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
884
Mean annual evaporation
The average depth of evaporation over period of enough years to give an approximate constant value.
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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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1160
Mean monthly discharge
Discharge observed or interpolated and averaged over a calendar month.
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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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1199
Mean depth, or Average depth
The cross-sectional area of a stream channel or conduit divided by the surface width.
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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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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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1343
Meander scrolls
Depressions and rises on the convex side of the bends formed, as the channel migrates laterally down the valley and towards the concave bank......
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1368
Standard fall velocity
The average rate of fall that a particle would finally attain if falling alone in quiescent distilled water.
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1441
Meander, or Full meander
Two consecutive loops in a river, one flowing clockwise, the other anti-clockwise (illustrated).
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1442
Meandering
A description of river morphology in which the river follows a sinuous path due to natural physical causes not imposed by external restraint, and is characterized by a curved flow and alternating shoals and bank erosion......
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1443
Meander belt
The distance between lines drawn tangential to the extreme limits of consecutive and fully developed meanders (illustrated)......
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1444
Meander ratio
The ratio of the meander width to the meander length.
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1445
Meander length
The distance along the river between the corresponding points at the extreme limits of successive and fully developed meanders (illustrated)......
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1446
Meander width
The amplitude of swing of a fully developed meander, measured from midstream to midstream. (illustrated).
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