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
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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1049
Alluvial-slope spring, Boundary spring, or Border spring
A spring that occurs on the lower slope of an alluvial cone at the point where the water table slope and the surface gradient are equal. This point is often located at the point of gradation from pervious sand with a flat water table slope to less pervious alluvial material which calls for a steep slope to carry the water supplied from above......
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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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1158
Water surface slope
The inclination of the water surface expressed as change of elevation per unit of length. The tangent of the angle that the surface makes with the horizontal. .....
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1159
Slope
The inclination of a line, channel bed, water surface, pipeline or other structure, expressed as the difference in elevation of two points divided by their horizontal distance......
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1540
Slope protection
Riprap, paving, pitching, revetment, brush or other material laid or placed for protection on the sloping part of an embankment or levee or sea shore, to prevent erosion, slipping or caving, or to withstand external hydraulic pressure......
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1766
Exchange complex, or Absorbing complex
The surface-active constituents of soil (both inorganic and organic) that are capable of cation exchange.
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1768
Exchangeable
Describes ions capable of replacement in the exchange (absorbing complex).
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1769
Ion exchange, Cation exchange, or Anion exchange
The replacement in a colloidal system of an ion by another with a charge of the same sign. Cation exchange refers to the interchange of positively charged ions (cations) and anion exchange to the replacement of negatively charged ions (anions) by other anions......
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1770
Exchange capacity, Cation exchange capacity, Base exchange capacity, or Saturation capacity
The total cation exchange, usually expressed as milliequivalents per 100 grams. Measured value of cation exchange capacity depends somewhat on the method used for the determination......
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1786
Exchangeable-sodium percentage (ESP)
The degree of saturation of the soil exchange complex with sodium. It may be calculated by the formula :
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1788
Exchange acidity
Acidity produced by treating soil with a solution of a neutral salt.
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1789
Exchangeable acidity or Potential acidity
H+ ions held in reserve
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1824
Moisture characteristics (of soils)
Refers to the relation between the soil moisture content and the soil moisture tension. This may be expressed in terms of the soil moisture characteristic curve......
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1973
Productivity (of soil)
The capacity of a soil for producing a specified plant or sequence of plants under a specified system of management.
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2261
Slope weir
A weir with sloping surfaces extending from the crest, so that the water remains in contact with the weir surface all the way down and is guided by it as per design......
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2263
Solid slope masonry weir
An impermeable-slope weir made up of rock, stone, brick masonry or concrete. It may or may not have falling shutters for headwater control......
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3068
Eddy viscosity, Mechanical velocity, Exchange coefficient, or Eddy conductivity
Analogous to the dynamic viscosity, but depends upon the Reynolds number and other parameters. Referred to by various writers as the `mechanical velocity`, `exchange coefficient` and `eddy conductivity`......
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3085
Friction slope
The friction head or loss per unit length of conduit. For most conditions of flow the friction slope coincides with the energy gradient, but where a distinction is made between energy losses due to bends, expansions, impacts, etc., a distinction must also be made between the friction slope and the energy gradient. Friction slope is equal to the bed.....
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3163
Critical slope
Slope of a channel at which the normal depth for uniform flow will be the same as critical depth.
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3188
Side slope
The slope that the sides of a canal or embankment make with the horizontal (illustrated).
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