Accuracy assessment of WEPP-based erosion models for harvested and burned forest watersheds

Covert, S.A.; Robichaud, P.R.; ELliot, W.J. Under review. Accuracy assessment of WEPP-based erosion models for harvested and burned forest watersheds. USDA Forest Service, Rocky Mountain Research Station.

Keywords: GeoWEPP, erosion models, forested watersheds

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Abstract: This study assesses the accuracy of GeoWEPP model (Geospatial Water Erosion Prediction Project) and a modified version of WEPP for forest soils. Three small watersheds (2-9 ha) in the Interior Northwest were monitored for several years following timber harvest and prescribed fires. Observed site factors of climate variables, percent ground cover and soil erodibility values, along with digital slope data were used to drive the models. The GeoWEPP and WEPP model predictions of runoff and sediment yield were compared to observed yearly totals from each watershed. Monthly totals were also compared the results of the modified version of WEPP. The yearly results showed that GeoWEPP under-predicts runoff and sediment and the results were not acceptable at a 90 percent confidence interval. The same data was tested with the modified version of WEPP containing modified algorithms for deep percolation and subsurface lateral flow intended to better represent forest hydrology. This modified version of the WEPP model showed improvements to yearly predictions of runoff and sediment over the GeoWEPP model and generated acceptable results of runoff and sediment. Monthly values of runoff and sediment yield generated by the modified WEPP generated acceptable results compared to the observed monthly values. The GeoWEPP model has the potential to model erosion with the incorporation of digital elevation data, but lacks the ability to accurately represent forest hydrology. The incorporation of a WEPP algorithm that represent forest soils more realistically would improve the results of GeoWEPP predictions.

Moscow FSL publication no. 2004m