Although the intense, short duration summer rainstorms falling on the Wilson Creek Watershed in Manitoba, result in a rapid sortm runoff, indicating the possibility of a quick-impulse-response linear relationship, the scatter of points on a simple correlation of rainfall-runoff indicates some large effects of other hydrologic parameters. This study attempts to determine the major parameter affecting this storm rainfall - storm runoff relationship. Three techniques of groundwater separation are considered for derivation of direct storm runoff values. An arbitrary groundwater separation technique with the aid of a composite recession curve is selected in the final analysis. The findings point out that the antecedent basin moisture, as represented by a depth to groundwater table parameter, is the major parameter affecting the storm rainfall - runoff process in the Wilson Creek Watershed. A preliminary attempt to derive a unit hydrograph for the basin indicates that both the peak and its time distribution are variable.