Terms of Hydrology (R)

radar (-rainfall) equation :

Equation defining the maximum range to be anticipated from a particular rad ...

radioactive dating :

Method of age determination based on the property of radioactive decay of i ...

radioactive tracer :

Radioactive material detectable by its nuclear radiation and suitable for w ...

radius of influence :

Distance from the axis of a pumped or recharged well at which the effect of ...

rain :

Precipitation of liquid water, either in the form of drops of more than 0.5 ...

rain shadow :

Region, situated on the lee side of a mountain, or mountain range, where th ...

rain simulator :

Device to apply water in a form and at a rate comparable with natural rainf ...

rainfall (depth) :

Supply of liquid water falling from the atmosphere (expressed as depth of w ...

rainfall distribution :

Manner in which the depth of rainfall varies in space and time.

rainfall excess :

That part of rainfall which contributes directly to surface runoff.

rainfall intensity :

Rate at which rainfall occurs, expressed in units of depth per unit of time ...

rainfall intensity pattern :

Distribution of rainfall rate, in time, during a storm.

rainfall intensity return period :

Average time interval in years between the occurrence of rainfall of a give ...

rainfall maximization :

Procedure used to derive probable (possible) maximum precipitation.

raingauge shield; rain gage shield (A) :

Protective attachment placed around the funnel of a raingauge to eliminate ...

raingauge; rain gage (A) :

Instrument for measuring the depth of water from precipitation at a point.

random error :

Deviation of a computed, estimated or measured value from the true value, t ...

random process :

Generally synonymous with the more usual and preferable ""stochastic proces ...

random walk model :

Statistical model of sequences (e.g. of consecutive movements of a particle ...

rapids :

Reach of a stream where the flow is very swift and shooting, and where the ...

rate of accretion :

Amount of water added to an aquifer per unit area and per unit time.

rating curve (rating table) :

Curve showing the relation between stage and discharge of a stream at a hyd ...

rating curve shift :

Change in the stage-discharge relationship.

rating flume :

Open conduit built in a channel to maintain a stable regimen for the purpos ...

rational method :

Formula expressing the estimated peak rate of storm runoff as the product o ...

raw water :

Water which has received no treatment whatsoever, or water entering a plant ...

reach :

Length of open channel between two defined cross-sections. (TR)

real-time processing :

Concurrent processing of data upon their reception.

real-time transmission :

Transmission of data immediately upon observation.

receding front :

Air/water interface in dewatering of a water-table aquifer.

recession :

Period of decreasing discharge as indicated by the falling limb of a hydrog ...

Recharge :

Process by which water is added from outside to the zone of saturation of a ...

recording raingauge; recording rain gage (A) :

Instrument which includes an arrangement for the time recording of the dept ...

recovery :

(1) Rising movement of the water table or the piezometric surface caused by ...

recovery test :

Pumping test consisting of the measurement, at pre- determined time interva ...

redox potential (rH) :

Index, analogous to pH, giving a quantitative measure for the oxidation or ...

reduction :

Chemical process leading to loss of oxygen or increase of electrons by a co ...

reference climatological station :

Climatological station the data of which are intended for the purpose of de ...

reflectivity :

Ratio of the energy reflected by a given surface to that incident on it: th ...

regime channel :

Channel in erodible material which is in average equilibrium in its cross-s ...

regional analysis :

Extension of the results of the analysis of point data to a region.

Regression Analysis :

Statistical method developed to investigate the interdependence or relation ...

regression coefficient :

Coefficient of an independent variate in a regression equation. For a first ...

regression line :

Diagrammatic exposition of a regression equation, generally referring to a ...

regulated flow :

Flow in a stream that has been subjected to regulation by water control str ...

regulating reservoir :

Reservoir used to release controlled amounts of water to a river for abstra ...

relative humidity :

At a given pressure and temperature, the percentage ratio of the mole fract ...

relative permeability :

Ratio of the effective permeability for a given flowing phase to the intrin ...

remote sensing :

Measurement or acquisition of information on some property of an object or ...

representative basin :

(1) Basin permitting the study of the hydrological cycle in a characteristi ...

reservoir :

Body of water, either natural or man-made, used for storage, regulation and ...

reservoir life expectancy :

Period of time a reservoir can be expected to be economically usable determ ...

reservoir release rules :

Rules governing the way in which volumes of water are released from a reser ...

reservoir trap efficiency :

Percentage of incoming sediment trapped by a reservoir.

Residence time :

Period during which water or a substance remains in a component part of the ...

residual :

(1) If a model is fitted to data, the difference between model-computed and ...

residual mass curve :

Graph of the cumulative departures from a given reference, such as the arit ...

residual rain :

Rain that falls at the end of a storm at a rate less than the infiltration ...

resolution :

(1) In remote sensing: ability of an entire remote sensor system, including ...

response function :

Mathematical representation of the behaviour of a (hydrological) system due ...

resurgence :

Reappearance above ground, at the end of its underground course, of a surfa ...

retarded flow :

Flow in which the velocity decreases with time at a certain point, or in wh ...

retarding basin :

Basin which reduces peak flood flows of a stream through temporary storage.

retention :

That part of the precipitation falling on a drainage area which does not es ...

retention curve :

Graph representing the suction pressure versus the moisture or water conten ...

return flow :

Any flow which returns to a stream channel or to the groundwater after use.

return period :

Long-term average interval of time or number of years within which an event ...

Reynolds number :

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

rheology :

That branch of the mechanics of continua which deals with stress, deformati ...

ridging :

Pressure process by which floating ice becomes forced up in ridges.

riffle :

Shallow rapids in an open stream, where the water surface is broken into wa ...

rill :

Very small channel created by erosion in which the flow is concentrated.

rime :

Deposit of ice composed of grains more or less separated by trapped air, so ...

rip :

Oscillatory waves caused by the interaction of water currents or by a rapid ...

ripening of snow :

Saturating of snow cover by liquid water.

Rippl method (mass curve storage analysis) :

Procedure for determining required reservoir storage using a graphical (or ...

ripples :

Small, undulating ridges and furrows (or crests and troughs) formed by the ...

rising limb :

Part of a hydrograph in which the discharge is increasing towards a peak.

rising stage :

Water stage in a stream which increases continuously during a certain perio ...

Risk :

(1) Potential realization of unwanted consequences of an event, a function ...

river :

Large stream which serves as the natural drainage channel for a drainage ba ...

river bed :

Lowest part of a river valley shaped by the flow of water and along which m ...

river mouth :

Place of discharge of a river into a sea or a lake.

river pool :

A small and rather deep body of quiet water in a watercourse.

river training :

Engineering river-works built in order to direct the flow, or to lead it in ...

roiliness :

Turbid, milky appearance of water due to suspended particles of silt or cla ...

root zone :

Layer of the soil containing plant roots.

rotten ice :

Floating ice which has become honeycombed in the course of melting, and whi ...

Runoff :

That part of precipitation that appears as streamflow.

runoff coefficient :

(1) Ratio of runoff depth to precipitation depth. (2) Coefficient used in t ...

runoff plot :

Small, experimental area for the study of surface runoff.

rush of snowmelt flood :

Rate of water rise and fall during spring snowmelt flood.