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
342
Base units
The seven fundamental units of measurement upon which the International System of Units is based viz. Length (metre), weight mass (kilogram), time (second), electric current (ampere), thermodynamic temperature (kelvin), amount of substance (mole) and luminous intensity (candela)......
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350
Supplementary units
The SI units radian and steradian are called supplementary units. They are `dimensionless` derived units (more precisely, derived units of dimension one) with special names and symbols. Although the coherent unit for plane angle and for solid angle is expressed by the number 1, it is convenient to use the special names radian (rad) and steradian (s.....
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351
Derived units
Derived units are expressed algebraically in terms of base units. Their symbols are obtained by means of the mathematical signs of multiplication and division. The expression for the coherent derived units in terms of base units can be obtained from the dimensional products by using the following format substitution : L-->m, M-->kg, T-->s, I-->A, Q.....
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382
Non-SI units
There are certain units, recognized by the International Committee for Weights and Measures (CIPM) as having to be retained because of their practical importance (as given in the following tables)......
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410
Unified atomic mass unit
The unified atomic mass unit is equal to 1/12 of the mass of an atom of the nuclide 12C.
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577
British thermal units
img:equations//566_595_e.jpg
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578
British Thermal Units
img:equations//566_595_e.jpg
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579
British thermal units
img:equations//566_595_e.jpg
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910
Coefficient of permeability, Hydraulic conductivity, Coefficient of conductivity, Unit of permeability, Transmission constant, Coefficient of transmission
1   The rate at which groundwater flows through a soil in response to a given hydraulic head. 2   The rate of flow of a fluid through a unit cross section of a porous mass under a unit hydraulic gradient, at a specified temperature. 3 - See 6497......
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923
Unit hydrograph, or Unit graph (USA)
Hydrograph of direct runoff resulting from a unit amount of effective rainfall generated uniformly over a watershed during a specified duration......
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929
Synthetic unit hydrograph
A unit hydrograph developed on the basis of an estimation of coefficients expressing various physical features of a catchment......
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1958
Baule unit
Named after the scientist Baule, a unit of growth factor that will produce 50 per cent of the maximum possible yield or yield-producing capacity......
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2578
Unit column method (for buttress dam)
It is a method of designing a buttress dam evolved by Herman Shorer. It is assumed that the buttress comprises a series of hypothetical curved struts that transmit the water load to the foundations by uniform axial compression without interaction between struts. The axes of the curved struts are analogous to trajectories of first principle stress i.....
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2609
Unit seepage force
The measure of seepage force, equivalent to the product of the hydraulic gradient and the unit weight of water (or other fluid)......
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2661
Dry unit weight, or Unit dry weight
The weight of soil-solids per unit of volume (total) of soil mass.
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2662
Effective unit weight
Unit weight of a soil that when multiplied by the height of the overlying column of soil gives the effective pressure due to the weight of the overburden......
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2663
Maximum unit weight
The dry unit weight defined by the peak of a compaction curve.
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2664
Saturated unit weight
The wet unit weight of a soil mass when saturated.
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2665
Submerged unit weight, or Buoyant unit weight
The weight of the solids in air minus the weight of water displaced by the solids per unit of volume of soil mass; the saturated unit weight minus the unit weight of water......
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2666
Wet unit weight, or Mass unit weight
The weight (solids plus water) per unit of total volume of soil mass, irrespective of the degree of saturation.
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2667
Zero air voids unit weight
The weight of solids per unit volume of a saturated soil mass.
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2685
Gunite
A concrete-like lining applied to canals, reservoirs or embankments to form a watertight membrane and provide stability.   It is formed by pneumatically conveying a dry mix of sand and Portland cement to a nozzle with water added just prior to ejection......
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4726
Head station, Head installation, Control head or Head unit
All the equipment installed at the upstream end of a pressurized irrigation system to fulfil such functions as starting and stopping, perhaps scheduling, irrigation; regulating pressure and flow rate; measuring and totaling water use; filtering the water supply; introducing fertilizers; and  issuing alerts or stopping the system in event of malfunc.....
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4872
Profitable crop water requirement, or Unit water requirement
The volume of water actually used by crops in producing a unit mass of dry matter.
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5021
Unit irrigation efficiency
Ratio of the sum of volume of irrigation water used in evapotranspiration in the specified area and that necessary to maintain a favourable salt concentration in the soil solution, to the volume of water delivered to the area. .....
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