HYDROLOGIC PARAMETERIZATION OF WATERSHEDS FOR RUNOFF PREDICTION USINGSWAT

The use of continuous time, distributed parameter hydrologic models li ke SWAT (Soil and Water Assessment Tool) has opened several opportunit ies to improve watershed modeling accuracy. However, it has also place d a heavy burden on users with respect to the amount of work involved in parameterizing the watershed in general and in adequately represent ing the spatial variability of the watershed in particular Recent deve lopments in Geographical Information Systems (GIS) have alleviated som e of the difficulties associated with managing spatial data. However, the user must still choose among various parameterization approaches t hat are available within the model. This paper describes the important parameterization issues involved when modeling watershed hydrology fo r runoff prediction using SWAT with emphasis on how to improve model p erformance without resorting to tedious and arbitrary parameter by par ameter calibration. Synthetic and actual watersheds in Indiana and Mis sissippi were used to illustrate the sensitivity of runoff prediction to spatial variability, watershed decomposition, and spatial and tempo ral adjustment of curve numbers and return flow contribution. SWAT was also used to predict stream runoff from actual watersheds in Indiana that have extensive subsurface drainage. The results of this study pro vide useful information for improving SWAT performance in terms of str eam runoff prediction in a manner that is particularly useful for mode ling ungaged watersheds wherein observed data for calibration is not a vailable.