THE WEPP WATERSHED MODEL: II. SENSITIVITY ANALYSIS AND DISCRETIZATION ON SMALL WATERSHEDS

Abstract

The Water Erosion Prediction Project (WEPP) watershed scale model was developed by the USDA for purposes of erosion assessment and conservation planning. The purpose of this study was to verify that the watershed model behaves rationally and consistently over a range of discretization structures and channel parameter inputs for applications to small watersheds. Effects of watershed discretization were evaluated for selected events within a one-year continuous simulation by comparing results for two watersheds under various discretization schemes. Impacts of channel input parameters were assessed by comparing the value of a linear sensitivity coefficient for user-specified parameters. Hillslope length, Manning’s coefficients, and channel slope were found to be key parameters in the prediction of watershed sediment yields. Erodibility and critical shear stress were found to be important for events where channel scour was active, and the results were sensitive to the hydraulic conductivity for events with small runoff and small sediment contributions from hillslopes. Improvements in the WEPP model are suggested where limitations were observed.