Abstract
Core Ideas Lack of spatial erosion data restricts model improvement and application. Spatially distributed erosion data along a hillslope were derived using 137Cs. For the first time, WEPP‐predicted spatial erosion rate was rigorously evaluated. Rill spacing is a key input parameter for simulating erosion on a hillslope. The lack of spatial soil erosion data has been a major constraint on the refinement and application of physically based erosion models. Spatially distributed models can only be thoroughly validated with distributed erosion data. Fallout 137Cs has been widely used to generate spatial soil redistribution data. The objectives of this study were to compare the soil redistribution patterns predicted using the 137Cs technique and the Water Erosion Prediction Project (WEPP) model and to diagnose potential shortcomings in the configuration, functionality, and application of the WEPP model, if any. An experimental hillslope (80 m wide by 200 m long with 1–4% slope) was used. The plot was sampled in a 10‐m grid for 137Cs measurement. Measured rainfall, runoff, soil loss, and crop management were used to calibrate WEPP. Soil redistribution patterns predicted by the two methods were vastly different on the study hillslope. Compared with 137Cs, the average soil loss rates predicted by WEPP were overly sensitive to slope lengths exceeding 100 m if the 1‐m default rill spacing was used. The spatial erosion patterns were well matched if different rill spacings along the hillslope were used. This study shows that rill spacing is a key input parameter for correctly simulating soil redistribution patterns with WEPP. Knowledge of rill distribution along a hillslope is critical to satisfactorily predicting rates of soil erosion and sediment deposition on a hillslope. The conclusion needs further testing on more hillslopes having different gradients and shapes.
Published Version
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