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Effects of uncertainties on the limits of on‐farm improvement in irrigation rehabilitation
Author(s) -
Sritharan Subramania Iyer,
Clyma Wayne
Publication year - 1992
Publication title -
water resources research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.863
H-Index - 217
eISSN - 1944-7973
pISSN - 0043-1397
DOI - 10.1029/92wr01476
Subject(s) - irrigation , environmental science , hydrology (agriculture) , variance (accounting) , mathematics , statistics , soil science , infiltration (hvac) , hydraulics , agricultural engineering , geology , agronomy , meteorology , engineering , geotechnical engineering , geography , accounting , aerospace engineering , biology , business
Procedures for analyzing the effects of uncertainties on the on‐farm time of application and applied depth of irrigation have been presented using two parameter‐gamma densities for the different variables. The critical coefficient of variation (CV) in delivered farm flow rate beyond which variations in targeted depths cause more deviations in time of application is found to be 0.25. For a typical set of values for on‐farm variables, reducing the CV of farm flow below 0.12 does not improve the variance in applied depth for the case of fixed CV values of 0.10 for farm area and time of application. A distribution function for time of application has been derived which will enable the computation of reliable levels of application time. Solving the yield problems considering the application system hydraulics in a deterministic mode does not lead to large errors when the variances in the on‐farm variables do not exceed 0.20. Generally, for shorter basins which are common in many countries, higher efficiencies can be achieved. Efficiencies less than 85% begin to occur when the length of the basin exceeds 275 ft (84 m) for typical values of field parameters in soils belonging to the Soil Conservation Service infiltration family of 3.0.