HYDROMETRIC AND STREAM CHEMISTRY EVIDENCE OF 3 STORM FLOWPATHS IN WALKER-BRANCH WATERSHED

Hydrometric and stream chemistry measurements were made across a network of sites to identify the dominant flowpaths producing storm runoff in Walker Branch Watershed, a small forested catchment with deep soils overlying dolomitic bedrock in eastern Tennessee. Recession analysis of storm hydrographs and an end-member mixing analysis using Ca and SO4 concentrations suggested that three subsurface flowpaths were important in streamflow generation during a storm in March 1991. The chemical end-member mixing analysis indicated that vadose zone, saturated soil zone, and bedrock zone flowpaths contributed to streamflow, but the contribution of each varied over space and time. Bedrock zone flow, with high concentrations of Ca and low concentrations of SO4, dominated during baseflow prior to the storm, and was more important at a lower stream site than an upper stream site. Vadose zone water, with low concentrations of Ca and high concentrations of SO4, dominated the stormflow response at both stream sites, but was more important at the upper site than the lower site. Water level observations from shallow and deep hillslope and ridgetop wells showed the development of transient, perched groundwater tables within the top several meters of soil. Large increases in streamflow generated via vadose zone and saturated soil zone flowpaths appeared to be dependent on development of these zones of perched saturation in the upper soil profile and the initiation oflateraI and vertical preferential flow.