The WEPP model for runoff and erosion prediction under sprinkler irrigation

Potential runoff and erosion is a serious problem for some types of sprinkler irrigation systems, particularly traveling laterals and center pivots on medium– to heavy–textured soils operating on sloping land. Prediction of when runoff might occur is part of the system design process. The USDA–ARS Water Erosion Prediction Project (WEPP) model was tested with 3 years of field data under high–rate sprinklers in southern Idaho. Runoff and soil loss were measured on the upper, middle, and lower portions of a hillslope. The main parameter affecting infiltration and runoff was the effective hydraulic conductivity. Model predictions for average runoff and soil loss were improved when hydraulic conductivity values were adjusted to account for soil variability across the field. Runoff amounts were small, and prediction variability for individual furrows was quite high, but no more than would be expected from previous studies of infiltration variability. Soil loss predictions were unreliable for the small runoff amounts occurring in this study. The most reasonable use of WEPP for sprinkler irrigation would be for estimating when potential runoff might occur under center pivots for different soils, slopes, and crop management practices, and to determine limits on application depths and rates to avoid serious runof