USE OF SWAT TO COMPUTE GROUNDWATER TABLE DEPTH AND STREAMFLOW IN THE MUSCATATUCK RIVER WATERSHED

Abstract

Groundwater table depth oscillation over time is an important issue for planning drainage systems in ruralwatersheds. Its proximity to the soil surface impacts soil properties, crop development, and agricultural chemical transport.Even though hydrologic models are valuable tools for simulating and predicting changes in water dynamics, groundwatertable depth is usually difficult to predict. The Soil Water Assessment Tool (SWAT) is a continuous and distributed hydrologicmodel created to simulate the effect of land management practices on water, chemicals, and sediment movement for largewatersheds. However, groundwater table depth is not computed by the model. A procedure to compute perched groundwatertable depth using SWAT outputs is proposed, based on the theory used by DRAINMOD, in order to expand SWATs capabilities.SWAT was calibrated and validated for streamflow for three watersheds, and for groundwater table depth for three soils, atsites located within the Muscatatuck River basin in southeast Indiana. The Nash-Sutcliffe model efficiency (R2N) for monthlystreamflow was 0.49, 0.61, and 0.81 for the three watersheds for the validation period (1995-2002). SWAT-predictedgroundwater table depths provided R2N values of 0.61, 0.36, and 0.40 for the three soils in the calibration period (1992-1994)and 0.10, -0.51, and 0.38 for the validation period (1995-1996). Even though the model performance for predictinggroundwater table depth was not as good as for streamflow, SWAT predictions resembled the seasonal variation of thegroundwater table with correlation coefficients (r) of 0.68, 0.67, and 0.45 for the three wells during the validation period.