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Abstract
Interflow (throughflow or lateral flow), is shallow lateral subsurface flow that moves over a horizon that restricts percolation. Interflow is important for a number of reasons. First, rapid saturated interflow through macropores can travel to streams and alluvial aquifers with high celerity. Also, experimental studies have shown that interflow can be an important source of baseflow and stormflow. Because interflow travels through a biologically active region of soil with roots and relatively high OM content, the final outcome is the potential contamination of surface water bodies from subsurface water. 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 hundreds of centimeters. The degree to which these argillic horizons alter subsurface movement of infiltrated water is not well known. This research +investigates how often and under what conditions a relatively deep (20-150cm) argillic horizon on low slope (2-12%) hillsides causes interflow to occur. Research was conducted at the Savannah River Site, Aiken, South Carolina, on a small (38 ha) zero-order watershed. In the first phase of this research, a high resolution topographic map of the horizon was developed. This map was used to instrument designated low spots with 65 max-rise piezometers in order to determine the controls these low spots impart on subsurface flow. In situ hydraulic conductivities of the argillic layer and the surface horizons were measured using an Amoozegar meter, soil cores were taken to develop moisture release curves and estimate bulk density. Along with soil topographic measurements, 13 data-logging piezometers were installed to measure the piezometric head above, in, and below the argillic horizon. The stream that drains the catchment was instrumented with a 2-foot (61cm) H-flume with a data-logged pressure transducer. Climate data including precipitation, barometric pressure, and temperature, was continuously collected in an open area approximately mile (300m) from the study site. Combining the shallow surface and subsurface piezometric heads with stream flow rates, it was possible to determine if and when the horizon could contribute to streamflow. Results from the study indicate a thin transient water table occurred at some locations across the hillslope for a few storm events. This water table is thought to be attributed to the water restrictive argillic horizon. Relatively warm weather and dry conditions that characterized the monitoring period likely limited observations of saturated conditions above the argillic horizon.