FracturingDeformation process whereby ice is permanently deformed, and fracture occurs.
Frazil IceFine spicules, plates, or discoids of ice suspended in water. In rivers and lakes, frazil is formed in supercooled, turbulent water.
Frazil SlushAn agglomerate of loosely packed frazil which floats or accumulates under the ice cover.
Free Ground WaterUnconfined ground water whose upper boundary is a free water table.
FreeboardPortion of the dam above spillway level to protect the dam against washout.
Freeze-thaw damageDamage to concrete caused by extreme temperature variations as noted by random pattern cracking.
FreezeoutDeeply frozen over for long periods of time.
Freezeup dateDate on which the water body was first observed to be completely frozen over.
Freezup jamIce jam formed as frazil ice accumulates and thickens.
French DrainA covered ditch containing a layer of fitted or loose stone or other pervious material.
Frequency CurveA curve that expresses the relation between the frequency distribution plot, with the magnitude of the variables as abscissas and the number of…
Frequency demand schedulingMethod of irrigation scheduling similar to demand scheduling, but typically involves a fixed duration of the delivery, such as 24 hours.
freshwaterA term referring to bodies of water that do not have salt.
FrictionResistance to motion when one body is sliding or tending to slide over another.
Friction HeadThe energy lost from the movement of a fluid in a conduit (pipe) due to the disturbances created by the contact of the moving fluid with the surfaces of…
Front end loaderA tractor loader that both digs and dumps in front.
Frost actionFreezing and thawing of moisture in materials and the resultant effects on these materials and on structures of which they are a part of with which they…
Frost heaveThe raising of a surface due to the accumulation of ice in the underlying soil or rock.
Frost lineThe greatest depth to which ground may be expected to freeze.
Froude numberThe ratio of inertial forces to gravitational forces in flow. It is also the ratio of the flow velocity to the velocity of a small gravity wave in the…
FryImmature fish from the time they hatch to the time they become fingerlings.
FS- U.S. Forest Service, feasibility study, factor of safety.
Fuel replacement energyElectric energy generated at a hydroelectric plant as a substitute for energy which would have been generated by a thermal electric plant.
Full irrigation service landIrrigable land now receiving, or to receive, its sole and generally adequate water supply through facilities which have been or are to be constructed by…
Full poolVolume of water in a reservoir at normal water surface. The reservoir level that would be attained when the reservoir is fully utilized for all project…
FurrowA natural or man-made narrow depression in the earth's surface. A narrow trenchlike plowed depression in the earth surface to keep surface water away from…
FuseA safety device consisting of a short length of relatively fine wire, mounted in a holder or contained in a cartridge and connected as part of an…
Fuse plug spillwayA form of auxiliary spillway consisting of a low embankment designed to be overtopped and washed away during an exceptionally large flood.
Future withoutWhat would occur if no action were taken. The future without taking any action to solve the problem. See baseline condition.
GabionWire basket, filled with stones, used to stabilize banks of a water course and to enhance habitat.
Gabion damSpecial name given to a crib dam when built with gabions. See dam.
Gage(1) A device for indicating the magnitude or position of a thing in specific units, when such magnitude or position undergoes change, for example: The…
Gage DatumThe arbitrary zero datum elevation which all stage measurements are made from.
Gage HeightThe water-surface elevation referred to some arbitrary gage datum. Gage height is often used interchangeably with the more general term stage, although…
Gage height (G.H.)The water surface elevation referred to some arbitrary gage datum. Gage height is often used interchangeably with the more general term "stage," although…
Gage ZeroThe elevation of zero stage. (Same as gage datum.)
Gaging StationA particular site on a stream, canal, lake, or reservoir where systematic observations of hydrologic data are obtained.
Gaining streamStream or reach that receives water from the zone of saturation.
GalleryA passageway within the body of a dam, its foundation, or abutments used for inspection, foundation grouting, and/or drainage.
GallonA unit of measure equal to four quarts or 128 fluid ounces.
GalvanizeTo coat a metal (especially iron or steel) with zinc. Galvanization is the process of coating a metal with zinc.
GantryAn overhead structure that supports machines or operating parts, such as a gantry crane.
Gantry craneA fixed or traveling, bent-supported crane for handling heavy equipment.
Gaseous supersaturationCondition of higher levels of dissolved gases in water due to entrainment, pressure increases, or heating.
GateA device that controls the flow in a conduit, pipe, or tunnel without obstructing any portion of the waterway when in the fully open position.
Gate chamber (valve chamber)A chamber in which a guard gate in a pressurized outlet works or both the guard and regulating gates in a free-flow outlet works are located.
Gate hangerA device used to maintain a set gate opening.
Gate structurePortion of spillway between inlet channel and chute, tunnel or conduit, which contains gates, such as radial gates.
Gate valveA valve with a circular-shaped closing element that fits securely over an opening through which water flows.
Gated pipePortable pipe with small gates installed along one side for distributing irrigation water to corrugations or furrows.
Gated spillwayOverflow section of dam restricted by use of gates that can be operated to control releases from the reservoir to ensure the safety of the dam.
Gauge (gage)Device for registering water level, discharge, velocity, pressure, etc. Thickness of wire or sheet metal.
Gauge heightElevation of water surface measured by a gauge. See gage height.
Gauge pressureAbsolute pressure minus atmospheric pressure. The pressure within a closed container as measured with a gauge. Sometimes referred to as relative pressure.
Gauging stationSpecific location on a stream where systematic observations of hydrologic data are obtained through mechanical or electrical means. See gauge.
GenerationThe electricity generated by a system as recorded by a KWH meter, recorded in KWH or MWH.
Generation dispatch and controlAggregating and dispatching (sending off to some location) generation from various generating facilities, providing backup and reliability services.
GeneratorA device for converting mechanical energy to electrical energy.
Generator nameplate capacityThe full-load continuous rating of a generator, prime mover, or other electric power production equipment under specific conditions as designated by the…
Geographic Information System (GIS)(GIS)A set of computer tools and procedures used to collect, manage, analyze and display information associated with a specific location; a computerized…
GeohydrologyGeological study of the character, source, and mode of ground water.
GeologyThe science that deals with the study of the materials, processes, environments, and history of the Earth, including the rocks and their formation and…
GeomorphicPertaining to those processes that affect the form or shape of the surface of the earth.
GeomorphologyGeological study of the configuration, characteristics, origin, and evolution of land forms and earth features.
GeophysicsRefers to the physics of the earth, e.g., seismology, oceanography, volcanology, geomagnetism, etc.
GeotextilesAny fabric or textile (natural or synthetic) used as an engineering material in conjunction with soil, foundations, or rock.
Giant salvinia (Salvinia molesta)An aquatic fern prohibited in the United States by Federal law. An invasive, rapidly growing plant that covers the surfaces of lakes and streams forming…
Gigawatt (GW)(GW)A unit of power equal to 1 billion Watts; 1 million kilowatts, or 1,000 megawatts.
Glacial moraineA mass of loose rock, soil, and earth deposited by the edge of a glacier.
Glacial striationsLines carved into rock by overriding ice, showing the direction of glacial movement.
Glacial tillAn unsorted, unstratified mixture of fine and coarse rock debris deposited by a glacier.
GlacierBodies of land ice that consist of recrystallized snow accumulated on the surface of the ground, and that move slowly downslope.
Glacier (ice sheet)A large thick mass of ice formed on land by the compacting and recrystallization of old snow and move under the influence of gravity.
Glacier Dammed LakeThe lake formed when a glacier flows across the mouth of an adjoining valley and forms an ice dam.
Global positioning systems (GPS)Space-based radio positioning systems that provide 24-hour, three-dimensional position, velocity, and time information to suitably equipped users anywhere…
GneissMetamorphic rock that displays distinct banding of light and dark mineral layers.
GOES Data Collection System (DCS)(DCS)A data collection system under NESDIS which is comprised of the DCPs, and the NESDIS Command and Data Acquisition (CDA) System components.
GrabenDown-dropped block of rock bounded on both sides by faults. See fault-block.
GradationProportion of material of each grain-size present in a given soil. The proportions by mass of a soil or fragmented rock distributed in specified…
Grade (pitch)The elevation of a surface or a surface slope. The elevation of the invert of the bottom of a pipeline, canal, culvert, or conduit.
Grade stakeA stake indicating the amount of cut or fill required to bring the ground to a specified level.
Graded streamStreams that receive and carry away equal amounts of sediment.
GraderA machine with a centrally located blade that can be angled to cast to either side, with independent hoist control on each side.
GradientGeneral slope or rate of change in vertical elevation per unit of horizontal distance of water surface of a flowing stream.
GraniteA coarse-grained felsic intrusive (or plutonic) igneous rock with at least 65% silica.
GraniticGeneral term for all light-colored, granite-like igneous rocks.
GranodioriteCoarse-grained intrusive igneous rock with less quartz and more feldspar than true granite and typically darker.
GrappleA clamshell-type bucket having three or more jaws.
GravelLoose rounded fragments of rock that will pass a 3-inch sieve and be retained on a No. 4 U.S. Standard sieve (3/16 inch).
Gravel blanketThin layer of gravel spread over an area either of natural ground, excavated surface, or embankment.
Gravel surfacingLayer of gravel spread over an area intended for vehicular or personnel traffic, such as roads, parking lots and sidewalks.