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
23
Average error
The mean of all the errors taken without regard to sign.
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106
Average sample number
The average number of sample units inspected per lot in reaching a decision to accept or reject. It is dependent on the actual quality level of the lot in question......
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107
Consecutive average, Moving average, or Consecutive mean
The mean of a small group of consecutive values, especially annual means, assigned to the middle time-term of the group in the process of smoothing, e.g. 5-year mean......
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113
Weighted average, or Weighted mean
An average of quantities that attaches a series of weights to it in order to make proper allowance for their relative importance. A value obtained by multiplying each of a series of values by its assigned weight and dividing the sum of those products by the sum of the weights. For example, a weighted arithmetic mean of x1, x2 ... xn with weights w1.....
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117
Average deviation, or Mean deviation
A measure of dispersion derived from the average deviation of observations from some central value, such deviations being absolute, i.e. without reference to algebric sign......
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134
Standardized averages, or Standardized means
A method of allowing or `adjusting` the effects of other variables, or for differences in the composition of the groups that are to be compared, by using a standard set of weights to combine the means of sub-groups into a single mean. Used mainly for the construction of index numbers......
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267
Semi-average fit
When a straight line trend appears to fit the data well, the data may be divided into two equal parts and arithmetic means calculated for the first and second half, plotted and joined by a straight line which gives the `semi-average fit`. It is more objective than the freehand method, but because of its reliance on arithmetic means, it can be undul.....
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268
Moving average method of fit
The averaging at the central year of a series of overlapping means to smooth out, or damp down, undue high and low, short-term values. Hence, the `moving average fit`. (See also 279)......
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279
Moving average
If a time series is x1,x2,...xn , and these are chosen set of weight
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364
Speed, or Velocity
img:equations//362_368_e.jpg
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417
Angular velocity
img:equations//415_417_e.jpg
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418
Velocity
img:equations//418_421_e.jpg
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548
Velocity
img:equations//547-548_e.jpg
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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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1086
Water surface (groundwater)
The very irregular and integerated upper surface of the saturated zone in a porous media. This surface typically consists of many little surfaces that are concave upwards, each occupying an interstitial chamber that may be connected with its neighbour by a tiny start or walled off from it by a solid particle. Capillary forces typically cause this s.....
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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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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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