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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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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884
Mean annual evaporation
The average depth of evaporation over period of enough years to give an approximate constant value.
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1160
Mean monthly discharge
Discharge observed or interpolated and averaged over a calendar month.
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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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1217
Mean velocity curve
A curve showing the relation between mean velocity and stage at a given section of an open channel.
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1343
Meander scrolls
Depressions and rises on the convex side of the bends formed, as the channel migrates laterally down the valley and towards the concave bank......
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1441
Meander, or Full meander
Two consecutive loops in a river, one flowing clockwise, the other anti-clockwise (illustrated).
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1442
Meandering
A description of river morphology in which the river follows a sinuous path due to natural physical causes not imposed by external restraint, and is characterized by a curved flow and alternating shoals and bank erosion......
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