Terms of Hydrology (F)

fall :

(4) Drop of water level at a point of a stream during a certain time.

fall velocity :

Final velocity of solid particles falling in water or air or of raindrops i ...

falling limb :

Part of a hydrograph in which the discharge is decreasing from a peak.

fallout :

Material, especially when radioactive, deposited from the atmosphere.

fall-stage-discharge relation :

Family of curves which expresses the relationship between water surface slo ...

false colour picture; false color picture (A) :

Picture with colours artificially changed for a better recognition of certa ...

fast ice :

Sea ice which remains fast or fixed, generally in the position where origin ...

fault spring :

Spring fed by deep groundwater which rises through a fault.

fetch :

Area in which ocean, lake and reservoir waves are generated by the wind. Th ...

field :

Field of a scalar (e.g. pressure) , vector (e.g. velocity) , tensor (e.g. s ...

field capacity :

Amount of water held in a soil after gravitational water has drained away.

Filtration :

Process of passing a liquid through a filtering medium for the removal of s ...

Fines :

Clay and silt fractions of a rock or soil.

fingering :

Displacement process of one fluid by another whereby irregular movement (in ...

firm yield :

Minimum assured yield of water from a reservoir during its life.

firn (snow) :

Snow which has become granular and dense under the action of various proces ...

firn line :

Boundary which, at the glacier's surface, separates the zone of accumulatio ...

fissure spring :

Spring which issues from a fissure.

fissured rock model :

Model comparing flow through soils to flow through a rock with a system of ...

five-point method :

Method for determining the mean velocity in the vertical in a stream of dep ...

flash flood :

Flood of short duration with a relatively high peak discharge.

flashy stream :

Stream which is susceptible to carry flash floods.

flat-V weir :

Long-base weir with a triangular or other shape of longitudinal profile and ...

float :

Any natural or man-made body which is supported and partly or fully immerse ...

float gauge; float gage (A) :

Gauge consisting essentially of a float which rides on the water surface an ...

floating pan :

Evaporation pan floating on a body of water.

flood :

(1) Rise, usually brief, in the water level in a stream to a peak from whic ...

flood channel :

(1) Channel for flood water. (2) Enlarged stream channel occupied during pe ...

flood control :

Protection of land areas from overflow, or minimization of damage caused by ...

flood control reservoir :

Reservoir used only for the temporary storage of flood water which is then ...

flood control works :

Levees, banks or other works along a stream, designed to confine it to a pa ...

flood crest :

Highest (peak) elevation of the water level during a flood in a channel.

flood forecasting :

Estimation of stage, discharge, time of occurrence, and duration of a flood ...

flood frequency :

Number of times a flood above a given discharge or stage is likely to occur ...

flood marks :

Natural marks left on a structure or objects indicating the maximum stage o ...

Flood plain :

Nearly level land along a stream flooded only when the streamflow exceeds t ...

flood probability :

Probability of a flood of a given stage or discharge being equalled or exce ...

flood proofing :

Techniques for preventing flood damage in a flood-hazard area.

flood routing :

Technique used to compute the movement and change of shape of a flood wave ...

flood warning :

Advance notice that a flood may occur in the near future at a certain stati ...

flood wave :

Rise in streamflow to a maximum crest, and its subsequent recession, caused ...

flooded area :

Area covered by water when streamflow exceeds the carrying capacity of a ch ...

flooding :

(1) Overflowing by water of the normal confines of a stream or other body o ...

floodwall :

Wall built to confine a stream to prevent flooding.

floodway :

Channel constructed to carry excess flood water (in excess of the quantity ...

flow net :

System of streamlines and equipotential lines. The drop of potential betwee ...

flow pattern :

Set of streamlines at a given instant.

flow velocity :

Vector indicating the speed and direction, at a point, of a moving liquid, ...

flow-duration curve :

Curve showing the percentage of time during which the flow of a stream is e ...

flowmeter :

Instrument for measuring the rate of flow in a conduit or open channel.

flowmeter logging :

Measurement of varying velocities of water movement in a well, due to both ...

fluid line :

Line in a moving fluid continuum followed by a given fluid particle.

fluidization :

State of solid particles suspended in a moving fluid and flowing with it.

flume (measuring flume) :

Man-made channel with clearly specified shape and dimensions which may be u ...

flushing :

Removal by sudden flow of deposits which have lodged in conduits, sewers, o ...

fluvial dynamics :

Branch of potamology which deals with the action of forces on riverbed mate ...

fluvial morphology :

Science of the formation of beds and flood plains and of forms of streams b ...

foehn :

Wind warmed and dried by descent, in general on the lee side of a mountain.

ford :

Shallow place where a stream may be crossed by traffic or by wading.

forebay :

Small reservoir or pond located at the head of a penstock or a pipeline. It ...

forecast :

Definite statement or statistical estimate of the occurrence of a future ev ...

forecast (warning) lead time :

Interval of time between the issuing of a forecast (warning) and the expect ...

forecast updating :

Revising a previous estimate of a quantity by using information acquired be ...

forecast verification :

Determination of the accuracy of a forecast through the statistical analysi ...

forecasting error :

Difference between a forecast and the observed value.

fork :

(1) Place where two or more streams flow together to form a larger stream. ...

fossil water :

Water infiltrated into an aquifer during an ancient geological period under ...

fracture porosity :

Porosity resulting from the presence of openings produced by the breaking o ...

fracture spring :

Spring flowing from a fracture in rock.

frazil ice :

Fine spicules, plates or discoids of ice suspended in water. In rivers and ...

free acidity :

Amount of strong acids in water, usually expressed as milliequivalents of a ...

free nappe :

Nappe the underside of which is not in contact with the overflow structure ...

free water content of snow :

That fraction, by weight, of liquid water which is contained in the interst ...

free weir :

Weir the flow of which is not submerged by the tail water.

freeboard :

Vertical distance between the normal maximum level of the surface of a liqu ...

freeze-up :

Formation of ice cover on a water surface due to seasonal cooling.

freezing point :

Temperature of solidification of a liquid under given conditions.

frequency analysis :

Procedure involved in interpreting a past record of hydrological events in ...

frequency curve :

Curve relating the possible values of a variate, e.g. the value of a specif ...

frequency distribution :

Specification of the way in which the frequencies of members of a populatio ...

fresh water :

Naturally occurring water having a low concentration of salts, or generally ...

fresh/salt-water interface :

Surface separating a body of fresh water and one of brackish or salt water, ...

freshet :

Minor flooding or overflowing of a stream caused by heavy rains or snowmelt ...

freshwater barrier :

Ridge of fresh groundwater kept at a sufficient head to avoid intrusion of ...

freshwater head :

Water head at a given point in an aquifer which would be measured in a piez ...

freshwater lens :

Freshwater body floating above saline groundwater.

friction losses :

Total energy losses in the flow of water due to friction between the water ...

front :

(1) Surface of separation of two air or water masses. (2) Moving air/water ...

frontal precipitation :

Precipitation caused by the expansion of air on ascent along or near a fron ...

frost :

Covering of ice, in one of its many forms, produced by the sublimation of w ...

Froude number :

Dimensionless number expressing the ratio of inertia forces to gravity forc ...

fully penetrating well :

Well which extends through the whole saturated depth of an aquifer and is c ...

funicular water :

Water present in the larger pores surrounding the solid particles of soil, ...