International Commission on Irrigation & Drainage Commission Interationale des Irrigation et du Drainage

Multilingual Technical Dictionary (MTD)
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Term No.Term Name/Term DescriptionAction
364
Speed, or Velocity
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417
Angular velocity
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418
Velocity
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548
Velocity
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788
Effective rainfall
1 – Rain that produces runoff. 2 – In irrigation practice, that portion of the total precipitation which is retained by the soil so that it is available for use for crop production. 3 – In geohydrology, that part of the precipitation that percolates through soil to recharge aquifers......
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789
Essential effective rainfall
Part of a rainfall that produces the main part of the runoff (according to a hydrograph).
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790
Maximum effective rainfall
Part of rainfall producing the maximum flow (according to a hydrograph).
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816
Effective snowmelt
Part of the snow melt that reaches the channels of streams as runoff.
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822
Snowfield
An unbroken expanse of snow.
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1028
Intake area (of an aquifer)
The area of earth`s surface where the water, from precipitation or surface flow, that eventually reaches the zone of saturation of an aquifer, is absorbed......
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1029
Catchment area, or Basin (of an aquifer)
The surface area composed of the intake area of an aquifer and all other areas that contribute surface water to the intake......
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1086
Water surface (groundwater)
The very irregular and integerated upper surface of the saturated zone in a porous media. This surface typically consists of many little surfaces that are concave upwards, each occupying an interstitial chamber that may be connected with its neighbour by a tiny start or walled off from it by a solid particle. Capillary forces typically cause this s.....
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1094
Effective porosity
The ratio between the volume of water that a saturated pervious material will yield under specified hydraulic conditions and the total volume of the material......
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1095
Field coefficient of permeability
Coefficient of permeability at the prevailing temperature of water.
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1097
Field capacity, Normal field capacity, Normal moisture capacity, Maximum field carrying capacity, Field capillary (moisture) capacity, Effective water-holding capacity, Specific retention
1 - The amount of water held in the soil after the excess gravitational water has drained away and after the rate of downward movement of water has materially decreased. Essentially the same as `specific retention`, a more general term used in studies of groundwater, except that specific retention is generally given as a percentage by volume wherea.....
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1099
Effective velocity (of groundwater), Actual velocity (of groundwater), True velocity (of groundwater), or Field velocity (of groundwater)
The velocity measured by the volume of groundwater passing per unit time through unit cross sectional area divided by the effective porosity of the water transmitting material......
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1100
Apparent velocity (of groundwater)
The apparent distance moved in unit time by groundwater. It is determined by V = Q/F where F is the cross sectional area perpendicular to the streamlines and Q the volume of water passing through this cross section in unit time......
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1101
Average velocity (of groundwater)
The volume of groundwater passing through a unit cross-sectional area in unit time divided by the porosity of the water transmitting material......
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1102
Critical velocity (of groundwater )
For porous media the maximum velocity under which laminar flow can occur.
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1171
Cloud-velocity gauging, Allen`s method of velocity gauging, Colour-velocity gauging
A method of determining the velocity of a slug of dye between two stations in the channel. This velocity, assumed to be the mean velocity of flow, multiplied by the cross-sectional area of the channel, gives the discharge. `Allen`s method` and `colour-velocity method` are different forms of cloud-velocity gauging......
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1174
Discharge site, Gauging site, or Velocity-area gauging station
A location on a stream where gauge, velocity and cross-sectional areas are measured, or other gauging methods are deployed, in order to determine the discharge......
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1212
Mean velocity, Average velocity, Overall mean velocity
The velocity at a given section or reach of a stream obtained by dividing the discharge of the stream by the cross-sectional area at that section. .....
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1213
Mean velocity position
The point lying between the water surface and the bed of a channel at which the velocity is equal to the mean velocity on a vertical......
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1216
Velocity rod correction
The correction to be applied to the velocity given by a velocity rod in order to convert it into mean velocity.
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1217
Mean velocity curve
A curve showing the relation between mean velocity and stage at a given section of an open channel.
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