Firn LineThe highest level to which the fresh snow on a glacier's surface retreats during the melting season.
First Contingency Reliability CriteriaThe requirement that an electric system be planned and operated so that it can safely withstand the loss of the largest single system element (i.e.
First Law of ThermodynamicsStates that energy cannot be created or destroyed, but only changed from one form to another.
Fiscal Impact AnalysisThe analysis of the estimated taxes that a development project would generate in comparison to the cost of providing municipal services demanded by that…
Fiscal Year (FY)The U.S. Government's 12-month financial year, from October to September, of the following calender year; e.g.: FY 1998 extends from Oct. 1, 1997 to Sept.
Fischer & Porter Punched Tape Recorder GageA precipitation gage which converts weight into a code disk position. The code disk position is then punched on paper tape in a binary decimal format…
Fischer-Tropsch FuelsLiquid hydrocarbon fuels produced by a process that combines carbon monoxide and hydrogen.
FISHA laboratory technique used to look at genes or chromosomes in cells and tissues.
Fish & Wildlife Service (FWS)The U.S. Fish and Wildlife Service is the principal Federal agency responsible for conserving, protecting and enhancing fish, wildlife and plants and…
Fish ladder (fishway)An inclined trough which carries water from above to below a dam so that fish can easily swim upstream.
FisheryA term used for a lake, river or stream where people can catch fish, or even a particular kind of fish, such as a bass or trout fishery.
Fishery Closure AreaA fishery closed or restricted by a government entity. Such closure prohibits fishing for commercial, recreational, or subsistence purposes.
Fishery Management CouncilsRegional councils which were established under the Magnuson-Stevens Fishery Conservation and Management Act.
Fishery Management ZoneAreas where fishing for some or all species is prohibited to protect critical habitats, rebuild fish stocks, ensure against overfishing, or enhance…
FishingThe operation of recovering an object left or dropped in a drill hole.
FissionThe splitting of heavier atomic nuclei into lighter ones. In the case of heavy atoms (e.g., uranium, plutonium), this will release energy.
Fission productsNuclei formed by the fission of heavy elements. They are of medium atomic weight and almost all are radioactive. Examples: strontium-90, cesium-137.
Fissure, earth or groundSurface fractures resulting from subsidence, often due to the withdrawal of groundwater and compaction of an aquifer.
FitnessThe survival value and the reproductive capability of an individual, compared to that of competitor individuals of the same or other species within a…
fixationThe situation in which only one allele for a given gene/locus is present in a population.
Fixed amount-frequency schedulingMethod of irrigation scheduling that involves water delivery at a fixed rate or a fixed volume and at constant intervals.
fixed bedA bed of closely spaced particles through which gases move up or down for purposes of gasification or combustion.
fixed carbonThe carbon remaining after heating in a prescribed manner to decompose thermally unstable components and to distill volatiles.
Fixed price transactionsBuying or selling a commodity at a fixed price. For example, fixed physical gas prices are used to form indices at some locations; and fixed basis prices…
Flame Spread RatingA measure of the relative flame spread, and smoke development, from a material being tested.
flamingA technique for sterilizing instruments, to remove live micro-organism contaminants.
FlangeA ridge that prevents a sliding motion. A rib or rim for strength or for attachments. A rim or collar attached to one end of a pipe to give support.
Flanking LineA line of cumulus or towering cumulus clouds connected to and extending outward from the most active part of a supercell, normally on the southwest side.
Flanking regionThe DNA sequences extending on either side of a specific locus or gene.
Flap GateA 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…
FlareA rapid release of vast magnetic energy in a sunspot region, causing temperatures to rise tens of millions of degrees in a small area above the solar…
FlaringThe burning of waste gases through a flare stack or other device before releasing them to the air.
FlashA sudden, brief illumination of a conductive channel associated with lightning, which may contain multiple strokes with their associated stepped leaders…
Flash FloodA sudden flood event through a valley, canyon, or wash, following a short duration, high-intensity rainfall.
Flash Flood Guidance(FFG) Forecast guidance produced by the River Forecast Centers, often model output, specific to the potential for flash flooding (e.g.
Flash Flood Guidance (FFG)An internal product produced by the RFCs containing rainfall threshold values which must be exceeded in order to produce a flash flood.
Flash Flood Statement(FFS) In hydrologic terms, a statement by the NWS which provides follow-up information on flash flood watches and warnings.
Flash Flood Statement (FFS)A statement by the NWS which provides follow-up information on flash flood watches and warnings.
Flash Flood TableA table of pre-computed forecast crest stage values for small streams for a variety of antecedent moisture conditions and rain amounts.
Flash PointThe minimum temperature at which a liquid gives off vapor within a test vessel in sufficient concentration to form an ignitable mixture with air near the…
Flash-Steam Geothermal PlantsWhen the temperature of the hydrothermal liquids is over 350 F (177 C), flash-steam technology is generally employed.
FlashboardsTemporary barriers, consisting of either timber, concrete or steel, anchored to the crest of a spillway as a means of increasing the reservoir storage.
FlashingStrips of sheet metal bent to fit the angle between any two roof surfaces or between the roof and any projection, such as a chimney.
FlashpointThe minimum temperature at which sufficient vapor is released by a liquid or solid (fuel) to form a flammable vapor-air mixture at atmospheric pressure.
Flat Plate Solar Photovoltaic ModuleAn arrangement of photovoltaic cells or material mounted on a rigid flat surface with the cells exposed freely to incoming sunlight.
Flat Plate Solar Thermal/Heating CollectorsLarge, flat boxes with glass covers and dark-colored metal plates inside that absorb and transfer solar energy to a heat transfer fluid.
Flat RoofA slightly sloped roof, usually with a tar and gravel cover. Most commercial buildings use this kind of roof.
Flat slab or slab and buttress damA buttress dam with buttresses which support the flat slab of reinforced concrete which forms the upstream face.
Flat UniverseA universe where the geometry of space does not curve but is flat like a tabletop. In a flat universe the total energy density equals the critical density.
Flat-Black PaintNonglossy paint with a relatively high absorptance.
Flat-plate PVA type of photovoltaic solar energy technology that uses a flat plate onto which are installed solar cells.
Flat-plate reflector (heliostat)One of many components of a CSP power tower facility consisting of a large nearly-flat mirror, mounted on a support structure that tracks the sun's…
FlatironsTriangular-shaped landforms along mountain ranges formed by erosion of steeply inclined rock layers or hogbacks.
Flatness ProblemUnder normal gravity, any slight deviation from flatness should quickly get larger : for example a closed universe should recollapse or an open universe…
FlatsLevel or nearly level areas of land marked by little or no relief.
Flats wetlandA level landform composed of unconsolidated sediments, usually mud or sand. Flats are unvegetated or support sparse plant communities, often composed of…
flavin adenine dinucleotide(Abbreviation: FAD). A co-enzyme important in various biochemical reactions. It comprises a phosphorylated vitamin B2 (riboflavin) molecule linked to AMP…
Fleet angleThe angle between the position of a rope or cable at the extreme end wrap on a drum and a line drawn perpendicular to the axis of the drum.
Flexible pipePipe designed to transmit the backfill load to the soil at the sides of the pipe.
Flexible-fuel vehicleA vehicle with a single fuel tank designed to run on varying blends of unleaded gasoline with either ethanol or methanol.
FlingRefers to a near field long period pulse from a strong ground motion resulting in a unidirectional ground heave after rupture.
Flip bucketAn energy dissipator located at the downstream end of a spillway and shaped so that water flowing at a high velocity is deflected upwards in a trajectory…
Float-Zone ProcessIn reference to solar photovoltaic cell manufacture, a method of growing a large-size, high-quality crystal whereby coils heat a polycrystalline ingot…
Floatable daysThe number of days during the recreation season on which it is safe to allow floating activities on recreation facilities.
Floatable flowsRiver flows which make rafting and other floating recreation possible.
Floating price transactionsBuying or selling a commodity at a price that is not fixed and will be set by mutual agreement, usually based a published price index.
Floating StorageUse of LNG tanker ships for LNG storage, rather than simply for transportation, to take advantage of temporal and geographic LNG price differences.
FlocLoose, open-structured mass formed in a suspension by the aggregation of minute particles.
flocculantA chemical agent that causes small particles to aggregate (flocculate).
FlocculationThe process of forming flocs. A step in water filtration in which alum is added to cause particles to clump together.
flocculeA micro-organism aggregate or colloidal particle floating in or on a liquid. The cloudy appearance of micro-organism contaminated liquid media illustrates…
FloeAn accumulation of frazil flocs (also known as a "pan") or a single piece of broken ice.
FloodA general and temporary condition of partial or complete inundation of two or more acres of normally dry land area or of two or more properties (at least…
Flood boundaryLine drawn or outer edge of colored (inundation) area on an inundation map to show the limit of flooding.
Flood CategoriesTerms defined for each forecast point which describe or categorize the severity of flood impacts in the corresÂponding river/stream reach.
Flood control capacityReservoir capacity assigned to the sole purpose of regulating flood inflows to reduce flood damage downstream. See exclusive flood control capacity.
Flood control pool (flood pool)Reservoir volume above active conservation capacity and joint use capacity that is reserved for flood runoff and then evacuated as soon as possible to…
Flood CrestThe maximum height of a flood wave as it passes a location.
Flood frequencyRefers to the probability (in percent) that a flood will occur in a given year.
Flood Frequency Curve(1) A graph showing the number of times per year on the average, plotted as abscissa, that floods of magnitude, indicated by the ordinate, are equaled or…
Flood GateA gate to control flood releases from a reservoir.
Flood Hazard AreaTotal stream and adjacent area periodically covered by overflow from the stream channel containing 1) the floodway which is the channel itself and…
Flood hydrographA graph showing, for a given point on a stream, the discharge, height, or other characteristic of a flood with respect to time.