A three-equation model for subsurface response is presented. The model is based on storm events for various sized watersheds within the Susquehanna River Basin. The equations represent the peak flow, time to peak, and time base of the subsurface response. The model was developed using multiple variable regression and numerical optimization. The variables used in the regression analysis are related to the physical processes causing subsurface response and were obtained from streamflow and precipitation gauges, a digital elevation model, and land use and soils data. The measured peak subsurface discharge, time to peak, and time base required for the regression analysis were obtained by separating storm hydrographs into direct runoff and subsurface responses. A linear separation from the initial rise of the hydrograph to the inflection point on the recession limb was utilized. The model was developed from a dataset of 50 watersheds by 20 storms (1,000 watershed-events), with the watersheds ranging in size from 14 km(2) to 67,000 km(2). The results indicate that the measured and predicted subsurface response variables agree well, considering the great variation in the observed responses and the time and space scales of the available data.