Abstract The water erosion prediction project (WEPP) model is a physically-based hydrology and erosion model. In recent years, the hydrology prediction within the model has been improved for forest watershed modeling by incorporating shallow lateral flow into watershed

The water erosion prediction project (WEPP) model is a physically-based hydrology and erosion model. In recent years, the hydrology prediction within the model has been improved for forest watershed modeling by incorporating shallow lateral flow into watershed runoff prediction. This has greatly improved WEPP’s hydrologic performance on small watersheds with seasonal flows, but the current version of WEPP is not capable of estimating base flow rates which are more important on larger watersheds. This paper presents a method under development to accumulate the daily deep seepage values estimated by WEPP, and return a fraction of that deep seepage to channel flow each day, resulting in reasonable base flow estimates. The modeling principles and processes will be described, suggested values for hydrologic parameters will be presented, and areas requiring additional research to support this approach will be presented. Examples of the application to forested watersheds in the Lake Tahoe Basin and northern Idaho will be presented.