity.

ECOSYSTEM FUNCTIONS—Processes that are necessary for the self-maintenance of an Ecosystem such as primary production, nutrient cycling, decomposition, etc. The term is used primarily as a distinction from values.

ECOSYSTEM MANAGEMENT—(Environmental) An approach to managing the nation's lands and natural resources which recognizes that plant and animal communities are interdependent and interact with their physical environment (i.e., soil, water, and air) to form distinct ecological units called Ecosystems. The fact that these ecosystems span jurisdictional and political boundaries necessitates a more comprehensive and unified approach to managing them. Implementing the initial stage of a government-wide approach to ecosystem management typically requires clarifying the policy goals and undertaking certain practical steps to apply the principles being considered to include:

[1] Delineating the ecosystem; [2] Understanding the system(s) ecologies; [3] Making management choices; [4] Unifying disparate data and information needs and sources; and [5] Adapting management on the basis of new information.

ECOSYSTEM STRUCTURE—Attributes related to instantaneous physical state of an ecosystem; examples include species population density, species richness or evenness, and standing crop Biomass.

ECOTONE—(1) A habitat created by the juxtaposition of distinctly different habitats; an edge habitat; or an ecological zone or boundary where two or more ecosystems meet. (2) A transition line or strip of vegetation between two communities, having characteristics of both kinds of neighboring vegetation as well as characteristics of its own.

ECOTYPE—A locally adopted population of a species which has a distinctive limit of tolerance to environmental factors.

EDAPHIC—Soil characteristics, such as water content, pH, texture, and nutrient availability, that influence the type and quantity of vegetation in an area.

EDDY—A current, as of water or air, moving contrary to the direction of the main current, especially in a circular motion.

EDEMA, also Oedema—(Botany) Extended swelling in plant organs caused primarily by an excessive accumulation of water.

EFFECTIVE POROSITY—The amount of interconnected pore space through which fluids can pass, expressed as a percentage of the total volume occupied by the interconnecting interstices. Porosity may be primary, formed during deposition or cementation of the material, or secondary, formed after deposition or cementation, such as fractures. Part of the total porosity will be occupied by static fluid being held to the mineral surface by surface tension, so effective porosity will be less than total porosity.

EFFECTIVE PRECIPITATION (or Rainfall)—That portion of precipitation which remains on the foliage or in the soil that is available for Evapotranspiration, and reduces the withdrawal of soil water by a like amount. As described by the U.S. Bureau of Reclamation, that part of the precipitation falling on an irrigated area that is effective in meeting the Crop Consumptive Use requirements.

EFFICIENCY—(Irrigation) A measure of a distribution system's ability to transport and apply water to a desired effect with a minimum of effort, expense, or waste. With respect to irrigation project efficiency, the following terms generally apply:

[1] Canal Efficiency—The volume of water diverted into a canal system versus total water available for farm headgate deliveries; [2] Irrigation Efficiency—The percentage of water applied that can be accounted for in soil moisture increase; and [3] Farm Efficiency—The amount of water actually required for growing a crop compared to the amount of irrigation water that is diverted at the farm headgate.

EFFICIENT WATER MANAGEMENT PRACTICES (EWMP)—AGRICULTURAL WATER USE—The agricultural water use equivalent of Best Management Practices (BMP) as applied to urban water use, efficient water management practices cover the spectrum of methods to improve both the efficiency and conservation of agricultural water use by (1) enhancing irrigation management services, measurement, and accounting; (2) improving the physical system of irrigation delivery, distribution, and drainage; and (3) promoting the modification of and adjustments to the institutional system of water use by agricultural interests to include information and educational programs. See Appendix B-2, Efficient Water Management Practices, for a more complete itemization of irrigation management, physical improvement, and institutional adjustment practices.

EFFLORESCE—(Chemistry) To become a powder by losing water of crystallization, as when a hydrated crystal is exposed to air.

EFFLORESCENCE—(1) (Chemistry) The deposit that results from the process of Efflorescing, called bloom. (2) A growth of salt crystals on a surface caused by evaporation of salt-laden water.

EFFLUENT—(1) Something that flows out or forth, especially a stream flowing out of a body of water. (2) (Water Quality) Discharged wastewater such as the treated wastes from municipal sewage plants, brine wastewater from desalting operations, and coolant waters from a nuclear power plant.

EFFLUENT GUIDELINES—Technical U.S. Environmental Protection Agency (EPA) documents which set effluent limitations for given industries and pollutants.

EFFLUENT LIMITATION—An amount or concentration of a water pollutant that can be legally discharged into a water body by a Point Source (PS), expressed as the maximum daily discharge, the maximum discharge per amount of product, and/or the concentration limit in the wastewater stream, as a 24-hour or 30-day average. The applicable technology-based standard is set by the U.S. Environmental Protection Agency (EPA) by Standard Industrial Classification (SIC) Code, but differs between new and existing sources and by broad types of water pollutants: conventional pollutants, toxic pollutants, nonconventional, nontoxic pollutants; dredge and fill wastes; and heat discharges.

EFFLUENT SEEPAGE—Diffuse discharge of ground water to the ground surface.

EFFLUENT STANDARD—The maximum amounts of specific pollutants allowable in wastewater discharged by an industrial facility or wastewater treatment plant. The standards are set for individual pollutants and apply across all industrial categories. This term can be contrasted with Effluent Limitations, which are set for individual pollutants by Standard Industrial Classification (SIC) Code.

EFFLUENT STREAMS—Effluent streams are those leaving a lake. Also referred to as Gaining Stream. Also see Stream.

EJECTOR—(1) A device using a jet of water to withdraw a fluid from a space. (2) A device used to disperse a chemical solution into water being treated.

EKMAN DREDGE—A dredge that has opposable jaws operated by a messenger traveling down a cable to release a spring catch and that is used in ecology for sampling the bottom of a body of water.

ELECTRIC POWER WATER (Public Utility)—Water withdrawn by public utilities for hydroelectric power generation and condenser cooling.

ELECTRICAL CONDUCTIVITY—A measure of the salt content of water.

ELECTRICAL LOG—A record of electrical-resistivity tests made at various depths in a well.

ELECTRODIALYSIS—A treatment process that uses electrical current and an arrangement of permeable membranes to separate soluble minerals from water. Often used to desalinate salt or brackish water. In the electrodialysis process, salts are extracted from the feedwater by using a membrane with an electrical current to separate the ions. The positive ions go through one membrane, while the negative ions flow through a different membrane, leaving the end product of freshwater. Also see Reverse Osmosis.

ELECTRODIALYSIS REVERSAL (EDR)—A treatment process in which minerals and other constituents in water are separated by an electrical charge. The resulting ions are transferred through membranes from a less concentrated to a more concentrated solution. By varying the amount of the electrical charge input to the system, it is possible to remove the dissolved solids in water to the extent desired. The EDR process can also be used in desalinating sea water.

ELECTROLYSIS—The passage of an electric current through an Electrolyte, causing the migration of the positively charged ions to the negative electrode (cathode) and the negatively charged ions to the positive electrode (anode).

ELECTROLYTE—(1) (Chemistry) Any compound that dissociates into ions when dissolved in water. The solution that results will conduct an electric current. For example, table salt (NaCl) is an electrolyte. (2) (Physiology) Any of various ions, such as sodium, potassium, or chloride, required by cells to regulate the electric charge and flow of water molecules across the cell membrane.

ELECTROPHORESIS—The migration of charged colloidal particles (Colloids) or Molecules through a solution under the influence of an applied electric field usually provided by immersed electrodes. Also call Cataphoresis.

ELEMENT—(1) (Chemistry) Any substance that cannot be separated into different substances by ordinary chemical methods. (2) (Historical) Any of four substances (earth, air, fire, and water) formerly regarded as a fundamental constituent of the universe. (3) (Meteorology) Weather conditions, especially violent or severe weather.

ELEVATED DITCH—Earth-filled, constructed to specifications similar to those for earthfill dams, to provide normal grade as a substitute for flumes or siphons. Also referred to as Raised Ditches.

ELEVATION—The variation in the height of the earth's surface as measured by the vertical distance from a known datum plane, typically Mean Sea Level (MSL).

ELEVATION HEAD—The potential energy in a hydraulic system, represented by the vertical distance between the hydraulic system (pipe, channel, etc.) and a reference level, and expressed in length units. The sum of the elevation head and the Pressure Head is equal to the Hydraulic Head. Also referred to as the Total Head.

ELIGIBLE COSTS—The construction costs for waste-water treatment plants upon which U.S. Environmental Protection Agency (EPA) grants are based.

ELIMINATION—The act, process, or an instance of eliminating or discharging, as the removal from a molecule of the constituents of a simpler molecule for example, ethylene is formed by the elimination of water from ethanol.

EL NIÑO—(Oceanography and Meteorology) [From the child (i.e., the Christ child)] The name of a southward-flowing ocean current off the coast of Peru causing an irregularly occurring flow of unusually warm surface water along the western coast of South America that is accompanied by abnormally high rainfall in usually arid areas and that prevents upwelling of nutrient-rich cold deep water causing a decline in the regional fish population. It typically results in a warm inshore current flowing along the coast of Ecuador and about every seven to ten years it extends southward down the coast of Peru with frequently devastating effects on weather, crops, and fishing (due to adverse effects on plankton). El Niño's warm and nutrient-poor waters cause great damage to the fishing industry and also to the birds feeding there, which are an important source of guano. The climatic effects of large-scale El Niño disturbances also cause flooding and drought conditions over a wide area, sometimes extending as far as the southern Pacific Ocean, Europe, Africa, and Asia. Such disturbances have taken place in 1953, 1957-58, 1972-73, 1976, 1982-83, and 1992. It is also believed that this condition (El Niño Effect) has more far-reaching effects on climatological patterns in the Western Hemisphere and also influences storm patterns in the western Atlantic Ocean region (Caribbean and Gulf of Mexico). It has generally been found that the presence of El Niño tends to reduce hurricane activity while the presence of La Niña, or cool eastern Pacific waters, tends to increase hurricane activity. Also see Hurricane Forecasting.

EL NIÑO/SOUTHERN OSCILLATION (ENSO)—(Oceanography and Meteorology) The expansion of warm waters in the Pacific Warm Pool east across the International Date Line, sometimes all the way to the coast of Peru, at which time it is called an El Niño event. The Pacific Warm Pool, located north and east of New Guinea, is approximately the size of the United States and gets its name from the fact that surface temperatures never go below 86°F (30°C). When this body of water expands, as it did in the early 1980s, the consequences of a warming trend on the coast of South America are dire. Typically, the fishing industry collapses in Peru as the plankton die off and fish head for cooler waters and torrential rainfalls bring devastating floods.

ELUTRIATE—To purify, separate, or remove by washing, decanting, and settling.

ELUTRIATION—Separation of solid waste into heavy and light fractions by washing.

ELUVIATION—(1) The removal of soil material in suspension (or in solution) from a layer or layers of a soil. (2) The transportation of dissolved or suspended material within the soil by the movement of water when rainfall exceeds evaporation.

EMBANKMENT—An artificial deposit of material that is raised above the natural surface of the land and used to contain, divert, or store water, support roads or railways, or for other similar purposes.

EMBANKMENT DAM—A dam structure constructed of fill material, usually earth or rock, placed with sloping sides and usually with a length greater than its height. Types of embankment dams include:

[1] Earthfill or Earth Dam—An embankment dam in which more than 50 percent of the total volume is formed of compacted fine-grained material obtained from a borrow area (i.e., excavation pit); [2] Fill Dam—Any dam constructed of excavated natural materials or of industrial waste materials; [3] Homogeneous Earthfill Dam—An embankment dam constructed of similar earth material throughout, except for the possible inclusion of internal drains or drainage blankets; distinguished from a Zoned Earthfill Dam; [4] Hydraulic Fill Dam—An embankment dam constructed of materials, often dredged, that are conveyed and placed by suspension in flowing water; [5] Rockfill Dam—An embankment dam in which more than 50 percent of the total volume is comprised of compacted or dumped pervious natural or crushed rock; [6] Rolled Fill Dam—An embankment dam of earth or rock in which the material is placed in layers and compacted by using rollers or rolling equipment; and [7] Zoned Embankment Dam—An embankment dam which is composed of zones of selected materials having different degrees of porosity, permeability, and density.

EMERGENCY ACTION PLAN (Dam)—A predetermined plan of action to be taken to reduce the potential for property damage and loss of lives in a downstream area affected by a dam break or excessive spillway discharges.

EMERGENCY SPILLWAY—A dam spillway built to carry runoff in excess of that carried by the principal spillway; a secondary spillway designed to operate only during exceptionally large floods. Also referred to as Auxiliary Spillway. Also see Spillway.

EMERGENT—Rising above a surrounding medium, especially a fluid. Having part of a plant aerial and the rest submersed; with parts extending out of the water.

EMERGENT HYDROPHYTES—Erect, rooted, herbaceous Angiosperms that may be temporarily to permanently flooded at the base but do not tolerate prolonged inundation of the entire stem or plant. Familiar examples are cattails, bulrushes, and saltmarsh cordgrass.

EMERGENT MOSSES—Mosses occurring in wetlands, but generally not covered by water.

EMERGENT PLANT—A plant that grows in shallow water with the root system submerged under the water and the upper vegetation rising above the water surface. Also see Emergent Hydrophytes.

EMERGENT WETLAND—Typically, a wetland classification characterized by erect, rooted, herbaceous, hydrophytes, excluding mosses and lichens, and which is present for most of the growing season.

EMERSED—(Botany) Rising above the surface of water as emersed aquatic plants.

EMINENT DOMAIN—(Legal) The right of a government to appropriate private property for public use, usually with compensation to the owner.

EMPEDOCLES—Fifth century B.C. Greek philosopher who believed that all matter is composed of elemental particles of fire, water, earth, and air and that all change is caused by motion.

EMPIRICAL—(Statistics) Based on experience or observations, as opposed to theory or conjecture.

EMULSION—A suspension of small Globules of one liquid in a second liquid with which the first will not mix.

ENCROACHMENT—Any physical object placed in the floodplain that hinders the passage of water or otherwise affects flood flows, such as fill, excavation, storage of equipment and materials, or buildings.

ENDAMOEBA HISTOLYTICA—A waterborne disease organism causing amoebic dysentery.

ENDANGERED SPECIES—Any plant or animal species threatened with extinction by man-made or natural changes throughout all or a significant area of its range; identified by the Secretary of the Interior as "endangered", in accordance with the 1973 Endangered Species Act (ESA), below. [See Appendix E-1, Nevada's Endangered and Threatened Species.]

ENDANGERED SPECIES ACT (ESA)—An act passed by Congress in 1973 intended to protect species and subspecies of plants and animals that are of "aesthetic, ecological, educational, historical, recreational and scientific value." It may also protect the listed species' "critical habitat", the geographic area occupied by, or essential to, the protected species. The U.S. Fish and Wildlife Service (USFWS) and the National Marine Fisheries Service (NMFS) share authority to list endangered species, determine critical habitat and develop recovery plans for listed species. Currently, approximately 830 animals and 270 plants are listed as endangered or threatened nationwide at Title 50, Part 17, sections 11 and 12 of the Code of Federal Regulations. Further, under a settlement with environmental groups, USFWS has agreed to propose listing another 400 species over the next few years. The 1973 Endangered Species Act superseded and strengthened the Endangered Species Preservation Act of 1966 and the Endangered Species Conservation Act of 1969. The 1973 provisions required that the act be re-authorized by Congress every five years. Major provisions of the 1973 ESA included:

[1] Emphasis on the conservation of ecosystems upon which species depend; [2] Consolidated existing U.S. and foreign lists; [3] Established and defined categories of "endangered" and "threatened"; [4] Lowered the listing threshold to "in danger of extinction in a significant portion of range"; [5] Made eligible all classes of vertebrates, invertebrates, and plants; [6] Defined and prohibited "take" of endangered vertebrates and invertebrates; [7] Established prohibitions on take of threatened species available by special regulation; [8] Restricted import and export; [9] Required federal agencies to undertake conservation programs; [10] Prohibited federal agencies from authorizing, funding, or carrying out actions that may jeopardize the continued existence of listed species; [11] Authorized the establishment of National Wildlife Refuges to protect habitat; [12] Established a state grant program; and [13] Appropriated funding for programs through 1978 (5-year cycle).

1978 amendments included:

[1] Established cabinet level exception from jeopardy standard; [2] Critical habitat defined and designation required for listing; [3] Economic impacts considered when designating critical habitat; [4] Distinct population of vertebrates could be listed; [5] Required recovered plans for species listed as endangered; and [6] Appropriated funding for programs through 1982.

1982 amendments included:

[1] Listing based solely on best biological information available; [2] Critical habitat designation concurrent with listing only to maximum extent prudent and determinable; [3] Established time requirements for listing process; [4] Established recovery priority system; [5] Designation of experimental populations; [6] Limited prohibition on take of endangered plants; [7] Incidental take permits for development of private land; [8] Incidental take provision incorporated within Biological Opinions; and [9] Appropriated funds for programs through 1988.

1988 amendments included:

[1] Prohibited recovery preference based on Taxonomy; [2] Required monitoring of recovered and candidate species; [3] Established recovery plan content requirements; [4] Required public review and comment on recovery plans; [5] Required reporting of recovery expenditures and species status; [6] Strengthened take prohibitions for endangered plants; and [7] Appropriated funds for programs through 1992.

Also see National Oceanic and Atmospheric Administration (NOAA).

ENDANGERED SPECIES CONSERVATION ACT—Passed in 1969, this act superseded the Endangered Species Preservation Act of 1966 and would eventually be replaced by the Endangered Species Act (ESA) of 1973. Major provisions of this act included:

[1] Identified vertebrates and invertebrates in danger of worldwide extinction; [2] Prohibited interstate commerce of illegally taken species; [3] Prohibited import or subsequent sale within U.S. with only few exceptions; and [4] Required an international agreement on trade in endangered species.

ENDANGERED SPECIES PRESERVATION ACT—Passed in 1966, this represented the first legislated effort towards identification and protection of animal species in the United States threatened by extinction. It represented the forerunner of the Endangered Species Act (ESA) of 1973, but would first be replaced by the Endangered Species Conservation Act of 1969. Major provisions of this act included:

[1] Identification of native vertebrates in danger of extinction; [2] Directed federal agencies to preserve habitat when "practicable and consistent"; [3] Authorized establishment of National Wildlife Refuges to protect habitat; and [4] Provided no protection except on refuges.

ENDANGERMENT ASSESSMENT—A study to determine the nature and extent of contamination at a site on the National Priorities List and the risks posed to public health or to the environment. The U.S. Environmental Protection Agency (EPA) or the state would conduct the study when a legal action is to be taken to direct potentially responsible parties to clean up a sit or pay for it. An endangerment assessment supplements a Remedial Investigation (RI).

ENDEMIC—(Ecology) Confined to, or Indigenous in, a certain area or region, as an endemic plant or animal.

ENDOGENOUS—(Geology) Derived from within; geologic processes originating from internal causes within the earth or magma.

ENDOGENOUS VARIABLE—(Statistics) Variables which are determined solely within the series of equations of the model. Also referred to as dependent variables as their values are assumed to be dependent upon the behavior of other pre-determined or explanatory variables, referred to as Exogenous Variables. An exception to this is a Lagged Endogenous Variable, which may also be an explanatory variable but whose value is determined within the system of equations by past values of the explanatory variables. For example, in the equation below, for any time period t (where t=1, 2, ..., n),

Yt = a + ß Xt + ð Yt-1 + et

where Yt represents the endogenous variable, Xt represents the exogenous variable, and Yt-1 represents the lagged endogenous variable. Also referred to as the Dependent Variable or the variable to be explained (Explained Variable).

ENDOREIC—A term used to describe areas with terminal lakes and an interior drainage basin. Approximately 27 percent of the earth's total land surface is endoreic; only about 5 percent of the North American continent is endoreic.

ENDOSMOSIS, also Endosmotic—The inward flow of a fluid through a permeable membrane toward a fluid of greater concentration. Contrast with Exosmosis (Exosmotic).

ENDRIN—A pesticide toxic to freshwater and marine aquatic life that produces adverse health effects in domestic water supplies.

ENERGY—The capacity to perform work, or the potential for power and activity; energy may be captured or held in living matter (e.g., food is stored energy). Various forms of energy include kinetic, potential, thermal, nuclear, rotational, and electromagnetic. Hydroelectric power, a form of potential energy, is derived from flowing water, typically by allowing water to be raised to, or maintained at, an elevated height and then release energy as it flows to a lower level.

ENERGY DISSIPATOR—A structure for slowing the fast moving spillway flows of a dam in order to prevent erosion of the stream channel below the dam.

ENERGY GRADIENT—The change in energy per unit length in the direction of flow or motion.

(NATIONAL) ENERGY POLICY ACT (EPAct)—A federal act passed in 1992 that established maximum water-use standards for newly manufactured plumbing fixtures. According to the act, any tank-type toilet for household use manufactured after January 1, 1994, must use a maximum of 1.6 gallons per flush. The same requirement is mandatory for all tank-type toilets for commercial use manufactured beginning in 1997. The EPAct also sets water-use standards for all newly manufactured urinals (a maximum of one gallon per flush), kitchen and bath faucets, and showerheads. [See Appendix C-3, Conservation from Efficient Water Fixtures.]

ENFORCEABLE REQUIREMENTS—Conditions or limitations in permits issued under the Clean Water Act (CWA), Section 202 or 404, that, if violated, could result in the issuance of a compliance order or initiation of a civil or criminal action under federal or applicable state laws.

ENGLACIAL—Located or occurring within a glacier.

ENHANCED OIL RECOVERY—Techniques for the removal of the remaining thick, heavy oil from reservoirs after primary recovery and secondary recovery techniques have been used. Typically, steam is injected into the reservoir to reduce the viscosity and provide pressure to force the oil into collection wells.

ENHANCED SURFACE WATER TREATMENT RULE (ESWTR)—A proposed rule promulgated by the U.S. Environmental Protection Agency (EPA) to take effect in the year 2000 intended to reduce the number of Crypto Oocysts (Cryptosporidium parvum) found in raw water supplies used for drinking water.

ENHANCEMENT—Emphasis on improving the value of particular aspects of water and related land resources.

ENRICHMENT—The addition of nutrients, such as nitrogen and phosphorus and carbon compounds, into a lake or waterway to the point that the Trophic Level is greatly increased because of the stimulation of the growth of algae and other aquatic plants.

ENSALINE (Euhaline)—Salinity approximating seawater (33 parts per million).

ENTERIC FEVER—An acute, highly infectious disease caused by a bacillus (Salmonella typhi) transmitted chiefly by contaminated food or water and characterized by high fever, headache, coughing, intestinal hemorrhaging, and rose-colored spots on the skin. More commonly referred to as Typhoid Fever.

ENTERIC VIRUSES—A category of viruses related to human excreta found in waterways.

ENTRAIN—To trap bubbles in water either mechanically through turbulence or chemically through a reaction.

ENTRAINMENT—(Streams) The incidental trapping of fish and other aquatic organisms in the water, for example, used for cooling electrical power plants or in waters being diverted for irrigation or similar purposes.

ENTRANCE HEAD—The Head required to cause flow into a conduit or other structure, including both entrance loss and Velocity Head.

ENTRAPMENT ZONE—An area of an estuary or other watercourse where seaward-flowing fresh water overlays more dense, saline ocean water resulting in a two-layer mixing zone characterized by Flocculation, aggregation, and accumulation of suspended materials from upstream.

ENVIRONMENT—All of the external factors, conditions, and influences which affect the growth, development, and survival of organisms or a community. The components of an environment include climate, physical, chemical, and biological factors, nutrients, and social and cultural conditions. These influences affect the form and survival of individuals and communities.

ENVIRONMENTAL ANALYSIS—(1) An analysis of alternative actions and their predictable short and long-term environmental effects, which may include physical, biological, economic, social and environmental design factors and their interaction. (2) (NEPA) Systematic process for considering environmental factors in resource management actions.

ENVIRONMENTAL ASSESSMENT (EA)—An environmental analysis prepared pursuant to the National Environmental Policy Act (NEPA) that presents the first thorough examination of alternative plans to positively demonstrate that the environmental and social consequences of an applicable project or action were considered. If it is shown that such activities do, in fact, significantly impact the environment or are otherwise deemed controversial, then an Environmental Impact Statement (EIS) will normally be required.

ENVIRONMENTAL AUDIT—(1) An internal investigation of company compliance with environmental regulations. (2) A study of a site prior to a real estate transaction to uncover potential environmental liability associated with the property, such as the prior improper disposal of hazardous wastes into the ground. (3) An independent assessment of the current status of a party's compliance with applicable environmental requirements or of a party's environmental compliance policies, practices, and controls.

ENVIRONMENTAL DEFENSE FUND (EDF)—A national, non-profit environmental and conservation organization active in legal, economic, and scientific aspects of environmental issues. The EDF employs scientists, attorneys, economists, computer modelers, and other environmental professionals whose purpose is to propose practical and economically feasible solutions to major environmental problems. The EDF has been responsible for a number of important environmental law cases coming to the attention of the courts in the United States. The EDF is headquartered in New York City and has six other offices across the United States. The EDF was founded in the early 1970s when scientists documented the effects of the pesticide DDT on humans, wildlife, and the environment. The EDF subsequently joined with scientists and attorneys and successfully campaigned to have DDT banned nationwide in 1972. Currently, major EDF projects include: (1) limiting the greenhouse effect and climate change; (2) improving air quality; (3) tracing and blocking the sources of ocean pollution; (4) enforcing and extending the Endangered Species Act (ESA); (5) limiting chemical pollution and its effects on human health and the environment; (6) promoting water and energy conservation; (7) encouraging recycling and the reduction of solid waste; and (8) protecting endangered land areas such as Antarctica and the rain forests in Brazil, West Africa, and Indonesia.

ENVIRONMENTAL EVALUATION—That part of the planning process by governmental agencies that inventories and estimates the potential effects on the human environment of alternative solutions to resource problems, determines the need for an Environmental Assessment (EA) or an Environmental Impact Statement (EIS), and aids in the consideration of alternatives and the identification of available resources.

ENVIRONMENTAL IMPACT STATEMENT (EIS)—A report required by Section 102(2)(c) of Public Law 91-190, National Environmental Policy Act (NEPA), for all major projects which significantly impact on the quality of the human environment or are environmentally controversial. The EIS is a detailed and formal evaluation of the favorable and adverse environmental and social impacts of a proposed project and its alternatives. A tool for decision making, the EIS describes the positive and negative effects of an undertaking and cites possible, less environmentally disruptive alternative actions. Also see Environmental Assessment (EA).

ENVIRONMENTAL INDICATOR—A measurement, statistic or value that provides a proximate gauge or evidence of the effects of environmental management programs or of the state or condition of the environment.

ENVIRONMENTALISM—Advocacy for or work toward protecting the natural environment from destruction or pollution.

ENVIRONMENTAL MANIPULATION—Actions taken directly or indirectly by man to alter the natural characteristics and evolving patterns of an Ecosystem through alterations to plant or animal life, or habitat conditions.

(UNITED STATES) ENVIRONMENTAL PROTECTION AGENCY (EPA)—The U.S. Environmental Protection Agency (EPA) is responsible for implementing the federal laws designed to protect the environment. EPA endeavors to accomplish it mission systematically by proper integration of a variety of research, monitoring, standard-setting, and enforcement activities. As a complement to its other activities, EPA coordinates and supports research and anti-pollution activities of state and local governments, private and public groups, individuals, and educational institutions. EPA also monitors the operations of other Federal agencies with respect to their impact on the environment. EPA was created through Reorganization Plan #3 of 1970, which was devised to consolidate the federal government's environmental regulatory activities into a single agency. The plan was sent by the President to Congress on July 9, 1970, and the agency began operation on December 2, 1970. EPA was formed by bringing together 15 components from 5 executive departments and independent agencies. Air pollution control, solid waste management, radiation control, and the drinking water program were transferred from the Department of Health, Education, and Welfare (now the Department of Health and Human Services). The federal water pollution control program was taken from the Department of the Interior, as was part of a pesticide research program. From the Department of Agriculture, EPA acquired authority to register pesticides and to regulate their use, and from the Food and Drug Administration, EPA inherited the responsibility to set tolerance levels of pesticides in food. EPA was assigned some responsibility from the Atomic Energy Commission, and absorbed the duties of the Federal Radiation Council. The enactment of major new environmental laws and important amendments to older laws in the 1970s and 1980s greatly expanded EPA's responsibilities. The agency now administers ten comprehensive environmental protection laws:

[1] Clean Air Act (CAA) [2] Clean Water Act (CWA) [3] Safe Drinking Water Act (SDWA) [4] Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA, or "Superfund") [5] Resource Conservation and Recovery Act (RCRA) [6] Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) [7] Toxic Substances Control Act (TSCA) [8] Marine Protection, Research, and Sanctuaries Act (MPRSA) [9] Uranium Mill Tailings Radiation Control Act (UMTRCA) [10] Pollution Prevention Act

The primary mandates for the water-related programs administered through the EPA Water Management Division are the Federal Water Pollution Control Act (Public Law 92-500), as amended, commonly referred to as the Clean Water Act (CWA), and the Safe Drinking Water Act (SDWA—Public Law 93-523). The CWA addresses the discharge of pollutants from point and nonpoint sources into waters of the United States (as defined). The goal of the SDWA is to protect public health over lifetime exposure to drinking water by ensuring that the source water as well as the system storage distribution and service lines are free and protected from contamination. EPA water-related programs establish national and regional objectives, promote delegation of programs to states (primacy), and support that delegation in a manner that ensures achievement of required objectives. Also see Science Advisory Board (SAB). [See Appendix E-2 for a more complete description of the organizational structure of the U.S. Environmental Protection Agency.]

ENVIRONMENTAL WATER—The water for wetlands, the instream flow for a major river (based on the largest fish flow specified in an entire reach of that river) or, for wild and scenic rivers, the amount of water based on unimpaired natural flow. Also referred to as Dedicated Natural Flows.

ENZYME—Any of numerous proteins or conjugated proteins produced by living organisms and functioning as biochemical catalysts. Specifically, an organic catalyst that accelerates (catalyzes) specific transformations of material in plants and animals. Enzymes are elaborated by cells, but their action is independent of life processes and they are not consumed in the course of their action. They occur in all tissues, particularly in digestive secretions, and are of greatest importance for the cellular processes or the digestion and utilization of food.

EOLIAN SOIL MATERIAL—Soil material accumulated through wind action.

EPA—See (United States) Environmental Protection Agency (EPA).

EPHEMERAL STREAM—A stream that flows only in direct response to precipitation, and thus discontinues its flow during dry seasons. Such flow is usually of short duration. Most of the dry washes of more arid regions may be classified as ephemeral streams. Also see Stream.

EPIDEMIOLOGY—The study of the incidence, transmission, distribution, and control of infectious disease (including waterborne disease) in large populations.

EPILIMNION—The warm upper layer of a body of water with thermal stratification, which extends down from the surface to the Thermocline, which forms the boundary between the warmer upper layers of the epilimnion and the colder waters of the lower depths, or Hypolimnion. The epilimnion is less dense than the lower waters and is wind-circulated and essentially homothermous. Also see Thermal Stratification, Fall Overturn, and Spring Overturn.

EPIPHYTE—A plant that grows on another plant but is not a parasite and produces its own food by photosynthesis, as certain orchids, mosses, and lichens; an air plant.

EPITHERMAL—A Hydrothermal mineral deposit formed within approximately one kilometer (0.6 mile) of the earth's surface and in the temperature range of 50°C (122°F) to 200°C (392°F).

EQUAL DISCHARGE INCREMENT (EDI)—A method used in measuring suspended sediment in a stream wherein samples are obtained at the centroids of equal discharge increments. This method requires knowledge of the flow distribution in the stream cross section, but can save time over the Equal Transit Rate (ETR) method because fewer verticals are required.

EQUAL FOOTING DOCTRINE (U.S. Constitution)—A provision of the U.S. Constitution which provides to each state the title to tidelands and the beds of Navigable lakes and streams within its borders. In conjunction with the Public Trust Doctrine, which is generally recognized in some form by most states, these provisions embody the principle that the state holds title to such properties within the state in trust for the beneficial use of all its citizens and that public rights of access to and for the use of tidelands and navigable waters are inalienable. Traditional public trust rights include navigation, commerce, and fishing, and in some cases have been extended to include protection of fish and wildlife, preserving trust lands in their natural condition for scientific study and scenic enjoyment, and related open-space uses.

EQUAL TRANSIT RATE (ETR)—A method used in measuring Suspended Sediment in a stream wherein the sample volume taken is proportional to the streamflow at each of several equally spaced verticals. This technique results in a gross sample proportional to the total streamflow.

EQUILIBRIUM CONDITION—As used in the chemical sense, a state in which there are no changes in the relative concentrations of the chemical species present in a system. The specific relationship is given by the equilibrium constant for the reaction of interest. Used in reference to a groundwater system it describes a condition in which all inputs (of water) equal all outputs. The Groundwater Table is neither rising nor falling under equilibrium conditions.

EQUILIBRIUM CONSTANT—A value which describes the relationship between chemical species in a system at equilibrium. The value of the constant is dependent upon temperature.

EQUILIBRIUM DRAWDOWN—The ultimate constant drawdown for a steady rate of pumped discharge.

EQUILIBRIUM SURFACE DISCHARGE—The steady rate of surface discharge which results from a steady rate of net rainfall over a long period, with the discharge rate equal to the net rainfall rate.

EQUILIBRIUM TIME—The point in time when flow conditions become substantially equal to those corresponding to Equilibrium Surface Discharge or Equilibrium Drawdown.

EQUINOCTIAL—A violent storm of wind and rain occurring at or near the time of the equinox.

EQUIPOTENTIAL LINE—A line in a field of flow such that the total head is the same for all points on the line; therefore, the direction of flow is perpendicular to the line at all points.

EQUIPOTENTIAL SURFACE—A surface (or line) in a three-dimensional ground-water flow field such that the total hydraulic head is the same everywhere on the surface.

ERODIBLE—Susceptible to Erosion.

EROSION—The wearing away and removal of materials of the earth's crust by natural means. As usually employed, the term includes weathering, solution, corrosion, and transportation. The agents that accomplish the transportation and cause most of the wear are running water, waves, moving ice, and wind currents. Most writers include under the term all the mechanical and chemical agents of weathering that loosen rock fragments before they are acted on by the transportation agents; a few authorities prefer to include only the destructive effects of the transporting agents. Various types of water erosion include:

[1] Accelerated—Erosion much more rapid than normal, natural, or geologic erosion, primarily as a result of the influence of the activities of man or, in some cases, of other animals or natural catastrophes that expose bare surfaces, for example, forest fires; [2] Geological—The normal or natural erosion caused by geological processes acting over long geologic periods and resulting in the wearing away of mountains, the building up of floodplains, coastal plains, etc., and also referred to as natural erosion; [3] Gross—A measure of the potential for soil to be dislodged and moved from its place of origin, not necessarily the amount of soil that actually reaches a stream or lake, but the amount of soil that can be calculated from water and wind equations; [4] Gully—The erosion process whereby water accumulates in narrow channels and, over short periods of time, removes soil from this narrow area to considerable depths, ranging from 1-2 feet (0.3-0.6 meters) to as much as 75-100 feet (23-31 meters); [5] Natural—The wearing away of the earth's surface by water, ice, or other natural agents under natural environmental conditions of climate, vegetation, etc., undisturbed by man, and also referred to as geological erosion; [6] Normal—The gradual erosion of land used by man that does not greatly exceed natural erosion; [7] Overfall—Erosion caused by water flowing over an overfall; [8] Rill—An erosion process in which numerous small channels only several inches deep are formed; occurs mainly on recently cultivated soils and/or recent cuts and fills; [9] Sheet—The removal of a thin, fairly uniform layer of soil from the land surface by runoff waters; [10] Shore—Removal of soil, sand, or rock from the land adjacent to a body of water due to wave action; [11] Splash—The spattering of small soil particles caused by the impact of raindrops on wet soils. The loosened and spattered particles may or may not be subsequently removed by surface runoff; [12] Streambank—Scouring of material and the cutting of channel banks by running water; [13] Streambed—Scouring of material and cutting of channel beds by running water; [14] Undercutting—Removal of material at the base of a steep slope, overfall, or cliff by falling water, a stream, wind erosion, or wave action; the removal steepens the slope or produces an overhanging cliff.

EROSION, BANK—Destruction of land areas bordering rivers or water bodies by the cutting or wearing action of waves or flowing water.

EROSION, BEACH—The retrogression of the shore line of large lakes and coastal waters caused by wave action, shore currents, or natural causes other than Subsidence.

EROSION CONTROL—Materials, structures, and actions utilized and taken to reduce or prevent erosion.

EROSION, GROSS—The total of all sheet, gully, and channel erosion in a drainage basin, usually expressed in units of mass.

EROSION, GULLY—The widening, deepening, and headcutting of small channels and waterways due to erosion.

EROSION HAZARD—A predictive rating of the erosion potential for a specific soil or location.

EROSION POTENTIAL—A ranking of a soil's potential to erode.

EROSION, RILL—Removal of soil by running water with formation of shallow channels that can be smoothed out completely by normal cultivation (tillage).

EROSION, SHEET—The removal of a fairly uniform layer of soil or materials from the land surface by the action of rainfall and runoff water.

EROSION CONTROL—The application of necessary measures including artificial structures, vegetative manipulation, water control, or physical soil changes to minimize soil erosion.

EROSION FLOOD PLAIN—A flood plain that has been created by the lateral erosion and the gradual retreat of the valley walls.

EROSIVE—The action of wind or water having sufficient velocity to cause Erosion. Not to be confused with Erodible as a quality of soil.

ESA (ENDANGERED SPECIES ACT)—An act passed by Congress in 1973 intended to protect species and subspecies of plants and animals that are of "aesthetic, ecological, educational, historical, recreational and scientific value." It may also protect the listed species' "critical habitat", the geographic area occupied by or essential to the species. The U.S. Fish and Wildlife Service (USFWS) and the National Marine Fisheries Service (NMFS) share authority to list endangered species, determine critical habitat and develop recovery plans for listed species. As of July, 1993, nationwide, some 728 plants and animals were on the federal threatened or endangered list. Further, under a settlement with environmental groups, USFWS has agreed to propose listing another 400 species over the next few years.

ESCARPMENT—A steep slope or long cliff that results from erosion or faulting and separates two relatively level areas of differing elevations; the topographic expression of a fault.

ESCHERICHIA COLI (E. COLI)—A bacterial species which inhabits the intestinal tract of man and other warm-blooded animals. Although it poses no threat to human health, its presence in drinking water does indicate the presence of other, more dangerous bacteria.

ESKER—A narrow ridge of gravelly or sandy glacial outwash material deposited by a stream in an ice tunnel within a glacier. Also referred to as os3.

ESTUARINE—(1) Of, pertaining to, or formed in, an Estuary. (2) One of the classification systems under the Wetlands and Deepwater Habitats classification system. See Wetlands. [Also see Appendix W-3, Wetlands and Deepwater Habitats, for additional information on this classification system and specific characteristics of Estuarine Systems.]

ESTUARINE WATERS—Deepwater tidal habitats and tidal wetlands that are usually enclosed by land but have access to the ocean and are at least occasionally diluted by freshwater runoff from the land (such as bays, mouths of rivers, salt marshes, lagoons, etc.).

ESTUARINE ZONE—The area near the coastline that consists of estuaries and coastal saltwater wetlands.

ESTUARY—An area where fresh water meets salt water; for example, bays, mouths of rivers, salt marshes, and lagoons. The Coastal Zone Management Act of 1972 defines an estuary as "that part of a river or stream or other body of water having unimpaired connection with the open sea, where the sea-water is measurably diluted with freshwater derived from land drainage." These brackish water ecosystems shelter and feed marine life, birds, and wildlife.

EUPHOTIC—Of, relating to, or being the uppermost layer of a body of water that receives sufficient light for Photosynthesis and the growth of green plants. Also see Euphotic Zone.

EUPHOTIC ZONE—An area, particularly in regard to lakes, where there is sufficient light for Photosynthesis to take place. Contrast with Bathyal Zone and Abyssal Zone. Also see Zone of Net Metabolic Production.

EURYBATHIC—Capable of living in a wide range of water depths. Use of an aquatic organism.

EURYHALINE—Capable of tolerating a wide range of salt water concentrations. Use of an aquatic organism.

EURYTHERMIC—Capable of tolerating a wide range in temperature.

EUTROPHIC (WATER)—Pertaining to a lake or other body of water characterized by large nutrient concentrations such as nitrogen and phosphorous and resulting high productivity. Such waters are often shallow, with algal blooms and periods of oxygen deficiency. Slightly or moderately eutrophic water can be healthful and support a complex web of plant and animal life. However, such waters are generally undesirable for drinking water and other needs. Degrees of Eutrophication typically range from Oligotrophic water (maximum transparency, minimum chlorophyll-a, minimum phosphorus) through Mesotrophic, Eutrophic, to Hypereutrophic water (minimum transparency, maximum chlorophyll-a, maximum phosphorus). Also see Carlson's Trophic State Index (TSI) and (Mean) Trophic State Index (TSI).

EUTROPHICATION—The process of enrichment of water bodies by nutrients. Degrees of Eutrophication typically range from Oligotrophic water (maximum transparency, minimum chlorophyll-a, minimum phosphorus) through Mesotrophic, Eutrophic, to Hypereutrophic water (minimum transparency, maximum chlorophyll-a, maximum phosphorus). Eutrophication of a lake normally contributes to its slow evolution into a Bog or Marsh and ultimately to dry land. Eutrophication may be accelerated by human activities and thereby speed up the aging process. Also see Carlson's Trophic State Index (TSI) and (Mean) Trophic State Index (TSI).

EUTROPHIC LAKES—Lakes that are rich in nutrients and organic materials, therefore, highly productive for plant growth. These lakes are often shallow and seasonally deficient in oxygen in the Hypolimnion. Also see Oligotrophic Lakes.

EUTROPHIC ZONE—An area, particularly with respect to lakes, where there exists sufficient light for photosynthesis to take place.

EVAPORATION—The physical process by which a liquid (or a solid) is transformed to the gaseous state. In Hydrology, evaporation is vaporization that takes place at a temperature below the boiling point.

EVAPORATION, LAND—Evaporation from land surfaces, in contrast to evaporation from free water surfaces.

EVAPORATION, NET RESERVOIR—The evaporative water loss from a reservoir after making allowance for precipitation on the reservoir and runoff that would have occurred from that precipitation from the land area covered by the reservoir. Net reservoir evaporation equals the total evaporation minus the precipitation on the reservoir plus the runoff from the land area covered by the reservoir.

EVAPORATION OPPORTUNITY (Relative Evaporation)—The ratio of the rate of evaporation from a land or water surface in contact with the atmosphere, to the Evaporativity under existing atmospheric conditions. It is the ratio of actual to potential rate of evaporation, generally expressed as a percentage. The opportunity for a given rate of evaporation to continue is determined by the available moisture supply.

EVAPORATION PAN—An open tank used to contain water for measuring the amount of evaporation. The U.S. Department of Commerce Weather Bureau Class A pan is 4 feet in diameter, 10 inches deep, set up on a timber grillage so that the top rim is about 16 inches from the ground. The water level in the pan during the course of observation is maintained between 2 and 3 inches below the rim.

EVAPORATION PONDS—(Water Quality) Shallow ponds in which sewage sludge is placed to dry and then be removed for further treatment and/or disposal. Also, shallow ponds used to extract through evaporation various chemicals in solution or suspension, e.g., salt evaporation ponds. Also see Evaporites.

EVAPORATION RATE—The quantity of water which evaporates from a given surface per unit of time, usually expressed in inches or depth per day, month, or year.

EVAPORATION, TOTAL—The sum of water lost from a given land area during any specific period of time by transpiration from vegetation and the building of plant tissue; by evaporation from water surfaces, moist soil, and snow; and by interception. It has been variously termed Evaporation, Evaporation from Land Areas, Evapotranspiration, Total Loss, Water Loss, and Fly Off.

EVAPORATIVE COOLING—Cooling of a liquid, such as water, by allowing a portion to evaporate. The process is important in the operation of cooling towers used to cool heated effluents from power plants as well as in the cooling of the human body through the evaporation of perspiration. The process is more effective than convection cooling.

EVAPORATIVITY (Potential Rate of Evaporation)—The rate of evaporation under the existing atmospheric conditions from a surface of water that is chemically pure and has the temperature of the atmosphere.

EVAPORITES—Sediments deposited from an aqueous (water) solution as a result of extensive or local evaporation of a solvent, such as salts in the Great Salt Lake in the western United States.

EVAPOTRANSPIRATION (ET)—The combined processes by which water is transferred from the earth surface to the atmosphere; evaporation of liquid or solid water plus transpiration from plants. Evapotranspiration occurs through evaporation of water from the surface, evaporation from the capillary fringe of the groundwater table, and the transpiration of groundwater by plants (Phreatophytes) whose roots tap the capillary fringe of the groundwater table. The sum of evaporation plus transpiration.

EVAPOTRANSPIRATION, ACTUAL—The evapotranspiration that actually occurs under given climatic and soil-moisture conditions.

EVAPOTRANSPIRATION OF APPLIED WATER (ETAW)—The portion of the total Evapotranspiration which is provided by irrigation.

EVAPOTRANSPIRATION, POTENTIAL—(1) The maximum quantity of water capable of being evaporated from the soil and transpired from the vegetation of a specified region in a given time interval under existing climatic conditions, expressed as depth of water. (2) The water loss that will occur if at not time there is a deficiency of water in the soil for use by vegetation.

EVAPOTRANSPIROMETER—An instrument designed to measure Evapotranspiration as related to a particular place, soil type, and vegetation. The device consists of a block of soil with some planted vegetation enclosed in a container. Evapotranspiration is determined by maintaining a Water Budget for the container, that is, accounting for the water applied, water drained off the bottom, and the change in the moisture content of the soil. If there is a provision for drainage of the soil water, the device is referred to as a Lysimeter.

EVERGLADE—A tract of marshland, usually under water and covered in places with tall grass. Usually used in the plural.

EVERGLADES [Florida]—The Everglades are extensive marshlands in southern Florida. They originally extended about 100 miles (160 kilometers) from Lake Okeechobee south to the Gulf of Mexico. More than 40 miles (64 kilometers) wide in some sections, they have an area of 4,000 square miles (10,360 square kilometers). The northern part of the Everglades has been drained by a complex system of canals and dikes, and its rich soils are now used for farming. The southern part has been preserved as the 2,188 square mile (1,400,533-acre) Everglades National Park, which was established in 1947. The Everglades were formed in a flat, shallow basin with a limestone floor that slopes very gradually to the Gulf of Mexico. The area receives over 55 inches (140 centimeters) of rain annually. Water accumulates on the surface because the porous limestone floor has been sealed by peat deposits formed by decomposing vegetation. Evaporation and drainage to the Gulf of Mexico regulate the water level. The Everglades support a unique pattern of vegetation characterized by plains of saw grass and thick hummocks of pine, cypress, and mangrove trees. The mangrove may grow as high as 70-80 feet (21-24 meters). A unique ecological system, the Everglades are under threat from 100 years of dredging, draining, and land clearing. The flow of water across the area and into the Biscayne Aquifer has been drastically reduced; seawater has intruded into the aquifer; and fertilizer runoff has encouraged the growth of algae and of non-indigenous flora. A major rescue effort has begun, involving primarily the restoration of natural water courses throughout the Everglades based on early channelization efforts of the U.S. Army Corps of Engineers (COE).

EVERGREEN (PLANT)—(Botanical) Remaining verdant, as coniferous trees and many tropical plants. Contrasted with Deciduous whose leaves, fruit, or petals fall at the end of the growing period.

EVERGREEN STAND—A plant community where Evergreen trees or shrubs represent more than 50 percent of the total areal coverage of trees and shrubs. The canopy is never without foliage; however, individual trees or shrubs may shed their leaves.

EWMP—See Efficient Water Management Practices (EWMP).

EXCEEDENCE—(Water Quality) The violation of the pollutant levels permitted by environmental protection standards.

EXCEEDENCE INTERVAL—The average number of years between the occurrence of an event of a given magnitude and one that is more extreme.

EXCESSIVE PRECIPITATION—Standard U.S. Weather Bureau term for "rainfall in which the rate of fall is greater than certain adopted limits, chosen with regard to the normal precipitation (excluding snow) of a given place or area." Not the same as Excess Rainfall.

EXCESS LAND (USBR) —Irrigable land, other than Exempt Land, owned by any landowner in excess of the maximum ownership entitlement under applicable provision of reclamation law.

EXCESS RAINFALL—Effective rainfall in excess of infiltration capacity, resulting in runoff. Not the same as Excessive Precipitation.

EXEMPT LAND (USBR)—Irrigation land in a district to which the acreage limitation and pricing provisions of reclamation law do not apply. Also see Excess Land.

EXEMPTED AQUIFER—Underground bodies of water defined in the Underground Injection Control (UIC) program as aquifers that are potential sources of drinking water though not being used as such, and thus exempted from regulations barring underground injection activities.

EXEMPTED—(Water Quality) A state (with Primacy) may exempt a Public Water System (PWS) from a requirement involving a Minimum Contaminant Level (MCL), treatment technique, or both, if the system cannot comply due to compelling economic or other factors, or because the system was in operation before the requirement or MCL was instituted, and the exemption will not create a public health risk.

EXHAUST TRAIL—A condensation trail that is visible when water vapor in aircraft exhaust mixes with the air in the vehicle's wake and saturates it. Also referred to as a Contrail or Vapor Trail.

EXOGENOUS—(Geology) Geologic processes originating at or near the surface of the earth or magma.

EXOGENOUS VARIABLE—(Statistics) A variable whose value is determined completely outside the model system and whose behavior is used to describe that of the Endogenous Variable. As such the terms independent or explanatory variable are frequently used. An exception to this is a Lagged Endogenous Variable, which may also be an explanatory variable but whose value is determined within the system of equations by past values of the explanatory variables. For example, in the equation below, for any time period t (where t=1, 2, ..., n),

Yt = a + ß Xt + ð Yt-1 + et

where Yt represents the endogenous variable, Xt represents the exogenous variable, and Yt-1 represents the lagged endogenous variable. Also referred to as the Independent Variable or the Explanatory Variable.

EXOSMOSIS, also Exosmotic—The passage of a fluid through a semipermeable membrane toward a solution of lower concentration, especially the passage of water through a cell membrane into the surrounding medium. Contrast with Endosmosis (Endosmotic).

EXOTIC—An organism or species that is not native to the area in which it is found.

EXOTIC SPECIES—A non-native species that is introduced into an area.

EXPLORATORY HOLES—An excavation drilled to obtain engineering or geological data for the purposes of defining water bearing formations for production wells.

EXPONENTIAL DECAY—(Statistics) A rate of decay (decline) characterized by a fixed percentage each time period, e.g., a 10 percent decline in each period of time. Represented by the equation:

N(t) = N0e-kt

where N(t) is the value of the variable at time period t, N0 is the initial value, e is the base of the natural logarithm, k is a constant value, and t represents the various time period where t = 1, 2, ..., n.

EXPONENTIAL GROWTH—(Statistics) A rate of growth characterized by a fixed percentage each time period, e.g., a 10 percent growth each period of time. Represented by the equation:

N(t) = N0ekt

where N(t) is the population level at time t, e is the base of the natural logarithm, k is a constant value, and t represents time period where t = 1, 2, ..., n. Compare to Arithmetic Growth and Sigmoid Growth.

EXPOSURE—The amount of pollution present in a given environment that represents a potential health threat to living organisms.

EXPOSURE ASSESSMENT—Identifying the pathways by which toxicants may reach individuals, estimating how much of a chemical an individual is likely to be exposed to, and estimating the number likely to be exposed.

EXPOSURE INDICATOR—A characteristic of the environment measured to provide evidence of the occurrence or magnitude of a response indicator's exposure to a chemical or biological stress.

EXTENDED AERATION—(Water Quality) A modification of the activated sludge process which maintains a longer period of aeration, thus providing for sludge digestion within the aeration tank.

EXTENSION, COOPERATIVE—Associated with state land grant institutions of higher education, cooperative extension provides experts in agriculture and agribusiness, community and economic development, natural resources, family living and youth development. Most state extension faculty and staff are county-based giving them extensive knowledge in local conditions and concerns. Extension stresses partnership with the various levels of government, volunteers and the private sector in carrying out programming activities.

EXTERNALITY—The unintended or unwanted byproduct of production or consumption which must be borne by society in general. For example, water pollution may represent an externality of motorcraft operation.

EXTERNAL COST—The cost of production or consumption that must be borne by society and not specifically by the producer or consumer.

EXTINCTION—(Biology) The complete disappearance of a species because of failure to adapt to environmental change. Compare to Extirpation.

EXTINCTION DEPTH—The minimum depth from the surface to the groundwater table at which plant species that rely on groundwater can no longer survive.

EXTIRPATED SPECIES—A species rendered extinct in a given area.

EXTIRPATION—(Biology) To destroy or remove completely, as a species from an particular area, region, or habitat. Compare to Extinction.

EXTRACTABLE ORGANICS—(Water Quality) Organic chemical compounds that can be removed from a water sample by the solvent methylene chloride under conditions of pH greater than 11 or less than 2. Organic compounds in water represent a class of pollutants that are potentially toxic materials.

EXTRAPOLATE/EXTRAPOLATION—(Statistics) The continuation, by means of simple estimation or sophisticated analysis, of a trend of time series data beyond its last observed value. The function of time series model building is to add some degree of certainty and confidence to this extrapolation process by analyzing the past behavior of the data and attempting to fit a model to its historical patterns which may then be used to forecast (extrapolate) its future values. Also see Interpolate/Interpolation.

EXTREME HIGH WATER OF SPRING TIDES—The highest tide occurring during a lunar month, usually near the new or full moon. This is equivalent to extreme higher high water of mixed semidiurnal tides.

EXTREME LOW WATER OF SPRING TIDES—The lowest tide occurring during a lunar month, usually near the new or full moon. This is equivalent to extreme lower low water of mixed semidiurnal tides.

EXTREME VALUE SERIES—Hydrological series which includes the largest or smallest values, with each value selected from an equal time interval in the record.

EXTRUSIVE BEDROCK—(Geology) Those Igneous Rocks derived from volcanic lavas that cooled on the surface of the earth. This lava cools rapidly and forms fine-textured rocks such as basalt and andesite.

EXUDE—(1) To ooze forth. (2) To discharge or emit a liquid gradually.

F [F] (SELF-PURIFICATION FACTOR)—The self-purification factor is an indication of the ability of a stream to assimilate a waste discharge. It is defined as the ratio of the re-aeration (r) and the rate of deoxygenation (k), or F = r/k, where F is called the self-purification factor.

FACE (of a Dam)—The external surface of a structure, such as the surface of an appurtenance or a dam.

FACILITIES PLANS—Plans and studies related to the construction of water treatment works necessary to comply with the Clean Water Act (CWA). A facilities plan investigates needs and provides information on the cost effectiveness of alternatives, a recommended plan, an Environmental Assessment of the recommendation, and descriptions of the treatment works, costs, and a completion schedule.

FACULTATIVE BACTERIA—Bacteria that can live under Aerobic or Anaerobic conditions.

FACULTATIVE PHREATOPHYTE—Plants that utilize moisture from groundwater for a portion of their water requirements.

FAHRENHEIT (F)—(1) A unit of temperature. (2) Of or relating to a temperature scale that registers the freezing point of water as 32°F and the boiling point as 212°F at one atmosphere of pressure. See Fahrenheit Temperature Scale.

FAHRENHEIT TEMPERATURE SCALE—A thermometric scale on which the freezing point of water is at 32°F (Fahrenheit) above the 0°(F) mark on the scale, and the boiling point of water is at 212°F. Contrast with the Centigrade Temperature Scale, using degrees Celsius (C), in which 0°(C) marks the freezing point of water and 100°C indicates the boiling point of water (at sea level). The formula for converting a Fahrenheit temperature to Celsius is C°=5/9(F° - 32).

FAIRFIELD-HARDY DIGESTER—(Water Quality) A machine that decomposes garbage, sewage sludge, industrial and other organic wastes by a controlled continuous Aerobic-Thermophilic Process.

FALLON NATIONAL WILDLIFE REFUGE (NWR) [Nevada]—One of the nine National Wildlife Refuges (NWR) located in the State of Nevada, the Fallon NWR was established in 1931 and encompasses approximately 17,900 acres (28 square miles) where the Carson River terminates in the Carson Sink and is situated within the northwest portion of the Stillwater Wildlife Management Area near the town of Fallon in Churchill County, Nevada. Due to typically limited and uncertain flows of the Carson River at its terminus, generally not enough water enters this refuge to maintain it as a viable wetland area. The Fallon NWR is currently managed by the U.S. Fish and Wildlife Service (USFWS) along with the Stillwater National Wildlife Refuge and is included as part of the Stillwater Wildlife Management Area. Also see National Wildlife Refuge (NWR) System and National Wildlife Refuges (NWR) [Nevada].

FALL OVERTURN—A physical phenomenon that may take place in a body of water during early autumn. The sequence of events leading to fall overturn include:

[1] The cooling of surface waters; [2] A density change in surface waters producing convection currents from top to bottom; [3] The circulation of the total water volume by wind action; and [4] Eventual vertical temperature equality.

The overturn results in a uniformity of the physical and chemical properties of the entire water body. Also referred to as Fall Turnover. Also see Spring Overturn.

FALLOW—(1) Allowing cropland, either tilled or untilled, to lie idle during the whole or greater portion of the growing season. (2) Land plowed and tilled and left unplanted.

FALLS—A waterfall or other precipitous descent of water.

FANGLOMERATE—Heterogeneous materials that were originally deposited in an Alluvial Fan but since deposition have been cemented into solid rock.

FARM DELIVERY REQUIREMENT—The Crop Irrigation Requirement plus farm losses due to evaporation, deep percolation, surface waste, and nonproductive consumption. The losses are measured by the Farm Irrigation Efficiency, which is the percent of farm-delivered water that remains in the root zone and is available for crop growth.

FARM EFFICIENCY—The consumptive Crop Irrigation Requirement (CIR) divided by the farm water delivery.

FARM HEADGATE DELIVERY (DIVERSION)—That amount of water in acre feet (AF) delivered through a farm headgate.

FARM IRRIGATION EFFICIENCY—An expression comparing the amount of water actually required for growing a crop to the amount of irrigation water that is diverted at the farm headgate. Expressed as a percentage on an annual basis.

FARM POND—A water impoundment made by constructing a dam or embankment or by excavating a pit or "dug out".

FARM SURFACE RUNOFF (TAILWATER)—A portion of the Farm Headgate Delivery that flows off the lower portion of the farm or field surface (drain ditch) flow. This is one loss component considered in Farm Irrigation Efficiency.

FARM WASTE AND DEEP PERCOLATION—The amount of irrigation water delivered to the crop area from a canal turnout or ground water pump that is not consumptively used on the crop area. Includes water moving through the root zone to the water table, water intercepted by drainage systems, and surface waste to natural or constructed drainage systems, and non-cropped areas.

FATA MORGANA—See Mirage.

FATHOM—(1) A unit of length equal to 6 feet (1.83 meters), used principally in the measurement and specification of marine depths. (2) To measure the depth of a body of water as with a Lead Line.

FAUCET—A device for regulating the flow of a liquid from a reservoir such as a pipe or drum.

FAULT—(Geology) A fracture in rock along which movement can be demonstrated. A fracture in the earth's crust forming a boundary between rock masses that have shifted. Faults may be classified as follows:

[1] Active Fault—A fault that has moved recently and which is likely to move again, usually defined as one that has shown movement within the last 11,000 years and can be expected to move again within the next 100 years; [2] Potentially Active Fault—A fault that moved within the Quaternary Period (i.e., within the last 2 million years) or a fault which, because it is judged to be capable of ground rupture or shaking, poses an unacceptable risk for a proposed project or structure; [3] Historically Active Fault—A fault active within the last 200 years; [4] Inactive Fault—A fault which has shown no evidence of movement in recent geologic time and no potential for movement in the relatively near future.

FAULT CREEP—A very slow movement along a fault which is unaccompanied by perceptible earthquakes.

FAULT ESCARPMENT—(Geology) A fracture or fracture zone along which there has been displacement of one side with respect to the other.

FAULT-LINE SCARP—A steep slope produced along an old fault line by differential weathering and erosion, rather than by fault movement.

FAULT, RUPTURE—A break in the ground along the fault line during an earthquake.

FAULT SAG PONDS—A small, enclosed depression along an active or recent fault. It is caused by differential movement between slices and blocks within the fault zone or by warping and tilting associated with differential displacement along the fault, and it forms the site of a sag pond.

FAULT SCARP—A cliff formed by a fault, usually modified by erosion unless the fault is very recent.

FAULT TRACE—The intersection of a fault and the earth's surface as often revealed by dislocation of fences and roads and/or by ridges and furrows in the ground.

FAUNA—(1) A term used to describe the animal species of a specific region or time. (2) All animal life associated with a given habitat, country, area, or period.

FEASIBILITY STUDY (FS)—(1) A complete assessment of alternative courses of action to solve one or more problems, to meet needs, and to recommend the most practical course of action consistent with state and local planning objectives. (2) (Environmental) Analysis of the practicability of a proposal, e.g., a description and analysis of potential cleanup alternatives for a site such as one on the National Priorities List (NPL). The feasibility study usually recommends selection of a cost-effective alternative. It usually starts as soon as the Remedial Investigation (RI) is underway; together, they are commonly referred to as the "RI/FS".

FECAL BACTERIA—Any type of bacteria whose normal habitat is the colon of warm-blooded mammals, such as man. These organisms are usually divided into groups, such as Fecal Coliform or Fecal Streptococci (Streptococcus).

FECAL COLIFORM BACTERIA—A group of bacteria normally present in large numbers in the intestinal tracts of humans and other warm-blooded animals. Specifically, the group includes all of the rod-shaped bacteria that are non-sporeforming, Gram-Negative, lactose-fermenting in 24 hours at 44.5C, and which can grow with or without oxygen. The presence of this type of bacteria in water, beverages, or food is usually taken to indicate that the material is contaminated with solid human waste. Bacteria included in this classification represent a subgroup of the larger group termed Coliform.

FECAL MATERIAL—(Water Quality) Solid waste produced by humans and other animals and discharged from the gastrointestinal tract. Also referred to as feces or solid excrement, it is a component of domestic sewage and must be treated to avoid the transmission of fecal bacteria and other organisms or disease.

FECAL STREPTOCOCCUS—A group of bacteria normally present in large numbers in the intestinal tracts of warm-blooded animals other than humans. By assessing the ratio of coliforms to streptococci in a water sample, a rough estimate can be made of the relative contribution of fecal contamination from the two mentioned possible sources.

FEDERAL EMERGENCY MANAGEMENT AGENCY (FEMA)—The federal agency responsible for administering the National Flood Insurance Program.

FEDERAL POWER ACT—An act of Congress creating a federal licensing system administered by the Federal Energy Regulatory Commission (FERC) and requiring that a license be obtained for nonfederal hydroelectric projects proposing to use Navigable waters or federal lands. The act contains a clause modeled after a clause in the Reclamation Act of 1902 which disclaims any intent to affect state water rights law. Subsequently, in a number of decisions dating back to the 1940s, the U.S. Supreme Court held that the provisions of both the Reclamation Act and the Federal Power Act preempted inconsistent provisions of state law. Decisions under both acts found that these clauses were merely "saving clauses" which required the United States to follow minimal state procedural laws or to pay just compensation where vested non-federal water rights are taken. Later the Supreme Court overturned a number of its earlier decisions and required that the Bureau of Reclamation (USBR) comply with conditions in state water rights permits unless those conditions conflict with "clear Congressional directives." However, no such reversal of the Federal Power Act's provisions followed and more recent decisions (Sayles Hydro Association v. Maughan, February 1993) reinforced this fact by holding that federal law has "occupied the field," preventing any state regulation of federally licensed power projects other than determining proprietary water rights. This precedent has far-reaching implications over states' rights to regulate water projects and stream flows within their borders. There have been instances where holders of Federal Power Act licenses have claimed preemption from state safety of dams requirements, minimum stream flow requirements, and state designation of wild and scenic streams. Also see Equal Footing Doctrine (U.S. Constitution) and Public Trust Doctrine.

FEDERAL RESERVED WATER RIGHTS—A category of federal water rights, created by federal law. These rights are created when the federal government withdraws land from the public domain to establish a federal reservation such as a national park, forest, or Indian reservation. By this action, the government is held to have reserved water rights sufficient for the primary purpose for which the land was withdrawn. Also see Winters Rights (Decision), Reservation Doctrine, Reserved Rights Doctrine, and Winters Doctrine, and Water Law [Federal].

FEDERAL WATER POLLUTION CONTROL ACT (Public Law 92-500)—More commonly referred to as the Clean Water Act (CWA), constitutes the basic federal water pollution control statute for the United States. Originally based on the Water Quality Act of 1965 which began setting water quality standards. The 1966 amendments to this act increased federal government funding for sewage treatment plants. Additional 1972 amendments established a goal of zero toxic discharges and "fishable" and "swimmable" surface waters. Enforceable provisions of the CWA include technology-based effluent standards for point sources of pollution, a state-run control program for nonpoint pollution sources, a construction grants program to build or upgrade municipal sewage treatment plants, a regulatory system for spills of oil and other hazardous wastes, and a wetlands preservation program.

FEEDLOT—A confined area for the controlled feeding of animals. Tends to concentrate large amounts of animal waste that cannot be absorbed by the soil and, therefore, may be carried to nearby streams or lakes by rainfall runoff.

FEEDWATER—(Water Quality) Water input into a desalting or water treatment plant.

FEET PER SECOND (Ft./Sec.)—A measure of the velocity of moving water.

FEN—Low land covered wholly or partly with water; a Moor or Marsh. A type of Wetland that accumulates peat deposits. Fens are less acidic than Bogs, deriving most of their water from groundwater rich in calcium and magnesium. Also see Calcareous Fens.

FERMENTATION, ANAEROBIC—(Water Quality) The process in which carbohydrates are converted in the absence of oxygen to hydrocarbons (such as methane gas).

FERROUS SULFATE—A greenish crystalline compound, FeSO4 · H2O, used as a pigment, fertilizer, and feed additive, in sewage and water treatment, and as a medicine in the treatment of iron deficiency. Also called Copperas.

FERTIGATION—The use of irrigation water as a vehicle for spreading fertilizer on the land.

FERTILIZER—Any organic or inorganic material of natural or synthetic origin that is added to a soil to supply elements essential to plant growth. Various types of fertilizers include acid-forming, blended, bulk-blended, chemical, coated, conditioned, granular, liquid, non-granular, prilled, solution, straight, and suspension.

FETCH—(1) The distance traveled by waves in open water, from their point of origin to the point where they break. (2) The distance the wind blows over water or another homogeneous surface without appreciable change in direction.

FIELD—(1) A broad, level, open expanse of land; a meadow. (2) A cultivated expanse of land, especially one devoted to a particular crop. (3) A portion of land or a geologic formation containing a specified natural resource. (4) A wide, unbroken expanse, as of ice.

FIELD (MOISTURE) CAPACITY—The capacity of soil to hold water. It is measured by the soil scientist as the ratio of the weight of water retained by the soil to the weight of the dry soil.

FIELD DIVERSION—An interception channel near the contour to carry runoff to a waterway. Intervals vary with the precipitation, slope, and cropping.

FIELD-MOISTURE CAPACITY—The quantity of water which can be permanently retained in the soil in opposition to the downward pull of gravity.

FIELD-MOISTURE DEFICIENCY—The quantity of water which would be required to restore the soil moisture to Field-Moisture Capacity.

FIELD PERMEABILITY—Permeability corresponding to the temperature which occurs under field conditions.

FIELD SPRINKLER SYSTEM—A system of closed conduits carrying irrigation water under pressure to orifices designed to distribute the water over a given area.

FILAMENTOUS ALGAE—Aggregations of one-celled plants that grow in long strings or mats in water and are either attached or free floating and tend to plug canals, weirs, and other structures, but also provide habitat of invertebrate animals.

FILL—(Geology) Any sediment deposited by any agent such as water so as to fill or partly fill a channel, valley, sink, or other depression.

FILLING—Depositing dirt, mud or other materials into aquatic areas to create more dry land, usually for agricultural or commercial development purposes, and frequently with ruinous ecological consequences. Also see Wetland Banking, Wetland "Clumping" (Aggregation), and Wetland Mitigation.

FILTER—A device used to remove solids from a mixture or to separate materials. A porous material through which a liquid or gas is passed in order to separate the fluid from suspended particular matter. Suspended materials are frequently separated from water using filters.

FILTER BED—A layer of sand or gravel on the bottom of a reservoir or tank, used to filter water or sewage.

FILTER CAKE—(1) The solids or semisolids deposited on a filter as a fluid is moved through it. (2) The remaining solids or semisolids on a filter after the fluid in a material is extracted by a negative pressure.

FILTER FEEDER—An aquatic animal, such as a clam, barnacle, or sponge, that feeds by filtering particulate organic material from water.

FILTER STRIP—A strip or area of vegetation used for removing sediment, organic matter, and other pollutants from runoff and waste water.

FILTER ZONE (of a Dam)—A band or zone of granular material that is incorporated into a dam and is graded (either naturally or by selection) so as to allow seepage to flow across or down the filter without causing the migration of material from zones adjacent to the filter zone.

FILTERABLE—Of particles that are sufficiently small to allow their passage through filters capable of retaining most particles. For example, a filterable virus is one that will pass through a filter that will normally retain bacteria.

FILTRATE—Liquid that has been passed through a filter.

FILTRATION—(1) The process in which suspended matter is removed from a liquid through a medium which is permeable to the liquid but not to the suspended material. (2) (Water Quality) A treatment process, under the control of qualified operators, for removing solid (particulate) matter from water by means of porous media such as sand or a man-made filter; often used to remove particles that contain Pathogens.

FINAL CLARIFIER—(Water Quality) A gravitational settling tank installed as part of some wastewater treatment plants and placed after the biological treatment step. The tank functions to remove suspended solids. Also referred to as Secondary Clarifier.

FINDING OF NO SIGNIFICANT IMPACT (FONSI)—A document prepared by a federal agency showing why a proposed action would not have a significant impact on the environment and thus would not require the preparation of an Environmental Impact Statement (EIS). A FONSI is based on the results of an Environmental Assessment (EA).

FINISHED WATER—(Water Quality) Water that has completed a purification or treatment process; water that has passed through all the processes in a water treatment plant and is ready to be delivered to consumers. Contrast with Raw Water.

FIRM CAPACITY—For public drinking water supplies, the system delivery capacity with the largest single water well or production unit out of service.

FIRM YIELD—The maximum annual supply of a given water development that is expected to be available on demand, with the understanding that lower yields will occur in accordance with a predetermined schedule or probability. Sometimes referred to as Dependable Yield.

FIRN (FIRN SNOW)—Old snow on the top of glaciers that has become granular and compact through temperature changes, forming the transition stage to glacial ice. Also referred to as Neve.

FIRN LINE—The highest level to which the fresh snow on a glacier's surface retreats during the melting season; the line separating the accumulation area from the ablation area.

FIRST DRAW—The water that comes out when the tap is first opened, likely to contain the highest level of lead contamination from plumbing fixtures and materials.

FIRST IN TIME, FIRST IN RIGHT—A phrase indicating that older water rights have priority over more recent rights if there is not enough water to satisfy all rights. See (Prior) Appropriation Doctrine and Appropriative Water Rights.

FIRTH—A narrow inlet or arm of the sea; an Estuary.

(UNITED STATES) FISH AND WILDLIFE SERVICE (USFWS)—Part of the U.S. Department of the Interior, the early beginnings of the Fish and Wildlife Service go back to 1871 when the federal government established the Commissioner of Fisheries. In 1896, the Division of Biological Survey was established within the Department of Agriculture. In 1939, these functions were transferred to the Department of the Interior. Then in 1940, these functions were formally consolidated and redesignated as the Fish and Wildlife Service. Further reorganization came in 1956 when the Fish and Wildlife Act created the Bureau of Sport Fisheries and Wildlife. An amendment to this act in 1974 designated the Bureau as the U.S. Fish and Wildlife Service. Today the USFWS consists of a headquarters in Washington, D.C., eight regional offices, and over 700 field units and installations. Included are more than 470 National Wildlife Refuges, comprising more than 90 million acres, 57 fish and wildlife research laboratories and field units, 43 cooperative research units at universities across the country, nearly 135 national fish hatcheries and fishery assistance stations, and a nationwide network of law enforcement agents and biologists. The functions of the USFWS primarily includes the following:

[1] Acquires, protects and manages unique ecosystems necessary to sustain fish and wildlife, such as migratory birds and endangered species; [2] As specified in the Endangered Species Act (ESA) (1973), as amended, and in conjunction with the National Marine Fisheries Service (NMFS), determines critical habitat and develops recovery plans for protected endangered and threatened species of plants and animals; [3] Operates fish hatcheries to support research, develop new techniques and fulfill the public demand for recreational fishing; [4] Operates wildlife refuges to provide, restore, and manage a national network of lands and waters sufficient in size, diversity and location to meet society's needs for areas where the widest possible spectrum of benefits associated with wildlife and wildlands is enhanced and made available; [5] Conducts fundamental research on fish, wildlife and their habitats to provide better management and produce healthier and more vigorous animals; also protects fish and wildlife from dislocation or destruction of their habitats; [6] Renders financial and professional assistance to states, through federal aid programs, for the enhancement and restoration of fish and wildlife resources; [7] Establishes and enforces regulations for the protection of migratory birds, marine mammals, fish and other non-endangered wildlife from illegal taking, transportation or sale within the United States or from foreign countries; and [8] Communicates information essential for public awareness and understanding of the importance of fish and wildlife resources, and changes reflecting environmental degradation that ultimately will affect the welfare of human beings.

Also see National Wildlife Refuge System, Endangered Species Act (ESA), Endangered Species, Threaten Species, and National Oceanic and Atmospheric Administration (NOAA).

FISH CREDIT WATER —Generally, water reserved in upstream reservoirs for release for downstream fisheries purposes. Often provisions will be made such that other forms of water credits, e.g., Drought Reserve Water, will convert to fish credit water if snowpack water content or runoff is deemed sufficient by a stipulated date.

FISHING WATERS—Waters used for angling or for commercial fishing.

FISH LADDER—(1) A series of small pools arranged in an ascending fashion to allow the migration of fish upstream past construction obstacles, such as dams. (2) An inclined trough which carries water from above to below a dam so that fish can easily swim upstream. There are various types, some with baffles to reduce the velocity of the water and some consisting of a series of boxes with water spilling down from one box to the next. Also see Fishway.

FISHPOND—A small body of water managed for fish.

FISH SCREEN—A porous barrier placed across the inlet our outlet of a pond to prevent the passage of fish.

FISHWAY—A passageway designed to enable fish to ascend a dam, cataract, or velocity barrier. Also referred to as a Fish Ladder.

FISSURE—A surface of a fracture or crack in a rock along which there is a distinct separation.

FIX A SAMPLE—A sample is "fixed" in the field by adding chemicals that prevent water quality indicators of interest in the sample from changing before laboratory measurements are made.

FIXED GROUND WATER—Water held in saturated material within pore spaces so small that it is permanently attached to the walls, or moves so slowly that it is usually not available as a source of water for pumping.

FJORD, or Fiord—A long, narrow, deep inlet of the sea between steep slopes.

FLASH—To fill suddenly with water.

FLASHBOARD—A temporary barrier, relatively low in height and usually constructed of wood, placed along the crest of the spillway of a dam to allow the water surface in the reservoir to be raised above spillway level in order to increase the storage capacity. It is designed to be readily removed, lowered or carried away by high flow or floods.

FLASH FLOOD, also Flashflood—A sudden flood of great volume, usually caused by a heavy rain. Also, a flood that crests in a short length of time and is often characterized by high velocity flows. It is often the result of heavy rainfall in a localized area.

FLAT—A level landform composed of Unconsolidated Sediments—usually mud or sand. Flats may be irregularly shaped or elongate and continuous with the shore, whereas bars are generally elongate, parallel to the shore, and separated from the shore by water.

FLATBOAT—A boat with a flat bottom and square ends used for transportation of bulky freight, especially used in shallow waters.

FLAT-WATER—Of or on a level or slow-moving watercourse.

FLOAT—(1) To remain suspended within or on the surface of a fluid without sinking. To cause to remain suspended without sinking or falling. (2) To put into water; launch. (3) To flood (land), as for irrigation.

FLOATER—A Wetland plant that floats on the surface of the water.

FLOATING DOCK—(1) A structure that can be submerged to permit the entry and docking of a ship and then raised to lift the ship from the water for repairs. Also referred to as a Floating Drydock. (2) A dock that is supported by metal pipes on which it can move up and down with the rise and fall of the water level.

FLOATING PLANT—A non-anchored plant that floats freely in the water or on the surface; e.g., water hyacinth (Eichhornia crassipes) or common duckweed (Lemna minor).

FLOATING-LEAVED PLANT—A rooted, Herbaceous Hydrophyte with some leaves floating on the water surface; e.g., white water lily (Nymphae odorata), floating-leaved pondweed (Potamogeton natans). Plants such as yellow water lily (Nuphar luteum), which sometimes have leaves raised above the surface, are considered floating-leaved plants or emergents, depending on their growth habit at a particular site.

FLOC—Generally, a very fine, fluffy mass formed by the aggregation of fine suspended particles, as in a precipitate. In terms of water quality, clumped solids or precipitates formed in sewage by biological or chemical activity.

FLOCCULATE—To aggregate or clump together individual, tiny particles into small clumps or clusters.

FLOCCULATION—(Water Quality) In water and wastewater treatment, the agglomeration or clustering of colloidal and finely divided suspended matter after coagulation by gentle stirring by either mechanical or hydraulic means such that they can be separated from water or sewage.

FLOE—An ice flow. Also a segment that has separated from such an ice mass.

FLOE ICE—Ice usually several feet thick, which has formed on the surface of a body of water and then has broken into pieces and is floating on the water's surface.

(THE) FLOOD—(Biblical) The universal deluge recorded in the Old Testament as having occurred during the life of Noah.

FLOOD, or Flood Waters—(1) An overflow of water onto lands that are used or usable by man and not normally covered by water. Floods have two essential characteristics: The inundation of land is temporary; and the land is adjacent to and inundated by overflow from a river, stream, lake, or ocean. (2) As defined, in part, in the Standard Flood Insurance Policy (SFIP): "A general and temporary condition of partial or complete inundation of normally dry land areas from overflow of inland or tidal waters or from the unusual and rapid accumulation or runoff of surface waters from any source."

FLOOD, 100-YEAR—A 100-year flood does not refer to a flood that occurs once every 100 years, but to a flood level with a 1 percent or greater chance of being equaled or exceeded in any given year. Areas between the 100-year and the 500-year flood boundaries are termed Moderate Flood Hazard Areas. The remaining areas are above the 500-year flood level and are termed Minimal Flood Hazard Areas.

FLOOD, ANNUAL—The highest peak discharge in a water year.

FLOOD ABATEMENT—See Flood Control.

FLOOD-BASE DISCHARGE—A value of high flow usually computed during the first 5 years of station operation that, on the average, is exceeded about three times per year.

FLOOD BOUNDARY FLOODWAY MAP (FBFM)—Official map of a community where the boundaries of the flood, mudslide and related erosion areas having special hazards have been designated as Flood Zones A, M, and E. Now superseded by the Floodway Hazard Boundary Map (FHBM).

FLOOD CAPACITY—The flow carried by a stream or floodway at bankfull water level. Also, the storage capacity of the flood pool at a reservoir.

FLOOD CONTROL (STORAGE)—The control of flood waters by the construction of flood storage reservoirs, flood water retaining structures, channel improvements, levees, bypass channels, other engineering works, or vegetative changes.

FLOOD CONTROL POOL—Reservoir volume reserved for flood runoff and then evacuated as soon as possible to keep that volume in readiness for the next flood.

FLOOD CREST—The maximum stage or elevation reached by the waters of a flood at a given location.

FLOOD DAMAGE—The direct and indirect economic loss caused by floods including damage by inundation, erosion, or sediment deposition. Indirect damages may also include emergency costs and business or financial losses. Evaluation may be based on the cost of replacing, repairing, or rehabilitating; or the comparative change in market or sales value; or on the change in income or production caused by flooding.

FLOOD DURATION CURVE—A cumulative frequency curve that shows the percentage of time that specified discharges are equaled or exceeded.

FLOOD FORECASTING—Flood forecasts are primarily the responsibility of the National Weather Service, National Oceanic and Atmospheric Administration (NOAA), and are used to predict flood stages and times and indicate areas subject to flooding.

FLOOD FREQUENCY—A statistical expression or measure of how often a hydrologic event of a given size or magnitude should, on an average, be equaled or exceeded. For example, a 50-year frequency flood (2 percent change of occurrence) should be equaled or exceeded, on the average, once in 50 years. Also see Hundred-Year Flood, X-Year Flood, and X-Year Flood, Y-Duration Rain.

FLOOD FREQUENCY CURVE—(1) A graph showing the average interval of time within which a flood of a given magnitude will be equaled or exceeded once. (2) A similar graph but plotted with the Recurrence Intervals of floods plotted instead.

FLOODGATE—(1) A gate used to control the flow of a body of water. Also referred to as a Water Gate. (2) Something that restrains a flood or an outpouring.

FLOOD HAZARD ZONES (Defined)—Zones on the Flood Insurance Rate Map (FIRM) in which the risk premium insurance rates have been established by a Flood Insurance Study (FIS). The following flood hazard zone designations apply:

[1] Flood Zone A—Area of special flood hazard without water surface elevation determination; [2] Flood Zones A1-30 & AE—Areas of special flood hazard with water surface elevations determined; [3] Flood Zone AO—Area of special flood hazard having shallow water depths and or unpredictable flow paths between one and three feet; [4] Flood Zone A-99—Area of special flood hazard where enough progress has been made on a protective system, such as dikes, dams, and levees, to consider it complete for insurance rating purposes; [5] Flood Zone AH—Area of special flood hazard having shallow water depths and or unpredictable flow paths between one and three feet and with water surface elevations determined; [6] Flood Zones B & Shaded X—Areas of moderate flood hazard; [7] Flood Zones C & Unshaded X—Areas of minimal hazard; [8] Flood Zone D—Area of undetermined but possible flood hazard; [9] Flood Zone E—Area of special flood-related erosion hazards; [10] Flood Zone M—Area of special mudslide or mudflow hazards.

FLOODING—Temporary inundation of all or part of the floodplain along a well-defined channel or temporary localized inundation occurring when surface water runoff moves via surface flow, swales, channels, and sewers toward well-defined channels. Flooding is not necessarily synonymous with Flooding Problem.

FLOODING PROBLEM—The disruption to community affairs, damage to property and facilities, and the danger to human life and health that occurs when land use is incompatible with the hydrologic-hydraulic system.

FLOOD INSURANCE—A means of spreading the cost of flood losses. It enables interested persons to purchase insurance against loss resulting from floods.

FLOOD INSURANCE RATE MAP (FIRM)—Official map on which the Federal Emergency Management Agency (FEMA) has delineated both the areas of special flood hazards and the risk premium zones applicable to the community.

FLOOD INSURANCE STUDY (FIS)—A document containing the results of an examination, evaluation, and determination of flood hazards and, if appropriate, corresponding water surface elevations, mudslides and erosion hazards.

FLOOD, INTERMEDIATE REGIONAL—A flood having a one percent probability, or an average frequency of occurrence on the order of once in 100 years, although the flood may occur in any year. The intermediate regional flood is based on statistical analyses of streamflow records available for the watershed and analyses of rainfall and runoff characteristics in the "general region of the watershed."

FLOOD IRRIGATION—The application of irrigation water where the entire surface of the soil is covered by a sheet of water, called Controlled Flooding when water is impounded or the flow directed by border dikes, ridges, or ditches.

FLOOD, MAXIMUM PROBABLE—The greatest flood that may be expected at a place, taking into account all pertinent factors of location, meteorology, hydrology, and terrain.

FLOOD OF RECORD—The highest observed river stage or discharge at a given site during the period of record keeping. May not necessarily be the highest known stage.

FLOOD PEAK—The maximum instantaneous discharge of a flood at a given location. It usually occurs at or near the time of the flood crest, i.e., the maximum stage or elevation reached by the flood flow.

FLOOD PLAIN, also Floodplain—(1) A strip of relatively smooth land bordering a stream, built of sediment carried by the stream and dropped in the slack water beyond the influence of the swiftest current. It is called a Living Flood Plain if it is overflowed in times of high water but a Fossil Flood Plain if it is beyond the reach of the highest flood. (2) The lowland that borders a stream or river, usually dry but subject to flooding. (3) That land outside of a stream channel described by the perimeter of the Maximum Probable Flood. Also referred to as a Flood-Prone Area.

FLOODPLAIN FRINGE—The portion of the flood plain outside the floodway which is covered by floodwaters during the 100-year recurrence interval flood. It is generally associated with shallow, standing or slowly moving water rather than deep, rapidly flowing water.

FLOODPLAIN INFORMATION REPORTS—Reports prepared to provide local governmental agencies with basic technical data to assist in planning for wise use and development of their flood plains.

FLOODPLAIN MANAGEMENT—Comprehensive flood damage prevention programs which require the integration of all alternative measures (structural and nonstructural) in investigation of flood problems and planning for wise use of the floodplain. Includes corrective and preventive measures for reducing flood damage and preserving and enhancing, where possible, natural resources in the floodplain, including but not limited to emergency preparedness plans, flood control works and floodplain management regulations and ordinances.

FLOODPLAIN MANAGEMENT REGULATIONS—Any federal, state, or local government regulations and zoning ordinances, subdivision regulations, building codes, health regulations, special purpose ordinances (such as a grading permit and erosion control requirement) and other applications of regulatory power which control development in flood-prone areas specifically for the purpose of preventing and reducing flood loss and damage.

FLOODPLAIN MANAGEMENT MEASURES—Refers to an overall community program of corrective and preventive measures for reducing future flood damage. The measures take a variety of forms and generally include zoning, subdivision, or building requirements and special-purpose floodplain ordinances. Also see National Flood Insurance Program (NFIP) and Federal Emergency Management Agency (FEMA).

FLOODPLAIN OF AGGRADATION—A flood plain formed by the building up of the valley floor by sedimentation.

FLOOD PLANE—The position occupied by the water surface of a stream during a particular flood. Also, loosely, the elevation of the water surface at various points along the stream during a particular flood.

FLOOD PREVENTION—Methods or structural measures used to prevent floods.

FLOOD PROBABILITY—The statistical probability that a flood of a given size will be equaled or exceeded in a given period of time.

FLOOD PROFILE—A graph showing the relationship of water surface elevation to location, the latter generally expressed as distance above mouth for a stream of water flowing in an open channel. It is generally drawn to show surface elevation for the crest of a specific flood, but may be prepared for conditions at a given time or stage.

FLOOD PROOFING—Any combination of structural and nonstructural additions, changes, or adjustments to structures and properties subject to flooding primarily for the reduction or elimination of flood damage to real estate or improved property, water and sanitary facilities, structures and their contents.

FLOOD-RELATED EROSION—The collapse or subsidence of land along the shore of a lake or other body of water as a result of undermining caused by waves or currents of water exceeding anticipated cyclical levels or suddenly caused by an unusually high water level in a natural body of water, accompanied by a severe storm, or by an unanticipated force of nature, such as a flash flood or an abnormal tidal surge, or by some similarly unusual and unforeseeable event which results in flooding.

FLOOD-RELATED EROSION PRONE AREA—A land area adjoining the shore of a lake or other body of water, which due to the composition of the shoreline or bank and high water levels or wind-driven currents, is likely to suffer flood-related erosion damage.

FLOOD-RELATED EROSION AREA MANAGEMENT—The operation of an overall program of corrective and preventive measures for reducing flood-related erosion damage, including but not limited to emergency preparedness plans, flood-related erosion control works, and floodplain management regulations.

FLOOD ROUTING—The process of determining progressively downstream the timing and stage of a flood at successive points along a river. Also, the determination of the attenuating effect of storage on a flood passing through a valley, channel, or reservoir.

FLOOD STAGE—The elevation at which overflow of the natural banks of a stream or body of water begins in the reach or area in which the elevation is measured.

FLOOD STAGE PROFILE—A graph of flooding condition water surface elevation versus distance along a river or stream. The profile may correspond to an historic flood event or an event or a specified recurrence interval. The channel bottom, as well as bridges, culverts, and dams, are usually shown on the flood stage profile.

FLOOD, STANDARD PROJECT (SPF)—A hypothetical flood that might result from the most severe combination of meteorological and hydrological conditions that are reasonably characteristic of the geographical region involved. The SPF is the usual basis for design of flood control structures.

FLOOD TIDE, also Floodtide—The incoming or rising tide; the period between low water and the succeeding high water.

FLOODWATER—The water of a flood. Often used in the plural (Floodwaters).

FLOODWATER DETENTION CAPACITY—That part of the gross reservoir capacity which, at the time under consideration, is reserved for the temporary storage of floodwaters. It can vary from zero to the entire capacity (exclusive of dead storage) according to a predetermined schedule based upon such parameters as antecedent precipitation, reservoir inflow, potential snowmelt, or downstream channel capacities. Also referred to as Flood-Control Capacity.

FLOODWATER RETARDING STRUCTURE—A structure providing for temporary storage of floodwater and for its controlled releases.

FLOODWATER RETENTION—The capacity of Wetland sediments and vegetation to hold excess pulses of water for subsequent discharge.

FLOOD WAVE—A distinct rise in stage, culminating in a crest and followed by recession to lower stages.

FLOODWAY—The channel of a river or other watercourse and the adjacent land area that must be reserved in order to discharge the base flood without cumulatively increasing the water surface elevation more than a designated height.

FLOODWAY ENCROACHMENT LINES—The lines marking the limits of Floodways on federal, state, and local floodplain maps.

FLOODWAY FRINGE—The area of the floodplain on either side of the Regulatory Floodway where encroachment may be permitted.

FLOODWAY HAZARD BOUNDARY MAP (FHBM)—Official map of a community where the boundaries of the flood, mudslide and related erosion areas having special hazards have been designated as Flood Zones A, M, and E. Supersedes the Flood Boundary Floodway Map (FBFM).

FLOOD ZONE—The land bordering a stream which is subject to floods of about equal frequency; for example, a strip of the floodplain subject to flooding more often than once, but not as frequently as twice in a century (100-Year Flood).

FLORA—(1) A term used to describe the entire plant species of a specified region or time. (2) The sum total of the kinds of plants in an area at one time. All plant life associated with a given habitat, country, area, or period. Bacteria are considered flora.

FLORISTON RATES [California and Nevada]—Currently represents the primary operational criteria of the Truckee River between its source (Lake Tahoe) and its terminus (Pyramid Lake). The rates originated in a 1915 decree (Truckee River General Electric Decree) in which the U.S. Bureau of Reclamation (USBR) gained an easement to operate the Lake Tahoe outlet dam in return for providing year-round flow rates for run-of-the-river users—hydropower and a pulp and paper mill. Along with the Orr Ditch Decree (1944) and the Truckee River Agreement (1935), which has been incorporated into the Orr Ditch Decree, these requirements govern the Truckee River flows. The Floriston rates essentially constitute a minimum instream flow in the river, as long as water is physically available in Lake Tahoe and Boca Reservoir to support the rates. Water may only be stored in Lake Tahoe and Boca Reservoir when rates are being met. The precise definition contained in the Truckee River Agreement is as follows:

[1] Floriston Rates means the rate of flow in the Truckee River at the head of the diversion penstock at Floriston, California (to be measured at the Iceland gage, but currently measured at the Farad gage) consisting of an average flow of 500 cubic feet of water per second each day during the period commencing March 1 and ending September 30 of any year, and an average flow of 400 cubic feet per second each day during the period commencing October 1 and ending the last day of the next following February of any year. [2] Reduced Floriston Rates means rates of flow in the Truckee River, measured at the Iceland gage (currently the Farad gage), effective and in force during the period commencing November 1 and ending the next following March 31 of each year, determined as follows:

(a) 350 cubic feet per second whenever the elevation of the water surface of Lake Tahoe is below 6226.0 feet above sea level and not below 6225.25 feet above sea level; and (b) 300 cubic feet per second whenever the water surface elevation of Lake Tahoe is below 6225.25 feet above sea level.

Also see Truckee River Agreement [Nevada and California].

FLOTAGE—See Flotation.

FLOTATION, also Floatation—(1) The act, process, or condition of floating, also called Flotage. (2) The process of separating different materials, especially minerals, by agitating a pulverized mixture of the materials with water, oil, and chemicals. Differential wetting of the suspended particles causes unwetted particles to be carried by air bubbles to the surface for collection.

FLOW—The rate of water discharged from a source given in volume with respect to time.

FLOWAGE—(1) The act of flowing or overflowing. (2) The state of being flooded; a body of water, such as a lake or reservoir, formed by usually deliberate flooding. (3) An outflow or overflow.

FLOW AUGMENTATION—The addition of water to a stream especially to meet instream flow needs.

FLOW BOUNDARIES—Anything which inhibits ground water flow, such as a ground water divide or an impermeable geologic unit.

FLOW DURATION CURVE—A cumulative frequency curve that shows the percentage of time that specified discharges are equaled or exceeded.

FLOWLINE (STREAMLINE)—(1) The general path that a particle of water follows under laminar flow conditions. (2) The line indicating the direction followed by ground water toward points of discharge. Flow lines are perpendicular to Equipotential Lines.

FLOW METER—A device which allows for measurement of stream flow by measuring velocity in a given cross-sectional area.

(GROUND WATER) FLOW MODEL—(1) A digital computer model that calculates a hydraulic head field for the modeling domain using numerical methods to arrive at an approximate solution to the differential equation of ground-water flow. (2) Any representation, typically using plastic or glass cross-sectional viewing boxes, with representative soil samples, depicting ground-water flows and frequently used for educational purposes.

FLOW, LAMINAR—Flow of water in well-defined flow lines in which the viscous force is predominant; in channels it occurs at a Reynolds Number smaller than 500-2,000 and through porous media at Reynolds Number smaller than 1-10.

FLOW, MODIFIED—That streamflow which would have existed had the works of man in or on the stream channels and in the drainage basin been consistent throughout the period of record. Usually used with an adjective such as "present" or specific year to mean that the flow record was modified to represent the record that would have been obtained had the "present" conditions prevailed throughout the period of record. Modified flow is equal to Virgin Flow minus the amount of Streamflow Depletion occurring at the specified time.

FLOW, NATURAL—The rate of water movement past a specified point on a natural stream from a drainage area which has not been affected by stream diversion, storage, import, export, return flow or change in consumptive use resulting from man's modification of land use. Natural flow rarely occurs in a developed country.

FLOW, NET—A graphical representation of flow lines and Equipotential Lines for two-dimensional, steady-state ground-water flow.

FLOW, OVERLAND—The flow of rainwater or snowmelt over the land surface toward stream channels. Upon entering a stream, it becomes runoff.

FLOW PATH—The subsurface course a water molecule or solute would follow in a given ground-water velocity field.

FLOW RATE—The rate, expressed in gallons or liters-per-hour, at which a fluid escapes from a hole or fissure in a tank. Such measurements are also made of liquid waste, effluent, and surface water movement.

FLOW RESOURCES Versus STOCK RESOURCES—Flow resources are resources that are not permanently expendable under usual circumstances; they are resources which are replaced. They are commonly expressed in annual rates at which they are regenerated. Examples are fresh-water runoff and timber. Stock resources can be permanently expended and whose quantity is usually expressed in absolute amounts rather than in rates. Examples are coal and petroleum deposits.

FLOW, STEADY—A flow in which the magnitude and direction of the specific discharge are constant in time.

FLOWSTONE—A layered deposit of calcium carbonate, CaCO3, on rock where water has flowed or dripped, as on the walls of a cave. Also see Tufa.

FLOW, TURBULENT—A flow in which successive flow particles follow independent path lines, and head loss varies approximately with the square of the velocity. In stream channels it occurs at a Reynolds Number greater than 5,000.

FLOW, UNIFORM—A characteristic of a flow system where specific discharge has the same magnitude and direction at any point.

FLOW VELOCITY—The volume of water flowing through a unit cross-sectional area of an aquifer. Also referred to as Specific Discharge.

FLOW, VIRGIN—That streamflow which would exist had man not modified conditions on or along the stream or in the drainage basin.

FLOWING WELL—An Artesian Well having sufficient head to discharge water above the land surface; a well where the Piezometric Surface lies above the ground surface..

FLOWMETER—A gauge indicating the velocity of wastewater moving through a treatment plant or of any liquid moving through various industrial processes.

FLUE GAS SCRUBBER—A type of equipment that removes fly ash and other objectionable materials from flue gas by the use of sprays, wet baffles, or other means that require water as the primary separation mechanism. Also referred to as Flue Gas Washer.

FLUID—Having particles which easily move and change their relative position without a separation of the mass, and which easily yield to pressure; capable of flowing; liquid or gaseous.

FLUIDIZED—A mass of solid particles that is made to flow like a liquid by injection of water or gas is said to have been fluidized. In water treatment, a bed of filter media is fluidized by backwashing water through the filter.

FLUID OUNCE—(Abbreviated fl oz, fl. oz.) (1) A unit of volume or capacity in the U.S. Customary System, used in liquid measure, equal to 29.57 milliliters (1.804 cubic inches). (2) A unit of volume or capacity in the British Imperial System, used in liquid and dry measure, equal to 28.41 milliliters (1.734 cubic inches).

FLUID POTENTIAL—The mechanical energy per unit mass of a fluid at any given point in space and time with respect to an arbitrary state and datum. Loss of fluid potential results as the fluid moves from a region of high potential to one of low potential and represents the loss of mechanical energy which is converted to heat by friction.

FLUME—(1) A narrow gorge, usually with a stream flowing through it. (2) An open artificial channel or chute carrying a stream of water, as for furnishing power, conveying logs, or as a measuring device.

FLUORIDATE (FLUORIDATION)—To add a fluorine compound to a drinking water supply, for example, for the purpose of reducing tooth decay, particularly in children. Since 1962, the U.S. Public Health Service (PHS) has recommended an "optimal" fluoride concentration of 0.7 to 1.2 mg/l (milligrams per liter) to prevent dental caries and minimize mottling (fluorosis). In 1986, the U.S. Environmental Protection Agency (EPA) set the Maximum Contaminant Level (MCL) for fluoride at 4 mg/l.

FLUORIDE—A binary compound of Fluorine with another element; gaseous, solid, or dissolved compounds containing fluorine that result from industrial processes. Fluoride combines with tooth enamel to render it less soluble in acid environments and fluoride compounds are added to public water supplies to prevent tooth decay. Excessive amounts in food can lead to Fluorosis. Fluorine is a halogen with the chemical symbol F.

FLUORINE—A pale-yellow, highly corrosive, poisonous, gaseous halogen element, the most electronegative and most reactive of all the elements, used in a wide variety of industrially important compounds. Fluorine is a halogen with the chemical symbol F.

FLUOROSIS—An abnormal condition caused by excessive intake of Fluorine, as from fluoridated drinking water, characterized chiefly by mottling of the teeth.

FLUSH—(1) To flow suddenly and abundantly, as from containment; flood. (2) To be emptied or cleaned by a rapid flow of water, as a toilet. (3) To open a cold-water tap to clear out all the water which may have been sitting for a long time in the pipes. In new homes, to flush a system means to send large volumes of water gushing through the unused pipes to remove loose particles of solder and flux. (4) To force large amounts of water through liquid to clean out piping or tubing, storage or process tanks.

FLUSHLESS TOILET—A toilet that disposes of waste without using water, especially one that utilizes bacteria to break down waste matter.

FLUSHOMETER—A device for flushing toilets and urinals that utilizes pressure from the water supply system rather than the force of gravity to discharge water into the bowl, designed to use less water than conventional flush toilets.

FLUVIAL—Of or pertaining to rivers and streams; growing or living in streams ponds; produced the action of a river or stream.

FLUVIOGLACIAL—Pertaining to streams flowing from glaciers or to the deposits made by such streams.

FLUX—(1) A flowing or flow. (2) The flowing in of the tide. (3) The measure of the hydraulic rate of flow of water through a pressure osmosis membrane in gallons per square foot of membrane per day (GFD).

FLUX DENSITY—The rate of flow of any quantity, usually a form of energy, through a unit area of specified surface.

FOAM—(1) A mass of bubbles of air or gas in a matrix of liquid film, especially an accumulation of fine, frothy bubbles formed in or on the surface of a liquid, as from agitation or fermentation. (2) The sea.

FOG—Condensed water vapor in cloud-like masses lying close to the ground.

FOLD—(Geology) A bend or flexure in a layer or layers of rock.

FOOD CHAIN—A succession of organisms in an ecological community that constitutes a continuation of food energy from one organism to another as each consumes a lower member and in turn is preyed upon by a higher member.

FORAGE FISH—Small fish which breed prolifically and serve as food for predatory fish.

FORB—Any Herbaceous flowering plant, other than a grass; especially one growing under range conditions.

FORCE MAINS—Pipes in which wastewater is transported under pressure; the system is used in some areas having small elevation changes with distance and therefore needing to augment the gravity flow.

FORCE PUMP—A pump with a solid piston and valves used to raise a liquid or expel it under pressure.

FORD—A shallow place in a body of water, such as a river, where one can cross by walking or riding on an animal or in a vehicle.

FOREBAY—The water behind a dam. A reservoir or pond situated at the intake of a pumping plant or power plant to stabilize water levels; also a storage basin for regulating water for percolation into ground water basins. Compare with Afterbay.

FOREBAY RESERVOIR—A reservoir used to regulate the flow of water to a hydroelectric plant; it may also serve other purposes such as recreation. Also see Afterbay.

FORECAST (FORECASTING)—(Statistics) A forecast is a quantitative estimate (or set of estimates) about the likelihood of future events based on past and current information. This "past and current information" is specifically embodied in the structure of the econometric model used to generate the forecasts. By extrapolating the model out beyond the period over which it was estimated, we can use the information contained in it to make forecasts about future events. It is useful to distinguish between two types of forecasting, ex post and ex ante. In an ex post forecasts all values of dependent and independent variables are known with certainty and therefore provides a means of evaluating a forecasting model. Specifically, in an ex post forecast, a model will be estimated using observations excluding those in the ex post period, and then comparisons of the forecasts will be made to these actual values. An ex ante forecast predicts values of the dependent variable beyond the estimation period using values for the explanatory variables which may or may not be known with certainty.

FORECAST HORIZON—(Statistics) The number of time periods to be forecasted; also, the time period in the future to which forecasts are to be made.

FORESHORE—(1) The part of a shore that lies between high and low watermarks. (2) The part of a shore between the water and occupied or cultivated land.

FOREST HYDROLOGY—The study of hydrologic processes as influenced by forest and associated vegetation.

FOREST INFLUENCES—The effects resulting from the presence of forest or brush upon climate, soil water, runoff, streamflow, floods, erosion, and soil productivity.

FOREST LAND—Land which is at least 10 percent occupied by forest trees of any size or formerly having had such tree cover and not currently developed for non-forest use. Lands developed for non-forest use include areas for crops, improved pasture, residential, or administrative areas, improved roads of any width, and adjoining road clearing and power line clearing of any width.

(UNITED STATES) FOREST SERVICE (USFS)—The largest and most diverse agency of the U.S. Department of Agriculture, the Forest Service provides leadership in the management, protection, and use of the nation's forests and rangelands, which comprise almost two-thirds of the nation's federally owned lands. The creation of the Forest Service go back to 1891 when the President was authorized to establish Forest Reserves from forest and range lands in the Public Domain. In 1905 the responsibilities for the management and protection of these Forest Reserves was transferred from the Department of the Interior to the Department of Agriculture and the Forest Service was formally established. The Forest Reserves were then renamed National Forests. Today the Forest Services manages 156 National Forests, 19 National Grasslands, and 16 Land Utilization Projects that make up the National Forest System located in 44 states, Puerto Rico, and the Virgin Islands. Much of the nation's fresh water supply flows from National Forest System lands and insuring adequate yields of high quality water and continuing soil productivity are primary aims of the Forest Service's watershed management programs. The Forest Service manages more than 14 percent of the nation's 1.2 billion acres of forest range. This National Forest System (NFS) rangeland is managed to conserve the land and its vegetation while providing food for both domestic livestock and wildlife. The Forest Service manages fish and wildlife habitat on the National Forests and National Grasslands in cooperation with the individual states' fish and game departments. Of the 191 million acres of National Forests, 86.5 million acres are classified as commercial forests, available for, and capable of, producing crops of industrial wood. National Forest timber reserves are managed on a sustained-yield basis to produce a continuous supply of wood products to meet the nation's economic demands while maintaining the productive capacity of these lands. In 1924 the Forest Service pioneered the establishment of wilderness areas on National Forest lands. National Forest lands are a major source of mineral and energy supplies with regulatory and management responsibilities for mineral activities shared with the Department of the Interior, Bureau of Mines. The Forest Service, with one of the world's largest wildland firefighting forces, provides direct fire protection and control for National Forest System lands as well as cooperative fire control on several million additional acres. The Forest Service is responsible for the forest management aspects of the Watershed Protection and Flood Prevention Program administered by the Natural Resources Conservation Service (NRCS). The Forest Service also participates in the forestry aspects of the River Basin Program, which guides and coordinates water and related land resource planning among several federal departments. The Forest Service operates an extensive forestry research program consisting of eight Forest and Range Experiment Stations, a Forest Products Laboratory, and 75 research labs located throughout the U.S., Puerto Rico, and the Pacific Trust Territories. The Forest Service is organized into nine (9) regions as listed below (regional headquarters are in parentheses):

[1] Eastern Region (Milwaukee, Wisconsin)—Maine, New Hampshire, Vermont, Massachusetts, Rhode Island, Connecticut, New York, New Jersey, Pennsylvania, Delaware, Maryland, West Virginia, Ohio, Indiana, Michigan, Illinois, Missouri, Iowa, Wisconsin, Minnesota; [2] Southern Region (Atlanta, Georgia)—Virginia, North Carolina, South Carolina, Kentucky, Tennessee, Georgia, Florida, Alabama, Mississippi, Arkansas, Louisiana, Oklahoma, Texas; [3] Rocky Mountain Region (Denver, Colorado)—South Dakota, Nebraska, Kansas, Wyoming, Colorado; [4] Northern Region (Missoula, Montana)—North Dakota, Montana, Idaho (northern part only), South Dakota (northwest corner only), Wyoming (northwest corner only); [5] Intermountain Region (Ogden, Utah)—Nevada, Utah, Idaho (except northern portion), Wyoming (western portion only); [6] Southwest Region (Albuquerque, New Mexico)—Arizona, New Mexico; [7] Pacific Northwest Region (Portland, Oregon)—Washington, Oregon; [8] Pacific Southwest Region (San Francisco, California)—California, Hawaii; [9] Alaska Region (Juneau, Alaska)—Alaska.

FORFEITED WATER RIGHT—A water right that is no longer valid because of five or more consecutive years of nonuse. Also see Abandoned Water Right.

FORFEITURE—The invalidation of a water right because of five or more consecutive years of nonuse. Also see Abandonment.

FORMATION—(Geology) A body of rock or soil of considerable thickness that has characteristics making it distinguishable from adjacent geologic structures.

FOSSIL WATER—Limited subterranean water deposits laid down in past ages but drawn on by modern man.

FOUCAULT, Jean Bernard Léon (1819-1868)—A French physicist who estimated the speed of light and determined that it travels more slowly in water than in air (1850).

FOUNDATION (of a Dam)—The natural material on which the dam structure is placed.

FOUNDER—To sink below the water.

FOUNTAIN—(1) An artificially created jet or stream of water; a structure, often decorative, from which a jet or stream of water issues. (2) A spring, especially the source of a stream. (3) A reservoir or chamber containing a supply of liquid that can be siphoned off as needed.

FOUNTAINHEAD—(1) A spring that is the source or head of a stream. (2) The upper end of a confined-aquifer conduit, where it intersects the land surface.

FRACTURE—A general term for any break in rock, which includes cracks, joints, and faults.

FRACTURED BEDROCK AQUIFER—An aquifer composed of solid rock, but where most water flows through cracks and fractures in the rock instead of through pore spaces. Flow through fractured rock is typically relatively fast.

FRAGILE AREA—Areas that, due to steepness, soil type, exposure, and cover, are especially subject to soil erosion and rapid deterioration. Also referred to as Critical Area.

FRAGMENTATION (of Habitat)—Interruption of large expanses of one type of habitat or vegetation by man-made clearings. Generally used where roads or areas of cropland are cleared within forested areas, thereby breaking a large continuous area of forest into smaller parcels of forest.

FRAZIL (FRAZIL ICE)—A French-Canadian term for the fine spicular ice, derived from the French words for cinders which this variety of ice most resembles. When formed in slat water it is known as Lolly Ice. When first formed, frazil is colloidal and is not visible in the water.

FREEBOARD—The vertical distance between a design maximum water level and the top of a structure such as a channel, dike, floodwall, dam, or other control surface. The freeboard is a safety factor intended to accommodate the possible effect of unpredictable obstructions, such as ice accumulation and debris blockage, that could increase stages above the design water surface. (Nautical) The distance between the water line and the uppermost full deck of a ship. For dams, the terms "net freeboard", "dry freeboard", "flood freeboard", or "residual freeboard" refer to the vertical distance between the estimated maximum water level and the top of a dam. "Gross freeboard" or "total freeboard" is the vertical distance between the maximum planned controlled retention water level and the top of a dam.

FREE FLOW—(Hydraulics) Flow through or over a structure not affected by submergence or backwater.

FREE-FLOWING—Flowing without artificial restrictions.

FREE-FLOWING STREAM—A stream or a portion of a stream that is unmodified by the works of man or, if modified, still retains its natural scenic qualities and recreational opportunities.

FREE-FLOWING WEIR—A weir that in use has the tailwater lower than the crest of the weir.

FREE-FLOWING WELL—An Artesian Well in which the potentiometric surface is above the land surface. Also see Potentiometric Surface.

FREE GROUND WATER—Water in interconnected pore spaces in the Zone of Saturation down to the first impervious barrier, moving under the control of the water table slope.

FREE LIQUIDS—(Water Quality) Liquids capable of migrating from waste and contaminating ground water. Hazardous waste containing free liquids may not be disposed of in landfills.

FREE MOISTURE—Liquid that will drain freely from solid waste by the action of gravity only.

FREE WATER SURFACE (FWS) CONSTRUCTED WETLAND—A type of constructed wetland, a man-made marsh-like area used to treat wastewater. In this type of wetland, the effluent flows through various aquatic plants, with the water level exposed to the air. While this type of wetland is relatively easy to construct, it is not as effective as the Subsurface Flow (SF) Constructed Wetland with respect to associated odors, potential for insect breeding, and risk of public exposure and contact with the water in the system. Also see Wetlands, Benefits.

FREEZE—(1) To pass from the liquid to the solid state by loss of heat. (2) To acquire a surface of coat of ice from cold.

FREEZING—The change of a liquid into a solid as temperature decreases. For water, the freezing point is 32F (Fahrenheit) or 0C (Celsius).

FREEZING POINT—(1) The temperature at which a liquid of specified composition solidifies under a specified pressure. (2) The temperature at which the liquid and solid phases of a substance of specified composition are in equilibrium at atmospheric pressure.

FRENCH DRAIN—An underground passageway for water through the interstices among stones placed loosely in a trench.

FREQUENCY ANALYSIS—A statistical procedure involved in interpreting the past record of a hydrological event to occurrences of that event in the future (e.g., estimates of frequencies of floods, droughts, storage, rainfall, water quality, etc.).

FREQUENCY CURVE—A graphical representation of the frequency of occurrence of specific events. Also referred to as Frequency Distribution.

FREQUENCY DISTRIBUTION—An arrangement of quantities pertaining to a single event, in order of magnitude and frequency of occurrence.

FRESH—(1) Not saline or salty. (2) Free from impurity or pollution.

FRESHET—(1) A sudden overflow of a stream resulting from a heavy rain or a thaw. (2) A stream of fresh water that empties into a body of salt water.

FRESH-SALT WATER INTERFACE—The region where fresh water and salt water meet.

FRESHWATER—(1) Of, relating to, living in, or consisting of water that is not salty. (2) Water with salinity less than 0.5 (parts per thousand) dissolved salts. (3) Water that contains less than 1,000 milligrams per liter (mg/l) of dissolved solids; generally, more than 500 mg/l of dissolved solids is undesirable for drinking and many industrial uses. (4) (Nautical) Accustomed to sailing on inland waters only.

FRESHWATER MARSH—A Circumneutral Ecosystem of more or less continuously water-logged soil dominated by emersed herbaceous plants, but without a surface accumulation of peat.

FRET—To gnaw or wear away; erode. To form (a passage or channel) by erosion. To disturb the surface of (water or a stream); agitate.

FRICTION HEAD—Energy required to overcome friction due to fluid movement with respect to the walls of the conduit or containing medium.

FRICTION LOSSES—Total energy losses in the flow of water due to friction between the water and the walls of a conduit, channel, or porous medium, usually expressed in units of height.

FRICTION SLOPE—The energy loss per unit of length of open or closed conduit due to friction.

FRIENDS OF THE EARTH (FOE)—A conservation and environmental organization, founded in 1969, dedicated to preservation, restoration, and wise use of natural resources. The United States headquarters is located in Washington, D.C., with affiliates offices in 37 countries. Through the Friends of the Earth Foundation, the organization promotes public education and monitors enforcement of environmental policies.

FRINGE WATER—Water occurring in the Capillary Fringe.

FRINGE MARSH—A saturated, poorly drained area, intermittently or permanently water covered, close to and along the edge of a land mass.

FRONT—(1) Land bordering a lake or river. (2) (Meteorology) A line of separation or interface between air masses of different temperatures or densities.

FRONTAGE—Land adjacent to something, such as a body of water.

FROST—(1) Thin ice crystals in the shape of scales, needles, feathers or fans which are deposited by Sublimation at temperatures of 32°F (0°C) or lower. (2) A temperature low enough to cause freezing. (3) The process of freezing.

FROST HEAVE—Ruptured soil, rock, or pavement caused by the expansion of freezing water immediately beneath the surface.

FROST LINE—The depth to which frost penetrates the earth.

FROST POCKETS—A low area or depression at the base of a slope where frost collects.

FROTH—A mass of bubbles in or on a liquid; foam.

FROZEN—(1) Made into, covered with, or surrounded by ice. (2) Very cold.

FULL COST (USBR)—A water rate defined by Congress in the Reclamation Reform Act of 1982 intended to represent the federal government's actual cost in providing project water to irrigators. The full-cost rate for each project or district is calculated by amortizing the expenditures for construction properly allocable to irrigation facilities in service, including all operation and maintenance deficits funded, less payments, over such periods as may be required under federal reclamation law or applicable contract provisions. Interest on all charges accrues from October 12, 1982, on costs outstanding at that date or from the date incurred of costs arising subsequent to October 12, 1982. The term Full-Cost Rate means the full-cost charge plus actual operation, maintenance, and replacement costs.

FULL-COST RATE (USBR)—An annual rate as determined by the Secretary of the Interior that shall amortize construction expenditures that are properly allocable to irrigation facilities in service, including all operation and maintenance deficits funded, less payments, over such periods as may be required by reclamation law or applicable contract provisions, with interest on both accruing from October 12, 1982, on costs outstanding at that date, or from the date incurred in the cast of costs arising subsequent to October 12, 1982.

FULLY PERMANENT SPRINKLER SYSTEM—An irrigation system usually composed of buried enclosed conduits carrying water under pressure to fixed orifices to distribute water over a given area.

FUMAROLE—A hole or orifice in a volcanic region, and usually in lava, from which issue gases and vapors at high temperature.

FUNCTIONAL EQUIVALENT—A term used to describe the U.S. Environmental Protection Agency's (EPA) decision-making process and its relationship to the environmental review conducted under the National Environmental Policy Act (NEPA). A review is considered functionally equivalent when it addresses the substantive components of a NEPA review.

FUNCTIONAL RELATIONSHIP—(Statistics) A hypothetical relationship that describes the effect of one or more Independent Variables on a Dependent Variable, of the general form:

Y = f(X1, X2, ... , Xn)

where Y represents the dependent variable whose behavior is a function of, f( ), the values of the independent variables, X1, X2, ..., Xn. A fundamental assumption of a functional relationship is that changes in the independent variables, also referred to as the Exogenous Variables, prescribe or determine changes in the dependent, or Endogenous Variable, consequently leading to a flow of causation from the independent variables to the dependent variable. As such, a functional relationship is not exactly comparable to a mathematical equation in which variables may be moved from one side of the equation to the other without changing the validity of the equality. In a functional relationship by contrast, once the flow of causation has been prescribed (the Specification), the equation's (model's) structure is fixed.

FUNGI (Singular: Fungus)—Molds, mildews, yeasts, mushrooms, and puffballs, a group of organisms lacking in chlorophyll (i.e., are not photosynthetic) and which are usually non-mobile, filamentous, and multicellular. Some grow in soil, others attach themselves to decaying trees and other plants whence they obtain nutrients. Some are Pathogens, others stabilize sewage and digest composted waste.

FURROW—A long, narrow, shallow trench made in the ground by a plow for planting and irrigation.

FURROW DAMS—Small earth ridges or rows used to impound water in furrows.

FURROW IRRIGATION—Spreading water by directing it into small channels across the field. Also referred to as Corrugation Irrigation.

FURROW STREAM—The size of water flow released into the furrow; the size of the stream is adjusted to prevent erosion, limited in amount to the capacity of the furrow, and as needed for the intake rates of the soil involved.

GABION—A wire cage, usually rectangular, filled with cobbles and used as a component for water control structures or for channel and bank protection.

GAC (GRANULAR ACTIVATED CARBON)—In water treatment, granular activated carbon has been used mainly for taste and odor control, with some special applications that remove Synthetic Organic Chemicals (SOCs) or Volatile Organic Chemicals (VOCs) from contaminated water. Two basic forms of GAC are typically used: (1) a coal-based carbon manufactured as an adsorbent; and (2) a wood-based carbon manufactured primarily as a substrate for biological activity. Also see Biological Activated Carbon (BAC) Process.

GAGE, or Gauge—(1) An instrument used to measure magnitude or position; gages may be used to measure the elevation of a water surface, the velocity of flowing water, the pressure of water, the amount of intensity of precipitation, the depth of snowfall, etc. (2) The act or operation of registering or measuring magnitude or position. (3) The operation, including both field and office work, of measuring the discharge of a stream of water in a waterway.

GAGE HEIGHT—The height of the water surface above the gage datum (reference level). Gage height is often used interchangeably with the more general term, Stage, although Gage Height is more appropriate when used with a gage reading.

GAGE ROD—A measuring device that shows the water level in the reservoir.

GAGING STATION—A particular site on a stream, canal, lake, or reservoir where systematic observations of Gage Height or discharge are obtained.

GAGING STATION NUMBER—A U.S. Geological Survey (USGS) numbering system consisting of an eight-digit number assigned to a Gaging Station which identifies the station in downstream order relative to other gaging stations and sites where streamflow data are collected. The first two digits designate the major drainage basin, the others the station.

GAINING STREAM—A stream or reach of a stream, the flow of which is being increased by the inflow of ground water seepage or from springs in, or alongside, the channel. Also referred to as an Effluent Stream. Also see Stream.

GALLERY—(1) A passageway within the body of a dam or abutment; hence the terms "grouting gallery," "inspection gallery," and "drainage gallery." (2) A long and rather narrow hall; hence the following terms for a power plant: "valve gallery," "transformer gallery," and "busbar gallery."

GALLON [Imperial]—A unit of capacity in Great Britain containing four quarts, is used for both liquid and dry commodities, and is defined as the volume occupied by ten imperial pounds weight of distilled water, as weighed in air against brass weights with both water and air at 62° Fahrenheit, and the barometer at 30 inches (atmospheric pressure). It is equivalent to 4.5460 liters (277.420 U.S. cubic inches), or to 1.2003 U.S. gallons (defined below).

GALLON [U.S.]—A unit of capacity, containing four quarts, used in the United States primarily for liquid measure. One U.S. gallon contains 231 cubic inches, 0.133 cubic feet, or 3.7853 liters. One U.S. gallon is equivalent to the volume of 8.3359 pounds av. (avoirdupois) of distilled water at its maximum density (32.9°F or 4°C), weighed in dry air at the same temperature against brass weight of 8.4 density and with the barometer at 30 inches. It takes approximately 325,851 gallons to make up 1 acre-foot (AF). [Historical Note: The U.S. gallon is the same as the old English wine gallon which was originally intended in England to be equivalent to a cylinder of seven inches in diameter and six inches in height.]

GALLONS PER CAPITA (GPC)—A term used relative to water use per person per specified time, usually a day.

GALLONS PER CAPITA PER DAY (GPCD)—An expression of the average rate of domestic and commercial water demand, usually computed for public water supply systems. Depending on the size of the system, the climate, whether the system is metered, the cost of water, and other factors, Public Water Supply Systems (PWSS) in the United States experience a demand rate of approximately 60 to 150 gallons per capita per day. Also see Gallons per Employee per Day (GED) for information on the application of this concept to commercial water use by Standard Industrial Classification (SIC) Code. [See Appendix G-1, Gallons Per Capita Per Day (GPCD), Water Used for Public Water Supplies by State.]

GALLONS PER EMPLOYEE PER DAY (GED)—A measure or coefficient expressing an area's commercial water use per worker (employee), typically for distinct industry sectors. It is based on an analytical technique for measuring and forecasting commercial water use in a service area based upon the unique, seasonal, business-related water use by specific industrial sectors. GED commercial water-use coefficients are typically developed based upon Standard Industrial Classifications (SIC) codes for which comparable commercial water use and employment data are available. For forecasting more frequently than annually, GED coefficients will incorporate seasonal patterns (monthly or quarterly) as well. By deriving forecasts of trends in industry sector employment and combining them with appropriate, industry-specific GED coefficients, relatively accurate forecasts of the corresponding commercial water use may be obtained.

GALLONS PER MINUTE—A unit expressing rate of discharge, used in measuring well capacity. Typically used for rates of flow less than a few cubic feet per second (cfs).

GAMMA RADIATION—High energy photons which are emitted by many radioactive substances.

GAME FISH—Those species of fish considered to possess sporting qualities on fishing tackle, such as salmon, trout, black bass, striped bass, etc.; usually more sensitive to environmental changes than Rough Fish.

GAP ANALYSIS—A method for determining spatial relationships between areas of high biological diversity and the boundaries of National Parks, National Wildlife Refuges (NWR), and other preserves. The primary goal of Gap Analysis is to prevent additional species from being listed as threatened or endangered. Analyses are made and displayed using a Geographic Information System (GIS). Estimates of diversity are often derived from known or hypothesized relationships between mapped plant communities and animal populations. In addition to the National Biological Survey, which serves as the primary coordinating agency, there are over 200 collaborating organizations involved in performing Gap Analysis on a state-by-state basis, including businesses, universities, and state, local, and federal government entities. [The term Gap originated from an initial Biodiversity study in Hawaii which showed that for certain sensitive animal species there existed a physical (geographic) gap between the species and its habitat and wildlife preserves (national parks, forests, wildlife protection areas, etc.), indicating potential limitations of species and habitat protection.]

GAS—A state of matter; a substance that generally exists in the gaseous phase at room temperature.

GAS CHROMATOGRAPH/MASS SPECTROMETER (GC/MS)—A highly sophisticated instrument that identifies the molecular composition and concentrations of various chemicals in water and soil samples.

GAS CHROMATOGRAPHY (GC)—A method of separating chemical components of a mixture which involves the passage of a gaseous sample through a column having a fixed adsorbent phase. It is in widespread use in quantitatively analyzing volatile compounds.

GASIFICATION—The process of combining coal with air (or pure oxygen) and steam to yield a gaseous product suitable for use either as a direct source of energy or as a raw material used in the synthesis of chemicals, liquid fuels, or other gaseous fuels.

GATE—(1) (Irrigation) Structure or device for controlling the rate of water flow into or from a canal, ditch, or pipe. (2) (Dam) A device in which a leaf or member is moved across the waterway from an external position to control or stop the flow. The following types of gates apply to dams and other such structures:

[1] Bulkhead Gate—A gate used either for temporary closure of a channel or conduit to empty it for inspection or maintenance or for closure against flowing water when the head differential is small, e.g., a diversion tunnel closure. Although a bulkhead gate is usually opened and closed under nearly balanced pressures, it nevertheless may be capable of withstanding a high pressure differential when in the closed position. [2] Crest Gate (Spillway Gate)—A gate on the crest of a spillway to control overflow or reservoir water level. [3] Emergency Gate—A standby or reserve gate used only when the normal means of water control is not available. [4] Fixed Wheel Gate (Fixed Roller Gate, Fixed Axle Gate)—A gate having wheels or rollers mounted on the end posts of the gate. The wheels bear against rails fixed in side grooves or gate guides. [5] Flap Gate—A gate hinged along one edge usually either the top or bottom edge. Examples of bottom-hinged flap gates are tilting gates and fish belly gates, so-called due to their shape in cross section. [6] Flood Gate—A gate to control flood release from a reservoir. [7] Guard Gate (Guard Valve)—A gate or valve that operates fully open or closed. It may function as a secondary device for shutting off the flow of water in case the primary closure device becomes inoperable, but is usually operated under balanced pressure, no-flow conditions. [8] Outlet Gate—A gate controlling the outflow of water from a reservoir. [9] Radial Gate (Tainter Gate)—A gate with a curved upstream plate and radial arms hinged to piers or other supporting structures. [10] Regulating Gate (Regulating Valve)—A gate or valve that operates under full pressure and flow conditions to throttle and vary the rate of discharge. [11] Slide Gate (Sluice Gate)—A gate that can be opened or closed by sliding it in supporting guides.

GATED PIPE—(Irrigation) Portable pipe with small gates installed along one side for distributing water to corrugations or furrows.

GC-MS—An analytical technique involving the use of both Gas Chromatography (GC) and Mass Spectrometry (MS), the former to separate a complex mixture into its components and the latter to deduce the atomic weights of those components. It is particularly useful in identifying organic compounds.

GED [Gallons per Employee per Day]—A coefficient system for measuring and forecasting commercial water use by Standard Industrial Classification (SIC) code. See Gallons Per Employee Per Day (GED).

GEL—(Water Quality) A jellylike material formed by the coagulation of a colloidal suspension or sol.

(TRUCKEE RIVER) GENERAL ELECTRIC DECREE [California]—Represented the resolution, through a 1915 federal court consent decree, of a lengthy series of conflicts, litigation, and negotiations between the U.S. Bureau of Reclamation and the Truckee River General Electric Company (predecessor to the present-day Sierra Pacific Power Company), which, in 1902, through a complicated series of real estate transactions had obtained title to the Lake Tahoe Dam, surrounding lands, and the hydropower plants on the Truckee River. The U.S. Bureau of Reclamation was in desperate need of Lake Tahoe water for its Newlands Project, then nearing completion near Fallon in Churchill County. This decree granted the Bureau of Reclamation an easement to operate the Lake Tahoe Dam and to use surrounding property owned by the power company. On its part, the Bureau of Reclamation was required to provide certain year-round flow rates (the Floriston Rates), measured at a stream gage near the state line, to support hydropower generation. These rates, in fact, dated back to a 1908 river flow agreement among the Truckee River General Electric Company, the Floriston Land and Power Company, and the Floriston Pulp and Paper Company and required that "...there shall be maintained a flow of water in the said Truckee River at Floriston [California] of not less than 500 cubic feet per second from the First day of March to the 30th day of September inclusive, in each year, and of not less than 400 cubic feet per second from the 1st day of October to the last day of February, inclusive, in each year." While this decree did dictate how the Lake Tahoe Dam would be operated, it did little to solve the concerns of residents of the lake and lessen California's concerns over the apportionment of Lake Tahoe waters.

GENERAL IMPROVEMENT DISTRICT (GID) [Nevada]—A public entity created under the provisions of the Nevada Revised Statutes and authorized by the respective county commission to provide specific services to a limited geographical area. A GID may be formed to provide one or a combination of services such as road maintenance, parks and recreation facilities, water and sanitary sewer service. etc.

GENERATOR—A machine that changes water power, steam power, or other kinds of mechanical energy into electricity.

GEOGRAPHIC INFORMATION SYSTEM (GIS)—A computer information system that can input, store, manipulate, analyze, and display geographically referenced data to support the decision-making processes of an organization. A map based on a database or databases. System plots locations of information on maps using latitude and longitude.

GEOGRAPHY—The science of the earth and life, especially the description of land, sea, air, and the distribution of plant and animal life, including man and his industries, with reference to the mutual relations among these diverse elements. As general areas of study, geography is divided into:

[1] Mathematical Geography—deals with the figure and motion of the earth, of its seasons, tides, etc., of its measurement, and of its representation on maps and charts by various methods of projection; [2] Physical Geography—deals with the exterior physical features and changes of the earth's land, water, and air; [3] Biological Geography—has to do with the relation of living things to their physical environment; and [4] Commercial Geography—deals with commodities, their place of origin, paths of transactions, etc.

GEOHYDROLOGY—A term which denotes the branch of Hydrology relating to subsurface or subterranean waters; that is, to all waters below the surface. Related terms include Geohydrologic and Geohydrologist.

GEOLOGIC EROSION—Normal or natural erosion caused by geological processes acting over long geologic periods and resulting in the wearing away of mountains, the building up of flood plains, coastal plains, etc.

GEOLOGIC LOG—A detailed description of all underground features (e.g., depth, thickness, type of formation, etc.) discovered during the drilling of a well.

GEOLOGIC TIME (HISTORY)—Geologic history can be divided into five great Eras of recorded time. These Eras and approximate time periods include:

[1] Archeozoic—4,500 million years ago (MYA) to 3,500 MYA; [2] Proterozoic (or Prepaleozoic)—3,500 MYA to 586 MYA; [3] Paleozoic—570 MYA to 230 MYA; [4] Mesozoic—230 MYA to 65 MYA; and [5] Cenozoic—65 MYA to present.

Each time Era (except the first) is divided into Periods (e.g., the Cenozoic into the Quaternary and the Tertiary) and Periods are further divided into Epochs (e.g., the Tertiary into the Pliocene, Miocene, Oligocene, Eocene, and the Paleocene). For each time period, whether an Era, Period, or Epoch, there is a corresponding rock formation by which the time period has been dated. Rock formations constituting a specific (time) Era form a Group of rocks; those rocks having been formed during a specific (time) Period constitute a rock System; and those rock formations originating during a specific (time) Epoch are said to belong to a particular Series of rocks. Series of rock formations are further subdivided into Formations, Stages, etc.

GEOLOGICAL AGE—(Archeology) A period of time, earlier than the present postglacial period, which can only be effectively dated geologically, that is by its rock formations and fossilized matter within those rock formations.

GEOLOGICAL SURVEY—A systematic examination of an area to determine the character, relations, distribution and origin or mode of formation, of its rock masses and other natural resources.

(UNITED STATES) GEOLOGICAL SURVEY (USGS)—An agency of the U.S. Department of Interior responsible for providing extensive earth-science studies of the Nation's land, water, and mineral resources. The USGS was established by an act of Congress on March 3, 1879, to provide a permanent federal agency to conduct the systematic and scientific "classification of the public lands, and examination of the geological structure, mineral resources, and products of national domain." An integral part of that original mission is to publish and distribute the earth-science information needed to understand, plan the use of, and manage the nation's energy, land, mineral, and water resources. Since 1879, the research and fact-finding role of the USGS has grown and been modified to meet the changing needs of the nation it serves. As part of that evolution, the USGS has become the map-making agency for the federal government, the primary source of data on surface- and ground-water resources of the nation, and the employer of the largest number of professional earth scientists. The USGS is organized into three operational Divisions: the National Mapping Division (NMD), charged with development and application of mapping and Geographic Information System (GIS) technology; the Geologic Division (GD), which conducts geologic mapping and research; and the Water Resources Division (WRD). The mission of the Water Resources Division of the USGS is to provide the hydrologic information and understanding needed to manage the nation's water resources to benefit its residents. Typical water resource programs sponsored by the WRD include:

[1] Data collection to aid in evaluating the quantity, quality, distribution, and use of the nation's water resources; [2] Analytical and interpretive water-resources appraisals to describe the occurrence, quality, and availability of surface and ground water throughout the nation; [3] Basic and problem-oriented research in hydraulics, hydrology, and related fields of science and engineering; [4] Scientific and technical assistance in hydrology to other federal, state, and local agencies; [5] Development and maintenance of national computer data bases and associated Geographic Information Systems (GIS) of hydrologic data—streamflow, water quality and biology, groundwater characteristics, and water use; and [6] Public distribution of water-resources data and results of water-resources investigations through reports, maps, computerized information services, and other forms of release.

Programs of the Water Resources Division are funded under three types of arrangements:

[1] Federal Program—funding is appropriated directly to USGS by the U.S. Congress for projects of national interest; [2] Cooperative Program—funding is shared by USGS and interested state and local agencies; and [3] Other Federal Agencies (OFA) Program—funding is supplied by federal agencies requesting technical assistance from the USGS.

The Water Resources Division's headquarters is at the USGS National Center in Reston, Virginia. Regional offices are maintained in Reston; Atlanta, Georgia; Denver, Colorado; and Menlo Park, California. With the exception of the National Research Program (NRP) centers at Reston, Denver, and Menlo Park, most of the WRD program is distributed to 51 USGS District Offices organized by state boundaries.

GEOLOGY—The science that studies the physical nature and history of the earth.

GEOMORPHOLOGY (Geomorphic)—That branch of both physiography and geology that deals with the form of the earth, the general configuration of its surface, and the changes that take place in the evolution of land forms. The term usually applies to the origins and dynamic morphology (changing structure and form) of the earth's land surfaces, but it can also include the morphology of the sea floor and the analysis of extraterrestrial terrains. Sometimes included in the field of physical geography, geomorphology is really the geological aspect of the visible landscape. Also see Geomorphology, Historical, and Geomorphology, Process.

GEOMORPHOLOGY, HISTORICAL—Historical geomorphology represents one branch of Geomorphology which provides the means to analyze the long-term change in landforms through the concept of cyclic change. The concepts evolved at the turn of the 20th century and were put forward by the American geologist William Morris Davis. The theory stated that every landform could be analyzed in terms of structure, process, and stage. Structure and process are treated by the science of geomorphology. However, the concept of stage introduced the element of time, and is subject to a far greater degree of interpretation. As postulated by Davis, every landform underwent development through a predictable, cyclic sequence: i.e., youth, maturity, and old age. Historical geomorphology relies on various chronological analyses, notably those provided by stratigraphic studies of the last 2 million years, known as the Quaternary Period. The relative chronology usually may be worked out by observation of stratigraphic relationships, with the time intervals involved established more precisely by dating methods such as historical records, radiocarbon analysis, tree-ring counting (Dendrochronology), and paleomagnetic studies. By applying such methods to stratigraphic data, a quantitative chronology of events is constructed that provides a means for calculating long-term rates of change. Also see Geomorphology, Process.

GEOMORPHOLOGY, PROCESS—The second branch of Geomorphology, process geomorphology analyzes contemporary dynamic processes at work in landscapes. The mechanisms involved are weathering and erosion and combine processes that are in some respects destructive and in others constructive. The bedrock and soil provide the passive material, whereas the climatic regime and crustal dynamics together provide the principal active variables. Also see Geomorphology, Historical.

GEOPHYSICAL LOG—A record of the structure and composition of the earth encountered when drilling a well or similar type of test or boring hole.

GEOPHYSICS, also Geophysical—The study of the physical characteristics and properties of the earth, including geodesy, seismology, meteorology, oceanography, atmospheric electricity, terrestrial magnetism, and tidal phenomena.

GEOPONICS—The art or science of cultivating the earth; husbandry.

GEOPRESSURED RESERVOIR—A geothermal reservoir consisting of porous sands containing water or brine at high temperature or pressure.

GEOSOL—(Geography) A stratigraphic unit of distinctive material, laterally traceable.

GEOTHERMAL—Terrestrial heat, usually associated with water as around hot springs.

GEOTHERMAL ENERGY—The heat energy available in the earth's subsurface, extracted from three basic sources: (1) steam; (2) hot water; and (3) hot rocks or near surface intrusions of volcanic molten rock. The normal thermal gradient of the earth's crust is such that the temperature in a deep well or mine typically increases by about 1°F (0.56°C) for each 100 feet of depth.

GEOTHERMICS—The science pertaining to the earth's interior heat. Its main practical application is in finding natural concentrations of hot water, the source of Geothermal Energy, for use in electric power generation and direct heat applications such as space heating and industrial drying processes. Heat is produced within the crust and upper mantle of the earth primarily by decay of radioactive elements. This geothermal energy is transferred to the earth's surface by diffusion and by convection movement of magma (molten rock) and deep-lying circulating water. Surface hydrothermal manifestations include hot springs, geysers, and Fumaroles.

GEYSER—A periodic thermal spring that results from the expansive force of super heated steam. Also, a special type of thermal spring which intermittently ejects a column of water and steam into the air with considerable force.

GFD—Gallons per square foot of membrane per day—the flux for reverse osmosis membranes.

GIARDIA LAMBLIA—A flagellate protozoan that causes the severe gastrointestinal illness Giardiasis, when it contaminates drinking water.

GIARDIASIS—A disease that results from an infection by the protozoan parasite Giardia Intestinalis, caused by drinking water that is either not filtered or not chlorinated. The disorder is more prevalent in children than in adults and is characterized by abdominal discomfort, nausea, and alternating constipation and diarrhea.

GIGAWATT HOUR (GWh)—One billion Watt-hours (Wh).

GILL—(1) A unit of volume or capacity in the U.S. Customary System, used in liquid measure, equal to of a pint or four ounces (118 milliliters). (2) A unit of volume or capacity, used in dry and liquid measure, equal to of a British Imperial pint (142 milliliters).

GIS—See Geographical Information System (GIS).

GLACIAL—(1) Characterized or dominated by the existence of Glaciers. Used of a geologic or Glacial Epoch period of time, i.e., the Pleistocene epoch. (2) Extremely cold; icy. (3) Having the appearance of ice.

GLACIAL ACTION—The resultant effects caused by the movement of a Glacier. Also see Glacial Till, Glaciofluvial Deposits, Moraines, Lateral Moraines, and Terminal Moraines.

GLACIAL DRIFT—All earth material transported and deposited by the ice and/or by water flowing from a glacier. It consists of rock flour, sand, pebbles, cobbles, and boulders, and may occur in a heterogeneous mass or be reasonably well sorted, depending on the manner of deposition.

GLACIAL EPOCHS—(Geology) Any of those parts of geological time, from Pre-Cambrian time onward in both the Northern and Southern hemispheres, during which a much larger portion of the earth was covered by glaciers than at present. More specifically refers to the latest of the glacial epochs, that of the Quaternary period, known as the Pleistocene Epoch, beginning some 3 million years ago, during which Canada, northern and northeastern U.S., northern and northwestern Europe, and northern Asia, together with most high mountain regions in the Northern Hemisphere were largely covered with ice. It has been divided into a number of stages. Those recognized for the interior of North America are, in order of age: Jerseyan or Nebraskan (glacial); Aftonian (interglacial); Kansan (glacial); Yarmouth and Buchanan (interglacial); Illinoian (glacial); Sangamon (interglacial); Iowan (glacial); Peorian (interglacial); Earlier Wisconsin (glacial); an unnamed (interglacial) interval; Later Wisconsin (glacial); Champlain (glaciolacustrine epoch).

GLACIAL OUTWASH—Stratified material, chiefly sand and gravel deposited by meltwater streams in front of the margin of a glacier.

GLACIAL PERIOD—(Geology) The period of time encompassing the Glacial Epochs.

GLACIAL TILL—Till is the mixture of rocks, boulders, and soil picked up by a moving glacier and carried along the path of the ice advance. The glacier deposits this till along its path—on the sides of the ice sheet, at the toe of the glacier when it recedes, and across valley floors when the ice sheet melts. These till deposits are akin to the footprint of a glacier and are used to track the movement of glaciers. These till deposits can be good sources of ground water, if they do not contain significant amounts of impermeable clays. Also see Moraines, Lateral Moraines, and Terminal Moraines.

GLACIATE, also Glaciation—(1) Alteration of the earth's solid surface through erosion and deposition by glacier ice. (2) To cover with ice or a Glacier; to subject to or affect by Glacial Action. (3) To freeze.

GLACIATED VALLEY—A U-Shaped Valley formerly occupied by a Glacier.

GLACIER—A huge mass of ice, formed on land by the compaction and recrystallization of snow, that moves very slowly downslope or outward due to its own weight.

GLACIER MEAL—Finely ground rock particles produced by glacial abrasion. Also referred to as Rock Flour.

GLACIOEUSTACY—(1) The condition in which massive ice sheets store considerable quantities of water. Generally refers to periods of time during the Wisconsin age of the Pleistocene (glacial) epoch, when the oceans were some 300 to 330 feet lower than today and these waters were stored in the massive glaciers of this Ice Age period. (2) Changes in sea level due to storage or release of water on land as snow and glacier ice.

GLACIOFLUVIAL DEPOSITS—Material moved by glaciers and subsequently sorted and deposited by streams flowing from the melting ice. The deposits are stratified and may occur in the form of outwash plains, deltas, kames, eskers, and kame terraces. Also see Glacial Action, Glacial Drift and Glacial Till.

GLACIOLACUSTRINE—(Geology) Pertaining to, or characterized by, glacial and lacustrine processes or conditions applied especially to deposits made in lakes.

GLACIOLOGY—Collectively, the branches of science concerned with the causes and modes of ice accumulation and with ice action, on the earth's surface. Specifically, the branch of geology which studies the effects of glacial epochs, glaciation, and ice in modifying the earth's surface and in affecting the life and distribution of plants and animals.

GLADE—An open, spacious Wetland, as in the Everglades.

GLAUCONITE—A greenish clay mineral, a hydrous silicate of potassium, iron, aluminum, or magnesium, (K,Na)(Al,Fe,Mg)2(Al,Si)4O10(OH)2, found in greensand and used as a fertilizer and water softener.

GLAZE—Homogeneous, transparent ice layers which are built up, either from supercooled rain or drizzle, or from rain or drizzle, when the surfaces on which it forms are at temperatures of 32°F (0°C) or lower. Glaze often forms a matrix for sleet pellets that fall at the same time.

GLOB—A small drop; a globule.

GLOBAL POSITIONING SYSTEM (GPS)—A system which verifies latitude and longitude of a location on the ground through the use of a transmitter and a remote (satellite) vehicle.

GLOBULE—A tiny ball or globe, especially a drop of liquid.

GOBBET—A small amount of liquid; a drop.

GOODNESS OF FIT—(Statistics) Generally speaking, a "good" econometric model is one which helps to explain or account for a large proportion of the variance in the dependent variable. Large residuals, or unexplained variations, imply a poor fit, while small residuals imply a good fit. As a more precise measure of this goodness of fit, a Coefficient of Determination, R2, is used which measures the proportion of the total variation in the dependent variable explained by the variations in the independent variable(s). Also see Criteria Testing.

GOOSENECK—A portion of a water service connection between the distribution system water main and a meter. Sometimes referred to a Pigtail.

GORE-TEX—A trademark used for a water-repellant, breathable laminated fabric used primarily in outerwear and shoes.

GPCD—Gallons per capita (per person) per day—a measure of water use in municipalities. [See Appendix G-1, Gallons Per Capita Per Day (GPCD), Water Used for Public Water Supplies by State.]

GPD—Gallons per day, a measure of the rate of flow or the rate of water withdrawal from a well. Typically used when the rate of flow in cubic feet per second (cfs) is too low to be useful.

GRAB SAMPLE—Typically, a single water or air sample drawn over a short time period. As a result, the sample is not representative of long-term conditions at the sampling site. This type of sampling yields data that provides a snapshot of conditions or concentrations at a particular point in time.

GRABEN—(Geology) (1) A depressed tract bounded on at least two sides by faults and generally of considerable length as compared to its width. (2) A rather steeply sided valley formed when faulting caused a block-shaped area to drop relative to the surrounding terrain. Lake Tahoe, situated on the border between the states of California and Nevada, occupies a graben.

GRADE—(Hydraulics) The slope of a stream bed.

GRADED STREAM—A stream in which, over a period of years, the slope is delicately adjusted to provide, with available discharge and with prevailing channel characteristics, just the velocity required for transportation of the sediment load supplied from the drainage basin. Also, a stream in which most irregularities, such as waterfalls and cascades, are absent. Streams tend to cut their channels lower at a very slow rate after they become graded.

GRADE STABILIZATION STRUCTURE—A structure for the purpose of stabilizing the grade of a gully or other watercourse, thereby preventing further head-cutting or lowering of the channel grade.

GRADIENT—Degree of incline; slope of a stream bed. The vertical distance that water falls while traveling a horizontal distance downstream. Also see Hydraulic Gradient and Temperature Gradient.

GRADUALLY VARIED FLOW—(Hydraulics) Non-uniform flow in which depth of flow changes gradually through a reach. Typical of normal natural valley and channel flow, which can be either steady or unsteady flows.

GRAIN—A unit of weight equivalent to 1/7000th pound. The hardness of water is sometimes expressed in units of grains per gallon. Also see Avoirdupois Weight.

GRAM—The basic unit of weight in the Metric System equal to 1/1000 kilogram and nearly equal to the mass of one cubic centimeter of water at its maximum density; also equal to 1/28th of an ounce or 0.0022046 pound.

GRAM MOLECULAR WEIGHT (GMW)—The mass, in grams, of a substance equal to its molecular weight. For example, the molecular weight of water (H2O) is 18 (the sum of the atomic weights of two hydrogen atoms and one oxygen atom), so its gram molecular weight is 18 grams. The amount of a material equal to its gram molecular weight comprises one gram-mole of the substance.

GRANITE—(Geology) A light-colored plutonic igneous rock made up of interlocking grains of glassy or milky quartz, white or pink feldspar, and specks of dark mica or hornblende. The Sierra Nevada Mountains (California and Nevada) are made up of granite and similar rock types.

GRANULAR ACTIVATED CARBON (GAC)—In water treatment, granular activated carbon has been used mainly for taste and odor control, with some special applications that remove Synthetic Organic Chemicals (SOCs) or Volatile Organic Chemicals (VOCs) from contaminated water. Two basic forms of GAC are typically used: (1) a coal-based carbon manufactured as an adsorbent; and (2) a wood-based carbon manufactured primarily as a substrate for biological activity. Also see Biological Activated Carbon (BAC) Process.

GRANULAR ACTIVATED CARBON TREATMENT (GACT)—A filtering system often used in small water systems and individual homes to remove organics. This process can also be highly effective in removing elevated levels of radon from water.

GRASS/FORB—An early forest successional stage where grasses and forbs are the dominant vegetation.

GRASSED WATERWAY OR OUTLET—A natural or constructed waterway, usually broad and shallow and covered with erosion-resistant grasses, suitable to resist potential damages resulting from runoff.

GRASSLAND—An area, such as a prairie or meadow, of grass or grasslike vegetation. More specifically, grasslands constitute a geographical region dominated by shrubs and grasses, receiving 10 to 30 inches of rain annually. Alpine Grasslands are in cool, high-elevation areas. Temperate Grasslands, called Prairie (North America), Pampas (South America), Steppe, (Asia), or Veldt (South Africa), are found in regions with moderate temperatures. Tropical Grasslands, also called Savannas, are found in warmer climates. Also see Biome.

GRAVEL—A mixture composed primarily of rock fragments 2 mm (0.08 inch) to 7.6 cm (3 inches) in diameter. Usually contains much sand.

GRAVEL ENVELOPE—In well construction, a several-inch thickness of uniform gravel poured into the annular space between the well casing and the drilled hole. Also referred to as Gravel Pack.

GRAVITATIONAL HEAD—Component of total Hydraulic Head related to the position of a given mass of water relative to an arbitrary datum.

GRAVITATIONAL WATER—Water that moves into, through, or out of a soil or rock mass under the influence of gravity.

GRAVITY DAM—A dam constructed of concrete and/or masonry that relies on its weight for stability. Also see Dam.

GRAVITY FLOW—The downhill flow of water through a system of pipes, generated by the force of gravity.

GRAVITY IRRIGATION—(1) Irrigation in which the water is not pumped but flows and is distributed by gravity, includes sprinkler systems when gravity furnishes the desired head (pressure). (2) Irrigation method that applies irrigation water to fields by letting it flow from a higher level supply canal through ditches or furrows to fields at a lower level.

GRAYWATER—Waste water from a household or small commercial establishment which specifically excludes water from a toilet, kitchen sink, dishwasher, or water used for washing diapers. More commonly spelled Greywater.

GREAT BASIN [Nevada]—An area covering most of Nevada and much of western Utah and portions of southern Oregon and southeastern California consisting primarily of arid, high elevation, desert valleys, sinks (playas), dry lake beds, and salt flats. The Great Basin is characterized by the fact that all surface waters drain inward to terminal lakes or sinks. Principal excluded regions within Nevada include the extreme north-central portion of the state whose waters drain northward into the Snake River Basin, thence to the Columbia River and finally to the Pacific Ocean, and the south-eastern portion of Nevada whose surface waters drain into the Colorado River Basin, thence to the Gulf of California (Mexico) and the Pacific Ocean. Within this area referred to as the Great Basin, major river drainage areas include:

[1] Truckee River, whose source is Lake Tahoe (Basin) and whose terminus is Pyramid Lake in western Nevada; [2] Carson River, whose west and east forks originate along the eastern slopes of the Sierra Nevada Mountains and whose terminus is the Carson Sink (Playa) in west-central Nevada; [3] Walker River, whose west and east fork tributaries also originate along the eastern slopes of the Sierra Nevada Mountains and whose terminus is Walker Lake in western Nevada; and [4] Humboldt River, the only major river wholly contained in Nevada, whose principal source is the Ruby Mountains in eastern Nevada and whose terminus is the Carson Sink (Playa) in west-central Nevada.

Pyramid Lake and Walker Lake in western Nevada represent the remnants of the ancient Lake Lahontan, an Ice Age lake that covered a considerable portion of northwestern Nevada during the Pluvial Period of some 75,000-10,000 years ago. The Great Salt Lake in western Utah, the last major remnant of the ancient Ice Age Lake Bonneville, which covered a large portion of what is now the Utah portion of the Great Basin, is also contained within this area and acts as the terminus for surface water drainage from the western slopes of the Wasatch Range in north-central Utah.

GREAT DIVIDE—The watershed of North America comprising the line of highest points of land separating the waters flowing west from those flowing north or east, coinciding with various ranges of the Rocky Mountains, and extending south-southeast from Northwestern Canada to Northwestern South America. More commonly referred to as the Continental Divide.

GREENBELT—An area where measures are applied to mitigate fire, flood and erosion hazards to include fuel management (suppression of combustibles), land use planning, and development standards. More traditionally, an irrigated landscaped buffer zone between developed areas and wildlands, usually put to additional uses such as parks, bike and riding trails, golf courses, etc.

GREENHOUSE EFFECT—The phenomenon whereby the earth's atmosphere traps solar radiation, caused by the presence in the atmosphere of gases such as carbon dioxide, water vapor, and methane that allow incoming sunlight to pass through but absorb heat radiated back from the earth's surface. As the amount of carbon dioxide increases due to the combustion of fossil fuels and deforestation, especially of tropical rain forests, it is proposed that more heat energy will be retained by the earth's atmosphere, resulting in a change in rainfall and wind patterns and melting of the polar ice, thus raising the global sea level. The change in weather patterns could have devastating consequences to the world's present prime agricultural areas. A significant rise in seal level could flood many coastal cities and damage ecologically important coastal wetlands. Other heat-absorbing gases that are increasing in the atmosphere as a result of human activities are nitrous oxide and chlorofluorocarbons.

GREYWATER—Wastewater from clothes washing machines, showers, bathtubs, hand washing, lavatories and sinks that are not used for disposal of chemicals or chemical-biological ingredients. Less commonly spelled Graywater.

GRIT—Dense inorganic matter, such as sand and gravel, present in water or sewage.

GRIT CHAMBER—A small detention basin designed to permit the settling of inorganic materials while passing the organic fraction.

GRIT REMOVAL—The process of removing sand and fine gravel from a stream od domestic waste in a Grit Chamber.

GROIN—A small jetty extending from a shore to protect a beach against erosion or to trap shifting sands.

GROSS EROSION—The total of all sheet, gully, and channel erosion in a drainage basin, usually expressed in units of mass.

GROSS RESERVOIR CAPACITY—The total amount of storage capacity available in a reservoir for all purposes, from the streambed to the normal maximum operating level. It does not include surcharge (water temporarily stored above the elevation of the top of the spillway), but does include dead (or inactive) storage.

GROSS DUTY OF WATER—(Irrigation) The irrigation water diverted at the intake of a canal system, usually expressed in depth on the irrigable area under the system. Also see Net Duty of Water.

GROSS WATER REQUIREMENT (FARM)—The Farm Delivery Requirement plus the seepage losses in the canal system from the headworks to the farm unit plus the waste of water due to poor operation.

GROSS WATER YIELD—The available water runoff, both surface and subsurface, prior to use by man's activities, use by phreatophytes, or evaporation from free water surfaces.

GROUND—(1) The solid surface of the earth. (2) The floor of a body of water, especially the sea.

GROUND COVER—Plants grown to keep soil from eroding.

GROUND RUPTURE—The movement of the ground along one side of a Fault relative to the other side, caused by an earthquake.

GROUND TRUTH—(Data Analysis and Interpretation) Verification of aerial photointerpretation by observers on the ground.

GROUND WATER, also Groundwater—(1) Water that flows or seeps downward and saturates soil or rock, supplying springs and wells. The upper level of the saturate zone is called the Water Table. (2) Water stored underground in rock crevices and in the pores of geologic materials that make up the earth's crust. Ground water lies under the surface in the ground's Zone of Saturation, and is also referred to as Phreatic Water.

GROUND WATER BARRIER—Rock, clay, or other natural or artificial materials with a relatively low permeability that occurs (or is placed) below ground surface, where it impedes the movement of ground water and thus causes a pronounced difference in the heads on opposite sides of the barrier.

GROUND WATER BASIN—A ground-water reservoir together with all the overlying land surface and the underlying aquifers that contribute water to the reservoir. In some cases, the boundaries of successively deeper aquifers may differ in a way that creates difficulty in defining the limits of the basin. A ground-water basin could be separated from adjacent basins by geologic boundaries or by hydrologic boundaries.

GROUND WATER, CONFINED—Ground water under pressure significantly greater than atmospheric, with its upper limit the bottom of a bed with hydraulic conductivity distinctly lower than that of the material in which the confined water occurs.

GROUND WATER DISCHARGE—(1) The flow of water from the Zone of Saturation. (2) (Water Quality) Ground water entering near coastal waters which has been contaminated by landfill leachate, deep well injection of hazardous wastes, septic tanks, etc.

GROUND WATER DISPOSAL—Refers to wastewater that is disposed of through the ground either by injection or seepage. This includes the following discharge methods: absorption beds, injection wells, drain fields, percolation ponds, rapid infiltration basins, and spray fields (land application). Land application systems (reuse systems) are considered a groundwater disposal method as the wastewater used to irrigate turf or crops is generally intended to filter down through the soil.

GROUND WATER DIVIDE—A line on a water table on either side of which the water table slopes downward. It is analogous to a drainage divide between two drainage basins on a land surface. It is also the line of highest Hydraulic Head in the water table or Potentiometric Surface.

GROUND WATER FLOW—The movement of water through openings in sediment and rock that occurs in the Zone of Saturation.

GROUND WATER FLOW MODEL—(1) A digital computer model that calculates a hydraulic head field for the modeling domain using numerical methods to arrive at an approximate solution to the differential equation of ground-water flow. (2) Any representation, typically using plastic or glass cross-sectional viewing boxes, with representative soil samples, depicting ground-water flows and frequently used for educational purposes.

GROUND WATER, FREE—Unconfined ground water whose upper boundary is a free water table.

GROUND WATER HYDRAULICS—The study of the movement of water, especially water under pressure and water's movement through various soil medium.

GROUND WATER HYDROLOGY—The branch of Hydrology that deals with ground water; its occurrence and movements, its replenishment and depletion, the properties of rocks that control ground water movement and storage, and the methods of investigation and utilization of ground water. Also referred to as Ground Water Hydraulics, although this term pertains more to the study of the motion of water.

GROUND WATER LAW—The common law doctrine of Riparian Rights and the doctrine of prior appropriation (Appropriative Rights) as applied to ground water. See Appropriation Doctrine and Riparian Doctrine.

GROUND WATER MINING—The withdrawal of water from an aquifer in excess of recharge which, if continued over time, would eventually cause the underground supply to be exhausted or the water table could drop below economically feasible pumping lifts.

GROUND WATER MOUND—Raised area in a water table or other Potentiometric Surface, created by Ground Water Recharge.

GROUND WATER OUTFLOW—That part of the discharge from a drainage basin that occurs through the ground water. The term "underflow" is often used to describe the ground water outflow that takes place in valley alluvium (instead of the surface channel) and thus is not measured at a gaging station.

GROUND WATER OVERDRAFT—The condition of a ground water basin in which the amount of water withdrawn by pumping exceeds the amount of water that recharges the basin over a period of years during which water supply conditions approximate average. Sometimes used interchangeably with Ground Water Mining.

GROUND WATER, PERCHED—Ground water that is separated from the main body of ground water by an impermeable (unsaturated) layer.

GROUND WATER PLUME—A volume of contaminated groundwater that extends downward and outward from a specific source; the shape and movement of the mass of the contaminated water is affected by the local geology, materials present in the plume, and the flow characteristics of the area groundwater.

GROUND WATER PRIME SUPPLY—The long-term average annual percolation to the major ground water basins from precipitation falling on the land and from flows in rivers and streams. Also includes recharge from local sources that have been enhanced by construction of spreading ground or other means. Recharge of imported and reclaimed water is not included nor is recharge using applied irrigation water.

GROUND WATER RECHARGE—Inflow of water to a ground water reservoir (Zone of Saturation) from the surface. Infiltration of precipitation and its movement to the water table is one form of natural recharge. Also, the volume of water added by this process.

GROUND WATER REGISTRATION—A statement made by a well owner registering the Beneficial Use of ground water. See (Prior) Appropriation Doctrine.

GROUND WATER RESERVOIR—An aquifer or aquifer system in which ground water is stored. The water may be introduced into the aquifer by artificial or natural means.

GROUND WATER RESERVOIR STORAGE—The amount of water in storage within the defined limit of the aquifer.

GROUND WATER RUNOFF—A portion of runoff which has passed into the ground, has become ground water, and has been discharged into a stream channel as spring or seepage water.

GROUND WATER STORAGE—The storage of water in ground water reservoirs.

GROUND WATER STORAGE CAPACITY—The space or voids contained in a given volume of soil and rock deposits. Also, the reservoir space contained in a given volume of deposits. Under optimum conditions of use, the usable ground water storage capacity volume of water that can be alternately extracted and replaced in the deposit, within specified economic limitations.

GROUND WATER SYSTEM—All the components of subsurface materials that relate to water, including Aquifers (confined and unconfined), Zones of Saturation, and Water Tables.

GROUND WATER TABLE—The upper surface of the Zone of Saturation for underground water. It is an irregular surface with a slope or shape determined by the quantity of ground water and the permeability of the earth materials. In general, it is highest beneath hills and lowest beneath valleys. Also referred to as the Water Table.

GROUND WATER, UNCONFINED—Water in an aquifer that has a water table.

GROUND WATER UNDER THE DIRECT INFLUENCE (UDI) OF SURFACE WATER—Any water beneath the surface of the ground with: (1) a significant occurrence of insects or other microorganisms, algae, or large-diameter Pathogens; or (2) significant and relatively rapid shifts in water characteristics such as turbidity, temperature, conductivity, or pH which closely correlate to climatological or surface water conditions. Under direct influence conditions are determined for individual sources in accordance with criteria established by the state.

GROUND WATER VELOCITY—The rate of water movement through openings in rock or sediment. Also see Darcy's Law.

GROUT CURTAIN—(Dam) A barrier produced by injecting grout into a vertical zone, usually narrow horizontally, in the foundation of a dam to reduce seepage under the dam. Also referred to as Grout Cutoff.

GROWING SEASON—(1) The period and/or number of days between the last freeze in the spring and the first frost in the fall for the freeze threshold temperature of the crop or other designated temperature threshold. (2) Also, the average number of days exceeding 32°F (0°C).

GROWTH MANAGEMENT PROGRAM—A program comprised of several techniques to coordinate public and private decisions about the location and timing of development in order to best utilize environmental and physical resources.

GUSH—To flow forth suddenly in great volume.

GULF—A portion of an ocean or sea extending into the land; a partially landlocked sea, usually larger than a bay.

GULF STREAM—(Geography) The warm ocean current of the North Atlantic. It originates in the westward equatorial current caused by the trade winds, but is deflected northward by the coast of South America into the Gulf of Mexico; issuing thence, it follows approximately the coast of North America to the island of Nantucket, where it is deflected more to the eastward. Its influence is felt as far as Norway. Where it issues from the Gulf of Mexico, its velocity is more than four miles per hour, but in much of the northern part of the Atlantic its velocity is only 10 to 15 miles per day.

GULLY, also Gulley—(1) A channel or miniature valley cut by concentrated runoff but through which water commonly flows only during and immediately after heavy rains or during the melting of snow; may be Dendritic or branching or it may be linear, rather long, narrow, and of uniform width. (2) A small valley or gulch. The distinction between Gully and Rill is one of depth. A gully is sufficiently deep that it would not be obliterated by normal tillage operations, whereas a rill is of lesser depth and would be smoothed by ordinary farm tillage.

GULLY EROSION—The widening, deepening, and headcutting of small channels and waterways due to erosion; severe erosion in which trenches are cut to a depth greater than 30 centimeters (approximately one foot). Also see Erosion.

GULLY RECLAMATION—Projects designed to prevent erosion in gullies by either filling them in or planting vegetation to stabilize the banks. May include the use of small dams of manure and straw, earth, stone, or concrete to collect silt and gradually fill in channels of eroded soil.

GUMBO—A fine, silty soil, common in the southern and western United States, that forms an unusually sticky mud when wet.

GURGITATION—A whirling or surging motion, as of water.

GUTTATION—The loss of water in liquid form from the uninjured leaf or stem of the plant, principally through water stomata (the microscopic opening in the epidermis of plants, surrounded by guard cells and serving for gaseous exchange); the exudation of water from leaves as a result of root pressure.

GUTTER—(1) A channel at the edge of a street or road for carrying off surface water. (2) A trough fixed under or along the eaves of a building for draining rainwater from a roof. (3) A furrow or groove formed by running water.

GUZZLER—A manmade water collecting device used in wildlife management.

GYMNOSPERMS (GYMNOSPERMAE)—(Botanical) One of the two classes within the plant family Spermatophyta, or seed plants, the other being Angiosperms (Angiospermae). Gymnosperms are of lower phylogenetic rank, as they includes plants having the seeds naked, or not enclosed in an ovary. This class includes the extinct orders (sub-classes) Bennettitales and Cordaitales, and the orders Cycadales, Ginkgoales, Gnetales, and Pinales. Also see Angiosperms.

HABITAT—The native environment or specific surroundings where a plant or animal naturally grows or lives. The surroundings include physical factors such as temperature, moisture, and light together with biological factors such as the presence of food or predator organisms. The term can be employed to define surroundings on almost any scale from marine habitat, which encompasses the oceans, to microhabitat in a hair follicle of the skin.

HABITAT CONSERVATION PLAN (HCP)—A requirement under the Endangered Species Act (ESA) when economic development may result in harm to Threatened or Endangered Species. The plan does allow for some loss of individual animals or habitat of a species in exchange for a commitment that will insure long-term survival. Its intent is to better balance economic development and conservation.

HABITAT INDICATOR—A physical attribute of the environment measured to characterize conditions necessary to support an organism, population, or community in the absence of pollutants, e.g., salinity of estuarine waters or substrate type in streams or lakes.

HAIL—Precipitation which forms into balls or lumps of ice over 0.2 inch (5.08 mm) in diameter. Hail is formed by alternate freezing and melting as it is carried up and down by turbulent air currents within a cloud.

HAILSTONE—A hard pellet of snow and ice.

HAILSTORM—A storm with Hail.

HAIL SUPPRESSION—Any method of reducing the damaging effects of hailstorms by modifying the characteristics of the hail-producing cloud. The currently prevailing hypothesis is that silver iodide seeding provides more hailstone nuclei (and, at the same time, reduces the amount of supercooled water available to build up large hailstones) with the net effect that the hail that reaches the ground is smaller and less damaging, and also has a high probability of melting before reaching the ground.

HAIR HYGROMETER (HYGROGRAPH)—An instrument for measuring humidity which makes use of the fact that the length of hair varies with relative humidity.

HALCYON DAYS (Water)—With respect to water, generally refers to idyllic by-gone days when supplies of an area's fresh water were relatively abundant with respect to the demands of man.

HALINE—Term used to indicate dominance of ocean salt.

HALINE MARSHES—A saturated, poorly drained area, intermittently or permanently water covered, having aquatic and grasslike vegetation, influenced predominately by ocean salts.

HALO—A circular band of colored light around a light source, as around the sun or moon, caused by the refraction and reflection of light by ice particles suspended in the intervening atmosphere. Also see Rainbow for a similar refraction and reflection principal using water.

HALOCLINE—The boundary between surface fresh water and underlying saltwater in a stratified coastal environment. A location where there is a marked change in salinity.

HALOPHYTES—A group of salt-tolerant plants ranging from cacti to sea grass that can absorb salt and heavy metals such as cadmium and arsenic from the wastewater of power plants, particularly coal-fired generating plants which is typically laden with heavy-metal byproducts of coal combustion.

HAMMOCK, also Hummock—(1) In the southern United States, especially Florida, an area characterized by hardwood vegetation, the soil being of a greater depth and containing more humus than that of the flatwoods or pinelands, hence being more suitable for cultivation. Particularly, a tract of forested land that rises above an adjacent marsh. (2) A ridge or hill of ice in an ice field.

HANGING VALLEYS—Hanging valleys can be created when smaller tributary glaciers join the main ice sheet. Since the main glacier is larger and heavier than the tributary one(s), the main glacier will erode more deeply into its valley than will the tributary into its own valley. After the ice melts, the tributary valley will be left hanging part of the way up the wall of the larger canyon that it intersects. Many waterfalls in the high Sierras, including well-known ones at Yosemite National Park, occur at the juncture of a hanging valley with a larger canyon.

HARBOR—A sheltered anchorage for ships and boats. Also see Port.

HARDNESS—A property of water which causes an increase in the amount of soap that is needed to produce foam or lather and that also produces scale in hot water pipes, heaters, boilers and other units in which the temperature of water is increased materially. Hardness is produced almost completely by the presence of calcium and magnesium salts in solution. The following scale may assist in appraising water hardness, measured by weight of dissolved salts (in milligrams) per unit (in liters) of water:

[1] Soft—0-60 milligrams/liter (mg/l); [2] Moderately Hard—61-120 mg/l; [3] Hard—121-180 mg/l; and [4] Very Hard—over 180 mg/l.

HARDPAN—A hard impervious layer composed chiefly of clay or organic materials cemented by relatively insoluble materials, which does not become plastic when wet, and definitely limits the downward movement of water and roots.

HARD WATER—Water which forms a precipitate with soap due to the presence of calcium, magnesium, or ferrous ions in solution.

HARVESTED RAINWATER—The rain that falls on a roof or yard and is channeled by gutters or channels to a storage tank. The first wash of water on a roof is usually discarded and the subsequent rainfall is captured for use if the system is being used for potable water.

HAYSTACK—A vertical standing wave in turbulent river waters.

HAZARD RANKING SYSTEM (HRS)—A method for ranking hazardous waste disposal sites for possible placement on the National Priorities List (Superfund List), as provided for by the Comprehensive, Environmental Response, Compensation, and Liability Act (CERCLA). The ranking uses information gathered by the preliminary assessment and site inspection and the listing site inspection. The need for remedial action is scored on the basis of potential harm to human health resulting from: (1) releases into groundwater, surface water, or the atmosphere; (2) fire and explosion; and/or (3) direct contact with hazardous materials. The HRS evaluation assigns an overall numerical value to each site, which determines its priority for cleanup. Also see Hazardous Substance and Hazardous Substances Superfund.

HAZARDOUS MATERIAL (EPA)—An substance, pollutant or contaminant listed as hazardous under the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) of 1980, as amended, and the regulations promulgated pursuant to that act.

HAZARDOUS SUBSTANCE—(1) Any material that poses a threat to human health and/or the environment. Typical hazardous substances are toxic, corrosive, ignitable, explosive, or chemically reactive. (2) Any substance designated by the U.S. Environmental Protection Agency (EPA) to be reported if a designated quantity of the substance is spilled in the waters of the United States or if otherwise released into the environment. Also referred to as Hazardous Waste.

HAZARDOUS SUBSTANCES SUPERFUND—A federal trust fund for use in the cleanup of spills or sites containing hazardous waste that pose a significant threat to the public health or the environment. The fund, originally called the Hazardous Substances Response Trust Fund, was established by the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) in 1980. Beginning that year $1.5 billion was to be collected over five years, mainly from taxes on crude oil, petroleum products, petrochemicals, and certain inorganic chemicals. The 1986 re-authorization of the law, which changed the fund's name to the Hazardous Substances Superfund (or just "Superfund"), increased the fund to $8.5 billion and broadened the tax base to include a general corporate Superfund tax. Another one-half billion dollars was included to clean up leaks from underground storage tanks. Also see U.S. Environmental Protection Agency (EPA).

HAZARDOUS WASTE—See Hazardous Substance.

HAZE—Atmospheric moisture, dust, smoke, and vapor that diminishes visibility.

HEAD—Difference in elevation between intake and discharge points for a liquid. In geology, most commonly of interest in connection with the movement of underground water.

HEAD DITCH—The water supply ditch at the head end of an irrigated field.

HEADER—(1) A pipe that serves as a central connection for two or more smaller pipes. (2) A raised tank or hopper that maintains a constant pressure or supply to a system, especially the small tank that supplies water to a central heating system.

HEADGATE—The gate that controls water flow into irrigation canals and ditches. A watermaster regulates the headgates during water distribution and posts headgate notices declaring official regulations. Headgate also refers to a diversion structure which controls the flow rate from a conveyance system (canals and laterals) into the farm conveyance system.

HEADLAND—(1) A point of land, usually high and with a sheer drop, extending out into a body of water; a promontory. (2) The unplowed land at the end of a plowed furrow.

HEAD LOSS—(1) The decrease in total head caused by friction. (2) The effect of obstructions, such as narrow bridge openings or buildings, that limit the area through which water must flow, raising the surface of the water upstream from the obstruction.

HEADRACE—A channel that carries water to a water wheel or turbine; a forebay.

HEAD, STATIC—The height above a standard datum of the surface of a column of water (or other liquid) that can be supported by the static pressure at a given point. The static head is the sum of the Elevation Head and the Pressure Head.

HEAD, TOTAL—The sum of the Elevation Head (distance of a point above datum), the Pressure Head (the height of a column of liquid that can be supported by static pressure only at the point), and the Velocity Head (the height to which the liquid can be raised by its own kinetic energy. Also see Hydraulic Head.

HEAD WALL—A steep slope or precipice rising at the head of a valley or glacial Cirque.

HEADWARD EROSION—Erosion which occurs in the upstream end of the valley of a stream, causing it to lengthen its course in that direction.

HEADWATER(S)—(1) The source and upper reaches of a stream; also the upper reaches of a reservoir. (2) The water upstream from a structure or point on a stream. (3) The small streams that come together to form a river. Also may be thought of as any and all parts of a river basin except the mainstream river and main tributaries.

HEADWORKS—The diversion structures at the head of a conduit.

HEAT BUDGET, ANNUAL (of a Lake)—The amount of heat necessary to raise the water from the minimum winter temperature to the maximum summer temperature.

HEAT EXCHANGERS—Any mechanical device designed to transfer heat energy from one medium to another. In many such exchangers water is used as the primary medium of transfer.

HEATH—A tract of waste land; especially in Great Britain, an open, level area clothed with a characteristic vegetation consisting principally of undershrubs of the genus Erica, or a large genus of low evergreen shrubs. Also see Peatland.

HEAT OF CONDENSATION—The heat released when a vapor changes state to a liquid. See Heat of Vaporization.

HEAT OF VAPORIZATION—The heat energy (calories) required to convert one gram of liquid to vapor without a change in temperature of the substance which is being vaporized. For water at 100C (212F) and standard atmospheric pressure, the heat of vaporization if 540 calories per gram. Conversely, when a liquid condenses, it loses the heat absorbed upon vaporization, giving of Heat of Condensation.

HEAT PUMP—An apparatus for heating or cooling a building by transferring heat by mechanical means from or to a reservoir (as the ground, water, or air) outside the building.

HEAT SINK—Any material used to absorb heat. In the environment, this is usually air or water that absorbs waste heat produced in the operation of electric power plants or other industrial facilities.

HEAT TRANSFER AGENT—A liquid or gas that functions in a Heat Exchanger to facilitate the movement of heat from one location to another. For example, the engine coolant in an automobile serves to transfer heat from the engine block to the atmosphere. Likewise, water facilitates the movement of heat from the reactor core to the outside of a nuclear reactor.

HEAVY METALS—Metals having a specific gravity of 5.0 or greater; generally toxic in relatively low concentrations to plant and animal life and tend to accumulate in the food chain. Examples include lead, mercury, cadmium, chromium, and arsenic.

HEAVY WATER—Water composed of isotopes of hydrogen of atomic weight greater than 1 or of oxygen of atomic weight greater than 16, or both; especially water composed of ordinary oxygen and the isotope of hydrogen of atomic weight 2; Deuterium Oxide (D2O). Typically used as a moderator in certain nuclear reactors. Also see Heavy Water Moderated Reactor.

HEAVY WATER (MODERATED) REACTOR—A nuclear reactor that uses heavy water as its moderator. Heavy water is an excellent moderator and thus permits the use of inexpensive (unenriched) uranium as a fuel.

HECTARE—(Abbreviation ha) A metric unit of area equal to 100 Ares (2.471 acres) and equivalent to 10,000 square meters (107,639 square feet). Also see Metric System.

HEMIHYDRATE—A hydrate in which the molecular ratio of water molecules to anhydrous compound is 1:2.

HEPATITIS—Inflammation of the liver. A virus-caused disorder transmitted to humans by the consumption of raw oysters taken from water contaminated with sewage.

HEPATITIS A—A form of hepatitis caused by an RNA virus that does not persist in the blood serum and is transmitted by ingestion of infected food and water. The disease has a shorter incubation and generally milder symptoms than Hepatitis B. Also referred to as Infectious Hepatitis.

HERBACEOUS—With the characteristics of an herb; having the texture and color of a foliage leaf; a plant with no persistent woody stem above ground.

HERDING AGENT—A chemical applied to the surface of water to control the spread of a floating oil spill.

HETEROGENEITY—Characteristic of a medium in which material properties vary from point to point. Contrast with Homogeneity.

HIGHER AQUATIC PLANTS—Those plants whose seeds germinate in the water phases or substrate of a body of water and which must spend part of their life cycle in water. Includes plants which grow completely submerged as well as a variety of emersed and floating leaf types.

HIGHEST AND BEST USE—The classification of water based on an analysis of the greatest needs of the future. Certain quantities of water (rights) are reserved for appropriation according to this classification.

HIGH-LINE JUMPERS—Pipes or hoses connected to fire hydrants and laid on top of the ground to provide emergency water service for an isolated portion of a distribution system.

HIGH SEA—The open part of a sea or ocean, especially outside territorial waters; usually used in plural.

HIGH TIDE (HT)—(1) The tide at its fullest extent, when the water reaches its highest level. (2) The time at which this tide occurs.

HIGH WATER (HW)—(1) High tide. (2) The state of a body of water that has reached its highest level.

HIGH WATER MARK (HWM)—A mark indicating the highest level reached by a body of water.

HISTORICAL GEOMORPHOLOGY—See Geomorphology, Historical.

HISTOSOLS—Organic soils.

HOARFROST—A silvery-white deposit of ice needles formed by direct condensation at temperatures below freezing due to nocturnal radiation. Hoarfrost forms during still, clear nights, is small in amount, needlelike in texture, the "needles" approximately perpendicular to the objects on which they occur, and most abundant along the edges. Sometimes confused with Rime.

HOGBACK RIDGE—Any ridge with a sharp summit and steep slopes of nearly equal inclination on both flanks, and resembling in outline the back of a hog.

HOGSHEAD—Any of various units of volume or capacity ranging from 63 to 140 gallons (238 to 530 liters), especially a unit of capacity used in liquid measure in the United States equal to 63 gallons (238 liters).

HOLDING MEDIUM—(Water Quality) A special fluid employed for maintaining fecal bacteria in a viable state between the time that water samples are processed by filtration and the time that the filters used to remove the bacteria from water can be incubated properly. The medium protects viability between sampling and analysis.

HOLDING POND—A small basin or pond designed to hold sediment laden or contaminated water until it can be treated to meet water quality standards or be used in some other way.

HOLDING TANK—A prefabricated structure of concrete or steel or like materials constructed to store liquid manure from animals.

HOLDING TIME—(Water Quality) The time allowed between removal of samples from water sources for bacteriological analysis and the processing of those samples.

HOLE—A deep place in a body of water.

HOLISTIC—Of, concerned with, or dealing with wholes or integrated systems rather than with their parts. With respect to water-related issues, the term most typically describes an analytical and planning approach which examines and considers the inter-related linkages and interdependencies of a socioeconomic system with resource use, pollution, environmental impacts, and preservation of an entire ecosystem.

HOLOCENE—(Geology) The present epoch of time, beginning about 10,000 years ago. Also see Quaternary.

HOLOTHURIAN—A group of marine, bottom-dwelling animals related to the sea stars and sand dollars (echinoderms). Unlike these relatives, the holothurians have soft bodies and are long and slender in shape, such as the sea cucumber.

HOMEOWNER WATER SYSTEM—Any water system which supplies piped water to a single residence.

HOMOGENEITY—Characteristic of a medium in which material properties are identical throughout. A material is homogeneous if its hydrologic properties are everywhere identical. Although no known aquifer is homogeneous in detail, models based on the assumption of homogeneity have proven to be valuable tools for predicting the approximate relationship in aquifers between discharge and potential. Contrast with Heterogeneity

HOOKAH—An Eastern smoking pipe designed with a long tube passing through an urn of water that cools the smoke as it is drawn through. Also referred to as a Hubble-Bubble and Narghile.

HOOK GAGE—A pointed, U-shaped hook attached to a staff or vernier scale, used in the accurate measurement of the elevation of a water surface. The hook is submerged, and then raised, usually by means of a screw, until the point just makes a pimple on the water surface.

HORIZONTAL AND VERTICAL CONTROL POINTS—See Control Points (Horizontal and Vertical).

HORN—A body of land or water shaped like a horn.

HORSEPOWER (HP)—A unit of power, numerically equal to a rate of 33,000 foot-pounds of work per minute (or 550 foot-pounds per second), used in stating the power of an engine or any other prime mover, or in estimating the power required to drive machinery, or the like. The term horsepower was originated by Boulton and Watt to state the power of their steam engines. In a practical test it was found that the average horse could work constantly at a rate of 22,000 foot-pounds per minute. This was increased by one half (50 percent) in making this arbitrary, and now universal, unit of power. Electrical Horsepower is horsepower calculated from electric units whereby 746 watts of electrical energy is equivalent to one horsepower.

HORSEPOWER, ELECTRICAL—Horsepower calculated from electric units whereby 746 watts of electrical energy is equivalent to one horsepower.

HOSE—(1) A flexible tube for conveying liquids or gases under pressure. (2) To water, drench, or wash with a hose.

HOT ROCK RESERVOIR—A potential source of geothermal power. The "hot rock" system requires drilling deep enough to reach heated rock, then fracturing it to create a reservoir into which water can be pumped. This technique has not yet been perfected.

HOT SPRING—A spring that brings hot water to the surface. A thermal spring. Water temperature usually 15F (8C) or more above the mean air temperature.

HOVERCRAFT—A vehicle that is supported above the surface of land or water by a cushion of air produced by downwardly directed fans.

HUMAN ECOLOGY—(1) A branch of sociology dealing particularly with the spatial and temporal interrelationships between humans and their economic, social, and political organization; (2) The ecology of human communities and populations, especially as concerned with preservation of environmental quality (as of air or water) through proper application of conservation and civil engineering practices.

HUMAN ENVIRONMENT—Natural and physical environment and the relationship of people with that environment including physical, biological, cultural, social, and economic factors in a given area.

HUMID—Containing or characterized by perceptible moisture. Usually refers to the atmosphere.

HUMIDITY—The degree of moisture in the air.

HUMMOCK—(1) A small but steep, irregular hill rising above the general level of the surrounding land; a low mound or ridge of earth, a knoll. (2) Also Hammock. A tract of forested land that rises above an adjacent marsh in the southern United States. (3) A ridge or hill of ice in an Ice Field.

HUMMOCKY—Hilly, uneven landscape resulting from deep-seated soil movement, usually of a rotational nature.

HUMUS—A brown or black organic substance consisting of partially or wholly decayed vegetable or animal matter that provides nutrients for plants and increases the ability of soil to retain water.

HUNDRED-YEAR FLOOD—The magnitude of a flood which has one chance in one hundred (i.e., one percent) of being exceeded in any future one-year period. As the occurrence of floods is random in time, there is no guarantee that there will not be two one hundred-year floods within a given year, or that there will be one such flood within a given century (100 years). The boundary of the one hundred-year flood zone is used by the Federal Emergency Management Agency (FEMA) to designated Special Flood Hazard Areas. These areas are plotted on Flood Insurance Rate Maps (FIRMs), which are used in determining the flood risk to structures in the Flood Plain for flood insurance purposes. Also see X-Year Flood.

HURRICANE—(1) A severe tropical cyclone originating in the equatorial regions of the Atlantic Ocean or Caribbean Sea, traveling north, northwest, or northeast from its point of origin, and usually involving heavy rains. (2) A wind with a speed greater than 74 miles (119 kilometers) per hour, according to the Beaufort scale. Also see Cyclone and Typhoon.

HURRICANE FORECASTING—(Meteorology and Statistics) Hurricane tracking and estimation in the United States is centered in the federal government's National Hurricane Center in Coral Gables, Florida. However, one pioneering effort in the application of statistical analysis and econometric techniques to hurricane analysis and forecasting has been undertaken by William Gray, professor of meteorology at Colorado State University in Fort Collins, Colorado. Dr. Gray's research is based on the foundation that hurricanes are caused by global, rather than local factors, to include the influence of El Niño (El Niño Effect, resulting in reduced hurricane activity as opposed to the La Niña when hurricanes tend to be more common) in the eastern equatorial Pacific Ocean as well as wind directions (pressure differentials) and precipitation levels. His research has led to an extensive quantitative expression to estimate both the number and intensity of hurricanes in the western Atlantic region (to include the Caribbean and Gulf of Mexico) during the usual peak hurricane season of mid-August through mid-October. The following relationship represents an Econometric Model for forecasting hurricane activity based upon a number of climatological explanatory factors covering a vast geographic range.

Hurricane Activity = ß0 + ß1(1U50 + a2U30 + a3U50 - U30) + ß2(4Rs + a5Rg + a6ÞxP + a7ÞxT) + ß3(a8SLPA + a9ZWA + a10SSTA + a11ÞtSSTA + a12SOI + a13ÞtSOI) Hurricane Activity = ß0 + ß1(1U50 + a2U30 + a3U50 - U30) + ß2(4Rs + a5Rg + a6ÞxP + a7ÞxT) + ß3(a8SLPA + a9ZWA + a10SSTA + a11ÞtSSTA + a12SOI + a13ÞtSOI) Hurricane Activity = ß0 + ß1(1U50 + a2U30 + a3U50 - U30) + ß2(4Rs + a5Rg + a6ÞxP + a7ÞxT) + ß3(a8SLPA + a9ZWA + a10SSTA + a11ÞtSSTA + a12SOI + a13ÞtSOI)

where:

The ß's and a's are empirically derived coefficients (parameters) for prior years of data;

U50 and U30 are extrapolated September quasi-biennial oscillation (QBO—the tendency for equatorial winds 13 to 16 miles above the earth to change direction from east to west and vice versa) zonal winds at 30 and 50 mb at 10N latitude;

U50 - U30 is the absolute value of the extrapolated vertical wind shear between 50 and 30 mb; U50 - U30 is the absolute value of the extrapolated vertical wind shear between 50 and 30 mb;

Rs is the western Sahel (western portion of Africa's Sahara desert) precipitation in the previous August and September; Rs is the western Sahel (western portion of Africa's Sahara desert) precipitation in the previous August and September;

Rg is the previous year August to November precipitation in the Gulf and Guinea region; Rg is the previous year August to November precipitation in the Gulf and Guinea region;

ÞP is West African anomalous east-west pressure gradient deviation in February through May; ÞP is West African anomalous east-west pressure gradient deviation in February through May;

ÞT is West African anomalous west-east temperature deviation in February through May; ÞT is West African anomalous west-east temperature deviation in February through May;

SLPA is the April-May Sea Level Pressure Anomaly in the lower Caribbean basin; SLPA is the April-May Sea Level Pressure Anomaly in the lower Caribbean basin;

ZWA is the April-May Zonal Wind Anomaly in the Caribbean basin; ZWA is the April-May Zonal Wind Anomaly in the Caribbean basin;

SOI is the April-May normalized Tahiti minus Darwin Sea Level Pressure differences; SOI is the April-May normalized Tahiti minus Darwin Sea Level Pressure differences;

SSTA is the April-May Sea Surface Temperature Anomaly in Nino 3 (El Niño); SSTA is the April-May Sea Surface Temperature Anomaly in Nino 3 (El Niño);

ÞSOI is the recent months change in SOI from January-February to April-May; ÞSOI is the recent months change in SOI from January-February to April-May;

ÞSSTA is the recent months change in SSTA from January-February to April-May. ÞSSTA is the recent months change in SSTA from January-February to April-May.

HUSBANDRY—(Agriculture) The act or practice of cultivating crops and breeding and raising livestock. Also, the application of scientific principles to agriculture, especially to animal breeding. (Ecology) The careful management or conservation of resources.

HYADES—(Astronomy) A cluster of stars in the constellation Taurus, the five brightest of which form a V, supposed by ancient astronomers to indicate rain when they rose with the sun.

HYDATHODE—(Botany) A water-excreting microscopic epidermal structure in many plants.

HYDRANT—A discharge pipe with a valve and spout at which water may be drawn from a water main (as for fighting fires) called also fireplug; (2) Faucet.

HYDRATE—A solid compound containing water molecules combined in a definite ratio as an integral part of the crystal.

HYDRATED—Chemically combined with water, especially existing in the form of a Hydrate.

HYDRATION—The chemical combination of water with another substance.

HYDRAULIC—(1) Of, involving, moved by, or operated by a fluid, especially water, under pressure. (2) Able to set and harden under water, as Portland cement. (3) Of or relating to hydraulics.

HYDRAULIC BARRIER—Modifications to a ground-water flow system that restrict or impede movement of water and contaminants. Also, a barrier developed in the Estuary by the release of fresh water from upstream reservoirs to prevent intrusion of sea water into the body of fresh water.

HYDRAULIC CONDUCTIVITY—Simply, a coefficient of proportionality describing the rate at which water can move through an aquifer or other permeable medium. The density and kinematic viscosity of the water must be considered in determining hydraulic conductivity. More specifically, the volume of water at the existing kinematic viscosity that will move, in unit time, under a unit Hydraulic Gradient through a unit area measured at right angles to the direction of flow, assuming the medium is isotropic and the fluid is homogeneous. In the Standard International System, the units are cubic meters per day per square meter of medium (m3/day/m2) or m/day (for unit measures).

HYDRAULIC CONDUCTIVITY, EFFECTIVE—The rate of water flow through a porous medium that contains more than one fluid (such as water and air in the unsaturated zone), which should be specified in terms of both the fluid type and content and the existing pressure.

HYDRAULIC EARTHFILL DAM—An embankment built up from waterborne clay, sand, and gravel carried through a pipe or flume.

HYDRAULIC FRACTURING—Any technique involving the pumping of fluid under high pressure into an oil or gas formation to create fissures and openings in the reservoir rock and increase the flow of oil or gas.

HYDRAULIC GRADE LINE (HGL)—A line whose plotted ordinate position represents the sum of pressure head plus elevation head for the various positions along a given fluid flow path, such as a pipeline or ground-water streamline.

HYDRAULIC GRADIENT (I)—The gradient or slope of a water table or Piezometric Surface in the direction of the greatest slope, generally expressed in feet per mile or feet per feet. Specifically, the change in static head per unit of distance in a given direction, generally the direction of the maximum rate of decrease in head. The difference in hydraulic heads (h1 - h2), divided by the distance (L) along the flowpath, or, expressed in percentage terms:

I = (h1 - h2) / L X 100 I = (h1 - h2) / L X 100

A hydraulic gradient of 100 percent means a one foot drop in head in one foot of flow distance.

HYDRAULIC GRADIENT PIVOT POINT—A location along the water surface in a canal reach where the water level remains essentially constant during changes in flow.

HYDRAULIC HEAD—(1) The height of the free surface of a body of water above a given point beneath the surface. (2) The height of the water level at the headworks or an upstream point of a waterway, and the water surface at a given point downstream. (3) The height of a hydraulic grade line above the center line of a pressure pipe, at a given point.

HYDRAULIC JUMP—The rapid change in the depth of flow from a low stage to a high stage, resulting in an abrupt rise of water surface.

HYDRAULIC LOADING—(Water Quality) For a sand filter wastewater treatment unit, the volume of wastewater applied to the surface of the filtering medium per time period. The loading is often expressed in gallons per day per square foot (gpd/ft2), or cubic meters per square meter per day (m3/m2d).

HYDRAULIC MINING—Mining by washing sand and dirt away with water, leaving the desired mineral.

HYDRAULIC PERMEABILITY—The flow of water through a unit cross-sectional area of soil normal to the direction of flow when the Hydraulic Gradient is unity.

HYDRAULIC RADIUS—The cross-sectional area of a stream of water divided by the length of that part of its periphery in contact with its containing conduit; the ratio of area to wetted perimeter. Also referred to as Hydraulic Mean Depth.

HYDRAULIC RAM—A device which uses the energy of falling water to force a small portion of the water to a height greater than the source. A water pump in which the downward flow of naturally running water is intermittently halted by a valve so that the flow is forced upward through an open pipe into a reservoir.

HYDRAULICS—(1) The study of liquids, particularly water, under all conditions of rest and motion. (2) The branch of physics having to do with the mechanical properties of water and other liquids in motion and with the application of these properties in engineering.

HYDRAULIC TRANSIENT—(1) Interim stage when a flow changes from one steady-state condition to another steady-state condition because of a sudden acceleration or deceleration of flow. (2) A wave or pressure change propagated through a canal or pipeline during unsteady flow.

HYDRIC—Characterized by, relating to, or requiring an abundance of moisture; referring to a habitat characterized by wet or moist conditions rather than Mesic (moderate moisture conditions) or Xeric (dry conditions).

HYDRIC SOIL—A soil that, in its undrained condition, is saturated, flooded, or ponded long enough during the growing season to develop Anaerobic conditions that favor the growth and regeneration of hydrophytic vegetation (Hydrophytes).

HYDRILLA—An exotic (nonnative) aquatic weed, hydrilla (Hydrilla verticillata) has come to represent a serious threat to lakes, reservoirs, streams and canals in the United States. A native of Asia, Africa, and Australia, hydrilla is part of a group of rooted aquatic plants well adapted to growth under water. Hydrilla was first introduced to the U.S. in Florida during the 1950s, probably for use in aquariums. Hydrilla is capable of prodigious growth, expanding from a few acres to several thousand acres in two to three years. Due to its ability to photosynthesize under very low light conditions, hydrilla becomes easily established in turbid waters and at greater depths than other aquatic plants. Most populations in the U.S. comprise dioecious female plants; reproduction is asexual, including fragmentation and the formation of hardy, long-lived propagules, called turions or tubers, which form deep in the sediment and remain viable for as long as ten years. Once hydrilla has invaded a site, the diversity of other rooted, submersed aquatic plants plummets, resulting in monospecific stands of hydrilla and loss of biodiversity. At is peak population, hydrilla has reduced water flows in canal systems by up to 80 percent and in small, standing-water impoundments, such as lakes and ponds, hydrilla can often completely cover the water surface within two to three years.

HYDRO—The prefix denoting water or hydrogen.

HYDROBIOLOGY— The biological study of bodies of water, especially studies by Limnology Hydrobiologist.

HYDROCARBONS—Chemical compounds that consist entirely of carbon and hydrogen, such as petroleum, natural gas, and coal.

HYDROCOLLOID—A substance that forms a gel with water.

HYDROCOMPACTION—The settling and hardening of land due to application of large amounts of water for irrigation.

HYDRODYNAMIC DISPERSION—(1) Spreading (at the macroscopic level) of the solute front during transport resulting from both mechanical dispersion and molecular diffusion. (2) The process by which ground water containing a solute is diluted with uncontaminated ground water as it moves through an aquifer. Also see Dispersion Coefficient.

HYDRODYNAMIC LOADS—Forces imposed on structures by floodwaters due other impacts of moving water on the upstream side of the structure, drag along its sides, and eddies or negative pressures on its downstream side.

HYDRODYNAMICS—The branch of science that deals with the dynamics of fluids, especially incompressible fluids, in motion.

HYDROELECTRIC—Having to do with production of electricity by water power from falling water.

HYDROELECTRIC PLANT (CONVENTIONAL)—A hydroelectric power plant which utilizes streamflow only once as the water passes downstream; electric power plant in which the energy of falling water is used to spin a turbine generator to produce electricity.

HYDROELECTRIC PLANT (PUMPED STORAGE)—A hydroelectric power plant which generates electric power during peak load periods by using water pumped into a storage reservoir during off-peak periods.

HYDROELECTRIC POWER—Power (hydroelectricity) produced using water power as a source of energy. Electrical energy generated by means of a power generator coupled to a turbine through which water passes.

HYDROELECTRIC POWER WATER USE—The use of water in the generation of electricity at plants where the turbine generators are driven by falling water. This constitutes an Instream Use of water and is a nonconsumptive use of water.

HYDROELECTRICITY—Electric energy production by water powered turbine generators.

HYDROFOIL—(Nautical) (1) A wing-like structure attached to the hull of a boat that raises all or part of the hull out of the water when the boat is moving forward, thus reducing drag. (2) A boat equipped with hydrofoils. In this sense, also referred to as a Hydroplane.

HYDROGEN—(Chemical symbol H) An element commonly isolated as a colorless, tasteless, odorless gas, inflammable (burning with a hot, almost nonluminous flame to form water), and lighter than any other known substance. Free hydrogen occurs only very sparingly on the earth, though it is abundant in the atmospheres of the sun and many stars. Hydrogen is combined with Oxygen in Water (H2O), of which it constitutes 11.188 per cent by weight. It is also a constituent of most organic compounds, of acids and bases. Ordinary hydrogen gas is diatomic (its molecules consisting of two atoms, H2), but dissociates into free atoms at high temperatures. The hydrogen atom is the simplest of all atoms, the ordinary isotope (H1) consisting of a single proton and a single valence electron. It is accompanied by a minute amount of a heavier isotope called Deuterium (H2 or D) which is used in Heavy Water (D2O). Atomic number 1; atomic weight 1.00797; melting point -259.14°C (-434.45°F); boiling point -252.8°C (-423.04°F); density at 0°C (32°F) 0.08987 gram per liter.

HYDROGEN BOND—A type of chemical bond caused by electromagnetic forces, occurring when the positive pole of one molecule (e.g., water) is attracted to and forms a bond with the negative pole of another molecule (e.g., another water molecule).

HYDROGEN SULFIDE (Gas)—Chemical symbol H2S, hydrogen sulfide is produced naturally by the Anaerobic Decomposition of any type of organic or inorganic matter that contains sulfur, e.g., rotting eggs, wallboard decomposition in landfills, the formation of natural gas from decomposing plant life, sulfate decomposition in sewers, etc. However produced, hydrogen sulfide presents severe health and corrosion hazards as well as being an odor nuisance. Few gases are as potent as hydrogen sulfide to the human olfactory senses. The human nose can detect the rotten egg odor at a level of only 0.4 parts per billion (ppb); few other compounds can be detected at such low levels of concentration.

HYDROGEOLOGIC—Those factors that deal with subsurface waters and related geologic aspects of surface waters.

HYDROGEOLOGIC PARAMETERS—Numerical parameters that describe the hydrogeologic characteristics of an aquifer such as Porosity, Permeability, and Transmissivity.

HYDROGEOLOGIC UNIT—Any soil or rock unit or zone that because of its hydraulic properties has a distinct influence on the storage or movement of ground water.

HYDROGEOLOGICAL CYCLE—The natural process recycling water from the atmosphere down to (and through) the earth and back to the atmosphere again. Also see Hydrologic Cycle.

HYDROGEOLOGY—The part of geology concerned with the functions of water in modifying the earth, especially by erosion and deposition; geology of ground water, with particular emphasis on the chemistry and movement of water.

HYDROGEOMORPHIC UNIT—A land form characterized by a specific origin, geomorphic setting, water source, and hydrodynamic.

HYDROGRAPH—A graphic representation or plot of changes in the flow of water or in the elevation of water level plotted against time. A graph showing stage, flow, velocity, or other hydraulic properties of water with respect to time for a particular point on a stream. Hydrographs of wells show the changes in water levels during the period of observation.

HYDROGRAPHIC AREA [Nevada]—The 232 subdivisions (256 Hydrographic Areas and Hydrographic Sub-Areas) of the 14 Nevada Hydrographic Regions as defined by the State Engineer's Office, Department of Conservation and Natural Resources, Division of Water Resources. Primarily these are sub-drainage systems within the 14 major drainage basins. Hydrographic Areas (valleys) may be further subdivided into Hydrographic Sub-Areas based on unique hydrologic characteristics (e.g., differences in surface flows) within a given valley or area. A listing of these Hydrographic Areas and Sub-Areas is presented in Appendix A-1 (listed sequentially by Hydrographic Area number and Hydrographic Region/Basin), Appendix A-2 (listed alphabetically by Hydrographic Area and Sub-Area name), and Appendix A-3 (listed alphabetically by principal Nevada county(ies) in which located).

HYDROGRAPHIC REGION [Nevada]—Nevada has been divided into 14 hydrographic regions or basins, which are now used by the Nevada Division of Water Resources, Department of Conservation and Natural Resources, and the U.S. Geological Survey (USGS) to compile information pertaining to water resources and water use. These regions are also further subdivided into 232 Hydrographic Areas (256 Hydrographic Areas and Sub-Areas, combined) for more detailed study. See Basins [Nevada], for a complete listing and description of Nevada's 14 Hydrographic Regions.

HYDROGRAPHIC STUDY AREA—An area of hydrological and climatological similarity so subdivided for study purposes.

HYDROGRAPHIC SURVEY—An instrumental survey to measure and determine characteristics of streams and other bodies of water within an area, including such things as location, areal extent, and depth of water in lakes or the ocean, the width, depth, and course of streams; position and elevation of high water marks; location and depth of wells.

HYDROGRAPHY—The study, description, and mapping of oceans, lakes, and rivers, especially with reference to their navigational and commercial uses.

HYDROKINETICS—The branch of physics having to do with fluids in motion.

HYDROLOGIC BALANCE—An accounting of all water inflows to, water outflows from, and changes in water storage within a hydrologic unit over a specified period of time.

HYDROLOGIC BASIN—The complete drainage area upstream from a given point on a stream.

HYDROLOGIC BENCHMARK—A hydrologic unit, such as a basin or a ground-water body, that because of its expected freedom from the effects of man, has been designated as a benchmark. Data from such basins may provide a standard with which data from less independent basins can be compared so that changes wrought by man's interference can be distinguished from changes caused by variations in the natural regimen.

HYDROLOGIC BUDGET—An accounting of the inflow, outflow, and storage in a hydrologic unit, such as a drainage basin, aquifer, soil zone, lake, reservoir, or irrigation project.

HYDROLOGIC CONDITION—The runoff potential of a particular cropping practice. A crop under good hydrologic condition will have a higher infiltration rate and lower runoff potential than one under poor conditions.

HYDROLOGIC CYCLE—The circuit of water movement from the atmosphere to the earth and return to the atmosphere through various stages or processes such as precipitation, interception, runoff, infiltration, percolation, storage, evaporation, and transportation. Also referred to as the Water Cycle and Hydrogeologic Cycle.

HYDROLOGIC EQUATION—The water inventory equation: Inflow = [Outflow + Change in Storage], which balances the Hydrologic Budget and expresses the basic principle that during a given time interval the total inflow to an area must equal the total outflow plus the net change in storage.

HYDROLOGIC MODEL—Mathematical formulations that simulate hydrologic phenomenon considered as processes or as systems.

HYDROLOGIC REGION—A study area, consisting of one or more planning subareas, used to analyze water use and hydrologic conditions. Typically such areas are based on Watersheds.

HYDROLOGIC REGIONS [California]—For water planning and conservation purposes, the California Department of Water Resources (DWR) and the State Water Resources Control Board (SWRCB) have divided the state into 10 Hydrologic Regions, also referred to as a Hydrologic Study Area (HSA), and are based on the Watershed or Water Basin concept. These California HSAs include:

[1] North Coast Region—Comprises all of the California area tributary to the ocean from the mouth of Tomales Bay north to the Oregon border and east along the border to a point near Goose Lake, consisting of 19,590 square miles (12 percent of the state's total area), 571,750 persons (1.9 percent of the state's total population—all populations as of 1990), with average annual precipitation of 53 inches (range: 15 to over 100 inches), and average annual runoff of 28,886,000 acre-feet (40.8 percent of total state runoff); [2] San Francisco Bay Region—Extends from Pescadero Creek in southern San Mateo County to the mouth of Tomales Bay in the north and inland to the confluence of the Sacramento and San Joaquin rivers near Collinsville, consisting of 4,400 square miles (3 percent of the state's total area), 5,484,000 persons (18 percent of the state's total population), with average annual precipitation of 31 inches (range: 14 to almost 48 inches), and average annual runoff of 1,245,500 acre-feet (1.8 percent of total state runoff); [3] Central Coast Region—Encompasses the area adjacent to the Pacific Ocean including Santa Cruz County in the north through Santa Barbara County in the south to the Diablo and Temblor mountain ranges on the east, consisting of 11,280 square miles (7 percent of the state's total area), 1,292,900 persons (4 percent of the state's total population), with average annual precipitation of 20 inches (range: 14 to 45 inches), and average annual runoff of 2,477,000 acre-feet (3.5 percent of total state runoff); [4] South Coast Region—Extending eastward from the Pacific Ocean, the region is bounded by the Santa Barbara-Ventura county line and the San Gabriel and San Bernardino mountains on the north, the Mexican border on the south, and a combination of the San Jacinto Mountains and low-elevation mountain ranges in central San Diego County on the east, consisting of 10,950 square miles (7 percent of the state's total area), 16,292,800 persons (54 percent of the state's total population), with average annual precipitation of 18.5 inches (range: 10 to 45 inches), and average annual runoff of 1,227,000 acre-feet (1.7 percent of total state runoff); [5] Sacramento River Region—Contains the entire drainage area of the Sacramento River and its tributaries and extends almost 300 miles from Collinsville in the Sacramento-San Joaquin Delta north to the Oregon border to the crest of the Sierra Nevada and Cascade Ranges which form the eastern border to the crest of the Coast Range forming the western side, consisting of 26,960 square miles (17 percent of the state's total area), 2,208,900 persons (7 percent of the state's total population), with average annual precipitation of 36 inches (range: 10 to 80 inches), and average annual runoff of 22,389,700 acre-feet (31.6 percent of total state runoff); [6] San Joaquin River Region—Located in the heart of California bordered on the east by the crest of the Sierra Nevada and on he west by the coastal mountains of the Diablo Range, extending from the Delta and the Cosumnes River drainage south to include all of the San Joaquin River watershed, consisting of 15,950 square miles (10 percent of the state's total area), 1,430,200 persons (5 percent of the state's total population), with average annual precipitation of 13 inches (range: 9 to 35 inches), and average annual runoff of 7,933,300 acre-feet (11.2 percent of total state runoff); [7] Tulare Lake Region—Including the southern San Joaquin Valley from the southern limit of the San Joaquin River watershed to the crest of the Tehachapi Mountains, stretching from the Sierra Nevada Crest in the east to the Coast Range in the west, consisting of 16,520 square miles (10 percent of the state's total area), 1,554,000 persons (5 percent of the state's total population), with average annual precipitation of 14 inches, and an average annual runoff of 3,313,500 acre-feet (4.7 percent of total state runoff); [8] North Lahontan Region—Comprises the eastern drainages of the Cascade Range and the eastern Sierra Nevada, north of the Mono Lake drainage, consisting of 3,890 square miles (less than 3 percent of the state's total area), 78,000 persons (less than 0.3 percent of the state's total population), with average annual precipitation of 32 inches (range: 4 to 70 inches), and average annual runoff of 1,842,000 acre-feet (2.6 percent of total state runoff); [9] South Lahontan Region—Encompassing the area from the mountain divide north of Mono Lake to the divide south of the Mojave River, which runs through the Mojave Desert, bordered on the east by the Nevada state line and on the west by the crest of the Sierra Nevada, consisting of 29,020 square miles (18 percent of the state's total area), 599,900 persons (2 percent of the state's total population), with average annual precipitation of 8 inches (range: 4 to 10 inches, with extremes of 1.9 inches in Death Valley and over 120 inches at Mammoth Lakes), and an average annual runoff of 1,334,000 acre-feet (1.9 percent of total state runoff); [10] Colorado River Region—Encompassing the southeastern corner of California with the region's northern boundary, a drainage divide, beginning along the southern edge of the Mojave River watershed in the Victor Valley area of San Bernardino County and extending northeast across the Mojave Desert to the Nevada state line. The southern boundary is the Mexican border while a drainage divide forms the jagged western boundary through the San Bernardino, San Jacinto, and Santa Rosa mountains and the Peninsular ranges and the Nevada state line and the Colorado River form the region's eastern boundary, consisting of 19,730 square miles (12 percent of the state's total area), 464,200 persons (less than 2 percent of the state's total population), with average annual precipitation of 5.5 inches (range: 3 to 36 inches), and an average annual runoff of 178,700 acre-feet (less than 0.3 percent of total state runoff);

HYDROLOGIC SOIL GROUPS—The classification of soils by their reference to the intake rate of infiltration of water, which is influenced by texture, organic matter content, stability of the soil aggregates, and soil horizon development.

HYDROLOGIC STUDY APPROACH—The study of a project's water distribution based upon a hydrological balance, where inflow (diversion into project) is balanced with outflow (precautionary drawdowns, crop consumptive use, deep seepage, surface return flows, and undefined "losses").

HYDROLOGIC STUDY AREA (HSA)—See Hydrologic Regions [California].

HYDROLOGIC UNIT—(1) A geographic area representing part or all of a surface drainage basin or distinct hydrologic feature. (2) A classification of soils concerning water infiltration characteristics used in hydrologic analyses.

HYDROLOGY—The science of waters of the earth, their occurrence, distribution, and circulation; their physical and chemical properties; and their reaction with the environment, including living beings.

HYDROLYSIS—The splitting (lysis) of a compound by a reaction with water. Examples are the reaction of salts with water to produce solutions which are not neutral, and the reaction of an ester with water.

HYDROMANCY—Divination by the observation of water.

HYDROMECHANICS—The branch of physics having to do with the laws governing the motion and equilibrium of fluids.

HYDROMETEOR—Any type of condensation or frost formed from atmospheric water vapor, as rain, snow, fog, dew, etc. Contrasts with Lithometeor.

HYDROMETEOROLOGY—The science of the application of meteorology to hydrologic problems; the branch of meteorology that deals with the occurrence, motion, and changes of the state of atmospheric water. The combination of snowpack measurements and climatic forecasts to predict runoff.

HYDROMETER—An instrument used to determine specific gravity, especially a sealed, graduated tube, weighted at one end, that sinks in a fluid to a depth used as a measure of the fluid's specific density.

HYDROMETRIC NETWORK—Network of stations at which measurement of hydrological parameters is performed.

HYDRONIC—Of, relating to, or being a system of heating or cooling that involves transfer of heat by a circulating fluid (as water or vapor) in a closed system of pipes.

HYDROPATHY—Internal and external use of water as a therapeutic treatment for all forms of disease. Compare to Hydrotherapy.

HYDROPERIOD—The seasonal and cyclical pattern of water in a Wetland.

HYDROPHILE (HYDROPHILIC)—Having or denoting a strong affinity for water; said of Colloids which swell in water and which are not easily coagulated.

HYDROPHILOUS—(Botany) (1) Growing or thriving in water. (2) Pollinated by water, as the flowers of ribbon grass and hornwort.

HYDROPHOBE (HYDROPHOBIC)—Lacking strong affinity for water; said of Colloids which are easily coagulated.

HYDROPHOBIA—(1) An abnormal fear of water. (2) Rabies.

HYDROPHONE—An electrical instrument for detecting or monitoring sound transmitted through water.

HYDROPHYTE—(1) A perennial vascular aquatic plant having its overwintering buds under water. (2) A plant growing in water or in soil too waterlogged for most plants to survive. (3) A plant adapted to grow in water. (4) Any plant growing only in water or very wet earth, requiring large quantities of water for growth. Also see Mesophyte, Phreatophyte, Xerophyte.

HYDROPHYTIC (Vegetation)—Plants that grow in water or in saturated soils that are periodically deficient in oxygen as a result of high water content.

HYDROPLANE—(Nautical) (1) A motorboat designed so that the prow and much of the hull lift out of the water and skim the surface at high speeds. Also referred to as a Hydrofoil. (2) Seaplane. (3) A horizontal rudder on a submarine.

HYDROPNEUMATIC—A water system, usually small, in which a water pump is automatically controlled by the pressure in a compressed air tank.

HYDROPONICS—Cultivation of plants in nutrient solution rather than in soil.

HYDROPOWER—Power (e.g., electrical energy) produced by falling water; the utilization of the energy available in falling water for the generation of electricity.

HYDROSCOPE—An optical device used for viewing objects far below the surface of water.

HYDROSEEDING—Dissemination of seed under pressure, in a water medium. Mulch, lime, and fertilizer can be incorporated in the spraying mixture.

HYDROSOL—A disperse system (colloid) in which water is the disperse medium.

HYDROSPHERE—(1) The water on or surrounding the surface of the globe, as distinguished from those of the Lithosphere and the Atmosphere. (2) The region that includes all the earth's liquid water, frozen water, floating ice, frozen upper layer of soil, and the small amounts of water vapor in the earth's atmosphere. Together, the waters of the Hydrosphere, Atmosphere, Lithosphere, and Biosphere, constitutes the earth's Ecosphere.

HYDROSTATIC HEAD—A measure of pressure at a given point in a liquid in terms of the vertical height of a column of the same liquid which would produce the same pressure.

HYDROSTATIC LOADS—Forces imposed on a flooded structure due to the weight of the water.

HYDROSTATIC PRESSURE—The pressure in a fluid in equilibrium which is due solely to the weight of fluid above.

HYDROSTATICS—The branch of physics that deals with fluids at rest and under pressure.

HYDROTHERAPY—External use of water in the medical treatment of diseases. Compare to Hydropathy.

HYDROTHERMAL—(1) Having to do with hot water, especially having to do with the action of hot water in producing minerals and springs or in dissolving, shifting, and otherwise changing the distribution of minerals in the earth's crust. (2) (Geology) Of or relating to hot magmatic emanations rich in water. Of or relating to the rocks, ore deposits, and springs produced by such emanations.

HYDROTHERMAL DEPOSIT—(Geology) A mineral deposit formed when hot, aqueous solutions fill fractures or other open spaces in rocks or along faults. The minerals crystallize as the solutions cool.

HYDROTHERMAL RESERVOIR—One of three geothermal reservoir systems. It consists of naturally circulating hot water or steam ("wet steam") or that which contains mostly vapor ("dry steam"). The latter type of reservoir is the most desirable type according to present technology. Also see Geothermal Energy.

HYDROTHERMAL SOLUTION—A hot, watery solution that usually emanates from a magma in the late stages of cooling. Frequently contains and deposits in economically workable concentrations minor elements that, because of incommensurate ionic radii or electronic charges, have not been able to fit into the atomic structures of the common minerals of igneous rocks (rocks formed by volcanic activity).

HYDRO-TRANSPORT—(1) Mixing a crushed material, such as coal, gravel or sand, with water to facilitate its transport under pressure, through a pipes. (2) (Tar Sands) Mixing the crushed black sands containing bitumen—a heavy, molasses-like oil—with hot water in a "cyclo-feeder" to facilitate its transportation via pipeline to plants where the bitumen is separated from the water and then "cracked" in cokers into various hydrocarbon by-products, i.e., naphtha, kerosene, and heavy fuel oil.

HYDROTROPISM—Growth or movement in a sessile (fixed, root-bound) organism toward or away from water, as of the roots of a plant.

HYDROUS—Containing water, especially water of crystallization or hydration.

HYETAL—Of or relating to rain or rainy regions.

HYETOGRAPH—A chart showing the distribution of rainfall over a particular period of time or a particular geographic area.

HYETOGRAPHY—The branch of meteorology having to do with the geographical distribution and annual variation of rainfall. Also see Hyetograph.

HYGROMETER—Any of several instruments used to measure atmospheric humidity.

HYGROPHYTE—Plants extremely sensitive to dry air, growing only in habitats where relative humidity is always high. Also see Hydrophyte.

HYGROSCOPE—An instrument showing changes in humidity.

HYGROSCOPIC—Describing a chemical substance with an affinity for water, one that will absorb moisture, usually from the air. Silica gel and zinc chloride are hygroscopic materials that are used as drying agents.

HYGROSCOPIC NUCLEI—A piece of dust or other particle around which water condenses in the atmosphere. These tiny droplets then collide and coalesce, with numerous other nuclei, contributing to the formation of a raindrop.

HYGROSCOPIC WATER—Water which is absorbed from the air.

HYGROTHERMOGRAPH—An instrument which combines the features of the Hair Hygrograph and the Thermograph, recording both relative humidity and temperature on one chart.

HYPEREUTROPHIC (WATER)—Pertaining to a lake or other body of water characterized by excessive nutrient concentrations such as nitrogen and phosphorous and resulting high productivity. Such waters are often shallow, with algal blooms and periods of oxygen deficiency. Slightly or moderately eutrophic water can be healthful and support a complex web of plant and animal life. However, such waters are generally undesirable for drinking water and other needs. Degrees of Eutrophication typically range from Oligotrophic water (maximum transparency, minimum chlorophyll-a, minimum phosphorus) through Mesotrophic, Eutrophic, to Hypereutrophic water (minimum transparency, maximum chlorophyll-a, maximum phosphorus). Also see Carlson's Trophic State Index (TSI) and (Mean) Trophic State Index (TSI).

HYPERHALINE—Term used to characterize waters with salinity greater than 40 0/00 (parts per thousand), due to ocean-derived salts.

HYPERSALINE—Term used to characterize waters with salinity greater than 40 0/00 (parts per thousand), due to land-derived salts.

HYPOCHLOROUS ACID—An unstable strongly oxidizing but weak acid, HClO, obtained in solution along with hydrochloric acid by reaction of chlorine with water and used especially in the form of salts as an oxidizing agent, bleaching agent, disinfectant, and chlorinating agent.

HYPOLIMNETIC DISCHARGE—The process of removing nutrient-rich, oxygen-deficient water from the bottom of a lake or reservoir to improve water quality conditions.

HYPOLIMNION—The lowermost, non-circulating layer of cold water in a thermally stratified lake or reservoir that lies below the Thermocline, remains perpetually cold and is usually deficient of oxygen. Also see Thermal Stratification.

HYPOTHERMAL—(1) Moderately warm; tepid. (2) Pertaining or tending to reduction of temperature.

HYPOTHERMIA—Subnormal temperature of the body.

HYPOTHESIS—(Statistics) A statement made about the condition or behavior of a variable or event which lends itself to rigorous testing for validity. An informed theory that best describes a set of available data. The assumption is stated in such a way that subsequent experimentation or observations can test the validity of the theory.

HYPOTHESIS TESTING—(Statistics) The condition whereby the Null Hypothesis, which argues against the validity of the model's structure (Specification) is tested using various statistical criteria, e.g., Coefficient of Determination, or R2, t-Statistic, F-Statistic, etc., against the Alternative Hypothesis that there exists a significant relationship or correlation between the dependent variable, or variable to be explained, and the independent, or explanatory variable(s). In hypothesis testing, a rule for acceptance and rejection must be chosen, e.g., 5 percent level of significance, that is, there exists a 5 percent chance that in rejecting the null hypothesis, which states that the disturbances in the dependent variable are purely random, we will be wrong. Inversely, there is a 95 percent chance that by rejecting the null hypothesis and accepting the alternative hypothesis, we will be right.

HYPOXIA—A condition in which natural waters have a low concentration of dissolved oxygen (about 2 milligrams per liter as compared with a normal level of 8 to 10 milligrams per liter). Most game and commercial species of fish avoid waters that are Hypoxic.

HYPSOGRAPHY—(1) The science or art of describing elevations of land surfaces with reference to a datum, usually Mean Sea Level (MSL). (2) That part of topography dealing with relief or elevation of terrain.

HYPSOMETER—An instrument using the atmospheric pressure as measured by the change in the boiling point of water to determine land elevations.

ICE—A solid form of water. Water frozen, or reduced to the solid state by cold. Ice is a transparent, nearly colorless, crystalline, and brittle substance. Water in freezing expands about one eleventh of its volume, the specific gravity of ice being 0.9166, that of water at 4°C (39.2°F) being 1.0. Pure water freezes at 0°C (32°F), and ice melts at the same temperature.

ICE AGE—(1) A cold period marked by episodes of extensive glaciation alternating with episodes of relative warmth. 2. (Ice Age) The most recent glacial period, which occurred during the Pleistocene epoch.

ICE APRON—A wedge-shaped structure for protecting a bridge pier from floating ice.

ICE BARRIER—The outer margin of the antarctic ice sheet.

ICEBERG—A massive piece of ice that breaks off and floats away from a Glacier. Icebergs occur as huge blocks, or in peaked forms of great variety and beauty. About one ninth of the bulk of an iceberg projects above sea level.

ICEBLINK—(1) A white or yellow streak in the sky near the horizon, caused by the reflection of light from an area of ice. Also call Blink. (2) A coastal ice cliff.

ICEBOUND—Locked in or covered over by ice.

ICECAP, or Ice Cap—An extensive dome-shaped or plate-like perennial cover of ice and snow that spreads out from a center and covers a large area, especially land. A very large ice cap is an Ice Sheet, or continental Glacier, as that of the antarctic continent.

ICEFALL—(1) The part of a glacier resembling a frozen waterfall that flows down a steep slope. (2) An avalanche of ice.

ICEFIELD—A large, level expanse of floating ice that is more than eight kilometers (five miles) in its greatest dimension.

ICEFOG—A fog of ice particles. Also referred to as Pogonip.

ICEFOOT—A belt of ledge of ice that forms along the shoreline in Arctic regions.

ICE-FREE—(1) Free of ice and open to travel or navigation, as an ice-free channel in a river. (2) Marked by a lack of obstructive ice.

ICE-MINUS—Of or relating to a strain of genetically altered bacteria that are applied to crop plants to inhibit the formation of frost.

ICE NEEDLE—A thin ice crystal floating high in the atmosphere in certain conditions of clear, cold weather.

ICE NUCLEUS—Any particle that serves as a nucleus in the formation of ice crystals in the atmosphere.

ICE-OUT—The thawing of ice on the surface of a body of water, such as a lake.

ICE PACK—(1) A large area of floating pieces of ice driven together more or less closely. (2) A folded sac filled with crushed ice and applied to sore or swollen parts of the body to reduce pain and inflammation. Also referred to as an Ice Bag.

ICE POINT—The temperature, equal to 1.0°C (33.8°F), at which pure water and ice are in equilibrium in a mixture at 1 atmosphere of pressure.

ICESCAPE—A wide view or vista of a region of ice and snow.

ICE SHEET—A very large Ice Cap, also called continental glacier, as that of the antarctic continent.

ICE STORM—A storm in which snow or rain freezes on contact, forming a coat of ice on the surfaces it touches.

ICE WATER—Chilled or iced water, especially served as a beverage.

ICHTHYOLOGY—The study of fishes.

ICHTHYOSAURUS (ICHTHYOSAUR) [Nevada]—The chief genus of Ichthyosauria, also known by a prior name, Proteosaurus. An ancient, extinct marine reptile whose name means "fish-lizard" and who ruled the world's oceans during the Mesozoic era some 200 million years ago. Fossil remains of the Ichthyosaur have been found on every continent except Africa. Possessing a fish-like body, porpoise-like snout, short neck, dorsal and caudal fins with limbs flattened into paddles, the Ichthyosaur ruled the seas for some 135 million years as the pre-eminent marine predator. The Ichthyosaur attained a length of approximately 60-70 feet. The Ichthyosaurus shonisaurus popularis was the name given to a species discovered in Nevada in 1928. Some 40 of these reptiles became stranded in mud flats from a receding equatorial sea which once covered the state. The longest specimen found at this site, located at an elevation of 7,000 feet in the Shoshone Mountain Range near the town of Berlin in northwestern Nye County, Nevada, was 55 feet long and represented the only complete fossilized skeleton of the species ever found in the United States. In 1977 the Nevada State Legislature named the Ichthyosaurus Shonisaurus popularis as Nevada's official state fossil.

ICICLE—A tapering spike of ice formed by the freezing of dripping or falling water.

IDENTIFICATION—(Statistics) A term used to describe the ability to determine an econometric model's structural parameters, i.e., the coefficients of the exogenous (or independent) variables. An econometric model is said to be exactly identified if the data support a unique set of parameters for the independent variables. A model is said to be Under-identified if there is no way of estimating all the structural parameters and Over-identified if more than one value is obtainable for some parameters.

IGNEOUS ROCK—(Geology) A rock formed by the solidification of molten materials (magma). The rock is extrusive (or volcanic) if it solidifies on the surface and intrusive (or plutonic) if it solidifies beneath the surface.

ILLINOIAN—(Geology) Of or relating to one of the glacial stages of the Pleistocene epoch which occurred in North America, which consisted of the Nebraskan (first stage), Kansan (second stage), Illinoian (third stage), and Wisconsin (fourth stage).

ILLUVIAL—Describing soil material, usually minerals and colloidal particles, that is removed from the upper soil horizon to a lower soil horizon. Illuvial deposits can form a Hardpan.

ILLUVIATION—The deposition in an underlying soil layer of colloids, soluble salts, and mineral particles leached out of an overlying soil layer.

IMBIBITION—(Chemistry) Absorption of fluid by a solid or colloid that results in swelling.

IMHOFF CONE—A clear, cone-shaped container used to measure the volume of settleable solids in a specific volume of water.

IMHOFF TANK—An anaerobic sewage treatment tank in which solids are withdrawn from the bottom of the tank.

IMMERGE—To submerge or disappear in or as if in a liquid.

IMMERSE—To plunge, drop, or dip into or as if into a liquid, especially so as to cover completely.

IMMERSIBLE—Capable of being completely immersed in water without suffering damage.

IMMISCIBLE—Applied to liquids which are insoluble in each other. The chemical property where two or more liquids or phases do not readily dissolve in one another, such as oil and water.

IMPACT ZONE—The spot on a wave where the water is just about to collapse and explode, the spot of greatest danger to and opportunity for a surfer.

IMPERIAL VALLEY [California]—A valley, southeast California, bounded by the Salton Sea on the north, the Chocolate Mountains on the east, and the desert ranges of the Santa Rosa and Vallecito mountains on the west. The valley, crossed by the border between the United States and Mexico, is part of a larger valley that extends south into Mexico; the Mexican section is called Mexicali Valley. Lying below sea level, and formerly an arid desert, the valley is now one of the richest agricultural areas in the world and the largest year-round irrigated agricultural area in North America as a result of irrigation by waters of the Colorado River. The first waters from the Colorado were brought in through the Imperial Canal, opened in 1901. The same source was tapped for the All-American Canal, completed in 1940 as part of the Hoover Dam irrigation system built by the U.S. government. This canal, which is 80 miles (129 kilometers) long and 200 feet (61 meters) wide, is the largest irrigation canal in the U.S. and supplies most of the water for the approximately 404,700 irrigated hectares (about 1 million acres, or 1,562 square miles) of land in the Imperial Valley.

IMPERMEABILITY—Characteristic of geologic materials that limit their ability to transmit significant quantities of water under the pressure differences normally found in the subsurface environment.

IMPERMEABLE—Unable to transmit water; not easily penetrated. The property of a material or soil that does not allow, or allows only with great difficulty, the movement or passage of water. Not the same as Nonporous.

IMPERVIOUS—A term denoting the resistance to penetration by water or plant roots; incapable of being penetrated by water; non-porous.

IMPERVIOUSNESS—The portion of a subbasin, subwatershed, or watershed, expressed as a percentage, that is covered by surfaces such as roof tops, parking lots, sidewalks, driveways, streets, and highways. Impervious surfaces are important because they will not absorb rainfall and, therefore, cause almost all of the rainfall to appear as surface runoff.

IMPORT (Water)—Water piped or channeled into an area.

IMPORTATION (of Water)—The act or process whereby water is brought into an area or region which would not naturally receive such waters. Typically, it refers to the artificial transport of water through aqueducts, canals, or pipelines from one water basin, drainage area, or Hydrographic Area to another, thereby affecting the natural surface and groundwater drainage and flow patterns in both the water exporting and importing areas. In terms of a Water Banking or Water Marketing concept, such actions to move water from areas of low use to areas of high use place a more realistic monetary value on water as a scarce economic commodity and result in enhanced economic efficiency by putting existing water resources, wherever located, to more productive economic use. However, considerable public concern and controversy surround this practice. These concerns deal primarily with issues relating to altering the natural flows of both surface and ground waters, adverse environmental and habitat impacts on water exporting areas, the limitations placed on the long-term growth and development of the water exporting region or hydrographic area, the potentially adverse hydrologic effects on groundwater (water table and aquifer) conditions in the exporting area as well as the generally unknown effects on surrounding hydrographic areas and aquifer conditions, and the dependency acquired by the water importing area to continued diversions and water importations. The concept of a public policy limiting an area's development to its natural ability to support population growth only through existing and readily available natural resources, particularly water, is referred to as an Antediluvian Policy.

IMPOUND—To accumulate and store water as in a reservoir.

IMPOUNDMENT—(1) A body of water such as a pond, confined by a dam, dike, floodgate or other barrier. It is used to collect and store water for future use. (2) (Water Quality) Generally an artificial collection and storage area for water or wastewater confined by a dam, dike, floodgate, or other barrier.

IMPROVED IRRIGATED ACREAGE—Refers to farm acreage which has been leveled, planed and serviced by improved conveyance and control structures.

INCH—A fall, as of rain or snow, sufficient to cover the surface to the depth of one inch (2.54 centimeters).

INCH-DEGREES—The product of inches of rainfall times temperature in degrees above freezing (Fahrenheit), used as a measure of the snowmelting capacity of rainfall.

IN-CHANNEL STORAGE—Water storage volume in a canal above the minimum water level required for conveyance.

IN-CHANNEL USE—See Instream Use.

INCHOATE WATER RIGHT—An unperfected water right. See Perfected Water Right.

INCIDENCE—(Statistics) The rate of occurrence of a specific event within a given number of observations over a standard time period.

INCIDENTAL RECHARGE—Ground water recharge (infiltration) that occurs as a result of human activities unrelated to a recharge project, for example, irrigation and water diversion (unlined canals). Also see Artificial (or Induced) Recharge, Natural Recharge, and Perennial Yield.

INCIDENTAL WASTE WATER RECLAMATION—Treated waste water returned to fresh-water streams or other water bodies. Additional use made of this treated waste water is only incidental to waste water treatment and disposal.

INCINERATION—(Water Quality) A treatment technology involving the destruction of waste by controlled burning at high temperatures, e.g., burning sludge to remove the water and reduce the remaining residues to a safe, non-burnable ash that can be disposed of safely on land, in some waters, or in underground locations.

INCISED RIVER—A river which cuts its channel through the bed of the valley floor, as opposed to one flowing on a floodplain; its channel formed by the process of degradation.

INCLINED STAFF GAGE—A gage which is placed on the slope of a stream bank and graduated so that the scale reads directly in a vertical depth.

INCLINOMETER (INCLOMETER)—An instrument, usually consisting of a metal or plastic tube, inserted in a drill hole and a sensitized monitor either lowered into the tube or fixed within the tube. This measures at differential points the tube's inclination to the vertical. By integration, the lateral position at different levels of the tube may be found relative to a point, usually the top or bottom of the tube, assumed to be fixed. The system may be used to measure settlement.

INCUBATE—To maintain environmental conditions that are optimum for the growth of bacteria. For example, coliforms grow best when held at 37°C (98.6°F).

INDEPENDENT VARIABLE—(Statistics) A measurable quantity that, as it takes different values, can be used to predict the value of a Dependent Variable. Also referred to as the Exogenous Variable or variable to be explained (Explained Variable).

INDEX MODEL—A hydrologic computer model based on empirical, statistical relationships.

INDEX OF WETNESS—The precipitation for a given year expressed as a ratio to the mean annual precipitation.

INDIRECT DISCHARGE—The introduction of pollutants from a non-domestic source into a publicly owned waste-treatment system. Indirect dischargers can be commercial or industrial facilities whose wastes enter local sewers.

INDRA—(Hinduism) A principal Vedic deity associated with rain and thunder.

INDUSTRIAL WASTE—Unwanted materials from an industrial operation; may be liquid, sludge, or hazardous waste.

INDICATOR (ORGANISM)—(Water Quality) An organism, species, or community that shows the presence of certain environmental conditions.

INDICATOR BACTERIA—(Water Quality) Nonpathogenic bacteria whose presence in water indicate the possibility of pathogenic species in the water.

INDICATOR GAGE—A gage that shows by means of an index, pointer, dial, etc., the instantaneous value of such characteristics as depth, pressure, velocity, stage, discharge, or the movements or positions of water-controlling devices.

INDICATOR SPECIES—(Environmental) Any organism that by its presence or absence, its frequency, or its vigor indicates a particular property of its surrounding environment. A species whose presence is a sign that certain environmental conditions exist. Also see Management Indicator Species.

INDICATOR TESTS—(Water Quality) Tests for a specific contaminant, group of contaminants, or constituent which signals the presence of something else. For example, the presence of non-pathogenic coliforms indicate the presence of pathogenic bacteria.

INDIGENOUS—Existing, growing, or produced naturally in a region.

INDIRECT WATER USES—Uses of water that are not immediately apparent to the consumer. For example, a person indirectly uses water when driving a car because water was used in the production process of steel and other automotive components.

INDUCED RECHARGE—The designed (as opposed to the natural or incidental) replenishment of ground water storage from surface water supplies. There exist five (5) common techniques to effect artificial recharge of a groundwater basin:

[1] Water Spreading consisting of the basin method, stream-channel method, ditch method, and flooding method, all of which tend to divert surface water supplies to effect underground infiltration; [2] Recharge Pits designed to take advantage of permeable soil or rock formations; [3] Recharge Wells which work directly opposite of pumping wells although have limited scope and are better used for deep, confined aquifers; [4] Induced Recharge which results from pumping wells near surface supplies thereby inducing higher discharge towards the well; and [5] Wastewater Disposal which includes the use of secondary treatment wastewater in combination with spreading techniques, recharge pits, and recharge wells to reintroduce the water to deep aquifers thereby both increasing the available groundwater supply and also further improving the quality of the wastewater.

Also referred to as Artificial Recharge. Also see Natural Recharge, Incidental Recharge, and Perennial Yield.

INDUSTRIAL, SELF-SUPPLIED WATER—Water withdrawn from privately developed sources and delivered through water systems established entirely or primarily for commercial and industrial use. Includes water used by mining, manufacturing, military establishments, educational and penal institutions, golf courses, hotels, motels, restaurants, casinos and other small businesses.

INDUSTRIAL WASTEWATER FACILITY—Refers to those facilities that produce, treat or dispose of wastewater not otherwise defined as a domestic wastewater. May include the runoff and leachate from areas that receive pollutants associated with industrial or commercial storage, handling, or processing.

INDUSTRIAL WATER USE—Water used for industrial purposes such as fabricating, manufacturing, processing, washing, and cooling, and includes such industries as steel, chemical and allied products, paper and allied products, mining, and petroleum refining. The water can be obtained from a Public Water Supply System of may be self-supplied. Also see Self-Supplied Water.

INFAUNA—Aquatic animals that live in the substrate of a body of water, especially in a soft sea bottom.

INFERENCE, BAYESIAN—(Statistics) Bayes' theorem recognizes that a decision maker usually has some expectation (an a priori model) of what will occur even before acquiring information, and provides a procedure for using new evidence to produce a revised a posteriori estimate of probability. Also see Statistical Inference and Classical Inference.

INFERENCE, CLASSICAL—(Statistics) Statistical inference is based on two basic premises: (1) The sample data constitute the only relevant information; and (2) The construction and assessment of the different procedures for inference are based on long-run behavior under essentially similar circumstances. Also see Statistical Inference and Bayesian Inference.

INFERENCE, STATISTICAL—(Statistics) The area of statistics that describes the procedures by which we use the observed data (the sample) to draw conclusions about the population from which the data came or about the process by which the data were generated. Our assumptions is that there is an unknown process that generates the data and that this process can be described by a probability distribution, i.e., a likelihood of occurring. Statistical inference can be classified as Classical Inference and Bayesian Inference.

INFILTRATE, also Infiltration—(1) The flow of a fluid into a substance through pores or small openings; to cause a liquid to permeate a substance by passing through its interstices or pores. It connotes flow into a substance in contradistinction to the word Percolation, which connotes flow through a porous substance. Also the process whereby water passes through an interface, such as from air to soil or between two soil horizons. (2) The technique of applying large volumes of waste water to land to penetrate the surface and percolate through the underlying soil.

INFILTRATION AND INFLOW—(Water Quality) The entrance of groundwater (infiltration) or of surface water (inflow) into sewer pipes. Groundwater can seep through defective pipe joints or cracked pipe sections; roof or basement drains are sources of surface water inflow. Excessive infiltration and inflow can cause sewers to back up or can overload sewage treatment plants, causing a reduction in treatment time or a complete bypass of the treatment process during periods of significant rainfall.

INFILTRATION CAPACITY—The maximum rate at which the soil, when in a given condition, can absorb falling rain or melting snow.

INFILTRATION CAPACITY CURVE—A graph showing the time variation of infiltration capacity. A standard infiltration capacity curve shows the time variation of the infiltration rate which would occur if the supply were continually in excess of infiltration capacity.

INFILTRATION CAPACITY, ULTIMATE—The relatively steady, slow, infiltration capacity which exists after a sufficiently long period of infiltration at capacity rate.

INFILTRATION GALLERY—A sub-surface groundwater collection system, typically shallow in depth, constructed with open-jointed or perforated pipes that discharge collected water into a watertight chamber from which the water is pumped to treatment facilities and into the distribution system. Usually located close to streams or ponds.

INFILTRATION INDEX—The average rate of infiltration, in inches per hour, derived from a time intensity graph of rainfall, so that the volume of rainfall in excess of this rate equals the total direct runoff. Also referred to as a "ø" (Phi) or "W" index.

INFILTRATION RATE—Rate of downward movement or flow of water from the surface into the soil. (1) The rate at which infiltration takes place, expressed in depth of water per unit time, usually in inches per hour. (2) The rate, usually expressed in cubic feet per second, or million gallons per day per mile of waterway, at which ground water enters an infiltration ditch or gallery, drain, sewer, or other underground conduit.

INFILTROMETER—An instrument which determines the rate and amount of water percolating into the soil by measuring the difference between the amount of water applied and that which runs off. Essentially, the infiltrometer consists of a sprinkling mechanism (rain simulator) which provides a rather uniform sprinkling of water to a prescribed area at prescribed rates and size drops (impact), a rain gage (either total or intensity), and a catchment basin or receptacles in which either the rate or total flow of surface runoff is measured. Infiltration or amount absorbed by the soil is usually expressed in inches (of water) per standard interval of time.

INFLOW—(1) The act or process of flowing in or into. (2) Something that flows in or into. (3) (Water Quality) Water, other than wastewater, that enters a sanitary sewer system (including sewer service connections) from sources such as roof leaders, cellar drains, yard drains, area drains, foundation drains, drains from springs and swampy areas, manhole covers, cross connections between storm sewers and sanitary sewers, catch basins, cooling towers, surface runoff, street wash waters, or drainage. Inflow does not include, and is distinguished from, Infiltration.

INFLOW DESIGN FLOOD—The maximum probable flood defined as the largest flood that can be expected to occur on a given stream at a selected point. This flood is used for design to prevent failure of the dam and is determined by the U.S. Department of the Interior, Bureau of Reclamation.

INFLUENT—Water, wastewater, or other liquid flowing into a reservoir, basin, or treatment plant.

INFLUENT SEEPAGE—The movement of gravity water in the Zone of Aeration from the ground surface toward the water table.

INFLUENT STREAM—A stream that contributes water to the Zone of Saturation and to Bank Storage. This term has generally been replaced by the term Losing Stream. Also see Stream.

INFLUENT WATER—Water that flows into sink holes, open cavities, and porous materials and disappears into the ground.

INFORMATION—(Data Analysis) The synthesis and manipulation of Data through various analytical, tabular, graphical, presentation, or other techniques into a format that readily lends itself to hypothesis testing, planning, and decision making. The fundamental distinction between the data and the information is that the data represents the original observations of an event, characteristic, or phenomenon whereas information represents the transformation of that data, possibly along with the combination of other relevant data and/or other information, into formats that may be used for decision-making purposes.

INFORMATION COLLECTION RULE (ICR)—A rule promulgated by the U.S. Environmental Protection Agency (EPA) which took effect in January 1997 requiring water districts serving more than 100,000 connections to monitor water supplies for Cryptosporidium parvum.

INFORMATION MANAGEMENT—(Data Analysis) The manipulation, re-organization, analysis, graphing, charting, and presentation of data for specific management and decision-making purposes. Typically, a fundamental distinction is made between information and data, which constitutes the raw numbers (or descriptions, in the case of qualitative data). Also see Data Management.

INFRASTRUCTURE—(1) An underlying base or foundation, especially for an organization or a system. (2) The basic facilities, services, and installations needed for the functioning of a community or society, such as transportation and communications systems, water and power lines, and public institutions including schools, post offices, and prisons.

INFUSE—To steep in liquid (as water) without boiling so as to extract the soluble constituents or principles.

INITIAL DETENTION—The volume of water on the ground, either in depressions or in transit, at the time active runoff begins. It is that part of precipitation that does not appear either as infiltration or runoff at the time active runoff begins. It includes interception by vegetal cover, depression storage, and evaporation during precipitation, but does not include surface detention.

INITIAL LOSS—Rainfall which precedes the beginning of surface runoff. It includes interception, surface wetting, and infiltration, unless otherwise specified.

INITIAL STORAGE—That portion of precipitation required to satisfy interception by vegetation, the wetting of the soil surface, and Depression Storage.

INITIAL WATER DEFICIENCY—The quantity, usually expressed in depth of water in inches on a unit area, by which the actual water content of a given soil zone (usually the Root Zone) is exceeded by the field capacity of that zone at the beginning of the rainy season. Also referred to as Initial Moisture Deficiency.

INJECTION—Generally refers to a system of artificially introducing surface water into the ground water system as a means of storage or recharge. Most typically, this includes the use of Recharge Wells which work directly opposite of pumping wells to inject surface water into underlying formations. Depending on the water-bearing formation, these methods may have limited usefulness and are generally better used for pumping water into deep, confined aquifers. (Water Quality) Refers to a system of subsurface disposal of brine effluent into an acceptable formation. Also see Induced Recharge.

INJECTION WELL—Refers to a well constructed for the purpose of injection treated wastewater directly into the ground. Wastewater is generally forced (pumped) into the well for dispersal or storage into a designated aquifer. Injection wells are generally drilled into nonpotable aquifers, unused aquifers, or below freshwater levels.

INJECTION WELL CLASSES—Classifications of the U.S. Environmental Protection Agency (EPA) that determine the permit requirements of an Injection Well.

[1] Class I—A well into which liquid hazardous wastes or other fluids are pumped down, with the fluids being injected into an underground formation below the lowest underground source of drinking water that is within a one-quarter mile radius of the well; [2] Class II—A well used to dispose of fluids produced by oil and gas wells, to introduce fluids for enhanced oil recovery, or for liquid hydrocarbon storage; [3] Class III—A well used to pump fluids underground for mineral extraction; [4] Class IV—A well used to re-inject treated fluid from a superfund cleanup site into or above an underground formation within a one-quarter mile radius of the well (the use of these types of wells is currently banned by the EPA); [5] Class V—Wells not included in Classes I-IV, mainly shallow industrial disposal wells or Recharge Wells (see Appendix I-1, Class V Injection Well Classifications and Descriptions).

INJECTION ZONE—A geological formation receiving fluids trough a well.

INLAND FRESHWATER WETLANDS—Swamps, marshes, and bogs found inland beyond the coastal saltwater wetlands.

INLET—A recess, such as a bay or cove, along a coast. A stream or bay leading inland, as from the ocean; an estuary. Also, a narrow passage of water, as between tow islands. A drainage passage, as to a culvert.

IN-LINE FILTRATION—A pre-treatment method in which chemicals are mixed by the flowing water; commonly used in pressure filtration installations. Eliminates need for Flocculation and Sedimentation.

INLINE RESERVOIR—A reservoir constructed in line with the canal used to regulate flow for a balanced operation.

INORGANIC MATTER—Chemical substances of mineral origin, or more correctly, not of basically carbon compounds.

INPUT-OUTPUT (ECONOMIC IMPACT) ANALYSIS—(Data Analysis) An analytical technique used to assess economic, fiscal, resource, and environmental impacts to an economic system from a change to one or more economic sectors. The concept of input-output analysis, or economic impact modeling techniques is based on a mapping, or detailed delineation, of the economic linkages and financial flows and transactions between and among the various industry sectors of an economy (also see Standard Industrial Classification [SIC] Codes). The fundamental premise is that changes in production levels of an economy's basic, or export-oriented, industries, derived from either changes in output or changes in demand, will, through various and extensive inter-industry linkages, result in and iterative process of spending, income creation, and re-spending, thereby changing the production levels of other, directly and indirectly related industries. The input-output process results in a set of multipliers which prescribe the total economic, fiscal, resource, or environmental effects for a unit change to a given industry sector. Multipliers may be developed for any factor input which may be measured in terms of a unit of output. Typical economic impacts include total economic output, employment, incomes, population, housing units. Typical fiscal impacts include tax revenues generated, tax revenue expenditures, and anticipated economic infrastructure requirements. Typical resource impacts may include commercial and residential water use, electrical power use, and land use. Typical environmental impacts would include water and air pollution effects, and the like. Limitations to the input-output impact analysis technique include its extensive and detailed Primary Data requirements (versus Secondary Data), the fact that multipliers are derived only for a single point in time, and the assumption of a linear (constant) relationship between inputs and outputs. Even so, this technique represents a robust analytical methodology for assessing near-term impacts on a comprehensive basis.

INSET—An inflow, as of water; a channel.

IN SITU—In place. An in situ environmental measurement is one that is taken in the filed, without removal of a sample to the laboratory.

IN-SITU BIODEGRADATION—(Environmental) The treatment of soil in place to encourage contaminants to break down. It involves aerating the soil and adding nutrients to promote growth of microorganisms.

IN-SITU STRIPPING—A treatment system that removes or "strips" volatile organic compounds from contaminated ground or surface water by forcing an airstream through the water and causes the compounds to evaporate.

IN-SITU VITRIFICATION—(Environmental) A technology used to treat hazardous waste substances in soils. This process electrically melts the waste media at extremely high temperatures, then allows it to cool, creating an extremely stable, insoluble, grass-like solid. The contaminants are destroyed or immobilized and the total volume of material is reduced.

INSTREAM AERATION—The addition of air to a flowing stream to maintain the dissolved oxygen content of the water at an acceptable level.

INSTREAM FLOW—Nonconsumptive water requirements which do not reduce the water supply; water flows for uses within a defined stream channel. Examples of instream flows include:

[1] Aesthetics—Water required for maintaining flowing steams, lakes, and bodies of water for visual enjoyment; [2] Fish and Wildlife—Water required for fish and wildlife; [3] Navigation—Water required to maintain minimum flow for waterborne commerce; [4] Quality Dilution—Water required for diluting salt and pollution loading to acceptable concentrations; and [5] Recreation—Water required for outdoor water recreation such as fishing, boating, water skiing, and swimming.

Also referred to as Instream Use.

INSTREAM FLOW NEEDS—Those habitat requirements within the running water Ecosystem related to current velocity and depth which present the optimum conditions of density (or diversity) or physiological stability to the aquatic organisms being examined at various life cycle stages.

INSTREAM USE—Typically non-consumptive uses of water that do not require diversion from its natural watercourse (e.g., fish and other aquatic life, recreation, navigation, esthetics, and scenic enjoyment). Hydroelectric power production water use is also considered a non-consumptive, but may require temporary diversion from the natural stream flow. Also referred to as In-Channel Use, Nonwithdrawal Use, or Instream Flow.

INSULATED STREAMS—Streams or a reach of a stream that neither contribute water to the zone of saturation nor receive water from it. Such streams are separated from the zones of saturation by an impermeable bed. Also see Stream.

INTANGIBLE FLOOD DAMAGE—Estimated damage done by disruption of business, danger to public health, shock, loss of life, and other factors not directly measurable.

INTEGRATED (WATER) RESOURCE PLANNING (IRP)—A comprehensive, interdisciplinary approach to water resource planning that encompasses water resource assessment, demand considerations, analysis of alternatives, risk management, resource diversity, environmental considerations, least-cost analysis, multidimensional modeling, and participatory decision making and public input, among other factors. Integrated Resource Planning begins with specific policy objectives that are applied to extensive lists of options for water supply sources, distribution systems, or other operational requirements. The options are then narrowed after evaluating demand requirements, environmental impacts, conservation options, costs, risks, and other aspects of a project. IRP involves a dynamic process of assessing demand and supply conditions and creatively integrating alternatives and new technologies. While the concepts of IRP are relatively new to the process of water planning, it has been used extensively in the energy industry. As a planning process it helps decision makers select the best mix of water resources, facilities, and conservation measures to meet water demands. In addition to traditional planning techniques, IRP also

[1] Includes extensive public involvement; [2] Considers both supply-side (resources and facilities) and demand-side (conservation) alternatives as ways of meeting demands; [3] Considers goals and objectives in addition to dollar costs (e.g., environmental concerns, public acceptability, etc.); [4] Considers uncertainty in demand forecasts, regulations, etc.; and [5] Considers the effect of water rates on water demands.

INTENSIVE CROPS—Crops generally grown under irrigation in the Western United States requiring large inputs of labor and capital. Examples include potatoes, sugar beets, fruit, and corn.

INTER-BASIN TRANSFER (of Water)—A transfer or diversion of water (either groundwater or surface water) from one Drainage or Hydrographic Basin to another. Also referred to as Water Exports and/or Water Imports.

INTERCEPTING DRAIN—A drain constructed at the upper end of an area to intercept and carry away surface or ground water flowing toward the area from higher ground. Also referred to as Curtain Drain.

INTERCEPTION (HYDROLOGY)—The process of storing rain or snow on leaves and branches which eventually evaporates back to the air. Interception equals the precipitation on the vegetation minus streamflow and throughfall.

INTERCEPTOR SEWERS—Large sewer lines that, in a combined system, control the flow of sewage to the treatment plant. In a storm, they allow some of the sewage to flow directly into a receiving stream, thus keeping it from overflowing onto the streets. Also used in separate systems to collect the flows from main and trunk sewers and carry them to treatment points.

INTERDISCIPLINARY APPROACH—Addressing problems by means of different methodologies, education, training, and disciplines which, when shared and combined, provide for new, more innovative and more comprehensive solutions.

INTERFACE—The common boundary between two substances such as a water and a solid, water and a gas, or two liquids such as water and oil.

INTERFERENCE (WELLS)—A change in the water level of one well caused by the pumping at another well. The condition occurring when the area of influence of a water well comes into contact with or overlaps that of a neighboring well, as when two wells are pumping from the same aquifer or are located near each other.

INTERFLOW—(1) That movement of water of a given density in a reservoir or lake between layers of water of different density, usually caused by the inflow of water either at a different temperature, or with different silt or salt contents. (2) Runoff due to that part of the precipitation which infiltrates the surface soil (but not to the water table) and moves laterally through the upper soil horizons toward the stream channels. The interflow is included in direct runoff and is part of the Flood Hydrograph.

INTERGLACIAL—Occurring between Glacial Epochs. A comparatively short period of warmth during an overall period of Glaciation.

INTERMEDIATE ZONE—The subsurface water zone below the Root Zone and above the Capillary Fringe.

INTERMITTENT—Alternately containing and empty of water as an intermittent lake.

INTERMITTENT STREAM—A stream that carries water only part of the time, generally in response to periods of heavy runoff either from snowmelt or storms. Flow generally occurs for several weeks or months in response to seasonal precipitation, due to ground water discharge, in contrast to the Ephemeral Stream that flows but a few hours or days following a single storm. Also referred to as Seasonal Streams. Also see Stream.

INTERMITTENTLY EXPOSED—A water regime in wetland classification in which surface water is present throughout the year except in years of extreme drought.

INTERMITTENTLY FLOODED—A water regime in wetland classification in which the substrate is usually exposed, but surface water is present for variable periods without detectable seasonal periodicity.

INTERNAL DRAINAGE—(1) Movement of water down through soil to porous aquifers or to surface outlets at lower elevations. (2) Drainage within a basin that has no outlet.

INTERNAL EROSION (of a Dam)—The progressive development of erosion by seepage, appearing downstream of the dam as a hole or seam discharging water that contains soil particles. Also referred to as Piping.

INTERNAL SOIL DRAINAGE—The downward movement of water through the soil profile. The rate of movement is determined by the texture, structure, and other characteristics of the soil profile and underlying layers and by the height of the water table, either permanent or perched. Relative terms for expressing internal drainage are none, very slow, medium, rapid, and very rapid.

INTERPOLATE/INTERPOLATION—(Data Analysis) The fitting of data values between observed values. Frequently interpolation will be used when certain periods of data are missing, but data surrounding these missing data values is available. Interpolation techniques must be careful so as to attempt to repeat the patterns of the missing data with respect to trend, seasonality, and longer-term cycles.

INTERSTADIAL—(Geology) Long intervals of Desiccation occurring between Pluvial episodes.

INTERSTATE ALLOCATION [Nevada and California]—An agreement between the states of Nevada and California over the use of the waters of Lake Tahoe and the Truckee, Carson, and Walker rivers which was ratified by California (1970) and Nevada (1971), but was never ratified by Congress. Despite this, both states have enacted legislation to enforce to the allocation of the Truckee, Carson, and Walker rivers between these two states. Subsequently, in 1990 many of the compact's provisions dealing with the waters of Lake Tahoe and the Truckee and Carson rivers became formalized under Public Law 101-618 (the Negotiated Settlement).

INTERSTATE CARRIER WATER SUPPLY—A source of water for drinking and sanitary use on planes, buses, trains, and ships operating in more than one state. These sources are federally regulated.

INTERSTATE COMPACT—States administer water rights within their own political boundaries; however, the process becomes more complicated when involving an interstate body of water (Interstate Water). Under these conditions there are three possible ways to achieve an interstate allocation of water: (1) A suit for equitable apportionment brought by the states in the U.S. Supreme Court; (2) a Congressional act; and (3) an interstate compact. An interstate compact is an agreement negotiated between states, adopted by their state legislatures, and then approved by Congress. Once an allocation of interstate water is determined by such a means, the individual states may then issue water rights to its share of the water through their normal administrative process. Interstate compacts have been traditionally used in making water allocations in the western states. Also see Interstate Allocation [Nevada and California].

INTERSTATE WATERS—According to law, interstate waters are defined as: (1) rivers, lakes and other waters that flow across or form a part of state or international boundaries; (2) waters of the Great Lakes; and (3) coastal waters whose scope has been defined to include ocean waters seaward to the territorial limits and waters along the coastline (including inland steams) influenced by the tide.

INTERSTICES—The openings or pore spaces in a rock, soil, and other such material. In the Zone of Saturation they are filled with water. Synonymous with Void or Pore.

INTERSTITIAL—Referring to the Interstices or pore spaces in rock, soil, or other material subject to filling by water.

INTERSTITIAL MONITORING—The continuous surveillance of the space between the walls of an underground storage tank.

INTERSTITIAL PRESSURE—(Hydraulics) The upward pressure of water in the pores or Interstices of a material.

INTERSTITIAL WATER—Water in the pore spaces of soil or rock.

INTERTIDAL ZONE—That area of coastal land that is covered by water at high tide and uncovered at low tide.

INTERVALE—(New England) A tract of low-lying land, especially along a river.

INTRABASIN TRANSFER—The diversion of water within a drainage basin.

INTRINSIC PERMEABILITY—Pertaining to the relative ease with which a porous medium can transmit a liquid under a hydraulic or potential gradient. It is a property of the porous medium and is independent of the nature of the liquid or the potential field.

INTRUSIVE—Where a fluid (e.g., magma) has penetrated into or between other rocks, but has solidified before reaching the surface.

INTRUSIVE BEDROCK—(Geology) Denoting igneous rocks in a molten state which have evaded other, older rock formations and cooled below the surface of the earth. These magmas are slow-cooling and form coarse-textured rocks, such as granite.

INUNDATE—(1) To cover with water, especially floodwaters. (2) To overwhelm as if with a flood; swamp.

INUNDATION—The covering by water of lands not normally so covered.

INUNDATION MAP—A map delineating the area that would be inundated in the event of a dam failure.

INVASIVE PLANT—A plant that moves in and takes over an Ecosystem to the detriment of other species; often the result of Environmental Manipulation.

INVENTORY—A scientific survey of natural resources, e.g., plants, animals, water, timber, etc.

INVENTORYING—Gathering data needed for analyses and evaluation of the status or condition of a specific universe or area of concern.

INVERSION—An atmospheric condition where a lower layer of cool air is trapped below an upper layer of warm air. May cause serious air pollution problems.

INVERTED SIPHON—A closed pipeline with its end sections above the middle section, used for crossing under drainage channels, roadways, depressions, or other structures. The term is common but misleading as there is no siphon action involved. Also referred to as a Sag Pipe.

ION—(1) An atom or molecule that carries a net charge (either positive or negative) because of an imbalance between the number of protons and the number of electrons present. If the ion has more electrons than protons, it has a negative charge and is called an anion; if it has more protons than electrons it has a positive charge and is called a cation. (2) (Water Quality) An electrically charged atom that can be drawn from waste water during electrodialysis.

ION EXCHANGE—The substitution of one Ion for another in certain substances. Either Anion Exchange or Cation Exchange is possible. The most common cation exchange involves the conversion of Hard Water to Soft Water by means of a Water Softening process. Hard water contains the divalent ions of calcium (Ca+2) and magnesium (Mg+2), which cause soap and detergents to form precipitates in water. A Water Softener consists of a resin that is saturated with sodium ions (Na+). As hard water percolates through the resin, the ions of calcium or magnesium are removed as they attach to the resin, thus releasing (being exchanged for) sodium ions.

ION EXCHANGE TREATMENT—A common water-softening technique often found on a large scale at water purification plants that remove some organics and radium by adding calcium oxide or calcium hydroxide to increase the pH to a level where the metals will precipitate out.

IONIC STRENGTH—The weighted concentration of ions in solutions, computed by the formula:

Ionic Strength = 1/2 Sum(Zi2Ci)

where:

Z = the charge on a particular ionic species; and C = the concentration of a particular ionic species.

IONOSPHERE—The upper layer of the Atmosphere above the Stratosphere, from a distance of about 80 kilometers (50 miles) from the earth's surface. Incoming solar radiation is sufficiently intense to cause the ionization of the sparse gas molecules present.

IRRECOVERABLE LOSSES—Water lost to a salt sink or lost by evaporation or evapotranspiration from a conveyance facility, drainage canal, or in fringe areas.

IRREGULARLY EXPOSED—A water regime in wetland classification in which the land surface is exposed by tides less often than daily.

IRREGULARLY FLOODED—A water regime in wetland classification in which tidal water alternately floods and exposes the land surface less often than daily.

IRRIGABLE LAND—(1) Land capable of being irrigated by any method. (2) (USBR) Arable land under a specific project plan for which irrigation water is, can be, or is planned to be provided and for which facilities necessary for sustained irrigation are provided or are planned to be provided. For the purpose of determining the areas to which acreage limitations are applicable, it is that acreage possessing permanent irrigated crop production potential, after excluding areas occupied by and currently used for homesites, farmstead buildings, and related permanent structures such as feed lots, equipment storage yards, permanent roads, permanent ponds, and similar facilities, together with roads open for unrestricted use by the public. Areas used for field roads, farm ditches and drains, tailwater ponds, temporary equipment storage, and other improvements subject to change at will by the landowner are included in the irrigable acres.

IRRIGATE—(1) To supply (dry land) with water by means of ditches, pipes, or streams; to water artificially. (2) To wash out (a body cavity or wound) with water or a medicated fluid. (3) To make fertile or vital as if by watering.

IRRIGATED ACREAGE—The land area that is irrigated, which is equivalent to total irrigated crop acreage minus the amount of acreage that was double cropped.

IRRIGATED AREA—The area upon which water is artificially applied. This excludes farm roads, irrigation ditches, and farmsteads.

IRRIGATED CROP ACREAGE—The total amount of land area that is irrigated, including acreage that is double cropped.

IRRIGATED CROPLAND—All lands being supplied water by artificial means, excluding waterfowl refuges, that are being used for the production of orchard, field, grain crops and pasture.

IRRIGATED LAND—Land receiving water by controlled artificial means for agricultural purposes from surface or subsurface sources.

IRRIGATION—The controlled application of water for agricultural purposes through man-made systems to supply water requirements not satisfied by rainfall. A listing of the types of irrigation systems includes:

[1] Center-Pivot—Automated sprinkler irrigation achieved by automatically rotating the sprinkler pipe or boom, supplying water to the sprinkler heads or nozzles, as a radius from the center of the field to be irrigated. Water is delivered to the center or pivot point of the system. The pipe is supported above the crop by towers at fixed spacings and propelled by pneumatic, mechanical, hydraulic, or electric power on wheels or skids in fixed circular paths at uniform angular speeds. Water is applied at a uniform rate by progressive increase of nozzle size from the pivot to the end of the line. The depth of water applied is determined by the rate of travel of the system. Single units are ordinarily about 1,250 to 1,300 feet long and irrigate about a 130-acre circular area; [2] Drip—A planned irrigation system in which water is applied directly to the Root Zone of plants by means of applicators (orifices, emitters, porous tubing, perforated pipe, etc.) operated under low pressure with the applicators being placed either on or below the surface of the ground; [3] Flood—The application of irrigation water where the entire surface of the soil is covered by ponded water; [4] Furrow—A partial surface flooding method of irrigation normally used with clean-tilled crops where water is applied in furrows or rows of sufficient capacity to contain the designed irrigation system; [5] Gravity—Irrigation in which the water is not pumped but flows and is distributed by gravity; [6] Rotation—A system by which irrigators receive an allotted quantity of water, not a continuous rate, but at stated intervals; [7] Sprinkler—A planned irrigation system in which water is applied by means of perforated pipes or nozzles operated under pressure so as to form a spray pattern; [8] Subirrigation—Applying irrigation water below the ground surface either by raising the water table within or near the root zone or by using a buried perforated or porous pipe system that discharges directly into the root zone; [9] Traveling Gun—Sprinkler irrigation system consisting of a single large nozzle that rotates and is self-propelled. The name refers to the fact that the base is on wheels and can be moved by the irrigator or affixed to a guide wire; [10] Supplemental—Irrigation to insure increased crop production in areas where rainfall normally supplies most of the moisture needed; [11] Surface—Irrigation where the soil surface is used as a conduit, as in furrow and border irrigation as opposed to sprinkler irrigation or subirrigation.

IRRIGATION CANAL—A permanent irrigation conduit constructed to convey water from the source of supply to one or more farms.

IRRIGATION CONVEYANCE LOSS AND WASTE—The loss of water in transit from a reservoir, point of diversion, or ground water pump (if not on farm) to the point of use, whether in natural channels or in artificial ones, such as canals, ditches, and laterals.

IRRIGATION DELIVERY REQUIREMENT, FARM—The amount of water in acre-feet per acre required to serve the irrigated area. It is the crop irrigation requirement plus farm waste and deep percolation.

IRRIGATION DEPLETION—The amount of diverted water consumptively used, beneficially and nonbeneficially, in serving a cropped area. It is the gross diversion minus return flow and includes losses due to deep percolation.

IRRIGATION DISTRICT—(1) Quasi-political districts created under special laws to provide for water services to property owners in the district. (2) In the United States, a cooperative, self-governing public corporation set up as a subdivision of the State government, with definite geographic boundaries, organized and having taxing power to obtain and distribute water for the irrigation of lands within the district; created under the authority of a State legislature with the consent of a designated fraction of the landowners or citizens. Also see Truckee-Carson Irrigation District (TCID).

IRRIGATION EFFICIENCY (I.E.)—Basically, the efficiency associated with water application. Generally, the loss of water in transit from a reservoir, point of diversion, or ground water pump to the point of use, whether in natural channels or in artificial ones, such as canals, ditches, and laterals. More specifically, the percentage of water applied, and which can be accounted for, in the soil-moisture increase for Crop Consumptive Use, i.e., the Crop Requirement. It is defined as the ratio of the volume of water required for a specific Beneficial Use as compared to the volume of water delivered, or applied, for this purpose. It is commonly interpreted as the volume of water stored in the soil for Evapotranspiration compared to the volume of water delivered for this purpose, but may be defined and used in different ways. The Distribution Uniformity (DU) of a field's irrigation system is one of the limiting factors of a system's irrigation efficiency.

IRRIGATION FREQUENCY—Time interval between irrigations.

IRRIGATION LATERAL—A branch of a main canal conveying water to a farm ditch; sometimes used in reference to farm ditches.

IRRIGATION LEACHING REQUIREMENT—The amount of water required to move residual salts out of the root zone and maintain an adequate soil-salt balance for crop production. Also referred to as Crop Leaching Requirement.

IRRIGATION PERIOD—The number of hours or days that it takes to apply one irrigation to a given design area during the peak consumptive-use period of the crop being irrigated.

IRRIGATION PIT—A small storage reservoir constructed to regulate or store the supply of water available to the irrigator.

IRRIGATION RELEASES—Refers to those waters released from storage primarily for irrigation. Does not include Precautionary Drawdowns.

IRRIGATION REQUIREMENT, CROP—The amount of irrigation water in acre-feet per acre required by the crop; the quantity of water, exclusive of precipitation, that is required for production of a specific crop. It is the difference between Crop Consumptive Use or Crop Requirement and the effective precipitation for plant growth. To this amount the following items, as applicable, are added: (1) irrigation applied prior to crop growth; (2) water required for leaching; (3) miscellaneous requirements of germination, frost protection, plant cooling, etc.; and (4) the decrease in soil moisture should be subtracted.

IRRIGATION RETURN FLOW—Applied water which is not consumptively used, that is, water that is not transpired, evaporated, or deep percolated into a ground water basin, and returns to a surface or ground water supply. In cases of water rights litigation, the definition may be restricted to measurable water returning to the stream from which it was diverted, thereby excluding waters used for deep percolation and salt leaching. Also see Crop Leaching Requirement and Irrigation Leaching Requirement.

IRRIGATION STRUCTURE—Any structure or device necessary for the proper conveyance, control, measurement, or application of irrigation water.

IRRIGATION, SUPPLEMENTAL—An additional irrigation water supply which supplements the initial, or primary supply.

IRRIGATION SYSTEMS—See Irrigation.

IRRIGATION SYSTEMS TAILWATER RECOVERY—A water runoff collection and storage system to provide a constant quantity of water back to the initial system or to another field.

IRRIGATION WATER—Water diverted or pumped for irrigation of crops or pasture. It does not include undiverted water which naturally floods unimproved pastures by overflow during high-runoff years, and water which may beneficially subirrigate land for which no other source of water is diverted.

IRRIGATION WATER MANAGEMENT—The use and management of irrigation water where the quantity of water used for each irrigation is determined by the water-holding capacity of the soil and the need for the crop, and where the water is applied at a rate and in such a manner that the crop can use it efficiently and significant erosion does not occur.

IRRIGATION WATER REQUIREMENT—The total quantity of water, exclusive of effective precipitation, that is required for crop production, to include crop consumptive use, leaching requirements, and on-farm conveyance losses.

IRRIGATION WATER USE—Artificial application of water on lands to assist in the growing of crops and pastures or to maintain vegetative growth on recreational lands, such as parks and golf courses.

ISLAND—A land mass, especially one smaller than a continent, entirely surrounded by water. Also see Biome.

ISLET—A small or minor island.

ISOBAR—A line on a weather map connecting points of equal atmospheric pressure. Also referred to as Isopiestic.

ISOBATH—An imaginary line on the earth's surface or a line on a map connecting all points which are the same vertical distance above the upper or lower surface of a water-bearing formation or aquifer.

ISOCHRONE—Plotted line graphically connecting all points having the same time of travel for contaminants to move through the saturated zone and reach a well.

ISOCONCENTRATION—Graphic plot of points having the same contaminant concentration levels.

ISOHYET—A line drawn on a map connecting points that receive equal amounts of rainfall.

ISOHYETAL—Indicating equal rainfall, generally expressed as lines of equal rainfall.

ISOHYETAL LINE—A line drawn on a map or chart joining points that receive the same amount of precipitation. Also referred to as an Isohyet and Isopluvial Line.

ISOPIESTIC—Having, or denoting, equal pressure; Isobaric.

ISOPLETH—A graph showing the occurrence or frequency of any phenomenon as a function of two variables

ISOTHERM—A line drawn on a weather map or chart linking all points of equal or constant temperature.

ISOTHERMY—In Limnology, a state in which a lake is at the same temperature throughout and is well-mixed. Periods of isothermy occur in Spring and Autumn in Dimictic Lakes.

ISOTROPY—That condition in which a medium has the same properties in all directions.

ISTHMUS—A narrow strip of land connecting two larger masses of land.

JACKSON TURBIDITY UNIT (JTU)—The JTU is a measurement of the turbidity, or lack of transparency, of water. It is measured by lighting a candle under a cylindrical transparent glass tube and pouring a sample of water into the tube until an observer looking from the top of the tube cannot see the image of the candle flame. The number of JTUs varies inversely and nonlinearily with the height of the sample (e.g., a sample which measures 2.3 cm has a turbidity of 1,000 JTUs whereas a sample measuring 72.9 cm has a turbidity of 25 JTU's).

JAR TEST—A laboratory procedure that simulates a water treatment plant's coagulation/flocculation units with differing chemical doses, mix speeds, and settling times to estimate the minimum or ideal coagulant dose required to achieve certain water quality goals.

JET—A forceful stream of fluid (as water or gas) discharged from a narrow opening or a nozzle.

JET STREAM—A high-speed, meandering wind current, generally moving from a westerly direction at speeds often exceeding 400 kilometers (250 miles) per hour at altitudes of 15 to 25 kilometers (10 to 15 miles). In the Western United States, the jet stream's north-south latitudinal position largely determines the application and intensity of precipitation during the winter months when most rain and snowfall occur.

JETTY—A structure extending into a sea, lake, or river to influence the current or tide, in order to protect harbors, shores, and banks.

JIG—An apparatus for cleaning or separating crushed ore by agitation in water.

JOINT-USE CAPACITY—That reservoir capacity which has been assigned to flood control purposes during certain periods of the year and to other purposes during other periods of the year.

JOINT-USE STORAGE—Reservoir storage space which is used for more than one purpose. The operation may follow a fixed predetermined schedule or may be flexible and subject to adjustment, depending upon particular hydrologic conditions.

JOULE—A unit of energy or work equivalent to one watt per second, 0.737 foot-pounds, or 0.238 Calories, or 9.484 X 10-4 British Thermal Unit (BTU).

JURISDICTIONAL WETLAND—An area that meets the criteria established by the U.S. Army Corps of Engineers (Corps or COE) for a Wetlands (as set forth in their Wetlands Delineation Manual). Such areas come under the jurisdiction of the Corps of Engineers for permitting certain actions such as dredge and fill operations. See Wetlands. [Also see Classification of Wetlands and Deepwater Habitats of the United States, U.S. Department of the Interior, Fish and Wildlife Service (USFWS). Appendix W-3 presents a summarization of this Wetland and Deepwater Habitat Classification System based upon USFWS criteria.]

JUVENILE WATER—Water brought to the surface or added to underground supplies from magma.

KAME—A conical hill or short irregular ridge of gravel or sand deposited in contact with glacial ice.

KANSAN—(Geology) Of or relating to one of the glacial stages of the Pleistocene epoch which occurred in North America, which consisted of the Nebraskan (first stage), Kansan (second stage), Illinoian (third stage), and Wisconsin (fourth stage).

KARST, also KARSTIC REGION—Limestone and dolomite areas with a topography peculiar to and dependent on underground solution and the diversion of surface waters to underground routes. Characteristic of an area of irregular limestone in which erosion has produced fissures, sinkholes, underground streams, and caverns. Also referred to as Karst Topography.

KARST HYDROLOGY—The branch of Hydrology that deals with the hydrology of geological formations having large underground passages or fractures which enable underground movement of large quantities of water.

KARST TOPOGRAPHY—The structure of land surface resulting from limestone, dolomite, gypsum beds, and other rocks formed by dissolution and characterized by closed depressions, sinkholes, caves, and underground drainage.

KARSTIC RIVER—A river which originates from a karstic spring or flows in a Karstic Region.

KELPIE, also Kelpy—A malevolent water spirit of Scottish legend, usually having the shape of a horse and rejoicing in or causing drownings; a water sprite of Scottish folklore that delights in or brings about the drowning of wayfarers.

KELVIN (K)—The SI Unit of temperature. The base unit of temperature in the International System of Units that is equal to 1/273.16 of the Kelvin scale temperature of the triple point of water. Zero Kelvin is Absolute Zero, and an interval of 1 K is equal to 1° on the Celsius Scale (Centigrade Temperature Scale) and 1.8° on the Fahrenheit Temperature Scale. 0°C = 273.15 K.

KELVIN SCALE—An absolute scale of temperature in which each degree equals one kelvin. Water freezes at 273.15 K and boils at 373.15 K.

KETTLE—(1) (Geology) A depression left in a mass of Glacial Drift, formed by the melting of an isolated block of glacial ice. (2) A pothole.

KGAL—A thousand gallons (kilogallons).

KIBBLE—An iron bucket used in wells or mines for hoisting water, ore, or refuse to the surface.

KIESELGUHR—A fine, powdered diatomaceous earth used in industry as a filler, a filtering agent, and absorbent, a clarifier, and an insulator. More commonly referred to as Diatomite.

KILOGRAM—The base unit of mass in the International System of Units that is equal to the mass of a prototype agreed upon by international convention and that is nearly equal to 1,000 cubic centimeters of water at the temperature of its maximum density. Also see Metric System.

KILOWATT (KW)—The electrical unit of power which equals 1,000 watts or 1.341 horsepower. Since one watt equals one Joule per second, a kilowatt equals 1,000 joules per second. The Kilowatt-Hour (KWH) is the basic unit of electric energy. It equals 1 kilowatt of power applied for 1 hour.

KILOWATT-HOUR (KWH)—A unit of electrical energy equal to 1,000 watt-hours or a power demand of 1,000 watts for one hour. The equivalent of 3,600,000 Joules. Power company utility rates are typically expressed in cents per kilowatt-hour.

KINEMATIC VISCOSITY—The ratio of dynamic viscosity to mass density. It is obtained by dividing dynamic viscosity by the fluid density. Units of kinematic viscosity are square meters per second.

KINETIC ENERGY (k)—The energy inherent in a substance because of its motion, expressed as a function of its velocity and mass, or MV2/2.

KINETIC RATE COEFFICIENT—A number that describes the rate at which a water constituent such as a Biochemical Oxygen Demand (BOD) or Dissolved Oxygen (DO) rises or falls.

KNIFING—A means to incorporate slurry or liquid manures into the soil. The waste is injected just behind a thin, knifelike tool that opens a narrow slit in the soil.

KNOWN GEOTHERMAL RESOURCE AREAS (KGRA)—Basically, KGRAs fall into two categories: (1) areas of obvious geothermal activity such as hot springs designated by the U.S. Geological Survey (USGS); and (2) areas where applications to lease overlap to such a degree as to indicate strong geothermal potential. The latter are called competitive interest KGRAs.

KRILL—Small abundant crustaceans that form an important part of the food chain in Antarctic waters.

LABORATORY BLANK—An artificial sample, usually distilled water, introduced to a chemical analyzer to observe the response of the instrument to a sample that does not contain the material being measured. The blank can also detect any contamination occurring during laboratory processing of the sample.

LACUSTRINE—Pertaining to, produced by, or inhabiting a lake.

LACUSTRINE DEPOSITS—Stratified materials deposited in lake waters and later become exposed either by the lowering of the water level or by the elevation of the land.

LACUSTRINE WETLANDS—According to criteria of the U.S. Fish and Wildlife Service (USFWS), Lacustrine Wetlands are greater than 20 acres and have less than 30 percent cover of persistent vegetation. Also see Wetlands. [See Appendix W-3 for an explanation of the USFWS Wetland and Deepwater Habitat Classification System and more detailed information on these Systems.]

LADE—To take up or remove water with a ladle or dipper.

LAG (Time)—(Statistics) The difference in time units of a series value and a previous series value. In time series analysis, the lag typically represents the period of time between the change in the independent or predictor (Exogenous) variable and its strongest (most significant) effect on the dependent or predicted (Endogenous) variable. Also see Lead (Time).

LAGGED ENDOGENOUS VARIABLE—(Statistics) Refers to the use of a prior-period Dependent Variable used as an Explanatory Variable in the current period. The model below uses a prior Endogenous value, Yt-1, to explain the behavior of Yt:

Yt = ø1Yt-1 + ð + et

In many instances of social, economic, and natural phenomenon, the behavior of a variable in the current period may be dependent upon or somehow influenced by its prior behavior or level. This constitutes the fundamental underpinning of an Autoregressive Process in the analysis of Time-Series Data.

LAGOON—(1) A shallow lake or pond, especially one connected with a larger body of water. (2) The area of water enclosed by a circular coral reef, or atoll. (3) An area of shallow salt water separated from the sea by sand dunes. (4) (Water Quality) Lagoons are scientifically constructed ponds in which sunlight, algae, and oxygen interact to restore water to a quality equal to effluent from a secondary treatment plant.

LAGOON SYSTEM—(Water Quality) A system of scientifically construction Lagoons or ponds in which sunlight, algae, and oxygen interact to restore water to a quality equal to effluent from a Secondary Treatment Plant.

LAG TIME, also Lagtime—(1) The time from the center of a Unit Storm to the peak discharge or center of volume of the corresponding Unit Hydrograph. (2) (Flood Irrigation) The period between the time that the irrigation stream is turned off at the upper end of an irrigated area and the time that water disappears from the surface at the point or points of application.

LAHAR—A mudflow composed of volcanic debris and water.

LAHONTAN VALLEY WETLAND SYSTEM [Nevada]—An extensive wetland system in northwestern Nevada in Churchill County near the City of Fallon encompassing the Stillwater Wildlife Management Area and the Stillwater National Wildlife Refuge, as well as the Carson Lake and Carson Pasture, which serves as a key migration and wintering area for up to 1 million waterfowl, shorebirds, and raptors. Each spring and fall, it hosts a significant percentage of the Pacific Flyway's migratory birds. The Lahontan Valley Wetland System was named to the Western Hemisphere Shorebird Reserve Network in 1988, and it has been nominated for inclusion under the Convention of Wetlands of International Importance, attesting to the continental significance of this invaluable resource. By one estimate, in the early 1900s the Lahontan Valley Wetland System alone contained about 85,000 acres (34,400 ha) of wetlands visited by millions of waterfowl and shorebirds using the eastern edge of the Pacific Flyway during migration. With the advent of the Newlands Project, fresh water that traditionally charged the wetlands was replaced by a greatly diminished supply of agricultural drain water. Overall, wetland acreage in the Lahontan Valley declined by 85 percent. Because it is one of only three large interior basin wetland systems along the west coast, deterioration of Lahontan Valley wetlands has already markedly reduced the carrying capacity of the Pacific Flyway. In 1990, Congress passed Public Law 101-618 (the Negotiated Settlement) authorizing the purchase and transfer of enough water rights to maintain a total of 25,000 acres of primary wetlands in the Lahontan Valley. The U.S. Department of the Interior, Fish and Wildlife Service (USFWS) estimates this will require up to 125,000 acre-feet of water annually. Also see Newlands Project [Nevada] and Public Law 101-618 [Nevada].

LAKE—A considerable body of inland water or an expanded part of a river.

LAKE BONNEVILLE [Utah and Nevada]—An ancient Ice Age lake which during the last Glacial Epoch covered most of the Utah portion of the Great Basin, encompassing most of northwestern Utah and stretching into eastern Nevada. The present Great Salt Lake is the remaining remnant of this lake.

LAKE EVAPORATION—Normal evaporation such as from a pond or lake.

LAKE LAHONTAN [Nevada and California]—An ancient Ice Age lake which covered an extensive portion of northwestern Nevada during the last Glacial Epoch, a period when the Great Basin was covered with a considerable number of lakes and rivers. Lake Lahontan, along with Lake Bonneville far to the east, represented the major Ice Age lakes which covered vast portions of Nevada and Utah and provided a far more lush and hospitable environment for both flora and fauna. Now, only the Great Salt Lake remains to provide an indication of the prehistoric presence of Lake Bonneville, and only Pyramid Lake and Walker Lake remain to provide testament of the presence of Lake Lahontan. In its day, Lake Lahontan would cover some 8,655 square miles in northwestern Nevada, an area equal to almost 8 percent of Nevada's present surface area. This Ice Age lake was fed by the flows of the Truckee, Carson, Walker, Humboldt, Susan and Quinn rivers, attained a maximum surface elevation of approximately 4,380 feet, reached a maximum depth of at least 886 feet where Pyramid Lake, the lowest point in the system, now remains, covered the Lahontan Valley Wetlands (Stillwater Wildlife Refuge) to a depth of 500-700 feet, stretched from just below Nevada's northern boundary to Walker Lake, and extended well up the lower Truckee Canyon towards the city of Reno to near the present-day location of Lagomarsino Canyon near Lockwood. Lake Lahontan experienced at several peaking enlargements—approximately 65,000, 45,000, 30,000, and as recently as 12,500 years ago—and at times nearly dried up.

LAKE TRUCKEE [California]—In Neocene times, which occurred during the late Tertiary Period approximately 25 million to 13 million years ago and encompassed both the Pliocene and Miocene Epochs, Lake Truckee was formed from a basalt flow that dammed the upper Truckee River canyon just below the present-day site of Hirshdale, California. The lake covered an area of some 73 square miles, its surface level reached an elevation of at least 6,000 feet above mean sea level (MSL), and attained a maximum depth of 465 feet. Lake Truckee remained through part of the glacial (Pleistocene) period until the river eventually wore down the obstruction and subsequently drained the lake

LAKES, SEEPAGE—Lakes whose ecology is determined primarily by ground water rather than surface water.

LAKE WHITENING—A phenomenon which occurs in moderately productive lakes when photosynthetic uptake of carbon dioxide (CO2) causes the precipitation of small particles of calcite (mostly calcium carbonate, CaCO3). Since small particles have a greater effect on water transparency and typical calcite particles are only 1-2 micrometers (m) in diameter, lake water takes on a milky appearance, hence lending to its name.

LAMINAR FLOW—A flow in which fluid moves smoothly in streamlines in parallel layers or sheets. The stream lines remain distinct and the flow directions at every point remain unchanged with time. It is characteristic of the movement of ground water. Contrasts with turbulent flow. Synonymous with Streamline Flow and Viscous Flow.

LAND—The entire complex of surface and near surface attributes of the solid portions of the surface of the earth, which are significant to man. Water bodies occurring within land masses are included in some land classification systems.

LAND APPLICATION—The reuse of reclaimed water or the utilization or disposal of effluents on, above, or into the surface of the ground through spray fields or other methods.

LAND BREEZE—The land-to-sea surface wind that occurs in coastal areas at night. It is caused by the rising of the air above the ocean, which is warmer than the land due to the rapid cooling of the land after sunset. Contrast with Sea Breeze.

LAND CAPABILITY—The suitability of land for use without permanent damage. Land capability, as ordinarily used in the United States, is an expression of the effect of physical land conditions, including climate, on the total suitability for use, without damage, for crops that require regular tillage, for grazing, for woodland, and for wildlife. Land capability involves consideration of the risks of land damage from erosion and other causes and the difficulties in land use owing to physical land characteristics including climate.

LAND CAPABILITY CLASSIFICATION—The U.S. Department of Agriculture, Natural Resources Conservation Service (NRCS), formerly the Soil Conservation Service (SCS), has distinguished eight classes of land capability according to the risk of land damage or the difficulty of land use:

[1] Class I—Soils that have few limitations restricting their use; [2] Class II—Soils that have some limitations, reducing the choice of plants or requiring moderate conservation practices; [3] Class III—Soils that have severe limitations that reduce the choice of plants or require special conservation practices, or both; [4] Class IV—Soils that have very severe limitations that restrict the choice of plants, require very careful management, or both;

The following classes are generally not considered suitable for cultivation without some form of major treatment:

[5] Class V—Soils that have little or no erosion hazard, but that have other limitations, impractical to remove, that limit their use largely to pasture, range, woodland, or wildlife food and cover; [6] Class VI—Soils that have severe limitations that make them generally unsuited for cultivation and limit their use largely to pasture or range, woodland, or wildlife food and cover; [7] Class VII—Soils that have very severe limitations that make them unsuited to cultivation and that restricts their use largely to grazing, woodland, or wildlife; [8] Class VIII—Soils and land forms that preclude their use for commercial plant production and restrict their use to recreation, wildlife, water supply, or aesthetic purposes.

LAND DEVELOPMENT (for Irrigation)—The following constitutes a partial listing of land development and improvement activities normally associated with irrigation projects. While these techniques have been prevalent in the past and have had a beneficial effect on land from an agricultural productivity standpoint, more recent concerns over wetland preservation and restoration and wildlife habitat concerns have tended to more recently restrict their widespread usage.

[1] Land Leveling and Smoothing—Leveling to a more uniform grade to permit more efficient gravity irrigation and to facilitate surface drainage on undulating lands developed for sprinkler or drip irrigation; [2] Artificial Drainage—Installation of tile drains or ditches or installation of drainage wells to facilitate the removal of excess water from lands prone to accumulate excess water; [3] Deep Ripping—When some lands, especially older terrace deposits, develop hardpan or cemented layers, if relatively thin in nature, they can often be ripped by powerful equipment thereby deepening the effective root zone and improving internal soil drainage; [4] Soil Amendments—In order to improve the chemical and physical properties of the soil, it is sometimes necessary to apply gypsum, sulfur, or farm manure to the land; [5] Terracing—A technique specifically designed for sloping land to prevent accelerated erosion on exposed slopes; [6] Land Clearing—Initially and periodically, brush and trees must be cleared from irrigated lands to improve overall productivity; [7] Surface Outlet Excavation—A technique to provide an outlet for standing water, most common in prior glacial areas where many closed depressions allow for the accumulation of runoff during wet periods; [8] Tailwater Return Systems—Allow for the recycling and reuse of farm runoff water for additional irrigation; [9] Rock Removal—Particularly prevalent in glacial areas, initial and periodic surface rock is especially important for development and on-going use of irrigated lands; [10] Shelter Belt Planting—Mitigates wind erosion and provides cover for livestock and wildlife by planting tree lines in strategically located areas in and around irrigated fields.

LAND FARMING—A technique for the controlled biodegradation of organic waste that involves the mixture of waste sludges with soil. Microorganisms in the soil degrade the organic wastes. The biodegradation is enhanced by tilling the soil-waste mixture to ensure adequate oxygen and the control of moisture content, nutrient levels, and soil pH.

LANDFILL—(Water Quality) A disposal site which disposes of solid wastes on land. Wastes are deposited and compacted. At specific intervals, a layer of soil covers the waste and the process of deposit and compaction is repeated. The purpose is to confine the wastes to the smallest practical area and volume without creating nuisances or hazards to public health and safety, for example through leaching into the groundwater below the waste site.

LANDFORM—(Geography) A discernible natural landscape that exists as a result of wind, water or geological activity, such as a plateau, plain, basin, mountain, etc.

LAND IMPROVEMENT—See Land Development.

LANDLOCKED—(1) Enclosed or nearly enclosed by land, as a landlocked country without access to the sea or ocean. (2) Confined to fresh water by some barrier, as salmon.

LAND PAN—An evaporation pan located on land. See Evaporation Pan.

LAND RECLAMATION—Making land capable of more intensive use by changing its general character, as by drainage of excessively wet land, irrigation of arid or semiarid land, or recovery of submerged land from seas, lakes, and rivers.

LAND RECONSTRUCTION—(Mining) (1) Restoring land and water areas adversely affected by past mining practices and increasing the productivity of the areas for a beneficial use. (2) Restoring currently mined land to an acceptable form and for a planned use.

LAND RETIREMENT—(Agriculture) Taking land out of agriculture production by leaving it fallow or letting it return to a natural state.

LANDS—References to federally owned lands are defined as follows:

[1] Federal—All classes of land owned by the federal government, which includes Public Domain (Lands), withdrawn and acquired federal lands; [2] Acquired—Lands acquired by the federal government through purchase, condemnation, or gift; [3] Withdrawn—Federal lands for which formal withdrawal action has been taken which restricts the disposition of specific public lands and which holds them for specific public purposes; also, public lands which have been dedicated to public purposes; [4] National Forest—Federal lands which have been designated by executive order or statute as national forests or purchase units, and other lands under the administration of the Forest Service, including experimental areas and Bankhead-Jones Title III lands; and [5] Public Domain—Original public lands which have never left federal ownership. Also includes lands in federal ownership which were obtained by the federal government in exchange for public lands, or for timber on public lands.

Also see Public Domain (Lands).

LANDSCAPE—(Geography) All the natural features, such as fields, hills, forests, and water that distinguish one part of the earth's surface from another part. Usually refers to that portion of land or territory which the eye can comprehend in a single view, including all of its natural characteristics. These characteristics are a result not only of natural forces but of human occupancy and use of the land as well.

LANDSCAPE IMPOUNDMENT—A body of reclaimed water which is used for aesthetic enjoyment or which otherwise serves a function not intended to include contact recreation.

LANDSLIDE—A mass of material that has slipped downhill under the influence of gravity, frequently occurring when the material is saturated with water.

LAND SPREADING—The disposal of solid effluents derived from wastewater treatment facilities on the surface of the ground for dilution or dispersal.

LAND SUBSIDENCE—The sinking or settling of land to a lower level in response to various natural and man-caused factors, for example:

[1] earth movements; [2] lowering of fluid pressure (or lowering of ground water level); [3] removal of underlying supporting materials by mining or solution of solids, either artificially or from natural causes; [4] compaction caused by wetting (Hydrocompaction); [5] oxidation of organic matter in soils; or [6] added load on the land surface.

With respect to ground water, subsidence most frequently results from overdrafts of the underlying water table or aquifer and its inability to fully recharge, a process termed Aquifer Compaction. Also see Subsidence.

LAND TREATMENT MEASURES—The application of vegetative tillage, structural and land management measures, individually or in combination, to alter runoff, to reduce erosion and sediment production, to increase fertility, and to improve drainage and irrigation applications. Also refers to the land disposal of sludge from sewage treatment plants.

LANDTYPE—A land system with a designated soil, vegetation, geology, topography, climate, and drainage situation.

LAND USE—The primary or primary and secondary uses of land, such as cropland, woodland, pastureland, etc. The description of a particular land use should convey the dominant character of a geographic area, and thereby establish the types of activities which are most appropriate and compatible with primary uses.

LAND USE PLAN—A coordinated composite of information, ideas, policies, programs, and activities related to existing and potential uses of land within a given area and frequently the key element in a comprehensive plan for an area under development for public and private land uses, such as residential, commercial, industrial, recreational, and agricultural activities.

LAND USE PLANNING—The process of inventorying and assessing the status, potentials, and limitations of a particular geographic area and its resources, interacting with the populations associated and/or concerned with the area to determine their needs, wants, and aspirations for the future.

LAND VOIDING—The process of damaging land by gully action causing this land to be unproductive for agricultural uses and relegating its use primarily to wildlife and recreation.

LANGELIER INDEX (LI)—An expression of the ability of water to dissolve or deposit calcium carbonate scale in pipes. The index has important implications in industrial water system where the formation of scale or sludge can cause equipment or process failure. The index is calculated from direct measurements of the following in the water system: pH, alkalinity, calcium concentrations, total dissolved solids, and temperature. A positive value indicates a tendency to form scale, and a negative value means the water will dissolve scale and may be corrosive.

LAP—(1) To wash or slap against with soft liquid sounds. (2) A watery food or drink.

LAPSE RATE—The rate of change of temperature with height in the free atmosphere.

LARGE WATER SYSTEM—A water system that services more than 50,000 customers.

LASAGNA PROCESS—(Environmental) A cleanup technique involving the use of an electrical current to treat subsurface hazardous waste. The process, which derived its name from the layered structure of various treatment zones in the soil, grew from a cooperative initiative launched by the U.S. Environmental Protection Agency (EPA) in 1992 to develop innovative techniques to treat buried hazardous waste in situ, thereby requiring no excavation.

LASER LAND LEVELING—The use of instruments featuring laser beams to guide earth-moving equipment for leveling land for surface-type irrigation.

LATE SERAL CONDITION—Synonymous with good ecological conditions.

LATENT HEAT—(1) The quantity of heat absorbed or released by a substance undergoing a change of state, such as ice changing to water or water to steam, at constant temperature and pressure. (2) The heat released or absorbed per unit mass of water in a reversible, isobaric-isothermal change of phase. Also referred to as the Heat of Transformation.

LATENT HEAT OF CONDENSATION—The amount of heat released by a unit mass of substance, without change in temperature, while passing from the vapor to the liquid state.

LATENT HEAT OF VAPORIZATION—The amount of heat absorbed by a unit mass of substance, without change in temperature, while passing from the liquid to the vapor state.

LATENT HEAT TRANSFER—The removal or addition of heat when a substance changes state. In the environment, this almost always refers to the release of heat from water upon condensation and the absorption of heat by water upon evaporation. Also see Latent Heat of Condensation and Latent Heat of Vaporization.

LATERAL—(1) A branch canal or pipeline that diverges from the main canal or other branches. (2) (Irrigation) A water project or irrigation conveyance structure, smaller than a canal intended to convey water away from the main canal or ditch. (3) (Water Quality) A municipal wastewater drain pipe that connects a home or business to a branch or main line.

LATERAL LINE—A series of sensory pores along the head and sides of fish and some amphibians by which water currents, vibrations, and pressure changes are detected.

LATERAL MORAINES—The ridges of Glacial Till that mark the sides of a glacier's path. Also see Moraines, Terminal Moraines, and Recessional Moraine.

LATERAL SEWERS—Pipes that run under city streets and receive the sewage from homes and businesses, as opposed to domestic feeders and main trunk lines.

LATERITIC SOIL—Land that consist of minerals that are rich in iron and aluminum compounds, other minerals having been removed by Leaching. The land is hard and unsuitable for agricultural use.

LAUNCH—(Nautical) To put (a boat) into the water in readiness for use.

LAUNDERING WEIR—A sedimentation basin overflow weir.

LAVA FLOW—(Geology) A solidified mass of rock formed when a stream of viscous, molten lave from a volcano or fissure has cooled and congealed.

LAVAGE—A washing, especially of a hollow organ, such as the stomach or lower bowel, with repeated injections of water.

LAVATORY—(1) A room equipped with washing and often toilet facilities; a bathroom. (2) A washbowl or basin, especially one permanently installed with running water. (3) A flush toilet.

LC50 (LETHAL CONCENTRATION—50)—The concentration of a toxic substance which is fatal to 50 percent of the organisms tested under specific test conditions and time periods.

LD50 (LETHAL DOSE—50)—The dose of a toxicant that is fatal to 50 percent of the organisms tested in a specific time. The dose is the actual quantity administered to the organism.

LEACH—To remove soluble or other constituents from a medium by the action of a percolating liquid, as in leaching salts from the soil by the application of water.

LEACHATE—Liquid which has percolated through the ground, such as water seeping through a sanitary landfill, wastes, pesticides, or fertilizers. Leaching may occur in farming areas, feedlots, and landfills, and may result in hazardous substances entering surface water, ground water, or soil.

LEACHATE COLLECTION SYSTEM—An arrangement of reservoirs and pipes underlying a waste disposal site designed to accumulate and remove Leachate, water that migrates through the waste, and pump it to the surface for treatment.

LEACHED LAYER (SOIL)—A soil layer or an entire soil profile from which the soluble materials (CaCO3 and MgCO3 and material more soluble) have been dissolved and washed away by percolating waters.

LEACHING—The process by which soluble materials in the soil, such as salts, nutrients, pesticide chemicals or contaminants, are washed into a lower layer of soil or are dissolved and carried away by water. Also see Leachate.

LEACHING EFFICIENCY—The ratio of the average salt concentration in drainage water to an average salt concentration in the soil water of the root zone when near field capacity (also defined as the hypothetical fraction of the soil solution that has been displaced by a unit of drainage water).

LEACHING FIELD—The area used for disposal of liquid through a non-water-tight artificial structure, conduit, or porous material by downward or lateral drainage, or both, into the surrounding permeable soil.

LEACHING REQUIREMENT—(1) The amount of excess irrigation water passing through the Root Zone to reduce the salt concentration in the soil for reclamation purposes. (2) That fraction of irrigation water (Crop Water Requirement) that must be leached through the root zone to control soil salinity at a specified level. The extra water is used to dissolve the salts and move them from the soil root zone and out into a drainage tile or channel where they can be removed from the area entirely. Extra water can be added by irrigating more or by natural precipitation. The amount of water needed is governed by the amount of salt that the crop can tolerate in its root zone. As a general equation, this amount of water can be defined (U.S. Bureau of Reclamation, 1993) as a leaching requirement (LR):

LR = ECiw/ECdw X 100

where:

LR = leaching requirement in percent; ECiw = electrical conductivity of irrigation water in millimhos per centimeter (mmhos/cm); ECdw = electrical conductivity of soil drainage water at the bottom of the root zone (mmhos/cm).

Both natural precipitation (rainfall) and conservation efforts affect the leaching requirement. Rainfall that enters the soil in sufficient quantity to create deep percolation will help move the salts down through the soil. As irrigators increase conservation efforts and use less water, there will be a point at which the deep percolation requirements for soil salt balance will not be met, soil salinity will increase, and crop production will decrease.

LEAD—(1) To serve as a channel for a pipe as to conduct water to the house. (2) A channel of water, especially through a field of ice.

LEAD—Chemical symbol Pb, lead is a toxic metal present in air, food, water, soil, and old paint. Overexposure to this metal can cause damage to circulatory, digestive, and central nervous systems. Children less than six years old are considered the most susceptible. Atmospheric levels have dropped sharply with the introduction of unleaded gasolines. Lead in air, water, and food is regulated by a number of environmental statutes to include the Clean Air Act, Clean Water Act (CWA), Safe Drinking Water Act (SDWA), Food, Drug, and Cosmetic Act, among others.

LEAD AND COPPER RULE—Water quality standards covered under the Safe Drinking Water Act (SDWA), and amendments thereto, as set by the U.S. Environmental Protection Agency (EPA). The rule is a set of treatment technique requirements which apply to all community and non-transient non-community water systems (see Public Water Supply Systems). Treatment techniques rather than Minimum Contaminant Levels (MCLs) were established for lead and copper because the occurrence of these contaminants in a drinking water supply is usually the result of corrosion in plumbing materials within both the household plumbing and the distribution system. The rule requires all systems which do not meet the specified lead and copper action levels at the tap to optimize corrosion control treatment in an effort to minimize the levels of these contaminants. The action level is 0.015 mg/l (milligrams per liter) for lead and 1.3 mg/l for copper measured at the 90th percentile. See 90th Percentile.

LEAD (Time)—(Statistics) The difference in time units of a series value and a subsequent series value. In time series analysis, the lead represents the time by which the change in an independent or predictor (Exogenous) variable precedes the strongest (most significant) change in a dependent or predicted (Endogenous) variable. Also see Lag (Time).

LEAD LINE—(Nautical) A line marked at intervals of fathoms and weighted at one end, used to determine the depth of water. Also referred to as a Sounding Line.

LEAD SERVICE LINE—A service line made of lead which connects the water to the building inlet and any lead fitting connected to it.

LEADSMAN—A person who uses a sounding lead to determine depth of water.

LEAF AREA INDEX—The area of one side of leaves per unit area of soil surface.

LEAKAGE—(1) (Hydrology) The flow of water from one Hydrogeologic Unit to another. This may be natural, as through a somewhat permeable confining layer, or Anthropogenic, as through an uncased well. It may also be the natural loss of water from artificial structures, as a result of Hydrostatic Pressure. (2) (Dams) The uncontrolled loss of water by flow through a hole or crack.

LEAKY AQUIFER—An artesian or water table aquifer that loses or gains water through adjacent semipermeable Confining Units.

LE CHÂTELIER'S PRINCIPLE—A principle of dynamic equilibrium stating that a change in one or more factors that maintain equilibrium conditions in a system will cause the system to shift in a direction that will work against or adjust to the change(s), with a resulting reestablishment of equilibrium conditions. For example, assume the concentrations of gaseous oxygen in the atmosphere and dissolved oxygen in a stream are in equilibrium at a certain temperature. As oxygen dissolves in water, heat is released. If an outside influence (e.g., sunlight) raises the water temperature in the stream, this shifts the equilibrium back in the direction of lower dissolved oxygen and greater atmospheric oxygen, and oxygen escapes from the water. As a result, at higher water temperatures, equilibrium concentrations of dissolved oxygen are lower.

LEE—Located in or facing the path of an oncoming glacier. Used of a geologic formation.

LEFT ABUTMENT—That part of the left-hand side of a valley side wall against which a dam is constructed. The left abutment is viewed by an observer looking downstream.

LEFT BANK—The left-hand bank of a stream viewed when the observer faces downstream.

LEGIONELLA—A genus of bacteria, some species of which have caused a type of pneumonia called Legionnaires Disease.

LEMNA GIBBA (Duckweed)—The genus and species name of a small, stemless, free-floating plant used in experiments to determine the toxicity of pollutants to aquatic plant life. Commonly called duckweed.

LENTIC—Characterizing aquatic communities found in standing water. Compare to Lotic.

LENTIC SYSTEM—A non-flowing or standing body of fresh water, such as a lake or pond. Compare to a Lotic System.

LENTICULAR CLOUDS—Lenticular clouds are characteristic of all mountain ranges and form in response to wind. When strong winds blow over the mountains and force moist air up to cooler elevations, the moisture condenses. As the winds blow back down the other side of the mountains, the moisture re-vaporizes. The lenticular cloud is the condensed (visible) moisture under the wind stream; it doesn't drift like other clouds do because it's "trapped" in a pocket of relatively calm air just below the wind stream and just above warmer air below. The notion that the clouds are stationary is an optical effect. A lenticular cloud actually is forming on one end (front edge) and vanishing on the other, giving the appearance that it is in a fixed position. Lenticular clouds assume distinct shapes, generally resembling a disc (hence giving rise to a common name of "pancake clouds" or in a flat elongated shape stretching parallel to the mountain range. Also see Clouds and Sierra Wave [Sierra Nevada Mountains].

LENTIC WATERS—Ponds or lakes (standing water).

LETHE—A river in Hades whose waters cause drinkers to forget their past.

LEVEE—A natural or man-made earthen obstruction along the edge of a stream, lake, or river. Also, a long, low embankment usually built to restrain the flow of water out of a river bank and protect land from flooding. If built of concrete or masonry, the structure is usually referred to as a flood wall. The term Dike is commonly used to describe embankments that block an area on a reservoir rim that are lower than the top of the main dam.

LEVEE (NATURAL)—Bank of sand and silt built by a river during floods, where the Suspended Load is deposited in greatest quantity close to the river. The process of developing natural levees tends to raise river banks above the level of the surrounding flood plains. A break in a natural levee is sometimes called a Crevasse.

LEVEE (MANMADE)—An embankment, generally constructed on or parallel to the banks of a stream, lake or other body of water, for the purpose of protecting the land side from inundation by flood water or to confine the stream flow to its regular channel.

LEVEE SYSTEM—A flood protection system which consists of a levee, or levees, and associated structures, such as closure and drainage devices, which are constructed and operated in accord with sound engineering practices.

LEVEL OF DEVELOPMENT—In a planning study, the practice of holding constant the population, irrigated acreage, industry, and wildlife so that hydrologic variability can be studied to determine adequacy of supplies.

LEVIGATE—(1) To make into a smooth, fine powder or paste, as by grinding when moist; to separate fine particles from coarse by grinding in water. (2) To suspend in a liquid.

LIFE CYCLE ASSESSMENT (LCA)—(Environmental) An objective process to evaluate all the environmental burdens of a product or process through its entire existence (life cycle). This encompasses extracting and processing raw materials, manufacturing, transportation, distribution, use and maintenance, recycling and final disposal.

LIFELINE RATES—A system used by many water purveyors of providing subsidized water rates to needy individuals and those on fixed incomes for a minimum amount of water delivered.

LIFT STATION—A pumping facility that raises municipal sewage to a higher elevation to allow for further gravity flow. Such facilities are required in areas with a flat topography.

LIGHT-AND-DARK BOTTLE TECHNIQUE—A method used to determine the extent of Photosynthesis in an aquatic Ecosystem. Duplicate portions of a water sample are collected. One portion is Incubated in a clear bottle, and the other is incubated in a dark, light-impermeable bottle. Following incubation for a prescribed time period, the net uptake of carbon dioxide in each is measured and compared.

LIGHT WATER—(Chemistry and Physics) Ordinary water, H2O, as compared to Heavy Water.

LIGHT WATER REACTOR (LWR)—A nuclear power plant which uses ordinary Water (H2O) as distinguished from one that uses Heavy Water (D2O) or Deuterium Oxide. Fission energy is released in the form of heat and is transferred to a conventional steam cycle which generates electric energy. Heat generated by the fission of the uranium fuel raises the temperature of the water, which is then pumped to heat exchange units for the production of steam and subsequent generation of electricity. The process results in a continuous transfer of heat from the reactor to the outside. The water also functions as a moderator to reduce the energy level of neutrons released by the fission process in order to allow the neutrons to promote additional fission events. The light-water reactor is the most common type of nuclear reactor operated in the United States.

LIMB (Rising or Falling)—The part of the Hydrograph in which the discharge is steadily increasing or decreasing.

LIME—Calcium oxide (CaO) used in many water and wastewater treatment operations such as softening, coagulation and phosphorus removal. Also referred to as Quicklime.

LIMESTONE—(Geology) A sedimentary rock composed of calcite, or calcium carbonate (CaCO3), and sometimes containing shells and other hard parts of prehistoric water animals and plants. When chemical conditions are right, some calcite crystallizes in sea water and settles to the bottom to form limestone.

LIMESTONE SCRUBBING—The use of a Limestone and water solution to remove gaseous stack-pipe sulfur before it reaches the atmosphere.

LIMICOLOUS—Living in mud.

LIMING—The application of lime to land, primarily to reduce soil acidity and supply calcium for plant growth. Liming an acid soil to a pH of about 6.5 is desirable to maintain a high degree of availability of most of the nutrient elements required by plants.

LIMITED DEGRADATION—An environmental policy permitting some degradation of natural systems but terminating at a level well beneath an established health standard.

LIMITED WATER-SOLUBLE SUBSTANCES—(Water Quality) Water pollution chemicals that are soluble in water at less than one milligram of substance per liter of water.

LIMITING FACTOR—A condition whose absence or excessive concentration is incompatible with the needs or tolerance of a species or population and which may have a negative influence on their ability to thrive and/or survive. A factor such as temperature, light, water, or a chemical that limits the existence, growth, abundance, or distribution of an organism.

LIMNETIC—Referring to a standing water Ecosystem (ponds or lakes); of, relating to, or inhabiting the open water of a body of fresh water, as a limnetic environment or Limnetic Zone.

LIMNETIC ZONE—The open water of a pond or lake supporting Plankton growth. Contrast with Profundal Zone.

LIMNOLOGY—The branch of Hydrology pertaining to the study of freshwater, the aquatic environment and its life; the study of the physical, chemical, hydrological, and biological aspects of fresh water bodies. Related terms include Limnological, Limnologic, and Limnologist.

LIMNOLOGY HYDROBIOLOGIST—A person who undertakes the biological study of bodies of water.

LINDANE—A pesticide that causes adverse health effects in domestic water supplies and is toxic to freshwater fish and aquatic life.

LINEAMENT—(Geology) An essentially rectilinear topographic feature resulting from a fault or zone of faulting. Frequently such areas provide indications of available groundwater sources.

LINEAR—(Statistics) Indicating a constant (straight-line) relationship between two Variables. Linearity constitutes one of the principal underpinnings of the Classical Linear Regression (CLR) Model. Also see (Inherently) Linear Model, below.

(INHERENTLY) LINEAR MODEL—(Statistics) Regression Models which can be expressed in a linear form by an appropriate transformation of the Variables. It is this transformation, as represented by the model's Parameters, or Coefficients, that determines the linearity of the model. For example, the model

Y = ß2X2 + ß3X3 + ... + ßnXn + e

is inherently linear because it is linear with respect to the coefficients ß2, ß3, ..., ßn. Other transformations resulting in inherently linear models are as follows:

Polynomial Model:

Y = ß1 + ß2X2 + ß3X22 + e

Log-Log Model:

log Y = a1 + a2 log X2 + a3 log X3 + e

Multiplicative Model:

Y = ð1X2ð2X3ð3e

Exponential Model:

Y = exp (ß1 + ß2X2 + ß3X3) · e

Reciprocal Model:

Y = 1/(ß1 + ß2X2 + ß3X3 + e)

Semilog Model:

Y = ß1 + ß2 log X2 + e

LINEAR PROGRAMMING—(Mathematics) A mathematical method used to determine the most effective allocation of limited resources between competing uses when both the objective (e.g., profit, cost, or output) and the restrictions (constraints) on its attainment can be quantified as a system of linear equations representing equalities or inequalities.

LINED WATERWAY OR OUTLET—A waterway or outlet with an erosion-resistant lining of concrete, stone, or other permanent material. The lined section extends up the side slopes to a designed height.

LINER—(1) (Water Quality) A low-permeability material, such as clay or high-density polyethylene, used for the bottom and sides of a landfill. The liner retards the escape of Leachate from the landfill to the underlying groundwater. (2) An insert or sleeve for sewer pipes to prevent leakage or infiltration.

LINE STORM—A violent storm or a series of storms of rain and wind believed to take place during the equinoxes.

LINING—With reference to a canal, tunnel, shaft, or reservoir, a coating of asphaltic concrete, reinforced or unreinforced concrete, shotcrete, rubber or plastic to provide water tightness, prevent erosion, reduce friction, or support the periphery of the structure. May also refer to the lining, such as steel or concrete, of an outlet pipe of conduit of a dam or reservoir.

LINING (HYDRAULICS)—A protective covering over all or part of the perimeter of a reservoir or a conduit to prevent seepage losses, withstand pressure, resist erosion, reduce friction, or otherwise improve conditions of flow.

LIPID—Any of a group of organic compounds, including the fats, oils, waxes, sterols, and triglycerides, that are insoluble in water but soluble in common organic solvents, are oily to the touch, and together with carbohydrates and proteins constitute the principal structural material of living cells.

LIQUEFACTION—(1) (General) The act or process of making or becoming liquid; especially the conversion of a solid into a liquid by heat, or of a gas into a liquid by cold or pressure. (2) (Soils) The sudden and spontaneous large decrease of the shearing resistance of a cohesionless soil, caused by a collapse of the structure from shock or other types of strain and associated with a sudden but temporary increase in the pore-fluid pressure resulting in the temporary transformation of the material into a fluid mass.

LIQUEFY, also Liquify—(1) To cause to become liquid. (2) To melt (a solid) by heating.

LIQUID—A state of matter in which the molecules are closer and held more tightly by one another than in the gaseous state. Has a definite volume, but indefinite shape. See Water.

LIQUID FERTILIZER—A fluid in which the plant nutrients are in true solution.

LIQUID INJECTION INCINERATOR—Commonly used system that relies on high pressure to prepare liquid wastes for incineration, breaking them up into tine droplets to allow for easier combustion.

LIQUOR—(Water Quality) A liquid solution containing dissolved substances. A concentrated solution of process chemicals or raw materials added to an industrial process. Compare with Slurry.

LITER—The basic unit of measurement for volume in the Metric System equivalent to 0.001 cubic meters (10-3 m3); also equal to 61.025 cubic inches or 1.0567 liquid quarts.

LITHIA WATER—Mineral water containing lithium salts.

LITHOLOGY—(Geology) (1) The scientific study of rocks, usually with the unaided eye or with little magnification. (2) Loosely, the structure and composition of a rock formation.

LITHOMETEOR—Solid material, except ice (water), suspended in the atmosphere, as dust, smoke, or pollen. Contrasts with Hydrometeor.

LITHOSPHERE—That part of the earth which is composed predominantly of rocks (either coherent or incoherent, and including the disintegrated rock materials known as soils and subsoils), together with everything contained in this rocky crust.

LITHOTRIPTER—A device that pulverizes kidney stones by passing shock waves through a water-filled tub in which the patient sits. The device creates stone fragments small enough to be expelled in the urine.

LITMUS—A water-soluble blue powder derived from certain lichens that changes to red with increasing Acidity and to blue with increasing Basicity.

LITMUS PAPER—An unsized white paper impregnated with Litmus and used as a Ph or acid-base indicator.

LITTORAL—The region along the shore of a non-flowing body of water; corresponds to Riparian for a flowing body of water. More specifically, the zone of the sea flood lying between the tide levels.

LITTORAL TRANSPORT—The movement of material along the shore by waves and currents.

LITTORAL WATER RIGHTS—The equivalent of Riparian Water Rights for a lake, reservoir, or other non-flowing body of water. As with riparian water rights, littoral water rights allow persons who own land adjacent to a body of water to make reasonable use of those waters on lands within the watershed. Littoral users share the waters among themselves and the concept of priority use (Prior Appropriation Doctrine) is not applicable. Under drought conditions, the lake or waterfront users also share shortages. Littoral rights cannot be sold or transferred to use on other (nonriparian) lands. Also see Riparian Doctrine, Riparian Water Rights, Appropriative Water Rights, Prescribed Water Rights, and Reserved Water Rights.

LITTORAL ZONE—(1) The shallow area near the shore of a non-flowing body of water; that portion of a body of fresh water extending from the shoreline lakeward to the limit of occupancy of rooted plants. (2) A strip of land along the shoreline between the high and low water levels.

LIVESTOCK WATER USE—Water use for stock watering, feed lots, dairy operations, fish farming, and other on-farm needs. Livestock as used here includes cattle, sheep, goats, hogs, and poultry. Also included are such animal specialties as horses, rabbits, bees, pets, fur-bearing animals in captivity, and fish in captivity. Also see Rural Water Use.

LOAD—The amount of material that a transporting agency, such as a stream, a glacier, or the wind, is actually carrying at a given time. Also, the amount of power delivered to a given point. In this respect:

[1] Base Load = The minimum load in a stated period of time. [2] Firm Load = That part of the system load which must be met on demand. [3] Peak Load = Literally, the maximum load in a stated period of time. Sometimes the term peak load is used in a general sense to describe that portion of the load above the base load.

LOAD ALLOCATION (LA)—(Water Quality) The portion of the pollution Load of a stream attributable to human Nonpoint Sources (NPS) of pollution. The amount of pollution from each point source is the Wasteload Allocation.

LOADING—Synonym for the pollution Load of a stream.

LOADING CAPACITY—The greatest amount of chemical materials or thermal energy that can be added to a stream without exceeding water quality standards established for that stream.

LOAD LINE—The line on a ship indicating the depth to which it sinks in the water when properly loaded. Also referred to as Plimsoll's Mark.

LOAM—A soil consisting of a friable mixture of varying proportions of clay, silt, and sand.

LOCAL FLOODING—Flood conditions which occur over a relatively limited area.

LOCAL (TEST-WELL) SITE DESIGNATION [Nevada]—The local test-well site designation used in Nevada is based on the identification of a site by hydrographic area and by the official rectangular subdivision of the public lands referenced to the Mount Diablo (located east of Walnut Creek, California) base line and meridian and is based on the Public Land Survey System (PLSS). Each site designation consists of four units: The first unit is the hydrographic area number. The second unit is the township, preceded by an N or S to indicate location north or south of the base line. The third unit is the range, preceded by an E to indicate location east of meridian. The fourth unit consists of the section number and letters designating the quarter section, quarter-quarter section, and so on (A, B, C, and D indicate the northeast, northwest, southwest, and southeast quarters, respectively), followed by a number indicating the sequence in which the site was recorded. For example, site 210 S12 E63 29DABC2 is in Coyote Spring Valley (hydrographic area 210). It is the second site recorded in the southwest quarter (C) of the northwest quarter (B) of the northeast quarter (A) of the southeast quarter (D) of Section 29, Township 12 South, Range 63 East, Mount Diablo base line and meridian.

LOCH—A lake; also, a bay or arm of the sea especially when nearly landlocked.

LOCK—A section of a waterway, such as a canal, closed off with gates, in which vessels in transit are raised or lowered by raising or lowering the water level of that section.

LOESS (SOIL)—A fine-grained, yellowish-brown, extremely fertile loam deposited mainly by the wind and found widely in North America, Asia, and Europe. Such soils are highly susceptible to water erosion.

LOG—An apparatus for measuring the rate of a ship's motion through the water that consists of a block fastened to a line and run out from a reel.

LOG AND SAFETY BOOM—A net-like device installed around the discharge facility of a dam to prevent logs, debris, or boaters from entering the outlet device.

LOGARITHM (LOG)—(Mathematics) The value of the exponent that a fixed number (the base) must have to equal a given number. It is calculated as bx = y, where b is the base and x is the logarithm. The base for the common logarithm is 10. As an example, the logarithm of 100 is 2 since 102 is equal to 100. This may also be written as log10 100 = 2. The base of the Natural Logarithm is approximately equal to 2.718282.

LOGARITHMIC TRANSFORMATION—(Statistics) A transformation applied to a Time Series to remove exponential growth, that is, when a series grows by some percentage of itself. The logarithmic transformation is frequently used in conjunction with simple (linear) differencing, especially for series like U.S. Gross Domestic Product (GDP), the Consumer Price Index (CPI), money supplies, and other time series subject to both growth and inflation.

LOGGED—Sodden, especially with water, i.e. Waterlogged.

LONG-TERM ACCEPTANCE RATE (of Soils)—A term used to describe the permeability or porosity of various soils and their ability to drain water; usually expressed in gallons per square foot per day.

LOSING STREAM—A stream or reach of a stream that is losing water by seepage into the ground. Also referred to as an Influent Stream. Also see Stream.

LOSSES INCIDENTAL TO IRRIGATION—The quantity of water depleted by irrigation in excess of the beneficial irrigation consumptive use.

LOTIC—(1) Of, relating to, or living in moving water. (2) Referring to a running water Ecosystem (streams and rivers). Compare to Lentic.

LOTIC ENVIRONMENT—Characterizing aquatic communities found in running water. Also referred to as a Lotic Habitat.

LOTIC SYSTEM—A flowing body of fresh water, such as a river or stream. Compare to Lentic System.

LOTIC WATERS—Describing the waters of rivers and streams (flowing waters) as compared to Lentic Waters of ponds or marshes (standing waters).

LOUGH—(Irish) (1) A lake. (2) A bay or an inlet of the sea.

LOW—(1) Situated below the surrounding surfaces as in water standing in low spots. (2) Of less than usual or average depth; shallow, as in the river is low.

LOWER BASIN STATES [Colorado River Basin]—Arizona, Nevada, and California. Also see Colorado River Compact.

LOW FLOW FREQUENCY CURVE—A graph showing the magnitude and frequency of minimum flow for a specified period of time (duration).

LOWLAND FLOODING—Inundation of the very lowest portions of floodplain areas near a river, stream or lake, which are normally subject to frequent flooding; usually considered nuisance flooding.

LOW-LEVEL DRAWDOWN—A discharge feature of a dam allowing water to be removed from the bottom of a reservoir.

LOW-LEVEL OUTLET—An opening at a low level from a reservoir generally used for emptying or for scouring sediment and sometimes for irrigation releases. Also referred to as Bottom Outlet or Sluiceway.

LOW-LYING—Lying close to water or ground level as low-lying coastal areas.

LOW-PRESSURE/LOW-VOLUME IRRIGATION—Irrigation systems that apply water directly, or very near to the soil surface, either above the ground or into the air, in discrete drops, continuous drops, small streams, mist, or sprays. These include drip systems, spray systems, jet systems, and bubbler systems. Also referred to as Micro or Trickle Irrigation. The efficiencies of these low pressure irrigation systems range from 75 to 95 percent; however, the average of 80 percent is commonly used.

LOW TIDE—(1) The lowest level of the tide. (2) The time at which the tide is lowest. Also referred to as Low Water.

LOW WATER (LW)—(1) The lowest level of water in a body of water, such as a river, lake, or reservoir. (2) (Navigation) The depth of a navigation channel is generally referenced to the low water stage which coincides with the lowest sustained flow over a 15-day period. On most streams this is referred to as "adopted low water"; on the lower Columbia, for example, it is the "Columbia River Datum".

LOW-WATER MARK (LWM)—The lowest level attained by a varying water surface level.

LTAR (of Soils)—See Long-Term Acceptance Rate (of Soils).

LUNETTE—A broad, low-lying, typically crescent-shaped mound of sandy or loamy matter that is formed by the wind, especially along the leeward side of a lake basin.

LYSIMETER—A field-situated tank or container filled with soil and planted to a crop. Crop consumptive use is measured by weighing or volumetrically monitoring this tank. Also a device for measuring the percolation of water through soils and for determining the soluble constituents removed in the drainage.

M&I (MUNICIPAL AND INDUSTRIAL) WATER USE—Water supplied for municipal and industrial uses provided through a municipal distribution system.

MAAR—A flat-bottomed, roughly circular volcanic crater of explosive origin that is often filled with water.

MACROCLIMATE—The general large-scale climate of a large area or country, as distinguished from Mesoclimate and Microclimate.

MACRONUTRIENT—A chemical element necessary in relatively large amounts (usually more than one part per million [ppm] in the plant) for the growth of plants.

MACROPHYTE—A member of the macroscopic plant life, especially of a body of water.

MACROPHYTIC ALGAE—Algal plants large enough either as individuals or communities to be readily visible without the aid of optical magnification.

MAELSTROM—A whirlpool of extraordinary size or violence.

MAGMA—(Geology) Molten rock found in the mantle, beneath the cruse of the earth. When forced toward the surface, magma cools and solidifies to become Igneous rock.

MAGMATIC WATER—Water driven out of Magma during crystallization.

MAGNETIC SEPARATION—The use of magnets to separate ferrous materials from mixed municipal waste stream.

MAIN—A relatively large pipe in a distribution system for drinking water or in a collection system for municipal wastewater. Of or relating to utility distribution mains for transferring water. Often used in the plural, as in water mains.

MAIN CANAL SYSTEM—A canal that delivers water from a primary source of supply to several points of diversion or canal-side turnouts to smaller distribution systems.

MAIN CHANNEL POOL [California]—A pool formed by mid-channel scour that encompasses greater than sixty percent of the wetted channel.

MAINSTEM—The major reach of a river or stream formed by the smaller tributaries which flow into it.

MAJOR FLOODING—Flood conditions resulting in extensive inundation and property damage. Typically characterized by the evacuation of people and livestock and the closure of both primary and secondary roads. Also see Minor Flooding and Moderate Flooding.

MAJORS—Larger Publicly-Owned Treatment Works (POTWs) with flows equal to at least one million gallons per day (mgd) or servicing a population equivalent to 10,000 person, certain other POTWs having significant water quality impacts. Contrast with Minors.

MAKEUP WATER—Water added to the flow of water used to cool condensers in electric power plants. This new water replaces condenser water lost during passage of the cooling water through cooling towers or discharged in blowdowns.

MANAGEMENT INDICATOR SPECIES (MIS)—(Environmental) A species selected because its welfare is presumed to be an indicator of the welfare of other species in the habitat. A species whose condition can be used to assess the impacts of management actions on a particular area. Managing for these species usually requires significant allocations of land or resources. Also see Indicator Species.

MANAGERIAL CONTROLS—(Irrigation) Methods of nonpoint source pollution control based on decisions about managing agricultural wastes or application times or rates for agrochemicals.

MANGROVE—Tropical evergreen trees and shrubs that have stilt like roots and stems, and often form dense thickets along tidal shores. Also see Mangrove Swamp.

MANGROVE SWAMP—A tidal swamp forest populated by plant species capable of growth and reproduction in areas that experience periodic tidal submergence in seawater with a resulting increase in saline conditions. These forests develop along coastal regions in tropical climates. Mangrove swamps are dominated by trees referred to as red mangrove, Rizophora mangle, black mangrove, Avicennia germinans, and white mangrove, Laguncularia racemosa. Typically, these trees have large, exposed root systems.

MANMADE LAKE—Any manmade body of water, including lakes, ponds, lagoons, and reservoirs (excluding tank-type reservoirs which are fully enclosed and contained), that are filled or refilled with water or reclaimed wastewater from any source and used for recreational, scenic, or landscape purposes, except swimming pools.

MANOMETER—An instrument for measuring pressure which usually consists of a U-shaped tube containing a liquid, the surface of which in one end of the tube moves proportionally with changes in pressure on the liquid in the other end. The term is also applied to a tube-type differential pressure gage.

MANTLE—(Geology) The division of the earth's interior between the core and the crust. It is composed mainly of silicate rock and is around 2,900 kilometers (1,800 miles) thick.

MARE CLAUSUM—A navigable body of water, such as a sea, that is under the jurisdiction of one national and closed to all others.

MARE LIBERUM—A navigable body of water, such as a sea, that is open to navigation by vessels of all nations.

MARE NOSTRUM—A navigable body of water, such as a sea, that is under the jurisdiction of one nation or that is shared by two or more nations.

MARICULTURE—The cultivation of marine organisms for use as a food resource. Compare to Aquiculture.

MARINA—A water-based facility used for storage, service, launching, operation, or maintenance of watercraft.

MARINE—(1) Of or pertaining to the sea; having to do with the ocean or the things peculiar to the ocean. (2) A system within the Wetlands and Deepwater Habitat Classification System. Also see Deepwater Habitats and Wetlands. [See Appendix W-3 for an explanation of the Wetland and Deepwater Habitat Classification System according to USFWS criteria.]

MARINE LIFE—Plants and animals of the sea, from the high-tide mark along the shore (also see Shore Life) to the depths of the ocean. These organisms fall into three major groups: (1) Benthos—plants such as kelp and animals such as brittle stars that live on or depend on the bottom; (2) Nekton—swimming animals such as fishes and whales that move independently of water currents; and (3) Plankton—various small to microscopic organisms that are carried along by the currents.

MARINE PROTECTION, RESEARCH, AND SANCTUARIES ACT (MPRSA)—A 1972 federal law that includes provisions requiring citizens of the United States to obtain a permit from the U.S. Environmental Protection Agency (EPA) before disposing of materials in the oceans. Subsequent amendments to the act have limited the types of waste that may be permitted for ocean disposal.

MARINE SANITATION DEVICE—Any equipment or process installed on board a vessel to receive, retain, treat, or discharge sewage.

MARINE (NAUTICAL) SURVEYING—The branch of surveying that comprises a topographic survey of the coast and a hydrographic survey of adjacent waters. Also see National Oceanic and Atmospheric Administration (NOAA).

MARITIME LAW—Branch of law relating to commerce and navigation on the high seas and on other navigable waters. Specifically, the term refers to the body of customs, legislation, international treaties, and court decisions pertaining to ownership and operation of vessels, transportation of passengers and cargo on them, and rights and obligations of their crews while in transit.

MARK—(Nautical) A knot or piece of material placed at various measured lengths on a lead line to indicate the depth of the water, or, more generally, measurement indicators of water depth, e.g., a Plimsoll mark.

MARL—A mixture of clays, carbonates of calcium and magnesium, and remnants of shells, forming a loam useful as a fertilizer.

MARSH—A term frequently associated with Wetlands. An area of soft, wet, low-lying land, characterized by grassy vegetation that does not accumulate appreciable peat deposits and often forming a transition zone between water and land. A tract of wet or periodically inundated treeless land, usually characterized by grasses, cattails, or other monocotyledons (sedges, lilies, irises, orchids, palms, etc.). Marshes may be either fresh or saltwater, tidal or non-tidal.

MARSH GAS—Gas produced during the decomposition of organic material buried in wetland soils. The primary gas produced is Methane, CH4.

MARSHLAND—Treeless land in which the water table is at, above, or just below the surface of the ground; it is dominated by grasses, reeds, sedges, and cattails. These plants typify Emergent Vegetation, which has its roots in soil covered or saturated with water and its leaves held above water.

MARSH, TIDAL—A low, flat area traversed by interlacing channels and tidal sloughs and periodically inundated by high tides. Vegetation in such areas usually consists of salt-tolerant plants, or Halophytes.

MASS CURVE—A graph of the cumulative values of a hydrologic quantity (such as precipitation or runoff), generally as the Ordinate (y-axis), plotted against time or date as the Abscissa (x-axis). Mass curves may also be used to show the excavated or filled material per unit of distance for a canal or other earth structure.

MASS MOVEMENT—(Geology) The downslope movement of a portion of the land's surface (i.e., a single landslide or the gradual downhill movement of the whole mass of loose earth material) on a slope face. All movement of soil and bedrock materials occurring below the soil surface such as landslips, landflows, rock slides, slumps, etc.

MASS SPECTROMETRY—An analytical technique wherein ions are separate according to their ratio of charge to mass. From the mass spectrum produced, the atomic weight of the particle can be deduced.

MATHEMATICAL MODEL—A representation of physical laws or processes expressed in terms of mathematical symbols and expressions (i.e., equations). The model is used as a basis for computer programs for examining the effect of changing certain variables in the analysis of the effect of flow changes in a water delivery system, for example. Also see Econometric Model Building.

MATRIC POTENTIAL—The work per unit quantity of pure water that has to be done to overcome the attractive forces of water molecules and the attraction of water to solid surfaces. The matric potential is negative above a water table and zero below a free water table.

MATRIX—(1) Solid framework of a porous material or system. (2) The material in which an environmental sample is embedded or contained, whether it is soil, water, dried biomass, or other substance.

MATRIX INTERFERENCE—The adverse influence of the environmental sample Matrix on the ability to detect the presence or amount of a chemical substance in the sample.

MATTER—Anything which is solid, liquid, or gas and has mass.

MATTRESS—(Environmental) A blanket of poles, brush, or other material interwoven or otherwise lashed together and weighted with rock, concrete blocks, or held in place to cover an area subject to scouring by flowing water.

MASONRY DAM—A dam constructed mainly of stone, brick, or concrete blocks that may or may not be joined with mortar. A dam having only a masonry facing should not be referred to as a masonry dam. Also see Dam.

MAXIMUM ACCEPTABLE TOXICANT CONCENTRATION (MATC)—The highest concentration at which a pollutant can be present and not exert an adverse effect on the Biota, used to experimentally determine the toxicity of the chemical.

MAXIMUM CONTAMINANT LEVEL (MCL)—The designation given by the U.S. Environmental Protection Agency (EPA) to water quality standards promulgated under the Safe Drinking Water Act (SDWA) (Public Law 93-523). As prescribed by the EPA after research of a contaminant, the MCL is the greatest amount of a contaminant that can be present in drinking water without causing a risk to human health. MCLs are set for certain inorganic and organic chemicals, turbidity, coliform bacteria, and certain radioactive materials. Also see Drinking Water Standards and Drinking Water Standards [Nevada].

MAXIMUM CONTAMINANT LEVEL GOAL (MCLG)—The designation given by the U.S. Environmental Protection Agency (EPA) to water quality standards promulgated under the Safe Drinking Water Act (SDWA) (Public Law 93-523). This is a number which is associated with no adverse health effects. If someone drinks water for a lifetime containing the contaminant at this level, there should be no ill effects. As implied by the name, this number is a goal, not an enforceable standard. For chemicals which are believed to cause cancer (carcinogens), the MCLG is set at zero because there is no known safe level for this type of chemical.

MAXIMUM DEPTH (RESERVOIR)—The greatest depth of the body of water measured in feet and 10ths of feet.

MAXIMUM HOLDING TIME—The longest time period that water samples can be retained between the taking of the sample and the laboratory analysis for a specific material before the results are considered invalid. The times vary from none in the case of the test for residual chlorine levels to six months for the testing of radioactivity. Some types of analyses require that preservatives be added to the sample, and some require storage of samples at refrigerated temperatures.

MAXIMUM PROBABLE FLOOD—The largest flood for which there is any reasonable expectancy.

MAXIMUM SUSTAINABLE YIELD—The greatest amount of a renewable natural resource (e.g., forests or wildlife) that can be removed without diminishing the continuing production and supply of the resource.

MAXIMUM THERMOMETER—An instrument used to measure the highest temperature since its last setting. A constriction near the bulb prevents the mercury from returning to the bulb as the temperature falls.

MAXIMUM WATER SURFACE (RESERVOIR)—The maximum water-surface elevation is the highest water surface elevation for which the dam is designed. It is also the top of the surcharge capacity.

MBAS (METHYLENE BLUE ACTIVE SUBSTANCES)—Generally interpreted as an indication of the presence of detergents in a solution.

MCL—See Maximum Contaminant Level.

MCLG—See Maximum Contaminant Level Goal.

MEADOW—An area of moist low-lying grassland usually along a watercourse supporting a more dense stand of grasses and perhaps dwarf shrubs as compared to adjacent more arid uplands.

MEADOW, DRY—An area where during the spring, early summer, and in some open winters there is a greenup of succulent vegetation. These areas are relatively few in number and highly important for sustaining animal populations within whose habitat these meadows exist. During the summer and fall there is normally dry vegetation.

MEADOW, WET—A perennial wet area where the water table is maintained at or close to the ground surface to maintain shallow rooted water-dependent vegetative complexes.

MEAN—(Statistics) The sum of a set of observations divided by the number of observations. Also referred to as Arithmetic Mean and Sample Mean. Compare to Mode and Median.

MEAN ANNUAL FLOOD—The average of all the annual flood stages or discharges of record. It may be estimated by regionalization, correlation, or any other process that can furnish a better estimate of the long-term average than can the observed data. Some investigators arbitrarily define the mean annual flood as the stage or discharge having an exceedence interval of 2.33 years.

MEAN ANNUAL PRECIPITATION—The average of all annual precipitation values known, or an estimated equivalent value derived by such methods as regional indexes or Isohyetal maps.

MEAN ANNUAL RUNOFF—The average value of all annual runoff amounts usually estimated from the period of record or during a specified base period from a specified area.

MEAN ANNUAL TEMPERATURE—The average of the daily maximum and minimum temperatures.

MEAN DEPTH—The average depth of water in a stream channel or conduit. It is equal to the cross-sectional area divided by the surface width.

MEAN FREE PATH—The average distance that a molecule in a fluid (air or water) moves before colliding with another molecule.

MEAN HIGH WATER (MHW)—The average height of the high water over 19 years.

MEAN HIGHER HIGH TIDE—The average height of the higher of two unequal daily high tides over 19 years.

MEAN LOW WATER (MLW)—The average height of the low water over 19 years.

MEAN LOWER LOW WATER—The average height of the lower of two unequal daily low tides over 19 years. Tides of the northeastern Pacific Ocean are characterized as mixed, with two unequal highs and two unequal lows daily. The plane of reference for navigation channels is the long term average of the daily lower lows, termed mean lower low water.

MEAN SEA LEVEL (MSL)—The level of the surface of the sea between mean high and mean low tide; used as a reference point for measuring elevations.

MEAN TIDE LEVEL—A plane midway between mean high water and mean low water.

MEANDER—The turn of a stream, either live or cut off. The winding of a stream channel in the shape of a series of loop-like bends.

MEANDER AMPLITUDE—The distance between points of maximum curvature of successive meanders of opposite phase in a direction normal to the general course of the Meander Belt, measured between centerlines of channels.

MEANDER BELT—The zone along a valley floor that encloses a meandering river.

MEANDER BREADTH—The distance between the lines used to define the Meander Belt.

MEANDER LENGTH—The distance in the general course of the meanders between corresponding points of successive meanders of the same phase.

MEANDER LINE—A line delineated by government survey for the purpose of defining the bends or windings of the banks of a stream or the shore of a body of water, and as a means for ascertaining the quantity of land embraced by the survey.

MEAN MONTHLY TEMPERATURE—The average of the mean monthly maximum and minimum temperatures.

MEASUREMENT UNCERTAINTY—The estimated amount by which the measured quantity may depart from the true value.

MEASURING WEIR—A shaped notch, typically in rectangular, trapezoidal, or triangular shape, through which flowing water is measured.

MECHANICAL AERATION—The use of mechanical energy to inject air into water to cause a waste stream to absorb oxygen.

MECHANICAL DISPERSION—Process whereby solutes are mechanically mixed during advective transport, caused by the velocity variations at the microscopic level. Synonymous with Hydraulic Dispersion. Also see Coefficient of Mechanical Dispersion.

MECHANICAL TURBULENCE—The erratic movement of air or water influenced by local obstructions.

MEDIAN—(Statistics) In a set of observations, the middle-most value with an equal number of observations lying above and below the median value. Also see Mean and Mode.

MEDIAN STREAM FLOW (MEDIAN HYDRO)—The rate of discharge of a stream for which there are equal numbers of greater and lesser flow occurrences during a specified period.

MEDIAN TOLERANCE LIMIT—The concentration of a test substance at which just 50 percent of the test animals are able to survive for a specified period of exposure.

MEDITERRANEAN—Surrounded nearly or completely by dry land. Used of large bodies of water, such as lakes or seas.

MEDITHERMAL—(Climatology) The present period of climatological conditions, beginning approximately 4,500 years ago and following the warmer Altithermal period. Also see Anathermal.

MEDIUM-SIZE WATER SYSTEM—A water system that serves 3,300 to 50,000 customers.

MEGAWATT (MW)—A unit of electricity equivalent to 1 million watts or 1,000 kilowatts (KW).

MELT—To be changed from a solid to a liquid state by application of heat or pressure or both.

MELTING—The changing of a solid into a liquid as in changing ice to water.

MELTING POINT—The temperature at which a solid changes to a liquid. The temperature will vary, and is consistent at equal temperatures and pressures, for each element or solid. At a standard barometric pressure of one atmosphere, water will change from a solid to a liquid at 0°C (32°F).

MELTWATER—Water that comes from the melting ice of a glacier or a snow bank.

MEMBRANE—A plastic material used in the electrodialysis and reverse osmosis processes. Electric current is the driving force that moves salt ions through solution in electrodialysis, and hydraulic pressure the driving force in reverse osmosis.

MEMBRANE FILTER—Filter made of plastic or modified cellulose and having a known pore diameter. Such filters are used in the bacteriological examination of water and the separation of suspended matter before laboratory analyses. In additional to their analytical use, these filters area also used for public health purposes as well as for the sterilization of liquids. The membranes are available in a variety of sizes, with a diameter of 47-50 millimeters being the most common. Membrane filter water purification technologies are rapidly emerging as a viable and cost effective water treatment option for municipalities confronted with complex regulatory issues and increasingly stringent water treatment regulations. Membranes can be used as the primary means to remove materials from water, but they can also be used in conjunction with other physical, chemical, or biological processes to either separate the phases of water treatment or isolate specific organisms.

MEMBRANE FILTER METHOD—A procedure used to recover and count bacteria in samples of liquid substances, such as water. The liquid is drawn through a Membrane Filter using a slight vacuum, with the bacteria in the liquid being retained on the filter. The filter disk is then transferred to a medium suitable for the growth and incubation of the bacteria.

MENISCUS—The curved surface of the liquid at the open end of a capillary column.

MERE—(Middle English, from Old English) A small lake, pond, or marsh. Also, an expanse of standing water; a lake, pool.

MEROMICTIC LAKE—A lake in which some water remains partly or wholly unmixed with the main water mass at circulation periods. The process leading to a meromictic state is called Meromixts. The perennially stagnant deep layer of a meromictic lake is the Monimolimnion. The part of the meromictic lake in which free circulation can occur is the Mixolimnion. The boundary between the monimolimnion and the mixolimnion is the Chemocline. Compare to Dimictic Lake.

MEROMIXIS—A condition of permanent stratification of water masses in lakes.

MESA—Table land, flat in nature, moderately elevated, and well drained.

MESIC—Refers to environmental conditions that have medium moisture supplies as compared to wet conditions (Hydric) or dry conditions (Xeric).

MESOCLIMATE—The climate of small areas of the earth's surface; it may not be representative of the general climate of the district; intermediate in scale between Macroclimate and Microclimate. Places considered in mesoclimatology include small valleys, "frost hollows", forest clearings and open spaces in towns.

MESOHALINE—Term to characterize waters with salinity of 5 to 18 0/00 (parts per thousand), due to ocean-derived salts.

MESOPHYTE—A plant that grows under medium or usual conditions of atmospheric moisture supply, as distinguished from one which grows under dry or desert conditions (Xerophyte) or very wet conditions (Hydrophyte).

MESOSALINE—Term to characterize waters with salinity of 5 to 18 0/00 (parts per thousand), due to land-derived salts.

MESOSPHERE—The division of the Atmosphere above the Stratosphere. The mesosphere begins about 50 kilometers (31 miles) in altitude and extends to about 80 kilometers (50 miles).

MESOTROPHIC (WATER)—Pertaining to a lake or other body of water characterized by moderate nutrient concentrations such as nitrogen and phosphorous and resulting significant productivity. Such waters are often shallow, with algal blooms and periods of oxygen deficiency. Slightly or moderately eutrophic water can be healthful and support a complex web of plant and animal life. However, such waters are generally undesirable for drinking water and other needs. Degrees of Eutrophication typically range from Oligotrophic water (maximum transparency, minimum chlorophyll-a, minimum phosphorus) through Mesotrophic, Eutrophic, to Hypereutrophic water (minimum transparency, maximum chlorophyll-a, maximum phosphorus). Also see Carlson's Trophic State Index (TSI) and (Mean) Trophic State Index (TSI).

META- OR MET- (Prefix)— Derived from by loss of water, as meta phosphoric acid.

METABOLISM—(Biology) The sum of the processes concerned in the building up of protoplasm and its destruction incidental to life; the chemical changes in living cells, by which the energy is provided for the vital processes and activities, and new material is assimilated to repair the waste. Metabolism may be considered as including two aspects or processes: constructive metabolism (termed Anabolism or Assimilation) or destructive metabolism (termed Catabolism or Dissimilation). Anabolism and Catabolism go on together, but one may predominate and obscure the other. Also see Zone of Net Metabolic Production.

METALIMNION—The middle layer of a thermally stratified lake or reservoir. In this layer there is a rapid decrease in temperature with depth. Also referred to as Thermocline.

METAMORPHIC ROCK—(Geology) A sedimentary or igneous rock that has been changed by pressure, heat, or chemical action. For example, limestone, a sedimentary rock, is converted to marble, a metamorphic rock.

METAMORPHISM—A change in the constitution of rock; specifically a pronounced change effected by pressure, heat, and water that results in a more compact and more highly crystalline condition.

METEORIC WATER—Ground water derived primarily from precipitation and the atmosphere.

METEOROLOGY—The science that deals with the phenomenon of the atmosphere, especially weather and weather conditions.

METER—A unit of length which constitutes the basis of the Metric System, was intended to be, and is very nearly, one ten-millionth part of the distance measured on a meridian of the earth from the equator to the pole, being equal to 39.37 U.S. inches or about 3 feet 3-3/8 inches. See Metric System.

METHANE—A colorless, nonpoisonous, flammable gas, CH4, created by Anaerobic decomposition of organic compounds.

METHOD BLANK—Laboratory grade water taken through the entire analytical procedure to determine if samples are being accidentally contaminated by chemicals in the lab.

METHYLCELLULOSE—Any of various gummy products of cellulose methylation that swell in water and are used especially as emulsifiers, adhesives, thickeners, and bulk laxatives.

METHYLENE BLUE—A basic aniline dye, C16H18N3SCl · 3H2O, that forms a deep blue solution when dissolved in water. It is used as an antidote for cyanide poisoning and as a bacteriological stain.

METHYLENE BLUE ACTIVE SUBSTANCES (MBAS)—Any material which forms a blue colored salt with methylene blue, but generally interpreted as an indication of the presence of detergents in solution.

METRIC SYSTEM—A decimal system of measures and weights with the meter and the gram as bases. The units of the metric system at the outset were all derived from the unit of length, the Meter, which was intended to be, and is very nearly, one ten-millionth part of the distance measured on a meridian of the earth from the equator to the pole, being equal to 39.37 U.S. inches or about 3 feet 3-3/8 inches. Upon the meter were originally based the other primary units of measure: the square meter (area), the cubic meter (volume), the Liter (liquid volume), and the Gram (mass and weight). It was found, however, that masses could be compared with a higher degree of accuracy than that with which volumes could be determined, and it was therefore preferable to have a material standard of mass specifically defined rather than one derived from the unit of length through the unit of volume. A definite mass, the International Prototype Kilogram was, therefore, adopted as the standard of mass, and the unit of volume, the liter, was then redefined in terms of the standard of mass; the liter being defined as the volume of a kilogram of pure water at the temperature of its maximum density (4°C or 39.2°F), and equal to 1.000027 cubic decimeters. Also see Avoirdupois Weight.

STANDARD METRIC TABLES

[1] Length

Metric Name Myriameter Kilometer Hectometer Decameter Meter Decimeter Centimeter Millimeter

[2] Area

Metric Name Hectare Are Centiare

[3] Volume

Metric Name Measure Measure Kiloliter Hectoliter Decaliter Liter Deciliter Centiliter Milliliter

Volume Table Notes:

dm = decimeter = 1/10 meter cm = centimeter = 1/100 meter bu = bushel = 4 pecks = 32 quarts pk = peck = 1/4 bushel = 8 quarts qt = quart = 2 pints = 1/4 gallons liq qt = liquid quart = 1.1635 (dry) quarts gill = 1/4 pint fl dram = fluid dram = 1/16 ounce = 27.34375 grains = 1.772 grams

[4] Weight

Metric Name Quantity Metric Ton Quintal Myriagram Kilogram Hectogram Decagram Gram Decigram Centigram Milligram

MGD—Million gallons per day. Used in many applications of water and wastewater treatment processes.

MICROBE—Short for Microorganism. Small organisms that can be seen only with the aid of a microscope. The term encompasses viruses, bacteria, yeast, molds, protozoa, and small algae; however, microbe is used most frequently to refer to bacteria. Microbes are important in the degradation and decomposition of organic materials added to the environment by natural and artificial mechanisms. Also referred to as Germs.

MICROBIAL GROWTH—The activity and growth of microorganisms such as bacteria, algae, diatoms, plankton, and fungi.

MICROBIAL LOAD—The total number of bacteria and fungi in a given quantity of water or soil or on the surface of food. The presence of the bacteria and fungi may not be related to the presence of disease-causing organisms.

MICROBIOLOGICAL ANAEROBIC DEGRADATION—The use of Microbes, either already present at a site or introduced for a specific treatment process, to degrade and render harmless hazardous wastes and toxic compounds in soil and water. Under such conditions, the microbes are used to break down organic compounds in contaminated soil and groundwater in an environment of little or no oxygen. Also see Attenuation and Natural Attenuation.

MICROBIOLOGICAL TUBERCULATION—(Water Quality) A condition in older water distribution pipes characterized by reddish brown mounds of various heights attached to the interior of the pipe wall. These mounds are the result of many years of iron and manganese bacterial growth that deposit iron and/or manganese oxides along with particulate matter from the water trapped in the biomass from generations of bacteria. An aging distribution system experiencing this problem is typically characterized by red water, taste and odor problems, turbidity, reduced pressure and flow rates, and a low chlorine residual. Iron bacteria are very common in all water sources with over twenty different iron bacteria that can cause tuberculation. They are generally considered to be non-pathogenic. Tuberculation usually begins with a slime that may show signs of iron oxide precipitation. The iron bacteria, which attach themselves to the interior surface of the pipe, metabolize ferrous ions from the water as an energy source, precipitating ferrous oxide which becomes trapped in the biomass of the tuberculation. In the past, tuberculation usually resulted in replacement of the water distribution pipe; however, more recently, chemical treatments of isolated sections of pipeline have proven both highly effective and less costly. Also referred to as Tuberculation.

MICROBIOLOGY—The study of organisms that can be seen only with the aid of a microscope. The science deals with the structure and chemical composition of various Microbes, the biochemical changes within the environment that are caused by members of this group, the diseases caused by microbes, and the reaction of animals, including humans, to their presence.

MICROBIOTA—The plants, animals, and microorganisms that can only be seen with the aid of a microscope.

MICROCLIMATE—The local climate conditions, brought about by the modification of general climatic conditions by local differences in elevation and exposure. The detailed climate of a very small area of the earth's surface. Also, the localized climate conditions within an urban area or neighborhood.

MICROCOSM—A laboratory model of a natural Ecosystem in which certain environmental variables can be manipulated to observe the response. The model test results are not always applicable to an actual ecosystem because the microcosm is, of necessity, a simplified collection of selected physical, chemical, and biological ecosystem components.

MICROFAUNA—Animals invisible to the naked eye, such as copepods and mites.

MICROFILTRATION—(Water Quality) Similar to Reverse Osmosis, the microfiltration process utilizes filtering membranes with larger-sized pores to remove suspended particles from water. This water filtration technique provides an economical and practical treatment process for smaller-sized water systems. Unlike other treatment processes, microfiltration relies on mechanical retention instead of chemical treatment and so long as the pore size of the membranes is smaller than the contaminant to be filtered, the constituent will not pass through.

MICROFLORA—Plants invisible to the naked eye, such as diatoms and algae.

MICROGRAMS PER LITER (g/l)—One one-thousandth of a Milligram per Liter (mg/l). This measure is equivalent to Parts Per Billion (PPB).

MICRON (µ)—A unit of length equivalent to a micro-meter (µm), or one-millionth of a meter (10-6 meter). Micro-meter is the preferred term.

MICRONUTRIENT—A chemical element required only in small amounts (usually less than one part per million [ppm] in the plant) for the growth of plants.

MICROSCOPIC PARTICULATE ANALYSIS (MPA)—(Water Quality) A process used to assess water treatment plant performance. This form of analysis compares type, size, and quantities of Bioindicators, or microbiota (1-600 m) in particles found in Raw Water to those found in the Finished Water. This method is particularly effective in evaluating filtration efficiencies, as log reduction, of conventional treatment systems, as well as for on-site evaluation of alternate filtration technologies.

MICROSYSTEM IRRIGATION—Method of precisely applying irrigation water to the immediate root zone of the target plant at very low rates.

MICROWAVE OVEN—An oven in which food is cooked by the heat produced by the absorption of microwave energy by water molecules in the food.

MID-SERAL CONDITION—Synonymous with fair ecological conditions.

MIDSTREAM—The middle part of a stream.

MIGRATION—The movement of oil, gas, contaminants, water, or other liquids through porous and permeable rock.

MILLDAM—A dam constructed across a stream to raise the water level so that the overflow will have sufficient power to turn a mill wheel.

MILLIEQUIVALENTS PER LITER (MEQ/L)—An expression of the concentration of a material dissolved in water, calculated by dividing the concentration, in milligrams per liter, by the Equivalent Weight of the dissolved material. For example, the equivalent weight of aluminum is 9.0. A water concentration of aluminum of 1.8 milligrams per liter equals an aluminum concentration of 0.2 milliequivalent per liter.

MILLIGRAM (MG)—One-thousandth of a gram.

MILLIGRAMS PER LITER (mg/l)—A unit of the concentration of a constituent in water or wastewater. It represents 0.001 gram of a constituent in 1.000 milliliter (ml) of water. It is approximately equal to one part per million (PPM). The term has replaced parts per million in water quality management.

MILLION GALLONS PER DAY (MGD)—A rate of flow of water equal to 133,680.56 cubic feet (cf) per day, or 1.5472 cubic feet per second (cfs), or 3.0689 acre-feet per day. A flow of one million gallons per day (mgd) for one year equals 1,120 acre-feet (365 million gallons).

MILLIPORE FILTER—A thin membrane of modified cellulose that is used as a filter in the bacteriological examination of water or wastewater. The filter is typically used to filter a given quantity of aqueous sample followed by transfer of the filter to the surface of a special medium to allow for the growth of the bacteria that have been retained by the filter. At one time the only commercial source of these filters was the Millipore Corporation, although presently a variety of sources are now available. Even so, the common name Millipore filter has been retained.

MILLPOND—A pond created by damming a stream to produce a head of water for operating a mill.

MILLRACE—(1) The fast-moving stream of water that drives a mill wheel. (2) The channel for the water that drives a mill wheel. Also referred to as Millrun.

MILLSTREAM—The rapid stream of water flowing in a Millrace.

MILL WHEEL—A wheel, typically driven by water, that powers a mill.

MINE DRAINAGE—Water pumped or flowing from a mine.

MINERAL—Any naturally occurring inorganic material with an orderly internal arrangement of atoms and specific physical and chemical properties.

MINERALIZATION—(1) The general process by which elements present in organic compounds are eventually converted into inorganic forms, ultimately to become available for a new cycle of plant growth. (2) The process whereby concentrations of minerals, such as salts, increase in water, often as a natural process resulting from water dissolving minerals found in rocks and soils through which it flows.

MINERAL RESOURCE—Known mineral deposits of an area which have present or future utility.

MINERAL SOIL—Soil composed of predominantly mineral rather than organic materials.

MINERAL WATER—Naturally occurring or prepared water that contains dissolved mineral salts, elements, or gases, often used therapeutically. Also see Bottled Water [General], Bottled Water [Food and Drug Administration], and Bottled Water [Nevada].

MINER'S INCH [Western United States]—The rate of discharge through an orifice one inch square under a specific head. An old term used in the western United States, now seldom used except where irrigation or mining water rights are so specified. The equivalent flow in cubic feet per second is fixed by state statute. One miner's inch is equivalent to 0.025 cubic foot per second in Arizona, California, Montana, Nevada, and Oregon; 0.020 cubic foot per second in Idaho, Kansas, Nebraska, New Mexico, North and South Dakota, and Utah; 0.026 cubic foot per second in Colorado; and 0.028 cubic foot per second in British Columbia.

MINER'S INCH [Nevada]—Defined as a rate of flow or discharge equivalent to 1/40 of 1 (0.025) cubic foot per second (cfs).

MINE WASH—Water-deposited accumulation of sandy, silty, or clayey material recently eroded in mining operations.

MINIM—A unit of fluid measure, in the United States equal to 1/60 of a fluid dram (0.0616 milliliters, or 0.00208 fluid ounces), and in Great Britain equal to 1/20 of a scruple (0.0592 milliliters or 0.00200 fluid ounces).

MINIMAL FLOOD HAZARD AREAS—Areas between the 100-year and the 500-year flood boundaries are termed Moderate Flood Hazard Areas. The remaining areas are above the 500-year flood level and are termed Minimal Flood Hazard Areas.

MINIMUM FLOW APPROPRIATION—An appropriation designed to preserve a specified minimum flow in a stream. When the flow in the stream drops to that which is specified in the appropriation, junior appropriations will be required to stop diverting water in order to maintain the minimum flow. See (Prior) Appropriation Doctrine.

MINIMUM MOISTURE CONTENT—The amount of water in soil during the driest time of the year.

MINIMUM POOL—A term used to describe the lowest level of reservoir capacity safe for maintaining fish and aquatic life or for some other designated beneficial purpose. This term differs from Dead Storage Capacity in that the reservoir level may still be reduced below minimum pool, whereas the dead storage capacity represents a level below the lowest outlet level.

MINIMUM STREAMFLOW—The specific amount of water reserved to support aquatic life, to minimize pollution, or for recreation. It is subject to the priority system and does not affect water rights established prior to its institution.

MINIMUM THERMOMETER—An instrument with an index which remains at the lowest temperature occurring since its last setting.

MINIMUM TILLAGE FARMING—A farming technique that reduces the degree of soil disruption. Crop residues are not plowed under after harvest, and special planters dig narrow furrows in the crop residue when new seeds are sown. Advantages of the technique include reductions in energy consumption by farm equipment, less soil erosion, and lower soil moisture losses during the fallow season. Disadvantages include the possibility of encouraging insect pests by leaving the crop residue in the field and the use of herbicides to control weeds in the place of mechanical cultivation. Sometimes incorrectly termed No-Till Farming.

MINING (of an Aquifer)—Withdrawal over a period of time of ground water that exceeds the rate of recharge of the aquifer.

MINING WATER USE—Water use for the extraction of minerals occurring naturally including solids, such as coal and ores; liquids, such as crude petroleum; and gases, such as natural gas. Also includes uses associated with quarrying, well operations (Dewatering), milling (crushing, screening, washing, flotation, and so forth), and other preparations customarily done at the mine site or as part of a mining activity, such as dust control, maintenance, and wetland restoration. Generally, most of the water used at a mining operation is self-supplied. Also see Self-Supplied Water.

MINOR FLOODING—Flooding resulting in minimal or no property damage but some public inconvenience. Also referred to as Nuisance Flooding. Also see Major Flooding and Moderate Flooding.

MINORS—Publicly Owned Treatment Works (POTWs) with flows of less than 1 million gallons per day. Contrast with Majors.

MIRAGE—An optical phenomenon that creates the illusion of water, often with inverted reflections of distant objects, and results from distortion of light by alternate layers of hot and cool air. Also referred to as Fata Morgana.

MIRE—(1) An area of wet, soggy, muddy ground; a bog. (2) Deep, slimy soil or mud.

MISCIBLE (Liquids)—Liquids which are soluble in each other.

MISCIBLE DISPLACEMENT—Mutual mixing and movement of two fluids that are soluble in each other. Synonymous with Miscible-Phase Displacement.

MISMATCH—A condition in which water supplied to a given point in a conveyance or distribution system does not equal the demand for water at that point.

MISSED DETECTION—(Water Quality) The situation that occurs when a test indicates that a tank is "tight" when in fact it is leaking.

MIST—(1) A mass of fine droplets of water in the atmosphere near or in contact with the earth; liquid particles measuring 40 to 500 microns, formed by condensation of vapor. By comparison, fog particles are smaller than 40 microns. (2) Water vapor condensed on and clouding the appearance of a surface.

MITIGATION—(1) (Environmental, General) Actions designed to lessen or reduce adverse impacts; frequently used in the context of environmental assessment. (2) (NEPA) Action taken to avoid, reduce the severity of, or eliminate an adverse impact. Mitigation can include one or more of the following:

[1] avoiding impacts; [2] minimizing impacts by limiting the degree or magnitude of an action; [3] rectifying impacts by restoring, rehabilitating, or repairing the affected environment; [4] reducing or eliminating impacts over time; and [5] compensating for the impact by replacing or providing substitute resources or environments to offset the loss.

MIXED LIQUOR—(Water Quality) In wastewater treatment, the liquid in the aeration tank of an activated sludge system; a mixture of activated sludge and water containing organic matter undergoing activated sludge treatment in an aeration tank.

MIXED LIQUOR SUSPENDED SOLIDS (MLSS)—The quantity of suspended solids in the aeration tank of an activated sludge. Reported in units of milligrams per liter (mg/l).

MIXED LIQUOR VOLATILE SUSPENDED SOLIDS (MLVSS)—That portion of Mixed Liquor Suspended Solids (MLSS) that will vaporize when heated to 600°C (1,112°F). This volatile fraction is mainly organic material and thus indicates the biomass present in the aeration tank. The material that does not vaporize in this test, mostly inorganic substances, is said to be fixed.

MIXED MEDIA FILTRATION—A system using two or more dissimilar granular materials (such as anthracite, sand and garnet) blended by size and density. Such a filter is graded from coarse to fine in the direction of flow.

MIXOHALINE—Term to characterize water with salinity of 0.5 to 30 0/00 (parts per thousand), due to ocean salts. The term is roughly equivalent to the term brackish.

MIXOSALINE—Term to characterize water with salinity of 0.5 to 30 0/00 (parts per thousand), due to land-derived salts.

MIXOLIMNION—The uppermost region in a Meromictic Lake.

MIZZLE—To rain in fine, mist-like droplets; to drizzle. Also, a mist-like rain, a drizzle.

MOAPA NATIONAL WILDLIFE REFUGE (NWR) [Nevada]—One of the nine National Wildlife Refuges (NWR) located in the State of Nevada, the Moapa NWR was established in 1979 in order to protect and secure habitat for the Endangered Moapa dace and a candidate for listing, the White River springfish. The refuge contains 32 acres (0.05 square mile) and is located just north of the Moapa River Indian Reservation, 5 miles northwest of Moapa, Nevada, located in Clark County. Also see National Wildlife Refuge (NWR) System and National Wildlife Refuges (NWR) [Nevada].

MOAT—A deep, wide ditch, usually filled with water, typically surrounding a fortified medieval town, fortress, or castle as a protection against assault.

MODE—(Statistics) In a set of observations, the most frequently occurring value. Also see Mean and Median.

MODEL—(Statistics) A simulation, by descriptive, conceptual, statistical, or other means, of a process or thing that is difficult or impossible to observe directly, as in an Economic Consumption Model or a River Flow Model. A descriptive or conceptual model is one which represents the structure or mechanisms of a model but does not specify the relationships in numerical form. The concept of a (simulation) quantitative model is to approximate reality by means of a quantifiable process such as a mathematical equation or series of equations. In this way the model may be used to simulate various changes in conditions in a "what if" or predictive framework. The fundamental premise of model building is that within some defined bounds of statistical probability a model may be constructed based upon the past behavior of some numeric quantity or variable, or a set of such variables, so as to be able to predict the future behavior of that variable. The actual structure of the model represents the underlying set of assumptions about a phenomenon based on the model builder's view of reality, theoretical underpinnings, proven or probable causal relationships, and deductions and inferences from past observations and experience. To be manageable and useful as a predictive tool, the model must sufficiently simplify the complexities of reality so as to lend itself to some quantifiable structure. However, this simplifying process must not be so extensive as to weaken the model's validity and negate its usefulness as an explanatory and predictive tool.

(ECONOMETRIC) MODEL BUILDING—(Statistics) An iterative process for developing a model beginning with some information about the form and structure of the problem and with relevant data. The model building process typically follows a sequence of inter-related steps to include:

[1] Problem Identification and Data Selection—Data is selected, compilation, screened, and analyzed, and the various series tested based on hypotheses of probable causation; [2] Model Identification (or Specification)—Selection of a general model structure is made based on the nature of the data and the types of outputs desired. Some of these include, for example, a simple single mathematical equation, or multiple (sequential) equations, statistically-based univariate (deterministic) autoregressive functions, multivariate analysis, simple ordinary least squares (OLS) regression, multiple regression, simultaneous equation, etc.; [3] Estimation (Model Fitting)—Based on the selection of a model structure, the data is used to best describe the behavior of the variable under observation, e.g., stream flows, reservoir levels, runoff, economic output, employment, consumer spending, etc.; [4] Model Testing (and Refinement, as Necessary)—The model's structure and variables chosen are then validated by applying the data and observing forecast errors with respect to know (sample) values; [5] Forecasting—Based upon the ability of the model to accurately "fit" or predict historical values, the model is used to forecast beyond the last data point as prescribed by scenarios under analysis.

MODEL PLANT—A hypothetical plant design used for developing economic, environmental, and energy impact analyses as support for regulations or regulatory guidelines; the first step in exploring the economic impact of potential New Source Performance Standards (NSPS).

MODERATE FLOOD HAZARD AREAS—Areas between the 100-year and the 500-year flood boundaries are termed Moderate Flood Hazard Areas. The remaining areas are above the 500-year flood level and are termed Minimal Flood Hazard Areas.

MODERATE FLOODING—Flood conditions characterized by the inundation of secondary roads, transfer of property to higher elevations, and some evacuations of people and livestock. Also see Major Flooding and Minor Flooding.

MODERATOR—(Physics) A substance, such as water or graphite, that is used in a nuclear reactor to regulate the speed of fast neutrons and alter the likelihood of fission.

MOISTURE—(1) Diffuse wetness that can be felt as vapor in the atmosphere or condensed liquid on the surface of objects; dampness. (2) The state or quality of being damp.

MOISTURE EQUIVALENT—The ratio of: (1) the weight of water which the soil, after saturation, will retain against a centrifugal force 1,000 times the force of gravity, to (2) the weight of the soil when dry. The ratio is stated as a percentage.

MOISTURE STRESS—A condition of physiological stress in a plant caused by a lack of water.

MOISTURE TENSION—The equivalent negative pressure in the soil water. It is equal to the equivalent pressure that must be applied to the soil water to bring it to hydraulic equilibrium, through a porous permeable wall or membrane, with a pool of water of the same composition.

MOLAR—A solution containing the indicated number of Moles of solute per liter of solution.

MOLE—(Chemistry) The mass of a compound in grams numerically equal to its molecular weight. Also, the mass of a compound containing Avogadro's number of molecules.

MOLECULAR DIFFUSION—The process in which solutes are transported at the microscopic level due to variations in the solute concentrations within the fluid phases. Also see the Coefficient of Molecular Diffusion.

MOLECULAR WEIGHT—The sum of the atomic weights of the atoms in a molecule. For example, the molecular weight of water (H2O) is 18, the sum of the atomic weights of two hydrogen atoms (1+1=2) and oxygen (16).

MOLECULE—A group of atoms held together by chemical bonds. They may be either atoms of a single element (O2) or atoms of different elements that form a compound (H2O). The smallest amount of a compound which has all the properties of the compound.

MONIMOLIMNION—The lower region in a Meromictic Lake.

MONITOR—An articulated device holding a rotating nozzle with which a jet of water is regulated, used in mining and fire fighting.

MONITORING—Sampling and analysis of air, water, soil, wildlife, and other conditions, to determine the concentrations of contaminants.

MONITORING WELL—(1) A well used to obtain water quality samples or measure groundwater levels. (2) (Water Quality) A well drilled in close proximity to a waste storage or disposal facility, or hazardous waste management facility or Superfund Site to check the integrity of the facility or to keep track of leakage of materials into the adjacent groundwater.

MONOMICTIC—Lakes or reservoirs which are relatively deep, do not freeze over during the winter, and undergo a single stratification and mixing cycle during the year (usually in the fall).

MONOHYDRATE—A compound, such as calcium chloride monohydrate, CaCl2 · H2O, that contains one molecule of water.

MONSOON—(1) A wind system that influences large climatic regions and reverses direction seasonally. (2) A wind from the southwest or south that brings heavy rainfall to southern Asia in the summer; the rain that accompanies this wind.

MONTANE—A forest Ecosystem or Biome in mountainous areas of the tropics. The montane forest has far fewer plant species than does the Tropical Rain Forest, which is found at lower elevations below the mountains.

MONTANE ALKALI LAKES—Lakes with a water pH greater than 7 found in cool, upland habitats below the timber line.

MONTANE FRESHWATER LAKES—Circumneutral lakes found in cool, upland habitats below the timer line.

MONTE CARLO METHOD—(Statistics) A method that produces a statistical estimate of a quantity by taking many random samples from an assumed probability distribution, such as a normal distribution. The method is typically used when experimentation is infeasible or when the actual input values are difficult or impossible to obtain.

MOOR—An extensive area of waste ground in high, poorly drained country, overlaid with peat, and usually more or less wet. In popular usage, the word is restricted to the European moors, in which heather is often the prevailing plant, but similar phytogeographical areas occur elsewhere. Sphagnum moss is always characteristic of high moors, and especially in North America various insectivorous (insect feeding) plants flourish in them.

MORAINE—An accumulation of boulders, stones, or other debris carried and deposited by a glacier. Moraines, which can be subdivided into many different types, are deposits of Glacial Till. Lateral Moraines are the ridges of till that mark the sides of the glacier's path. Terminal Moraines are the material left behind by the farthest advance of the glacier's toe. Each different period of glaciation leaves behind its own moraines. Also see Recessional Moraine.

MOST PROBABLE NUMBER (MPN)—(Water Quality) A statistically determined number which represents the number of bacteria most likely present in a sample, based on test data. Widely used in the evaluation of waters from a bacterial standpoint.

MOUND SYSTEM—A septic tank effluent disposal system in which a mound of soil is built up and effluent distributed in the mound abut 3.3 feet (1 meter) above the normal soil surface.

MOULIN—A nearly vertical shaft or cavity worn in a glacier by surface or rock debris falling through a crack in the ice.

MOUTH OF STREAM—The point of discharge of a stream into another stream, a lake, or the sea.

MOUTONNÉE (also Moutonnéed)—(Geology) Rounded by glacial action into a shape resembling a sheep's back. Used of a rock formation.

MOVABLE BED—A stream bed made up of materials readily transportable by the streamflow.

MOVING AVERAGE PROCESS—(Statistics) As a simple mathematical process, the moving average process is merely a moving, fixed-interval average of a Time Series of data used to smooth fluctuations and distortions in the data and provide a more meaningful representation of underlying trends and cycles. As applied to econometric model development, a moving average process is one whereby future data values are expressed as a linear combination of past errors.

MUCK—(1) A moist, sticky mixture, especially of mud and filth. (2) Highly decomposed organic material in which the original plant parts are not recognizable. Muck contains more mineral matter and is usually darker than Peat. (3) Earth, rocks, or clay excavated in mining.

MUD—(1) A slimy sticky mixture of solid material with a liquid and especially water; especially soft wet earth. (2) Also, wet soft earth composed predominantly of clay and silt—fine mineral sediments less than 0.074 mm (0.0029 inch) in diameter.

MUD BALLS—(Water Quality) Accretions of siliceous incrustations on the exterior of sand grains in a rapid sand filter; typically removed by backwashing. Such deposits interfere with effective filtration.

MUDDLE—To make turbid or muddy.

MUDFLAT—Low-lying muddy land that is covered at high tide and exposed at low tide; A level tract lying at little depth below the surface of water or alternately covered and left bare by the tide.

MUDFLOW—Flow of a well-mixed mass of rock, earth, and water that behaves like a fluid and flows down slopes with a consistency similar to that of newly mixed concrete.

MUDSLIDE—A condition where there is a river, flow or inundation of liquid mud down a hillside usually as a result of a dual condition of loss of brush cover, and the subsequent accumulation of water on the ground preceded by a period of unusually heavy or sustained rain. A mudslide may occur as a distinct phenomenon while a landslide is in progress.

MUDSLIDE PRONE AREA—An area with land surfaces and slopes of unconsolidated material where the history, geology, and climate indicate a potential for mudflows.

MULCH—A natural or artificial protective layer of suitable materials, usually of organic matter such as leaves, straw, or peat, placed around plants that aid in soil stabilization, soil moisture conservation, prevention of freezing, and control of weeds, thus providing micro-climatic conditions suitable for germination and growth of selected vegetation.

MULCHING—The use of plant residues or other suitable materials on the soil surface, primarily to reduce evaporation of water and erosion of soil.

MULTI-CROPPING—The practice of producing two or more crops consecutively on the same parcel of land during a 12-month period. Also referred to as Double Cropping.

MULTIPLE-PURPOSE RESERVOIR—A reservoir planned and constructed to provide water for more than one purpose, e.g., irrigation, recreation, and flood control. Also referred to as MultiPurpose Project.

MULTIPLE REGRESSION (MODEL)—(Statistics) A Regression Model structure characterized by more than one Explanatory, or Exogenous Variable, of the form

Yt = a + ßX1t + ð X2t + et

where t represents the time periods of observation (where t=1, 2, ..., n), Yt represents the dependent (Endogenous) variable in time period t, a (alpha) represents the model equation's constant term (without a time reference), ß (beta, also a constant term without a time reference) represents the coefficient of the first independent variable, X1t represents the first independent variable in time period t, ð (delta, a constant term without a time reference) represents the coefficient of the second independent variable, X2t represents the second independent variable in time period t, and the error term, et (epsilon), represents the value of the unexplained disturbance term.

MULTIPLE USE—Harmonious and coordinated management of the various surface and subsurface resources, without impairment of the land, that will best meet the present and future needs of the people. Does not necessarily connotate the combination of uses that will yield the highest economic return or greatest unit of output.

MULTIPURPOSE PROJECT—A project designed to serve more than one purpose. For example, one that provides water for irrigation, recreation, fish and wildlife, habitat restoration and protection, and, at the same time, controls floods or generates electric power. Also see Multiple Purpose Reservoir.

MUNICIPAL AND INDUSTRIAL WATER USE (M & I)—Water supplied for municipal and industrial uses provided through a municipal distribution system for rural domestic use, stock water, steam electric powerplants, and water used in industry and commerce.

MUNICIPAL DISCHARGE—The discharge of effluent from waste water treatment plants which receive waste water from households, commercial establishment, and industries. Combined sewer/separate storm overflows are included in this category.

MUNICIPAL SEWAGE—Sewage (mostly liquid) originating from a community which may be composed of domestic sewage, industrial wastes, or both.

MUNICIPAL WASTEWATER FACILITY—Refers to those facilities that receive or dispose of wastewater derived principally from residential dwellings, business or commercial buildings, institutions, and the like. May also include some wastewater derived from industrial facilities. Also referred to as Domestic Wastewater Facility.

MUNICIPAL WATER—Municipal water may come from either ground water or surface water sources. Once water has entered a municipal water system, from whatever source, it will be considered municipal water.

MUNICIPAL WATERSHED—The watershed from which the runoff is used for drinking purposes in a city.

MUNICIPAL WATER SYSTEM—A water system which has at least five service connections or which regularly serves 25 individuals for 60 days. See Public Water System (PWS).

MUSKEG—A Swamp or Bog formed by an accumulation of sphagnum moss, leaves, and decayed matter resembling Peat. Prevalent in Canada and Alaska and part of the North American boreal forest Biome.

MUTAGENIC—Causing mutation, or the abrupt change in the genotype of an organism.

MUTCHKIN—(Scottish) A unit of liquid measure equal to 0.9 U.S. pint (0.42 liter).

90TH PERCENTILE—(Water Quality) Term used in conjunction with water sampling standards as required under the Safe Drinking Water Act (SDWA) and amendments thereto. The 90th percentile value is calculated by first placing all sample results in order from the lowest concentration to the highest concentration (i.e., concentration of specific contaminants). Next, assign each sample result a number, starting with the number 1 for the lowest (concentration) result up to the highest concentration being given the number equal to the total number of samples collected from a particular water supply system. Then multiply the total number of samples collected by 0.9. The sample result with the number corresponding to this calculated value is the 90th percentile.

NADIR—Refers to a low or the lowest point, as the lowest point of a lake or other body of water attained of a certain period of time (period of record).

NANOPLANKTON—Very minute plankton not readily retained in ordinary plankton nets.

NANSEN BOTTLE—An ocean-water sampling bottle with spring-loaded valves at both ends that are closed at an appropriate depth by a messenger device sent down the wire connecting the bottle to the surface.

NAPPE, also Nap—(1) A sheet or curtain of water flowing over a dam or weir or similar structure. (2) (Geology) A large sheetlike body of rock that has been moved far from its original position.

NARGHILE—A water pipe that originated in the Near East.

NARROW—(1) A body of water with little width that connects two larger bodies of water. (2) A part of a river or an ocean current that is not wide. Often used in the plural, i.e., narrows.

NATANT—Floating or swimming win water.

NATIONAL AUDUBON SOCIETY—An American environmental interest group founded in 1905 that emphasizes natural resource and wildlife conservation and protection. Named in honor of John James Audubon (1785-1851), who was one of the first American conservationists and who gained recognition for his paintings of birds.

NATIONAL ECONOMIC DEVELOPMENT—One of the two main objectives of planning for water and related land resources by governmental agencies whose activities involve planning and development of water resources. Such activities are reflected in the increase in the nation's productive output, an output which is partly reflected in a national product and income accounting framework to measure the continuing flow of goods and services into direct consumption or investment.

NATIONAL ENERGY POLICY ACT (EPAct)—See (National) Energy Policy Act (EPAct).

NATIONAL ENVIRONMENTAL POLICY ACT (NEPA)—A 1970 Act of Congress that requires all federal agencies to incorporate environmental considerations into their decision-making processes. The act requires an Environmental Impact Statement (EIS) for any "major federal action significantly affecting the quality of the human environment."

NATIONAL ESTUARY PROGRAM—(Water Quality) A nationwide program established under the Clean Water Act (CWA) Amendments of 1987 to develop and implement conservation and management plans for protecting estuaries and restoring and maintaining their chemical, physical, and biological integrity, as well as controlling point and nonpoint pollution sources. The program encompasses a watershed management approach to the identification and protection of nationally significant estuaries that are threatened by pollution, development, or overuse and to promote long-term planning and management processes that improve or protect water quality. If selected, the Environmental Protection Agency (EPA) will provide 75 percent of the funding for a three to five-year research and management effort to identify the various environmental problems in the "estuarine zone" and to develop a comprehensive conservation management plan.

NATIONAL FLOOD INSURANCE PROGRAM (NFIP)— A federal program enabling property owners in participating communities to purchase insurance protection against losses from flooding. This insurance is designed to provide an alternative to disaster assistance to meet the escalating costs of repairing damage to buildings and their contents caused by floods. Participation in the NFIP is based on an agreement between local communities and the federal government that if a community will implement and enforce measures to reduce future flood risks to new construction in Special Flood Hazard Areas (SFHA), then the federal government will make flood insurance available to protect against flood losses that do occur. The NFIP was established by Congress through the passage of the National Flood Insurance Act of 1968. Features of the program were modified and extended with the 1973 passage of the Flood Disaster Protection Act, and other legislative measures. The NFIP is administered by the Federal Insurance Administration (FIA), which is a component part of the Federal Emergency Management Agency (FEMA).

NATIONAL FOREST—A federal reservation, generally forest, range, or wildland, which is administered by the Forest Service, U.S. Department of Agriculture, under a program of multiple use and sustained yield for timer production, range, wildlife, watershed, and outdoor recreation purposes.

NATIONAL GEODETIC VERTICAL DATUM (NGVD)—As corrected in 1929, a vertical control measure used as a reference for establishing varying elevations.

NATIONAL MONUMENT—An area owned by the federal government and administered by the National Park Service, U.S. Department of the Interior, for the purpose of preserving and making available to the public a resource of archaeological, scientific, or aesthetic interest.

NATIONAL MUNICIPAL PLAN—A policy created in 1984 by the U.S. Environmental Protection Agency (EPA) and the states to bring all Publicly Owned Treatment Works (POTWs) into compliance with Clean Water Act (CWA) requirements.

NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION (NOAA)—An agency of the U.S. Department of Commerce, the National Oceanic and Atmospheric Administration was formed in 1970, but its origins may actually be traced as far back as 1807 when President Thomas Jefferson ordered a survey of the new nation's coastline. Today, NOAA has translated the United States' geographic, atmospheric, oceanic, and meteorological informational needs into an organization concentrating in the following principal areas:

[1] Research and Analysis—NOAA researchers and scientists in the areas of oceanography, meteorology, biology, and physics explore the sea and air for new clues aimed at understanding or reversing environmental damage such as ozone depletion, the greenhouse effect, and possible global warming; [2] Satellite Imaging and Mapping—NOAA's satellites provide essential information for accurate weather forecasts, monitor winter snowpack conditions across the country, and gauge the health of coastal estuaries; [3] Data Compilation and Dissemination—The results of NOAA's data collection, satellite mapping, and research and analysis affords vast stores of information in NOAA's global data centers available for climate, oceanographic and geophysical reports vital to the public and industry; [4] Forecasting and Weather Warning—Through the National Weather Service (NWS), NOAA provides extensive information and warnings when severe weather threatens life and property.

The National Oceanic and Atmospheric Administration consists of a number of separate agencies to effect these research, analysis, monitoring, informational, and forecasting requirements.

[1] National Weather Service (NWS)—The National Weather Service operates a vast network of automated weather stations around the nation equipped with sophisticated doppler radar systems on the ground as well as sophisticated satellites providing detailed imaging which provide meteorologists and citizens early warnings of severe weather conditions. In cooperation with the Federal Aviation Administration (FAA), the NWS is proceeding with establishing some 1,000 fully automated weather data collection sites, termed Automated Surface Observing Systems (ASOS). [2] National Ocean Service (NOS)—The National Ocean Service charts and surveys America's coastal waterways, providing safe passage for commerce and recreation interests. The NOS also plays a major role in managing America's coastlines and NOAA's Coastal Zone Management Program strives to protect wetlands, water quality, beaches, wildlife, and other important resources and uses of our coasts. As part of the NOS, NOAA's National Marine Sanctuaries, the nation's underwater national parks, provide unique undersea preserves to protect important coastal resources. The NOS monitors the health of the coast and probes how our use of the nation's nearshore waters affects the environment. [3] National Environmental Satellite, Data and Information Service (NESDIS)—The NESDIS operates the world's largest environmental data storage and distribution facility providing extensive and highly detailed data on weather, the oceans and geophysics. The NESDIS is also responsible for NOAA's polar orbiting and geostationary satellites which provide important information on the oceans and atmosphere. Other NESDIS satellites collect images of cloud and storm patterns which are then relayed to NOAA's National Weather Service and are extensively used by the nation's meteorologists for local weather reporting and forecasting. [4] National Marine Fisheries Service (NMFS)—The NMFS serves as steward for America's living marine resources, conducting research necessary to manage these valuable resources and enforces fishery regulations, maintains the wholesomeness of U.S. seafood products, and protects coastal fishery habitats and nurseries. The NMFS manages the 32 federal fishery resource plans, covering more than 230 species, and plays a key role in protecting coastal habitats, marine mammals and endangered and threatened species per the Endangered Species Act (ESA). [5] Office of Oceanic and Atmospheric Research—NOAA's scientists conduct leading edge research on weather, climate, air quality, the oceans and the Great Lakes through a network of environmental laboratories and monitoring stations as well as through university researchers supported by NOAA through the National Sea Grant College Program and the National Undersea Research Program. [6] NOAA Corps—NOAA also operates the nation's smallest uniformed service consisting of some 400 officers commanding NOAA's fleet of hurricane hunter aircraft and environmental research ships providing in a variety of scientific and research operations.

NATIONAL OIL AND HAZARDOUS SUBSTANCES CONTINGENCY PLAN (NOHSCP/NCP)—The federal regulation that guides determination of the sites to be corrected under both the Superfund program and the program to prevent or control spills into surface waters or elsewhere.

NATIONAL PARK—An area of unusual scenic or historic interest owned by the federal government and administered by the National Park Service, U.S. Department of the Interior, to conserve the scenery, the flora and fauna, and any natural and historical objects within its boundaries for public enjoyment in perpetuity.

NATIONAL POLLUTANT DISCHARGE ELIMINATION SYSTEM (NPDES)—The program established by the Clean Water Act (CWA) that requires all Point Sources (PS) of pollution discharging into any "waters of the United States" to obtain a permit issued by the U.S. Environmental Protection Agency (EPA) or a state agency authorized by the federal agency. The NPDES permit lists permissible discharges and/or the level of cleanup technology required for wastewater.

NATIONAL PRIMARY DRINKING WATER REGULATIONS (NPDWR)—Regulations for public drinking water supply systems that include health-based standards for various contaminants, and monitoring and analysis requirements. Issued by the U.S. Environmental Protection Agency (EPA) under authority of the Safe Drinking Water Act (SDWA). While the NPDWR set standards protective of the public health, the National Secondary Drinking Water Regulations (NSDWR) set aesthetic standards for drinking water, i.e., color, odor, taste, etc. Also see Drinking Water Standards, Drinking Water Standards [Nevada], Maximum Contaminant Level (MCL), and Maximum Contaminant Level Goal (MCLG).

NATIONAL PRIORITIES LIST (NPL)—A list of the hazardous waste disposal sites most in need of cleanup. The list is updated annually by the U.S. Environmental Protection Agency (EPA) based primarily on how a site scores using the Hazard Ranking System. A site must be on the NPL to receive money from the trust fund for remedial action. Also referred to as the Superfund List.

NATIONAL RESPONSE CENTER (NRC)—The U.S. Coast Guard unit that receives reports of hazardous chemical spills and is responsible for notifying other agencies which will help plan, coordinate, and respond to the release.

NATIONAL RESPONSE TEAM (NRT)—An organization of the federal government under the leadership of the U.S. Environmental Protection Agency (EPA) that includes representatives of 10 other federal agencies. The team serves as an umbrella organization at the federal level, and its functions include, among others, evaluating methods to respond to discharges or releases; recommending needed changes in the response organization; making recommendations relative to the training, equipping, and protection of response teams; evaluating response capabilities; reviewing regional responses to discharges; and coordinating the activities of federal, state, and local governments as well as private organizations in response to discharges.

NATIONAL SECONDARY DRINKING WATER REGULATIONS (NSDWR)—Regulations governing the operation of public water supply systems under the Safe Drinking Water Act (SDWA). The regulations define secondary maximum contaminant levels, the maximum concentrations of certain substances in drinking water that affect its aesthetic quality. While the NSDWR set aesthetic standards for drinking water, i.e., color, odor, taste, etc., the National Primary Drinking Water Regulations (NPDWR) set standards protective of the public health.

NATIONAL STREAM QUALITY ACCOUNTING NETWORK (NASQAN)—A data system operated by the U.S. Geological Survey (USGS) that compiles measurements of water pollutants concentrations taken at the downstream ends of all major water basins in the United States.

NATIONAL STRIKE FORCE (NSF)—An organization under the leadership of the U.S. Coast Guard that responds to spills of oil or hazardous substances in waters of the United States. The NSF operates through various teams organized in different regions of the country. They provide, among other services, communications support, advice, and assistance in the event of discharges; shipboard damage control; containment and removal of discharges; and diving activities related to damage assessment and surveys.

NATIONAL WEATHER SERVICE (NWS)—An agency of the (U.S. Department of Commerce) National Oceanic and Atmospheric Administration (NOAA), the primary mission of the National Weather Service is to protect life and property and enhance the nation's economy by providing warnings and forecasts of hazardous weather, including thunderstorms, flooding, hurricanes, tornadoes, winter weather, and tsunamis. The primary customer of the NWS is the private weather industry whose meteorologists receive data and information directly from the NWS and incorporate it into local news reports. The NWS also operates its own radio network; the NOAA Weather Radio is the sole government radio system providing direct warnings of hazardous weather conditions and natural disasters to private citizens through a network of 390 transmitters across the nation. The NWS provides short and long-range forecasts, severe weather warnings, and atmospheric data continually to private weather vendors for a fee using a telephone data transmittal system called Family of Services. NWS Doppler radar data is provided through the NWS NEXRAD Information Dissemination Service (NIDS) and is available from commercial weather vendors under an agreement with the NWS. The NOAA Weather Wire Service is the primary NWS telecommunications network for NWS forecasts, warnings, and other products to the mass media (TV, radio, newspaper) and emergency management agencies. It consists of a satellite communications system operated under contract by GTE/Contel. In a joint effort with the Federal Aviation Administration (FAA), some 250 NWS manual data collection field offices will be replaced with approximately 1,000 automated data collections sites, termed Automated Surface Observing Systems (ASOS), thereby greatly enhancing both the timeliness and frequency of the NWS weather reporting capabilities.

NATIONAL WILDERNESS PRESERVATION SYSTEM—All lands covered by the Wilderness Act of 1964 and subsequent wilderness designations, irrespective of the department or agency having jurisdiction.

NATIONAL WILDLIFE REFUGE (NWR) SYSTEM—The mission of the National Wildlife Refuge System is to provide, preserve, restore, and manage a national network of lands and waters sufficient in size, diversity, and location to meet society's needs for areas where the widest possible spectrum of benefits associated with wildlife and wildlands is enhanced and made available. The system comprises a unique and diverse network of over 92 million acres of lands and waters in the United States. This system spans the continent from the north coast of Alaska to the Florida Keys and beyond to tropical islands in the Caribbean and Central Pacific. Over 500 national wildlife refuges are included in the Refuge System. They are managed by the Department of the Interior, U.S. Fish and Wildlife Service (USFWS) for the conservation and enhancement of fish and wildlife and their habitats. Refuges may range in size from Minnesota's tiny Mille Lacs (less than an acre) to Alaska's sprawling Yukon Delta (almost 20 million acres). Refuges provide habitat—food, water, shelter, and space—for more than 60 endangered species and hundreds of other species of birds, mammals, reptiles, amphibians, fish, and plants. The first national wildlife refuge was Florida's Pelican Island, established in 1903 by President Theodore Roosevelt to protect egrets, herons, and other birds that were being killed for feathers used in the fashions of the time. Also see National Wildlife Refuges [Nevada].

NATIONAL WILDLIFE REFUGES (NWR) [Nevada]—There are currently nine (9) National Wildlife Refuges (NWR) in the State of Nevada, including the largest refuge located within the 48 contiguous states—the Desert National Wildlife Refuge. One refuge—the Sheldon National Wildlife Refuge—is contained mostly in Nevada with a small portion of its northern tip extending up into the State of Oregon. Nevada's National Wildlife Refuges, all of which are managed by the U.S. Fish and Wildlife Service (USFWS), include:

[1] Anaho Island National Wildlife Refuge—Established in 1913 by President Woodrow Wilson to protect the white pelican nesting colonies, the Anaho NWR consists of the 750-acre (1.2 square mile) Anaho Island in Pyramid Lake, which is wholly contained within the Pyramid Lake Paiute Indian Reservation. Located approximately 45 northeast of Reno, Nevada, the Anaho NWR contains one of the largest white pelican nesting colonies in North America, as well as cormorant, great blue heron, and gull nesting colonies. This refuge is closed to the public for the protection of the colony nesting birds. [2] Ash Meadows National Wildlife Refuge—Located approximately 90 miles northwest of Las Vegas in Nye County, Nevada, the Ash Meadows NWR, established in 1984, encompasses some 14,000 acres (approximately 22 square miles) and provides critical habitat for 25 plant and animal species found nowhere else in the world. This distinguishes the Ash Meadows NWR as having the greatest concentration of endemic species of any other local area in the United States. Of the 25 unique species, 12 have been listed as either Threatened or Endangered. Water is the key natural resource which makes the Ash Meadows NWR a unique Ecosystem in the dry Mojave Desert. In this area, water-bearing strata come to the surface in approximately 30 seeps and springs, providing a rich and complex variety of habitat. The earliest efforts to protect this area were undertaken by The Nature Conservancy, which purchased 12,613 acres of land in 1984 and subsequently sold it to the USFWS specifically to establish a wildlife refuge. [3] Desert National Wildlife Refuge—Established in 1936, the Desert NWR covers 1,588,459 acres (2,482 square miles) of the diverse Mohave Desert in southern Nevada and is the largest National Wildlife Refuge in the 48 contiguous United States. The Desert NWR's most important objective is the perpetuation of the desert bighorn sheep and its habitat. The refuge contains six major mountain ranges, the highest rising from a 2,500 foot elevation valley floor to nearly 10,000 feet. The dry climate and varying elevations provide varied plant life with creosote bush and white bursage dominant in the lower elevations, Mojave yucca and cactus dominant in the mid-elevations, blackbrush and Joshua trees prevalent near 6,000 feet, and single-leaf pinyon and Utah juniper become prominent at 6,000 feet. From 7,000-9,000 feet Ponderosa pine and white fir become dominant and near 10,000 feet the only remaining tree is the bristlecone pine. Throughout this area the big sagebrush is the most common shrub. Within this refuge, and in stark contrast to the typical habitat and wildlife prevalent throughout the refuge, are the numerous and diverse plant and animal communities at Corn Creek. Here springs turn the desert into an oasis attracting over 200 species of birds alone. [4] Fallon National Wildlife Refuge—Established in 1931, the Fallon NWR encompasses approximately 17,900 acres (28 square miles) where the Carson River terminates in the Carson Sink and is situated within the northwest portion of the Stillwater Wildlife Management Area. Due to typically limited and uncertain flows of the Carson River at its terminus, generally not enough water enters this refuge to maintain it as a viable wetlands. The area is currently managed by the USFWS along with the Stillwater National Wildlife Refuge and is included as part of the Stillwater Wildlife Management Area. [5] Moapa National Wildlife Refuge—The Moapa NWR was established in 1979 in order to protect and secure habitat for the Endangered Moapa dace and a candidate for listing, the White River springfish. The refuge contains 32 acres (0.05 square mile) and is located just north of the Moapa River Indian Reservation, 5 miles northwest of Moapa, Nevada, located in Clark County. [6] Pahranagat National Wildlife Refuge—Located approximately 90 miles north of Las Vegas, Nevada, the Pahranagat NWR is located at the northern end of the Desert NWR and consists of 5,380 acres (8.4 square miles) of marshes, open water, native grass meadows and cultivated croplands. Established in 1964, the Pahranagat NWR hosts numerous waterfowl and other migratory birds on the Pacific Flyway, which stretches from Alaska and Canada to Mexico. The name "Pahranagat" comes from the Paiute Indian word meaning "place of many waters." [7] Ruby Lake National Wildlife Refuge—This NWR, which was established in 1938, covers an area of 37,632 acres (58.8 square miles) consisting of marshes, open ponds and islands, bordered by wet meadows and grass/sagebrush-covered uplands. The Ruby Lake NWR, which collects the waters from over 160 springs along the base of the Ruby Mountains, lies within a closed drainage basin in Ruby Valley of northeastern Nevada approximately 65 miles southeast of the town of Elko along the eastern flank of the rugged and scenic Ruby Mountains at an elevation of 6,000 feet above sea level. During the Pleistocene Epoch, the Ruby Mashes were part of a much larger body of water known as Franklin Lake, an Ice Age lake which covered some 470 square miles and was over 200 feet deep; however, today, only the Ruby and Franklin Lake marshes remain and provide an important refuge to nesting and migratory waterfowl and water birds using the migration corridors of both the Pacific and Central Flyways. [8] Sheldon National Wildlife Refuge—Located in the northwestern corner of Nevada, the Sheldon NWR manages over 575,000 acres (approximately 900 square miles) of high-desert habitat as a representative area for native plants and wildlife. The Sheldon NWR was formally established in 1978 and represented a consolidation of two refuge and range protection areas: (1) the Charles Sheldon Wildlife Range, created in 1931 by President Herbert Hoover from the purchase of the 30,000-acre Last Chance Ranch by the Boone and Crockett Club and the National Audubon Society; and (2) the Charles Sheldon Antelope Range, an area of over one-half million acres created in 1936 by President Franklin D. Roosevelt for the conservation and development of natural wildlife resources. Today, this area encompasses remote settings, scenic vistas, numerous natural geothermal hot springs, old ranches and homesteads plus sites of archaeological significance. Some 20 million years ago this area was covered with pine forests and lush grasslands, nurtured by a mild climate and more than 50 inches of annual rainfall. Today, this area receives only from 4-8 inches of precipitation, primarily in the form of snowfall, and the prominent geological characteristic of this refuge is the subsequent volcanic activity which spewed rhyolitic magma over much of its area with basalt flows up to 100 feet thick. These have formed the large, broad tables prevalent in this area today. [9] Stillwater National Wildlife Refuge—Located approximately 15 miles east of Fallon, Nevada within Churchill County on the edge of the Carson Sink, the Stillwater NWR was formally established in 1991 when 77,500 acres (121 square miles) of the Stillwater Wildlife Management Area were set aside to preserve critical nesting and habitat for migratory waterfowl and other birds using the Pacific Flyway in western Nevada. In 1948, in order to preserve a shrinking wetland system, the U.S. Fish and Wildlife Service and the Nevada Fish and Game Commission entered into an agreement with the Truckee-Carson Irrigation District (TCID) to develop and manage 224,000 acres (350 square miles) of U.S. Bureau of Reclamation (USBR)-Newlands (Irrigation) Project lands, designated as the Stillwater Wildlife Management Area, for wildlife habitat protection and preservation. Today, the Stillwater NWR includes a variety of habitats, from freshwater sloughs and marshes to brackish-water marshes and alkali flats. Each habitat hosts a unique assemblage of plants and invertebrates, which in turn attracts more than 160 bird species and many other animals.

NATIVE SPECIES—A species that is a part of an area's original fauna or flora.

NATURAL ATTENUATION—The process of Microbiological Anaerobic Degradation in which hazardous wastes and toxic compounds are treated while not involving the addition of foreign microbes to the site but rather using naturally-occurring microbes already present. Also see Attenutation.

NATURAL CONTROL—A stream-gaging control which is natural to the stream channel, in contrast to an artificial control constructed by man.

NATURAL EROSION—Wearing away of the earth's surface by water, ice, or other natural agents under natural environmental conditions of climates and vegetation. Also see Erosion.

NATURAL FLOW—The rate of water movement past a specified point on a natural stream from a drainage area for which there have been no effects caused by stream diversion, storage, import, export, return flow, or change in Consumptive Use caused by man-controlled modification to land use. Natural flow rarely occurs in a developed county.

NATURAL HERITAGE PROGRAM [Nevada]—As a statewide program, the Nevada Natural Heritage Program serves as a centralized repository containing detailed and computer-retrievable information on sensitive (threatened or endangered) species of animals, plants, and communities. Species information includes biology, habitats, locations, population and conservation status, and management needs. [See Appendix E-1, Nevada's Endangered and Threatened Species.]

NATURAL LOGARITHM (LN)—(Mathematics) The value of the exponent that the base, e, must have to equal a given number. It is calculated as ex = y, where x is the logarithm. For example, the natural logarithm of 5 is the power (x) to which e (approximately equal to 2.718282) must be raised to equal 5, or ex = 5, which is equivalent to approximately 1.60944. Also written as ln 5 = 1.60944. Also see Logarithm (Log).

NATURAL PRECIPITATION—Represents the average annual precipitation (rainfall, snow, and sleet) measured at a number of different weather stations.

NATURAL RECHARGE—The replenishment of groundwater storage from naturally-occurring surface water supplies such as precipitation and stream flows. Also see Artificial (or Induced) Recharge, Incidental Recharge, and Perennial Yield.

NATURAL RESOURCE—A material source of wealth, such as timber, fresh water, or a mineral deposit, that occurs in a natural state and has economic value. Natural resources are considered Nonrenewable when they do not naturally replenish themselves within the limits of human time or Renewable when they are more or less continuously replenished in the course of natural events within the limits of human time.

(UNITED STATES) NATURAL RESOURCES CONSERVATION SERVICE (NRCS)—Formerly known as the Soil Conservation Service (SCS), an agency of the U.S. Department of Agriculture, the Natural Resources Conservation Service (NRCS) had its beginnings with a 1929 emergency act of Congress in response to the famous Dust Bowl when land practices, primarily in the Midwest Farm Belt, caused extensive soil erosion and threatened the food production of the United States. Initially, ten experiment stations were established to work with Land Grant Universities to study soil erosion and ways to prevent it. As a result of these initial efforts, the Soil Erosion Service was established in 1933 to show American farmers new ways of preventing and recovering from soil erosion. In 1935 Congress changed the Soil Erosion Service into the Soil Conservation Service and made it a permanent agency of the U.S. Department of Agriculture. In 1994 the name was change to Natural Resources Conservation Service to denote a broader role of responsibility in natural resource conservation. Presently, the NRCS works in three primary areas: (1) soil and water conservation; (2) resource inventories; and (3) rural community development. These activities are covered under a number of direct NRCS programs, involving only NRCS resources, and NRCS assisted programs, involving the NRCS and at least one other government agency.

Direct NRCS Programs:

[1] Technical Assistance [2] Great Plains Conservation Program [3] Watershed Protection, Long-Term Contracts (Public Law 566) [4] USDA Compliance Plans

NRCS Assisted Programs:

[1] Agriculture Conservation Program [2] Water Bank Program [3] Colorado River Salinity Control Program [4] Conservation Reserve Program [5] Water Quality Incentive Program [6] Emergency Conservation Program [7] Wetlands Reserve Program

NATURAL RESOURCES DEFENSE COUNCIL (NRDC)—A private American environmental organization emphasizing the proper management of natural resources. The NRDC has been an active participant in numerous precedent-setting lawsuits concerning national environmental policies.

NATURAL SINK—A habitat that serves to trap or immobilize chemicals such as plant nutrients, organic pollutants, or metal ions through natural processes. For example, a river that enters a swamp may carry a substantial amount of dissolved plant nutrients. The natural biological activity of the swamp may remove these nutrients to such an extent that the water exiting the swamp is relatively low in nutrient concentrations. The swamp has then served as a sink to trap the nutrients that are no longer available for subsequent plant growth downstream from the swamp. Also referred to as a Nutrient Sink.

[THE] NATURE CONSERVANCY—An international conservation organization incorporated in 1951 in the District of Columbia for scientific and education purposes. The mission of The Nature Conservancy is to preserve plants, animals and natural communities that represent the diversity of life on earth by protecting the lands and waters they need to survive. Current resource conservation efforts cover Canada, the United States, Latin America, and the Caribbean. Through private donations, The Nature Conservancy purchases lands and then either retains ownership or transfers ownership for management to other conservation groups, both public and private.

NATUROPATHY—A system of treatment of disease that avoids drugs and surgery and emphasizes the use of natural agents (as air, water, and sunshine) and physical means (as manipulation and electrical treatment).

NAUPLIUS—The free-swimming microscopic larval stage characteristic of many crustaceans, barnacles, etc.

NAUTICAL—Of, relating to, or characteristic of ships, shipping, sailors, or navigation on a body of water.

NAUTICAL MILE—A unit of length used in sea and air navigation, based on the length of one minute of arc of a great circle, especially an international and U.S. unit equal to 1,852 meters (about 6,076 feet). Also called Sea Mile.

NAVIGABLE—Capable of being navigated; deep enough and wide enough to afford passage to vessels. In the United States, for the purpose of defining the rights of ownership, some states have adopted the common-law test of flow of the tide, others that of actual navigability. For determining the right of the public to the use of a body of water as a public highway, however, the test in the U.S. is as to whether the water is navigable in fact or not. And waters are navigable in fact when they are used, or are susceptible of being used, in their ordinary condition as highways for commerce, over which trade and travel are or may be conducted in the customary modes of trade and travel on water. In truth, the law has a number of different and frequently confusing definitions of "navigable" rivers and lakes, although agreement exists that all tidal areas are considered navigable. For purposes of determining state title to the beds of rivers and lakes, they must have been capable of carrying commerce at the time the state entered the union. "Commerce" for this purpose includes more than boats carrying persons and cargo. The courts have found streams to be "navigable" where they have carried saw logs or shingle bolts. For purposes of some federal regulatory programs, a waterway must have carried, or be capable of carrying, interstate commerce. Other federal regulatory programs, for example, the Federal Power Act, include waterways which could carry interstate commerce with reasonable modifications. And finally, the Clean Water Act (CWA) defines "navigable" waters to include all waters of the United States which may affect or be affected by interstate commerce. Consequently, this encompasses most water bodies in the nation.

NAVIGABLE WATERS—The waters of the United States, including the territorial seas, and intrastate waters, which is any body of water with any connection to interstate waters or commerce and this includes virtually all surface water and wetlands. Despite its name, there is no requirement for vessels to be able to navigate these waters. Provisions of the Clean Water Act (CWA) apply to all such waters, including wetlands.

NAVIGABLE WATERS [Nevada]—In Nevada bodies of water are navigable if they are used, or are susceptible of being used, in their ordinary condition as highways for commerce, over which trade and travel are or may be conducted in the customary modes of trade and travel on water. In Nevada, this test of navigability (State of Nevada v. Julius Bunkowski, et al., 1972) held that the Carson River was navigable, and therefore the State of Nevada owned its bed, as logs were floated down the river from about 1860 to 1895 (the commerce requirement).

NAVIGATE—(Nautical) To voyage over water in a boat or ship; to travel by water; sail.

NAVIGATIONAL WATER USE—Water utilized as a means of commercial (and sometimes recreational) transportation. Includes water used to lift a vessel in a lock, or maintain a navigable channel level. Navigational water use is considered a non-consumptive instream use of water and is generally not measured or accounted for.

NEAP TIDE—A tide that occurs when the difference between high and low tide is least; the lowest level of high tide. Neap tide comes twice a month, in the first and third quarters of the moon. Contrast with Spring Tide.

NEBRASKAN—(Geology) Of or relating to one of the glacial stages of the Pleistocene epoch which occurred in North America, which consisted of the Nebraskan (first stage), Kansan (second stage), Illinoian (third stage), and Wisconsin (fourth stage).

NECK CUTOFF—The breakthrough of a river across the narrow neck separating two meanders, where downstream migration of one has been slowed and the next meander upstream has overtaken it. Compare with Chute Cutoff.

NEEDLE-LEAVED DECIDUOUS—Woody Gymnosperms (trees or shrubs) with needle-shaped or scale-like leaves that are shed during the cold or dry season; e.g., bald cypress (Taxodium distichum).

NEEDLE-LEAVED EVERGREEN—Woody Gymnosperms with green, needle-shaped, or scale-like leaves that are retained by plants throughout the year; e.g., black spruce (Picea mariana).

NEGOTIATED SETTLEMENT (Public Law 101-618) [Nevada and California]—Omnibus legislation passed by the 101st Congress at the end of its 1990 session intended to settle a number of outstanding disputes concerning the Truckee and Carson Rivers. The legislation authorized an ambitious environmental restoration program to benefit the Lahontan Valley Wetlands and Pyramid Lake and the lower Truckee River. It also established a framework for resolving separate by closely-related water-resource conflicts involving the Pyramid Lake Paiute and Fallon Paiute-Shoshone Tribes, the cities of Reno and Sparks (Nevada), the states of Nevada and California, and (pending the resolution of several as-yet unsatisfied controversies) the Newlands Project. The legislation contains two primary titles: TITLE I—The Fallon Paiute-Shoshone Indian Tribal Settlement Act; and TITLE II—The Truckee-Carson-Pyramid Lake Water Rights Settlement Act. Collectively, the legislation can be referred to as the Negotiated Settlement. The seven (7) main elements covered by the legislation include:

[1] Promote the Enhancement and Recovery of Endangered and Threatened Fish Species—A recovery program is to be developed for the Pyramid Lake endangered fish species cui-ui (Chasmistes cujus) and the threatened fish species Lahontan cutthroat trout (Oncorhynchus clarki henshawi) in compliance with the Endangered Species Act (ESA) and the Truckee-Carson-Pyramid Lake Water Rights Settlement Act. Water rights acquisitions are authorized for this purpose. [2] Protect Wetlands from Further Degradation—A water rights purchase program is authorized for Lahontan Valley Wetlands, with the intent of sustaining an average of 25,000 acres of wetlands (Stillwater National Wildlife Refuge: 14,000 acres; Carson Lake and Pasture: 10,200 acres; and Fallon Reservation and Indian Lakes: 800 acres) to both prevent further degradation and improve the habitat of the fish and wildlife which depend on those wetlands. The U.S. Fish and Wildlife Service (USFWS) has estimated that this will require up to 125,000 acre-feet (AF) of water per year. [3] Encourage the Development of Solutions for Demands on Truckee River Waters—An operating agreement is to be negotiated for the Truckee River—The Truckee River Operating Agreement (TROA)—covering procedures for using storage capacity in upstream reservoirs in California consistent with recovery objectives for listed Pyramid Lake fishes. This includes the implementation of the terms and conditions of the Primary Settlement Agreement (PSA) between SPPCo and the Pyramid Lake Paiute Tribe. [4] Improve Management and Efficiency of the Newlands Project—The Secretary of the Interior is authorized to operate and maintain the Newlands Project to serve additional purposes, including recreation, improved water quality flowing to the wetlands, improved fish and wildlife habitat, and municipal water supply for Lyon and Churchill counties. A project efficiency study is required. The 1973 Gesell Decision is recognized and the 1988 Operating Criteria and Procedures (OCAP) is to remain in effect at least through 1997. [5] Fallon Paiute-Shoshone Water Issues Settlement—Establishment of a settlement fund for the Fallon Paiute-Shoshone Tribe totaling $43 million. The Tribe is authorized to purchase land and water rights to consolidate tribal holdings within the reservation. Specific litigation filed by the Tribe is to be dismissed. [6] Pyramid Lake Paiute Tribe Issues Settlement—A tribal economic development fund of $40 million was established for the Pyramid Lake Paiute Indian Tribe to provide for the settlement of water, fish, and other issues. Another fund of $25 million was established for the Pyramid Lake fishery. [7] Interstate Water Apportionment Settlement—Facilitate an interstate allocation of the waters of the Truckee River, Carson River, and Lake Tahoe between the states of California and Nevada.

Also see Newlands Project [Nevada], Truckee River Agreement [Nevada and California], Truckee River Operating Agreement (TROA) [Nevada and California], and Operating Criteria and Procedures (OCAP) [Nevada].

NEKTON—Macroscopic organisms swimming actively in water, such as fish. Contrast to Plankton.

NEPHELOMETER—A device which measures the intensity of light scattered at right angles to its path through a sample. It is used to measure turbidity, and the results are expressed in Nephelometric Turbidity Units (NTUs).

NEPHELOMETRIC—A method of measuring turbidity in a water sample by passing light through the sample and measuring the amount of the light that is deflected.

NEPHELOMETRIC TURBIDITY UNIT (NTU)—A unit of measure for the turbidity of water resulting from the use of a Nephelometer and based on the amount of light that is reflected off the water. This unit is not identical to the Jackson Turbidity Unit (JTU).

NERITIC—Of the shallow regions of a lake or ocean that border the land. The term is also used to identify the biota that inhabit the water along the shore of a lake or ocean.

NERITIC ZONE—The relatively shallow water zone that extends from the high tide market to the edge of the Continental Shelf. May also refer to such shallow water regions of lakes.

NET CONSUMPTIVE USE—The Consumptive Use decreased by the estimated contribution by rainfall toward the production of irrigated crops. Net consumptive use is sometimes called the Crop Irrigation Requirement.

NET DUTY OF WATER—The amount of water delivered to the land to produce a crop, measured at the point of delivery to the field. Also see Gross Duty of Water.

NET ECONOMIC BENEFITS—Economic benefits minus economic costs.

NET PRECIPITATION—The potential for Leachate generation from a waste disposal site. It is computed for a specific location by subtracting the annual evaporation from lakes in the region from the normal annual rainfall.

NET (STORM) RAIN—The portion of rainfall during a storm which reaches a stream as direct surface flow.

NET RESERVOIR EVAPORATION—The difference between the total evaporation from the reservoir water surface and the Evapotranspiration from the reservoir area under pre-reservoir conditions, with identical precipitation considered for both conditions.

NET WATER DEMAND—The amount of water needed in an irrigation or water service area to meet all requirements. It is the sum of Evapotranspiration of Applied Water (ETAW) in an area, the Irrecoverable Losses from the distribution system, and the outflow leaving the irrigation area. It excludes, however, the water reused in the area. Sometimes used interchangeably with Net Water Use.

NET WATER USE—Refers to water withdrawals plus or minus water transfers. In most areas, the net water use and water withdrawals are equal. However, in areas involved in water transfers (imports and exports), the net water use represents the actual amount of water used regardless of the amount of water actually withdrawn. Sometimes used interchangeably with Net Water Demand.

NET WATER YIELD—The available water runoff at a given location, both surface and subsurface, after the upstream uses by man's activities, use by Phreatophytes, and evaporation from upstream free water surfaces.

NEUSTON—(1) The collection of minute or microscopic organisms that inhabit the surface layer of a body of water. (2) Organisms resting or swimming on the surface of still bodies of water.

NEUTRALIZATION—(1) (Chemistry) A reaction between an acid and a base that yields a salt and water. (2) The equalization of hydrogen and hydroxyl ion concentrations such that the resulting solution is neither acidic nor basic; also, decreasing the acidity or alkalinity of a substance by adding alkaline or acidic materials, respectively.

NEUTRAL SOIL—A soil in which the surface layer, at least to normal plow depth, is neither acid nor alkaline in reaction, approximately 7.0 pH.

NEVADA NATURAL HERITAGE SITE [Nevada]—Areas of land or water which either: (1) retain to some degree, or have re-established, a natural character (although it need not be completely undisturbed); or (2) have unusual flora, fauna, geological, scenic, or similar features or scientific, educational or recreational interest.

NEVADA PROJECT WET [Nevada]—See Water Education for Teachers (Project WET) [Nevada].

NÉVÉ—(1) The upper part of a glacier where the snow turns into ice. (2) A snow field at the head of a glacier. Also, the granular snow typically found in such a field.

NEWLANDS (IRRIGATION) PROJECT [Nevada]—One of the first Department of the Interior, U.S. Bureau of Reclamation (USBR) (Reclamation Service at that time) irrigation projects completed in the United States. The project was authorized originally as the Truckee-Carson Irrigation Project on March 14, 1903 by the Secretary of the Interior and was renamed the Newlands Project in 1919 in honor of Nevada Senator Francis G. Newlands, who originally sponsored the 1902 Reclamation Act. Derby Dam, located on the lower Truckee River, was completed in June 1905 to divert waters from the Truckee River Basin to the Carson River. In August 1906 the Truckee Canal was completed between the Truckee and Carson rivers. Waters began flowing through this canal in 1906 while 1907 proved to be the first full year of irrigation. Lahontan Reservoir was completed in 1915 on the Carson River to receive Truckee River waters through the Truckee Canal and provided a more stable supply of water for irrigation needs to a defined service area in the Town of Fernley and the lower Carson River Basin near the City of Fallon, Church