Technical Abstract: Recently, a new shallow water table depth (wtd) algorithm (Modified DRAINMOD) that relates drainage volume (vol) to wtd was incorporated into the Soil and Water Assessment Tool (SWAT), a continuous-time physically-based watershed-scale hydrologic model, to improve water table depth fluctuation profile simulation. In the Modified DRAINMOD approach, wtd is computed as a function of vol and a variable water table factor (wt_fctr), which converts vol into wtd. In the current SWAT wtd simulation method in (SWAT-M), wtd is computed beginning with the bottom soil layer above the confining layer. When the bottom soil layer reaches field capacity, additional water is allowed to fill the profile from the bottom of the soil layer upward from which the height of the water table above the restrictive layer and hence the wtd from the ground surface is computed. The Modified DRAINMOD wtd simulation approach has been evaluated at the field scale level in fields (hydrologic response units) without tile drainage. In this study, 1) the streamflow prediction accuracy performance of SWAT using SWAT-M and Modified DRAINMOD wtd simulation approaches will be tested using measured streamflow data from the South Fork watershed in north-central Iowa, and 2) the differences in simulated water budget components will be determined and their implications on water quality discussed. SWAT will be calibrated and validated for streamflow using the two wtd methods and the streamflow prediction performance and the simulated water budget computed using the two methods will be compared. The results of this study will be presented.