Statistical approach to incorporating the influence of land-grading precision on level-basin performance

Monte-Carlo simulation was used to determine the suitability of statistical equations for estimating the influence of soil surface elevations on the low-quarter distribution uniformity DUlq, of level-basin irrigation systems. It was shown that these equations give reasonable estimates of DUlq, provided that the advance curve is known. The Monte-Carlo simulations also provided an estimate of the variation in DUlq for different fields with the same standard deviation of elevations. The statistical equations demonstrate that irrigation uniformity is influenced by the ratio of soil surface elevation standard deviation to average depth infiltrated. For conditions that would be typical of laser-leveled basins within the U.S., the influence of elevation variations on DUlq is small. However for poorly leveled fields, as frequently occur in Egypt, these elevation variations can significantly reduce DUlq, thus limiting potential efficiencies. In some cases, these simple equations can be used to adjust level-basin designs to account for the variation in surface elevations without the need for extensive simulation studies.