Terms of Hydrology (R)

radar (-rainfall) equation :

Equation defining the maximum range to be anticipated from a part ...

radioactive dating :

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

radioactive tracer :

Radioactive material detectable by its nuclear radiation and suit ...

radius of influence :

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

rain :

Precipitation of liquid water, either in the form of drops of mor ...

rain shadow :

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

rain simulator :

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

rainfall (depth) :

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

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 runof ...

rainfall intensity :

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

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 ...

rainfall maximization :

Procedure used to derive probable (possible) maximum precipitatio ...

raingauge shield; rain gage shield (A) :

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

raingauge; rain gage (A) :

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

random error :

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

random process :

Generally synonymous with the more usual and preferable ""stochas ...

random walk model :

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

rapids :

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

rate of accretion :

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

rating curve (rating table) :

Curve showing the relation between stage and discharge of a strea ...

rating curve shift :

Change in the stage-discharge relationship.

rating flume :

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

rational method :

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

raw water :

Water which has received no treatment whatsoever, or water enteri ...

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 o ...

Recharge :

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

recording raingauge; recording rain gage (A) :

Instrument which includes an arrangement for the time recording o ...

recovery :

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

recovery test :

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

redox potential (rH) :

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

reduction :

Chemical process leading to loss of oxygen or increase of electro ...

reference climatological station :

Climatological station the data of which are intended for the pur ...

reflectivity :

Ratio of the energy reflected by a given surface to that incident ...

regime channel :

Channel in erodible material which is in average equilibrium in i ...

regional analysis :

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

Regression Analysis :

Statistical method developed to investigate the interdependence o ...

regression coefficient :

Coefficient of an independent variate in a regression equation. F ...

regression line :

Diagrammatic exposition of a regression equation, generally refer ...

regulated flow :

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

regulating reservoir :

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

relative humidity :

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

relative permeability :

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

remote sensing :

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

representative basin :

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

reservoir :

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

reservoir life expectancy :

Period of time a reservoir can be expected to be economically usa ...

reservoir release rules :

Rules governing the way in which volumes of water are released fr ...

reservoir trap efficiency :

Percentage of incoming sediment trapped by a reservoir.

Residence time :

Period during which water or a substance remains in a component p ...

residual :

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

residual mass curve :

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

residual rain :

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

resolution :

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

response function :

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

resurgence :

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

retarded flow :

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

retarding basin :

Basin which reduces peak flood flows of a stream through temporar ...

retention :

That part of the precipitation falling on a drainage area which d ...

retention curve :

Graph representing the suction pressure versus the moisture or wa ...

return flow :

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

return period :

Long-term average interval of time or number of years within whic ...

Reynolds number :

Dimensionless number expressing the ratio of inertia forces to vi ...

rheology :

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

ridging :

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

riffle :

Shallow rapids in an open stream, where the water surface is brok ...

rill :

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

rime :

Deposit of ice composed of grains more or less separated by trapp ...

rip :

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

ripening of snow :

Saturating of snow cover by liquid water.

Rippl method (mass curve storage analysis) :

Procedure for determining required reservoir storage using a grap ...

ripples :

Small, undulating ridges and furrows (or crests and troughs) form ...

rising limb :

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

rising stage :

Water stage in a stream which increases continuously during a cer ...

Risk :

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

river :

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

river bed :

Lowest part of a river valley shaped by the flow of water and alo ...

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 ...

roiliness :

Turbid, milky appearance of water due to suspended particles of s ...

root zone :

Layer of the soil containing plant roots.

rotten ice :

Floating ice which has become honeycombed in the course of meltin ...

Runoff :

That part of precipitation that appears as streamflow.

runoff coefficient :

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

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.