Erosion Alters Depth to the Argillic Horizon: What Impacts on Hillslope Interflow?.

The hydrology of hillslopes in the southeastern (SE) U.S. Piedmont is strongly influenced by the typical presence of a low permeability argillic horizon that often causes high lateral flow in periods of high rainfall. Numerical models of SE US piedmont hillslopes often represent this low permeability layer as parallel to the soil surface, which creates different zones of interflow along the hillslope. However, much of the SE US piedmont is highly eroded, with soil redistributed from higher to lower landscape positions. This redistribution leads to a low permeable layer that is not consistently parallel to the soil surface, creating zones of interflow that are difficult to predict without subsurface investigations. This study parameterizes two hillslope models from extensive soil texture and hydraulic conductivity data within highly eroded and undisturbed watersheds. These models contain both spatial variations in depth to the argillic horizon, and flow paths of the ground water. This spatially explicit hillslope data were used to compare outflows at the lower slope between the conventional parallel depth model and the non-parallel depth model. The groundwater in undisturbed hillslope (parallel depth model) showed more vertical oriented movement than that of the historically farmed hillslope (non-parallel depth model) which traveled in a perpendicular manner to the soil surface. The volumetric water content of the argillic horizon was higher in the undisturbed hillslope than that of the historically farmed hillslope at the end of the simulation period (1000 days), with a Θv of 0.332 and 0.238 respectively.