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
6
Accuracy of the mean
The closeness of agreement between the true value and the mean result obtained by applying the experimental procedure to a very large number of times. The smaller the systematic part of the experimental errors which affect the results, the more accurate is the procedure......
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105
Arithematic mean
The arithmetic mean of a set of values. Generally denoted by a bar, thus :
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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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109
Geometric mean
If the set of n values are all multiplied together and the nth root is taken, the results are known as the geometric mean (G), viz. G = (x1 . x2 ... x n-1 . xn)1/n .....
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110
Harmonic mean
The reciprocal of the arithmetic mean of the reciprocals of each observation.
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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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114
Root mean square
The square root of the arithmetic mean of the squares of each observation and is given by
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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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129
Mean square
In general, the mean square of a set of values is the arithmetic mean of the squares of their differences from some given value, namely their second moment about that value......
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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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208
Mean square error of estimate
The square root of the arithmetic mean of the squared deviations between the estimates for different samples and the population parameter under estimation......
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278
Mean consecutive
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`......
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759
Mean annual precipitation
The average over a period of years of the annual amounts of precipitation.
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760
Weighted mean monthly precipitation
The weighted mean precipitation for each month for a large area derived from the study of the isohyetal map of the area.
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845
Runoff
1 – The portion of the total precipitation from a given area that appears as streamflow in natural or manmade surface streams. 2 –The discharge of water in a surface stream at a particular point. 3 – The discharge of water in a surface stream at a particular point......
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846
Total runoff
The runoff, from all sources, from a drainage area for a definite period of time or for the duration of a particular storm.  It includes baseflow......
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847
Mean annual runoff
The value of the annual volume of water discharged by the stream drainage of the areausing  sufficiently long record to obtain a fair mean......
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848
Mean monthly runoff
Arithmetic mean of all the individual monthly mean discharges for a named month in a period of record.
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849
Depth of runoff
The total runoff from a drainage basin divided by the area.
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850
Runoff coefficient
The ratio of depth of runoff to precipitation over a specified period.
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852
Runoff cycle
Portion of the hydrologic cycle between incident precipitation over land areas and subsequent discharge through stream channels or direct return to the atmosphere through evapotranspiration......
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853
Storm runoff or Storm-water runoff
That portion of the total runoff from storm rainfall that reaches the point of measurement within a relatively short period of time subsequent to the occurrence of rain. It essentially excludes the base flow......
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854
Interflow, Subsurface runoff
That portion of the precipitation which has not passed down the water table but is discharged from the area as subsurface flow into stream channels. Also known as ‘subsurface runoff’ (illustrated)......
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856
Direct runoff
The sum of surface runoff, interflow and channel precipitation.
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858
Groundwater runoff
That part of the runoff which has passed into the ground, becomes groundwater, and is discharged into a stream channel as spring or percolation water (illustrated)......
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