Terms of Hydrology (D)

daily storage :

Volume of water which can be stored daily in a reservoir between minimum an ...

Dam :

Barrier constructed across a valley for impounding water or creating a rese ...

darcy :

Unit of intrinsic permeability, defined as the permeability of a medium in ...

Darcy's law :

Law expressing the proportionality of the specific discharge of a liquid fl ...

data archiving :

Storage of data on a set of catalogued files which are held in some backup ...

data bank :

Comprehensive set of related data files for a specific application, usually ...

data collection platform (DCP) :

Automatic measuring device with a radio transmitter to provide contact via ...

data collection system :

Coordinated system for collecting observations from a hydrological network ...

data processing :

Handling of observational data until they are in a form ready to be used fo ...

datum level :

Horizontal surface used as a reference to which elevations are related.

dead storage :

Storage volume which cannot be released under normal conditions.

dead water :

Water in a state of slow or no circulation, usually leading to an oxygen dÄ ...

debris :

Any accumulation of loose material arising from the waste of rocks. It may ...

debris cone :

Deposit of soil, sand, gravel and boulders at the point where a mountain st ...

decay rate :

Rate of reduction of the concentration of a quantity, e.g. a pollutant, or ...

deep seepage :

Water which percolates below the root zone and towards a deeper water table ...

degree-day :

Algebraic difference, expressed in degrees C, between the mean temperature ...

delta :

Alluvial deposit at the mouth of a river; the geographical and geomorpholog ...

dendrohydrology :

Use of tree rings to study hydrological phenomena.

density :

Ratio of the mass of any volume of a substance to the mass of an equal volu ...

density current :

Phenomenon of gravity flow of a liquid relative to another liquid, or of re ...

denudation :

(1) Erosion by rain, frost, wind or water of the solid matter of the earth. ...

Depletion :

(1) Continued withdrawal of water from groundwater or a reservoir at a rate ...

depletion curve :

Curve showing a decreasing rate of runoff or discharge, caused by depletion ...

depletion rate :

Rate at which withdrawal depletes the storage in an aquifer or reservoir.

depression spring :

Spring which flows at the surface due solely to the fact that the land surf ...

depression storage :

Volume of water which is required to fill small depressions to their overfl ...

depth (total) of runoff :

Runoff volume from a drainage basin, divided by its area, in a specified ti ...

depth-area curve :

Curve showing the relationship between average rainfall depth and the area ...

depth-area-duration analysis :

Analysis of areal distribution of precipitation from a storm, usually made ...

depth-duration curve :

Curve showing the relationship between average rainfall depth or intensity ...

depth-integration sediment sampling :

Method to obtain a representative discharge-weighted water-sediment sample ...

depth-velocity integration method :

Method for computing the discharge in a channel by determining first the ar ...

Desalination :

Any established process by which the salt content of water is reduced suffi ...

design flood :

Flood hydrograph or instantaneous peak discharge adopted for the design of ...

design storm :

Rainfall amount and distribution adopted over a given drainage area, used i ...

detention reservoir :

Flood-control reservoir with uncontrolled outlets.

detention storage :

That part of precipitation which is temporarily stored en route to or in th ...

deterministic hydrology :

Method of analysis of hydrological processes, using a deterministic approac ...

deterministic system :

A system is said to be deterministic if its response at any time due to a g ...

Detritus :

(1) In a biological context: organic particulate matter. (ISO/6107) (2) In ...

dew :

Deposit of water drops on objects at or near the ground, produced by the co ...

dewatering :

Removing of water from the soil or from an enclosure.

dewatering coefficient :

Amount of water removed from the soil per unit horizontal area and per unit ...

dewpoint :

Temperature to which moist air must be cooled at constant pressure and cons ...

diffusion :

Process of spreading of a solute as a result of the thermal movement of the ...

diffusion coefficient (in porous media) :

Amount of solute that passes across a unit cross section in a porous medium ...

diffusivity (of an aquifer) :

Coefficient of transmissivity of an aquifer divided by its storage coeffici ...

dilution gauging; dilution gaging (A) :

Method of determining the discharge of a stream by measuring the degree of ...

dimensional analysis :

Drawing conclusions by considering the dimensions of the various terms in t ...

dimensionless variable :

(1) by dividing a variable by an expression having the same dimensions, or ...

direct flow :

Flow of water entering stream channels promptly. It includes surface flow a ...

direct runoff :

That part of surface runoff which reaches the catchment outlet shortly afte ...

directional hydraulic conductivity :

Combined property of an anisotropic porous medium and the flow through it. ...

Discharge :

Volume of water flowing through a river (or channel) cross-section in unit ...

discharge coefficient :

Ratio of the observed or actual discharge to the theoretically computed dis ...

dispersion coefficient :

Coefficient of proportionality between the dispersive flux of a solute and ...

dispersive flux :

Difference between the flux of a fluid due to its actual velocity (microsco ...

dispersivity :

(1) Property of a porous matrix to cause spreading of a tracer travelling t ...

disposal well :

Well used for the disposal of polluted or drainage water, brines, etc.

distorted model :

Model with different scales in different directions (e.g. horizontal and ve ...

distribution graph :

Unit hydrograph modified to show the fraction of the volume of runoff that ...

disturbed soil sample :

Soil sample in which the composition or the spatial sequence of solids is c ...

ditch :

Man-made small open channel constructed through earth or rock for the purpo ...

diversion of water :

Transfer of water from one watercourse to another, such watercourses being ...

divide :

Summit or boundary line separating adjacent drainage basins.

divining :

Locating groundwater with a divining rod.

divining rod :

Twig, a metal rod, or any other object, through the use of which certain pe ...

doline :

Funnel-shaped cavity at the ground surface which communicates with the unde ...

double float :

Body of slightly negative buoyancy immersed in and moving with a stream at ...

double mass curve :

Plot of successive accumulated values of one variable against the contempor ...

downstream :

In the direction of the current in a river or stream.

drag :

Force exerted by a flowing fluid, e.g. water, on an object placed in or adj ...

drain :

Conduit or small open channel by which water is removed from a soil or an a ...

drainage :

Removal of surface water or groundwater from a given area by gravity or by ...

drainage basin :

Area having a common outlet for its surface runoff. (TR)

drainage density :

Total channel-segment lengths, accumulated for all orders within a drainage ...

drainage flood :

Flood which results from rainwater ponding at or near the point where it fa ...

drainage pattern :

Arrangement of natural or man-made drainage channels within an area.

drawdown :

(1) Lowering of the water table or piezometric surface caused by the extrac ...

drawdown curve :

(1) Vertical section through the centre of a cone of depression. (2) Graph ...

draw-off; drawoff (A) :

Water withdrawn from a surface reservoir.

drift :

Superficial deposit caused by a current of water or air.

driven well :

Well that is constructed by driving a casing into the ground.

driving head :

Difference in water level or in piezometric head between inflow and outflow ...

drizzle :

Fairly uniform precipitation composed exclusively of fine drops of water (l ...

drought :

Prolonged absence or marked deficiency of precipitation.

drought index :

Computed value which is related to some of the cumulative effects of a prol ...

dry year :

Year of drought during which precipitation or stream flow is significantly ...

dunes :

Bed forms with a triangular profile having a gentle upstream slope and whic ...

Dupuit's approximation :

In steady nearly horizontal aquifer flow it is assumed that the stream line ...

duration curve :

Graph representing the time during which the value of a given parameter, e. ...

dynamic pressure :

Pressure due to the kinetic energy of a fluid.

dynamic viscosity :

Measure of the internal resistance of a fluid to flow, usually expressed by ...

dystrophic water :

Water which is poor in nutrients and contains a high concentration of humic ...