Grid scale effects on watershed soil erosion models

The model CASC2D-SED was applied to the Goodwin Creek experimental watershed in Mississippi to define erosion model response to raster-based grid cell sizes. The model was parameterized at a 30 m grid, then calibrated and validated to three representative thunderstorms. The simulated hydrographs replicated the measurements of peak discharge, runoff volume, and time to peak. The model also calculated sediment yields within +/- 50% of the field measurements. Resampling the watershed digital elevation model at scales from 30 m to 330 m reduced the land surface slopes and changed the channel topology. In general, very good modeling results are obtained at grid sizes of 30 m and 90 m, which is comparable to the plot sizes of the universal soil loss equation. At grid sizes coarser than 150 m, the sediment source areas became less appropriately depicted and the calculated sediment delivery ratios became unrealistically high. Grid sizes smaller than 150 m are recommended for proper watershed simulation of upland erosion and sediment yield.