During recent years the Standford Watershed Model has become a popular means of predicting the hydrologic response of land use changes. A special trial and adjustment model of the Kentucky version is available for determining best-fit values for the input parameters to the Watershed Model. This study was initiated to evaluate the ability of OPSET to reflect changes due to urbanization in the best-fit estimates of those watershed parameters which cannot be estimated from historical records or watershed characteristics. This study also included an evaluation of the significance of these changes, particularly in the land phase parameters on water yield predictions from the Kentucky Watershed Model.

Changes in the vegetative cover (VINTMR) produced significant changes in the basic upper zone storage capacity factor (BUZC) and the basic interflow volume parameter (BIVF). No significant changes in the remaining land phase parameters were found.

Varying the amount of impervious area (FIMP) produced significant changes in all land phase parameters except the seasonal infiltration adjustment constant (SIAC).

There were significant year-to-year variations in all the land phase parameter estimates except the basic interflow volume parameter (BIVF). Water yield also changed from year to year.

OPSET seemed to produce best-fit parameters with which the Watershed Model could simulate flows compatible with those which might be expected from increased urbanization. Different sets of parameter estimates produced significantly different water yields.