MODELING SUBSURFACE DRAINAGE AND SURFACE RUNOFF WITH WEPP

The U.S. Department of Agriculture's Water Erosion Prediction Project (WEPP) is a new technology based on fundamentals of hydrology, soil physics, plant science, hydraulics, and erosion mechanics. WEPP hydrology includes simulation of excess rainfall using the Green-Ampt infiltration equation, surface runoff routing, evapotranspiration, percolation, and subsurface drainage to tiles (or ditch). Soil water flowing to an artificial drain (tiles or ditch) reduces the antecedent water content of soil and results in increasing soil-infiltration capacity and reduction of storm runoff. Hydrometeorological, vegetation, topographical, and soil data from a poorly drained watershed subjected to subsurface drainage system were used to evaluate the WEPP hydrology components. Model-simulated and measured storm-runoff hydrographs were compared for the pre- and postsubsurface drainage installation. The results indicate that, in general, the model does an acceptable job of predicting storm and peak runoff rate for pre- and postsubsurface drainage installation.