Modification and evaluation of WEPP water table management model

Three constructed Wetland-Reservoir-SubIrrigation Systems (WRSIS) have been built in Northwest Ohio. The overall goal of this study was to model the hydrology of a WRSIS using the Water Erosion Prediction Project (WEPP) model. Modifications were made in the water balance algorithms of the WEPP hillslope model to improve the model's capability for subsurface drained cropland.; Drain flow and water table depth predictions from WEPP were evaluated against measured drain flows from North Central Ohio and water table depths predicted using DRAINMOD. Results showed that (i) WEPP drain flow simulations produced large average deviations; (ii) daily drain flows were overpredicted for all storm events; and (iii) predicted cumulative drain flows at the end of the evaluation season for each year were almost four times larger than the measured drain flows. WEPP midspace water table depth predictions were very poor. WEPP does not predict continuous water table depths and it may not be truly simulating water table depth.; The WEPP hillslope model was modified to help improve the water balance, runoff, drain flow, and water table depth prediction capabilities for cropland where subsurface drainage, controlled drainage, and/or subirrigation systems exist or are planned. The modified model is WEPP-Water Table Management (WEPP-WTM). Most of the water balance algorithms related to subsurface drainage, controlled drainage, and subirrigation were taken from DRAINMOD. Upward flux rate from the water table was calculated using the concept of matrix flux potential.; The performance of the WEPP-WTM model in simulating runoff, drain flow, and water table depth for subsurface drained cropland conditions was tested against field measured data from two sites. Field data obtained from a North Central Ohio site were used to evaluate drain flow and runoff predictions. Water table depth predictions were evaluated against a field data set from Aurora, North Carolina. Overall, WEPP-WTM produced drain flow and runoff results similar to those from DRAINMOD and better than all of those obtained with WEPP. To evaluate the water table depth prediction accuracy of WEPP-WTM, standard errors were compared with those obtained from published results using DRAINMOD, ADAPT, and SWATREN. Overall, the predictions of water table depth from WEPP-WTM were very comparable to those from the other models.