Submitted to: Transactions of the ASAE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 18, 1995
Publication Date: N/A
Interpretive Summary: Soil erosion is a major factor causing crop yield reduction in many areas. To control soil loss effectively, a reliable assessment tool (model) must be developed. This paper is to evaluate the overall performance of the Water Erosion Prediction Project (WEPP) model (the new generation soil erosion prediction model) in predicting surface water runoff and soil loss. .Measured data from eight different locations with 34 different cropping an management systems were used. The WEPP model input files including soil, slope, climate, and crop systems were compiled based on measured data. Model predicted surface runoff and soil loss values were compared to measured values. Results showed the WEPP model predicted daily and annual surface runoff volumes reasonably well. Soil loss was also predicted well, but the accuracy and reliability of the predictions were improved when the model was used to predict long term average soil loss. Results also showed dthe WEPP model responded well to different cropping and management systems This indicates that the WEPP model can be used as an assessment and planning tool for laying out the best conservation plan.
Technical Abstract: Model testing and evaluation are critical to the acceptance of any new prediction tool. The objective of this study was to evaluate the overall performance of the Water Erosion Prediction Project (WEPP) hillslope model in predicting runoff and soil loss under cropped conditions. Data from 556 plot years with 34 cropping scenarios at eight locations were selected. The WEPP input files for soil, slope, climate, and crop management were compiled according to measured data. The comparisons between measured and WEPP predicted runoff and soil loss were made on event, annual, and average annual basis. The r**2 between model predicted and measured runoff volumes with optimized K**b (baseline hydraulic conductivity) was 0.77 for selected events, 0.76 for annual values, and 0.87 for average annual values. The slopes of the regression lines were 0.89, 0.91, and 1.02, respectively. The r**2 between predicted and measured soil losses (leaving out fallow and corn at Bethany, MO, which were particularly poor) was 0.36 for event predictions, 0.60 for annual predictions, and 0.85 for average annual values. The regression slopes were 0.43, 0.62, and 0.87, respectively. Similar predictions of runoff and soil loss were also obtained with WEPP internally estimated baseline hydraulic conductivities. In addition, the model was shown to respond well to the cropping and management effects. The r**2 between predicted and measured soil loss ratios was 0.80 using event totals, and 0.71 using average annual values. Based on this study, the WEPP model performed reasonably well in predicting runoff and average annual soil loss. The accuracy and reliability of the predictions were improved from an event to annual to average annual basis.