Modification and Evaluation of the WEPP Hillslope Model for Subsurface Drained Cropland

Abstract

Runoff, drain flow, and water table depth predictions from the WEPP hillslope model wereevaluated against eight years measured runoff and drain flows from North Central Ohio and watertable depths predicted using DRAINMOD. WEPP produced large average deviations between dailypredicted and measured runoff depths, overpredicted daily drain flow for all storm events, and maynot be truly simulating water table depth.Therefore, the WEPP was modified to improve the waterbalance, runoff, drain flow, and water table depth prediction capabilities for subsurface drainedcropland. The modified model is WEPP-Water Table Management (WTM). Most of the newalgorithms and modeling approaches and procedures were adapted from DRAINMOD. WEPP-WTMpredicts hourly runoff, drain flow, subirrigation flow, controlled drainage and subirrigation excessflows, water table depth, and daily sediment yields from fields that contain any combination of watertable management practices. Runoff, drain flow, and water table depth predictions from WEPP-WTMwere evaluated against the measured runoff and drain flows from Ohio, and field water table depthsfrom North Carolina. Overall, WEPP-WTM produced drain flow and runoff results similar to thosefrom DRAINMOD and better than all of those obtained with WEPP.