While historical measures describing implementation of conservation have sufficed within the conservation community, the investment in federal conservation programs now requires a compelling justification of the environmental benefits achieved from these funds. Such a justification must convince federal policy makers that funds committed to conservation measures are better spent there than toward other policies contending for the funds. Therefore, the Conservation Effects Assessment Project (CEAP) was initiated in 2003, comprised of a national assessment study led by USDA-NRCS and a watershed assessment study led by USDA-ARS. The USDA-ARS identified 12 research watersheds for involvement in CEAP, one of which is the Mark Twain watershed located in northeastern Missouri. Objectives of this study were to calibrate the Soil Water Assessment Tool (SWAT) model and compare simulated and measured streamflow and water quality data collected over a 15-year period from the Goodwater Creek watershed and to evaluate the sensitivity of the model to soil and cropping management changes. The Goodwater Creek watershed is a 7,250 ha mixed cropping watershed located in the upper reaches of the Mark Twain watershed that was instrumented for water quality sampling in 1991. Results from the calibration and validation of the SWAT model will be shown as well as those of exploratory sensitivity analyses of the model's capability for predicting the effects of land management changes. Particularly important is the model's performance for simulating the effects of adopting conservation tillage.