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
4698
V-drag, or V-crowder
A V-shaped wooden or steel implement for construction and maintenance of small ditches. In operation, the operator stands on the runner board parallel to the axis of the ditch and by changing position controls the depth of digging. The slopes of the bank and the width of the ditch can also be suitably regulated. .....
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1913
Vacuole
A cavity in the protoplasm of cells which contains a watery liquid, the cell-sap.
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5648
Vacuum concrete
A concrete produced by applying a vacuum to the poured concrete by means of the forms or a separate mat, so that the pressure of the atmosphere expels some of the excess water, and at the same time compacts the concrete, making it firm enough to support its own weight and allow removal of the shuttering. This is effected by providing a filter (of c.....
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5941
Vacuum liner
A special form liner made of two layers of screen or wire mesh covered by a layer of cloth. The liner is sealed with rubber or caulking material around the edges of the form panel or unit. A series of openings in the form panel backing is connected to vacuum pump, so a vacuum can be created on the surface of freshly poured concrete. See `Formwork w.....
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4502
Vacuum pump
1 - A pump for creating a partial vacuum in a closed space. 2 - A pump where water is forced up a pipe by the difference in pressure between the atmosphere and a partial vacuum. 3 - An air compressor used in connection with steam condensers for improving the suction head on other pumps; the compressor takes its suction at low absolute pressure, com.....
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8714
Vacuum tank
Closed unit where the pressures can be maintained to any desired degree of vacuum so that cavitation effects can be observed readily in a model......
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991
Vadose water, Gravity suspended water, or Gravitational water
1 - Water in excess of adsorption water and pellicular water seeping towards water table. 2 - See 1858.
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2321
Valley
1 - An elongated depression usually with an outlet between bluffs or between ranges of hills or mountains. 2 - See 2320.
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2463
Valley floor
Bottom of the canyon or valley.
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1057
Valley spring
Groundwater discharge to the earth`s surface caused by a sudden change of slope on the side of an erosion valley (See 1054)......
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7968
Valley storage
1 - The volume below the water surface profile. 2 - The natural storage capacity or volume occupied by a stream in flood after it has overflowed its banks. It includes the quantity of water within the main channel (channel storage) and that which has overflowed its banks (lateral storage)......
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919
Valley storage, Lateral storage
The natural storage capacity or volume occupied by a stream in flood after it has overflowed its banks. It includes the quantity of water within the main channel (channel storage) and that which has overflowed its banks (lateral storage)......
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1379
Valley trenching
Gully erosion occurring in floodplains.
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4790
Valve body
Main part of a valve through which water flows, and that contains the moving parts and which allows connection to the irrigation system......
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2725
Valve chamber, or Valve house
A structure housing the regulating valves, control mechanisms for operation of valves and equipment required to remove parts for repair, etc......
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6218
Valve control point
An electrical panel designed for only one directional valve. One side of it is connected to the directional valve, and the other to the field control panel by means of a special electric cable. A switch at the valve control point enables the closing or opening of the entire actuating unit......
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4799
Valve pressure test
A test that enables to determine the pressure resistance of a complete valve.
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1848
Vapour movement
Movement of moisture in the vapour stage.
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886
Vapour pressure
The partial pressure of water vapour in the air or atmosphere.
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4946
Vapour pressure
Pressure exerted by water vapour contained in the air.
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8579
Variable
A quantity that can change in a system.
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58
Variable
Generally, any quantity that varies. More precisely, a variable is a quantity that may take any one of a specified set of values. The variable may be a `continuous variable` or a `discrete variable`......
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2354
Variable radius arch dam, or Variable centre dam
A type of an arch dam when neither the radius nor the central angle is constant. This dam is a compromise between the constant radius and the constant angle arch dams (illustrated)......
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116
Variance
A measure of the degree of dispersion of a set of values around their mean, obtained by calculating the mean value of the squares of the deviations from the mean, equal to the square of the `standard deviation` (See 119)......
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5771
Varnish
A liquid coating material consisting essentially of a homogeneous mixture of resin, drying oil, drier and solvent and containing no pigment, that flows out to smooth coat when applied and dries to a smooth, glossy, relatively hard, permanent solid, in a thin film when exposed to air......
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