The subsurface hydrological response plays an important role in the hydrology of humid regions. In particular, the physical relationship between base flow dynamics and the fluctuations in spatially averaged water table depth, as described by the groundwater rating curve, determine to a significant extent the nature of statistical persistence of hydrological anomalies in the unconfined aquifers level and river flow. In this paper, we propose that the scale and shape of the groundwater rating curve reflect some of the geomorphological characteristics of the region such as relief, drainage density, and the hypsometric distribution of the elevation field. These connections between geomorphology and hydrology of river basins are investigated using a simple model of unconfined groundwater flow applied to synthetic basins as well as observed basins from Illinois.