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
83
Correction
A quantity that is applied to an observation or function thereof to diminish or eliminate the effects of errors and obtain an improved value of the observation or function. It is also applied to reduce an observation to some arbitrary standard. The correction corresponding to a given error is of the same magnitude, but of opposite sign......
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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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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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1205
Sounding rod, or Sounding stick
A graduated rod preferably with a flat disc at the bottom for measuring depth of water. For a deep quick-flowing stream, a weighted sounding wire may be used......
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1206
Air-line correction
One of two stream gauging corrections to determine true water depth under conditions that cause large vertical angles in air-line configuration. The air line correction is for that part of the line that is above the water surface (illustrated). .....
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1207
Wet-line correction
One of the two gauging corrections to determine true water depths under condition cause large vertical angles in air-line configuration. The wet line correction is for that portion of the line that is under water (Illustrated)......
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1208
Sag correction
The amount by which soundings must be reduced to obtain true vertical values.
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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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1215
Angularity correction, or Skew correction
The correction to be made to an observed velocity when the direction of the current is not exactly at right angles to the discharge section line......
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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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1218
Vertical velocity curve
A curve showing the relation between the depth and velocity along a vertical line at a given section of an open channel or conduit......
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1226
Rod float, or Velocity rod
A rod, which on being turned through a float run, gives the mean velocity of water between water surface and the bottom of the rod. The rod may be of fixed length or of an adjustable telescopic type, weighted at the base so that it floats in a vertical position......
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1232
Integration method of velocity measurement
A means of determining the mean velocity at a vertical depth of a stream by noting the total number of revolutions of a current meter vane and the time consumed, while the meter is slowly lowered from the surface to the bed and returned one or more times......
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1233
Velocity-head rod, Velocity-head stick, Run-up
A device for measuring velocity through culverts, or over weirs, dams, etc., by placing the rod vertically in the flow and observing the `run-up` (the difference in water levels obtained at upstream and downstream of the rod); the rod is, generally, calibrated to read velocity, or discharge......
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1318
Eroding river, or Degrading river
A river continuously eroding its bed or banks.
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