Occurrence of perched saturation and interflow over an argillic horizon in a low relief hillslope.

Many of the soils in the southeastern US are characterized by an argillic, or clay horizon, that largely parallels the soil surface at depths ranging from a few centimeters to 100 centimeters. The degree to which these argillic horizons alter subsurface movement of infil- trated water is not well known. Interflow, or through- flow, is shallow lateral subsurface flow that moves over a horizon that restricts percolation. This research investi- gates how often and under what conditions a relatively deep (20-150 + cm) argillic horizon on low slope (2-6%) hillsides causes interflow to occur. Research is being conducted at the Savannah River Site, Aiken, South Caro- lina, on a small zero-order watershed. In the first phase of this research, a high resolution topographic map of the clay layer was developed. This map will be used to in- strument designated "low" spots with max rise piezome- ters in order to determine if there is channelized subsur- face flow. In situ conductivities of the clay layer and the surface horizons were measured using an Amoozegar me- ter, and bulk density samples were taken and measured. Along with soil topographic measurements, data-logging piezometers have been installed to measure the piezomet- ric head above, in, and below the argillic horizon to fur- ther investigate interflow as a potential hydraulic routing mechanism. The stream that drains the catchment was instrumented with a 2' H flume and data-logging pressure transducer to measure stream flow. Climate data includ- ing precipitation, barometric pressure and temperature, are being continuously collected in an open area approxi- mately ¼ mile from the study site. Combining the shal- low surface and subsurface piezometric heads with stream flow rates, we should be able to determine if and when the clay layer is contributing to interflow.