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
130
Degrees of freedom
The degrees of freedom of a set of observations (ex- hypothesis are subject to sampling variation) is the number of independent values in the sample that could be assigned at will within the specification of the system......
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981
Zone of saturation
That part of the earth crust where the functional interstices of permeable rock or earth are completely filled with water under positive hydrostatic pressure, that is, pressure in excess of atmospheric pressure. It is that portion of the earth crust that supplies water to springs and wells and which contains the groundwater. Strictly speaking, part.....
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1144
Intermittent saturation zone
The zone between the highest and lowest levels of the groundwater table as it responds to seasonal and short term weather changes......
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1148
Zone of permanent non saturation
The strata above the highest water level reached in an aquifer when the groundwater table moves up and down in response to seasonal and shorter term weather changes; marks the lower limit of the permanent non saturation zone.  .....
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1149
Zone of permanent saturation
The saturated portion of an aquifer that lies below the lowest water level reached when the  groundwater table moves up and down in response to seasonal and shorter term weather changes......
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1653
Degree of dispersion
Extent to which soil aggregates are broken down to primary particles by any given treatment.
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1665
Degree of aggregation
Measure of the proportion in which aggregates are present.
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1720
Degree of aeration, or Air space ratio
Ratio between the volume of air and the volume occupied by the voids.
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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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1772
Base saturation
Exchange capacity saturated with metallic cations of pH 7 or over.
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1774
Degree of saturation (V)
Percentage ratio of exchangeable cations exclusive of H+ (= S ) to total exchangeable cations inclusive of H+ (= T ), i.e.  .....
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1802
Degree of saturation
1 - Ratio between the volume of water and the volume of voids. 2 - See 1774.
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1804
Saturation percentage
The moisture contents of saturated soil paste.
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1805
Saturation extract
The solution extracted from a soil at its saturation percentage.
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1812
Water of saturation
The total water that can be absorbed by water-bearing soil without dilation of the soil particles.
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1814
Water of supersaturation, or Water of dilation
Groundwater in excess of water of saturation occurring in earth, such as quicksand, plastic clay, or flowing mud, whose particles have lost contact and are more or less separated......
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1815
Moisture-holding capacity, Saturation capacity or Maximum water capacity
The amount of water required to fill all the pore spaces between the soil particles, i.e. the upper limit of the possible moisture content. It is often expressed as the percentage of the dry weight or as equivalent inches of water per foot of soil depth......
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1841
Saturation capillary head
The distance from the free water surface to the highest elevation at which complete saturation exists.
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2154
Degree of salinity
Percentage of soluble salts in the root zones.
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3200
Saturation line, Line of saturation, Percolation line, or Hydraulic grade line
1 -Line across the bank of a canal marking the upper level of saturation after the canal has been running for some time (illustrated). 2 - See 3052, 4206 and 5256......
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3842
Straight (line, surface) sharp cut-water, Equilateral cut-water, or Sixty degree straight sharp cut-water
A sharp cut-water formed by two straight surfaces meeting at a line. Since the two straight sides of the cut-water and the width of the pier form a triangle, it is, sometimes, classified according to triangle properties (viz. equilateral cut-water) and also according to the value of the nose angle (as 60o straight sharp cut-water)......
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4906
Day-degree, or Degree day
Variation of one degree per day in mean daily temperature, above an adopted standard reference temperature (usually 10oC). The number of degree days for a single day is the actual variation of mean temperature from the standard. The number of degree days is a month, or other interval, is the sum of daily values. When the mean temperature on a given.....
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4986
Saturation vapour pressure
Upper limit of vapour pressure at a given temperature or vapour pressure which the air would have if saturated at the air temperature......
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5031
Degree of durability of irrigation
The annual rate of variation in the depth of the groundwater level.
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5044
Degree of drainage
A qualitative measure of the efficacy of a drainage system in an area.
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