A  |   B  |   C  |   D  |   E  |   F  |   G  |   H  |   I  |   J  |   K  |   L  |   M  | N  |   O  |   P  |   Q  |   R  |   S  |   T  |   U  |   V  |   W  |   X  |   Y  |   Z

F

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 o