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Title: UPDATING SLOPE TOPOGRAPHY DURING EROSION SIMULATIONS WITH THE WATER EROSION PREDICTION PROJECT MODEL

Author
item Zhu, Jingcai
item Dabney, Seth
item Flanagan, Dennis

Submitted to: International Soil Conservation Organization (ISCO)
Publication Type: Proceedings
Publication Acceptance Date: 5/23/1999
Publication Date: N/A
Citation: N/A

Interpretive Summary: Soil erosion has a detrimental impact on land productivity and environment. Slope length and steepness are important factors influencing soil erosion. On strip cropped fields, sediment redistributed along slopes by erosion and deposition may change slope steepness over time and thus affect subsequent soil erosion. However, current erosion prediction models do not address this issue. To fix this, we wrote a computer program to update the slope description for the Water Erosion Prediction Project (WEPP) erosion model that reflects predicted detachment and deposition. We found that updating the slope profile reduced erosion prediction by 25% during the last half of a 8-yr simulation period of a cropped field with three 1.5-m grass strips that initially had a 7% slope, 80-m long. We concluded that slope profile changes can have a significant impact on future soil erosion and that long-term conservation planning will be improved by using our tool to account for these changes.

Technical Abstract: The Water Erosion Prediction Project (WEPP) is a process-based continuous simulation erosion prediction model. However, WEPP currently assumes a fixed soil surface topography, which does not change due to predicted detachment and/or deposition through a simulation period. While this approach might be satisfactory for slopes with uniform management, we hypothesized that long-term erosion predictions could be seriously altered by modifications of profiles having non-uniform slope, soil, and management properties. In this study, a computer program was written to update the input slope file for WEPP on a selected time. Currently, WEPP creates an output soil loss summary file that contains horizontal distance, elevation, erosion, and deposition at 100 points for each hillslope element. The slope updating program uses this output file as input. Sediment is redistributed above and in the grass hedges according to actual deposition patterns obtained by flume simulation and field survey observation. A new slope profile is then calculated based on the new elevations and exported to a file in a format which could be used directly by the WEPP model in subsequent erosion simulations. Results showed that updating slope profile for a uniform slope without grass hedge changed runoff and soil loss simulation only about 1%. However, for the slope with three grass hedges, updating slope file resulted in over 25% difference in erosion prediction during the last half of the simulation period. This demonstrates the need for profile updating for long term conservation planning on non-uniform slopes.