Submitted to: American Society of Agricultural Engineers Meetings Papers
Publication Type: Abstract Only
Publication Acceptance Date: June 18, 1995
Publication Date: N/A
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 WEPP hillslope model in predicting runoff and soil loss under cropped conditions as compared to the measured data from natural runoff plots. Data from 556 plot years with 34 cropping scenarios at eight locations were selected. The average length of record for the cropping scenarios was approximately 9 years. Several common crops and tillage systems were included. WEPP input files for soil, slope, climate, and crop management were compiled according to measured data. Plant growth parameters in the crop management files were adjusted on each site and for each crop to obtain reasonable residue biomass predictions. 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 between measured and predicted runoff 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. The accuracy and reliability of the predictions were improved from an event to annual to average annual basis.