Simulating subsurface drainage in the lower Mississippi Valley with DRAINMOD.
ABSTRACT DATA from a subsurface drainage-runoff-erosion field experiment near Baton Rouge, LA, were used to evaluate the water managment model, DRAINMOD, for simulating subsurface drainage in the lower Mississippi Valley. Predicted and measured surface runoff, subsurface drain flow, and water table depth were compared for 3 years, 1981, 1982 and 1983 which were, respectively, normal-to-wet, drier than normal, and very wet in growing season soil water conditions. Model predicted runoff, drain flow, and water table depth compared more closely with the field measured (observed) values during the wettest year, 1983. For the drier-than-normal year, 1982, runoff and drain flow were significantly overpredicted because evapotranspiration (ET) was underestimated by the model. Assumed deeper rooting for corn in 1982 increased soil water withdrawal by ET and significantly improved predictions of water table depth.