Terms of Hydrology (A)

abiotic :

Pertaining to the non-living part of an ecosystem or to an enviro ...

ablation :

(1) Combined processes (such as melting, sublimation, evaporation ...

abrasion :

Act or process of wearing down by friction, or the resulting effe ...

abrupt wave :

Translatory wave or rapid increase in depth of water in an open c ...

absolute humidity :

Mass of water contained in a unit volume of moist air.

absorption band :

Range of wavelengths (or frequencies) in the electromagnetic spec ...

absorption loss :

Loss of water by infiltration from a canal, reservoir or other bo ...

abstraction :

Removal of water from any source, either permanently or temporari ...

accelerated flow :

In channel hydraulics, flow in which the velocity increases in th ...

acceptance capacity :

Quantity of pollutants which a water body can accept without the ...

Accretion :

(1) Process of accumulation of sediment by flowing water. (2) Add ...

accumulation :

(1) Process of storage of products of erosion or abrasion, or of ...

accumulative precipitation gauge; cumulative precipitation gage (A) :

Precipitation gauge used at stations which are visited only at lo ...

accuracy :

Closeness of computations, estimates or measurements to the exact ...

acid rain :

Rain which in the course of its history has combined with chemica ...

acidity of water :

Amount of strong acids, given as milliequivalents of a strong bas ...

acidizing :

Process of forcing acid into carbonated rocks such as limestone, ...

active basin area :

Basin area excluding undrained parts.

active sensing system :

(1) Sensing system having its own source of electromagnetic radia ...

actual density of soil :

Mass of an oven-dry soil sample per unit volume (soil particles o ...

actual evaporation :

Quantity of water evaporated from an open water surface or from t ...

actual evapotranspiration :

Sum of the quantities of water evaporated from the soil and the p ...

adhesive water :

Water held in the soil by molecular attraction and forming a film ...

admissible concentration limit :

Upper limit of concentration of a substance in water which is not ...

advection :

Process of transfer of air-mass properties by the velocity field ...

Aeration :

Addition of air to water resulting in a rise of its dissolved oxy ...

aerobic condition :

Condition of water which contains dissolved oxygen sufficient to ...

afflux :

Rise in water level immediately upstream of, and due to, an obstr ...

aggradation :

Process of raising a land surface by the deposition of sediment.

aggressive water :

Water having the power of dissolving or disintegrating solids in ...

air humidity :

Water-vapour content of the air.

air moisture :

Water as it occurs in various forms in the air.

air-line correction :

Depth correction in sounding line for that portion of the line wh ...

alarm level :

Water level (stage) at, or approaching, flood level which is cons ...

Albedo :

Ratio of reflected to incoming radiation, usually given in per ce ...

Algal bloom :

Sudden proliferation of algae in a water body.

alkaline water :

Water with a pH value above 7.

alkalinity of water :

Amount of cations balanced by weak acids, expressed as milliequiv ...

alluvial :

deposited from flowing water or belonging to such a deposit. (2) ...

alluvial channel :

Channel with a movable bed in loose sedimentary materials.

alluvial fan :

Alluvial deposit of a steep stream where it issues on to a plain.

alluvial plain :

Plain formed by the deposition of alluvial material eroded from a ...

alluvium :

Clay, silt, sand, gravel, pebbles or other detrital material depo ...

altitude :

Vertical distance of a level, a point or an object con- sidered a ...

anaerobic condition :

Condition of water in which the dissolved oxygen is too low to su ...

analogue model; analog model (A) :

Representation of a physical system (prototype) by an analogous p ...

anchor ice :

Submerged ice found attached to underwater objects (such as the c ...

anemometer :

Instrument which measures wind speed or wind speed and direction.

angularity correction :

Correction to be made to an observed velocity at a cross section ...

annual exceedence series :

Series of values of independent events, such as floods, occurring ...

Annual flood :

(1) Highest peak discharge in a water year. (2) Flood which has b ...

annual maximum series :

Extreme-value series with largest annual values.

annual minimum series :

Extreme-value series with smallest annual values.

annual runoff :

Total volume of water that flows during a year, usually referring ...

annual series :

Hydrological series the terms of which represent some characteris ...

annual storage :

Volume of water that can be stored in a reservoir to cope, partly ...

anoxic :

Condition in which the concentration of dissolved oxygen is so lo ...

antecedent precipitation index :

Weighted summation of past daily precipitation amounts, used as a ...

antecedent soil moisture :

Soil moisture state in a catchment at the start of a rain storm.

antidunes :

Mobile bed forms which occur at a stream velocity higher than tha ...

applied hydrology :

That branch of hydrology which refers to its application to field ...

approach channel :

Reach of channel upstream of a gauging structure in which suitabl ...

aquiclude :

Saturated bed, formation, or group of formations of low hydraulic ...

Aquifer :

Permeable water-bearing formation capable of yielding exploitable ...

aquifer test :

Any test whereby the aquifer response to a stress imposed on the ...

aquifuge :

Formation which has no interconnected openings and hence cannot a ...

aquitard :

Geological formation of a rather impervious and semi-confining na ...

area of influence :

Area around a pumping or a recharging well in which the water tab ...

area-elevation curve :

Curve showing what part of the area of a river basin is situated ...

areal precipitation :

Precipitation in a specific area expressed as the average depth o ...

areal reduction factor (of rainfall) :

Ratio of a mean areal rainfall for a given duration and given ret ...

arheic :

Relates to areas which almost completely lack superficial drainag ...

arid zone :

(1) Zone in which precipitation is lacking to the extent that irr ...

aridity :

(1) Condition in which evaporation always exceeds precipitation. ...

arid-zone hydrology :

Hydrology of arid or semi-arid zones stressing the interaction be ...

arithmetic mean :

(1) Sum of a set of values x1, x2, ..., xn divided by their numbe ...

armouring; armoring (A) :

Formation of a resistant layer of relatively large particles resu ...

artesian aquifer :

Aquifer whose piezometric surface lies above the ground surface ( ...

artesian basin :

Geological structural feature, often of important dimensions, in ...

artesian head :

Elevation of the piezometric surface in an artesian aquifer above ...

artesian spring :

Spring yielding water from an artesian aquifer, generally through ...

artesian well :

Well tapping a confined or artesian aquifer in which the static w ...

artificial precipitation :

Precipitation of water particles, in the liquid or solid form, at ...

artificial recharge :

Augmentation of the natural replenishment of ground- water in aqu ...

aspect :

Direction towards which a land slope faces. The direction is meas ...

attached groundwater :

Portion of groundwater adhering to the pore walls. It is assumed ...

aufeis :

Ice formed when brook water or underground water emerges and free ...

auger sampler :

A screwlike boring tool designed for taking samples in soil, clay ...

autocorrelation :

Internal correlation between members of a series of observations ...

autocorrelation coefficient :

Measure of the autocorrelation between pairs of a series given by ...

automatic station :

Station at which instruments make and either transmit or record o ...

autoregressive process :

Process which produces series having autocorrelation and random c ...

autoregressive series :

Realization of an autoregressive process.

available head :

Amount of fall in a stream which is available for hydroelectric p ...

available soil moisture :

Water in the soil available to plants. It is normally taken as th ...

available storage capacity :

Volume of water in a reservoir between the minimum and the maximu ...

avalanche :

Mass of snow and ice falling suddenly down a mountain-side and of ...

average :

In ordinary usage, the average is often understood to refer to th ...

average velocity :

Discharge divided by the cross-sectional area at right angles to ...

average year :

Year for which the observed hydrological or meteo- rological quan ...