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Currently, the practice followed in the design of irrigation systems is to calculate the irrigation interval based on an empirically-derived peak consumptive use rate applied to the amount of available water which can be stored in the crop root zone. In these calculations, it is assumed that the peak use rate will occur continuously until the available soil moisture supply has been completely depleted. By employing this procedure, no consideration is given to the fact that use of a given peak consumptive rate over different periods of time incorporates a different probability of occurrence or level of risk to the design of different systems. That is, a peak consumptive use rate of 0.30 in/day for a period of 10 days will not occur with the same frequency of occurrence as the same use rate over a period of 20 days. Because of these differences, it would seem logical to attempt to standardize irrigation system design based on some acceptable level of risk (recurrence interval) as is followed in the design of other engineering facilities. The final test of the rationality of this approach for irrigation system design will depend, to a large extent, on whether the inclusion of a probability level will result in a significant reduction in the costs to the system over the cost of a system designed by conventional procedures.
frequency of occurrence of evaporation extremes as applied to the design of irrigation systems
Gray, D. M., Murray, James M. and W. Nicholaichuk 1966. FREQUENCY OF OCCURRENCE OF EVAPORATION EXTREMES AS APPLIED TO THE DESIGN OF IRRIGATION SYSTEMS. Canadian Agricultural Engineering 8(1):12-14.
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