The U.S. Department of Agriculture's Water Erosion Prediction Project
(WEPP) is a new technology based on fundamentals of hydrology, soil ph
ysics, plant science, hydraulics, and erosion mechanics. WEPP hydrolog
y includes simulation of excess rainfall using the Green-Ampt infiltra
tion equation, surface runoff routing, evapotranspiration, percolation
, and subsurface drainage to tiles (or ditch). Soil water flowing to a
n artificial drain (tiles or ditch) reduces the antecedent water conte
nt of soil and results in increasing soil-infiltration capacity and re
duction of storm runoff. Hydrometeorological, vegetation, topographica
l, and soil data from a poorly drained watershed subjected to subsurfa
ce 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 ind
icate that, in general, the model does an acceptable job of predicting
storm and peak runoff rate for pre- and postsubsurface drainage insta
llation.