Assessing water erosion in small watersheds using WEPP with GIS and digital elevation models

ABSTRACT:

Three different approaches using geographical information systems (GIS) and digital elevation models (DEMs) are described and evaluated for applying the Water Erosion Prediction Project (WEPP) model to assess water erosion in small watersheds. The first approach describes a typical application of the watershed version of WEPP using GIS only as an aid for construction of required input files. The second approach presents an automated method for the application of WEPP through the extraction of hillslopes and channels from DEMs. The third approach uses WEPP model simulations on all possible flowpaths within a watershed. The three method were applied to six research watersheds: one from Treynor, Ia., two from Watkinsville, Ga., and three from Holly Springs, Miss. A statistical analysis for all methods and watershed compared the predicted us. Measured runoff and sediment yield from watershed outlets on an event-by-event basis for runoff and sediment loss. The results indicate that the automatic hillslope method (the second approach) performs as well as the manual technique (the first approach) for all watershed. A comparison of erosion from only hillslopes for all three methods indicates that the flowpath method (the third approach) is statistically comparable to the other methods. Results of the analysis suggest that, given an accurate DEM and valid input data for a simple watershed, the automatic hillslope method can be used to facilitate the application of the watershed version of WEPP, and that predictions should be comparable to an expert user's application of WEPP.