Evaluation of WEPP Runoff And Soil Loss Predictions Using Natural Runoff Plot Data

Abstract

Model testing and evaluation are critical to the acceptance of any new prediction tool. This study was conducted to evaluate the overall performance of the Water Erosion Prediction Project (WEPP) hillslope model in predicting runoff and soil loss under cropped conditions. Natural runoff plot data, including 4,124 selected events, 556 plot years, and 34 cropping scenarios, from eight locations were selected. The average length of record for the cropping scenarios was about nine years. Several common crops and tillage systems were included. The WEPP input files for soil, slope, climate, and crop management were compiled based on measured data. The coefficient of determination (r2) between model-predicted and measured-runoff volumes for optimized Green and Ampt hydraulic conductivity (Kb) was 0.77 for selected events, 0.76 for annual values, and 0.87 for average annual values; the r2 between predicted and measured soil losses (excluding fallow and corn plots at Bethany, Mo.) was 0.36, 0.60, and 0.85, respectively. Similar predictions of runoff and soil loss were also obtained with WEPP internally estimated Kb values. Runoff and soil loss were slightly overpredicted for small storms and for years with low runoff and soil loss rates, and were underpredicted for large storms and for years with high runoff and soil loss rates. However, average runoff and soil loss rates for different cropping and management systems were adequately predicted. The accuracy and reliability of the predictions were shown to improve from an event to annual to average annual basis. Results of this study show that the WEPP model is a useful tool for predicting runoff and soil loss rates under cropped conditions.