Investigating the driving mechanism of subsurface runoff response on a vegetated hillslope in the Georgia Piedmont

Abstract

The near instantaneous runoff response of upland ephemeral channels to high intensity rainfall events has been shown to be minimally influenced by direct precipitation and Hortonian overland flow. Geochemical results have demonstrated that the majority of such runoff water is already present in the catchment before the onset of the storm. This work builds upon the work of McKinnon and Thomas at the USDA – ARS J. Phil Campbell research farm in Oconee County, GA. Their work suggested the significance of the kinematic, or pressure wave, phenomenon in generation of instantaneous subsurface runoff at the site. However their results were questioned as macropore flow may have been able to produce similar data. This work approaches the problem from two different angles, using physical and chemical evidence, to pinpoint the driving mechanism behind the observed runoff at the ARS study site established by McKinnon and Thomas. Our experiments suggest that the kinematic wave phenomenon drives the near instantaneous subsurface runoff observed at the site while demonstrating that the phenomenon is mutually exclusive with saturated conditions at the soil surface.