EXAMINING WATER FLOW PATHS AND STREAM RESPONSE OF A DISTURBED HEADWATER CATCHMENT IN THE SOUTHERN APPALACHIAN MOUNTAINS, NC

In the Gribble Gap watershed (0.4 km²) in Cullowhee, North Carolina, previous studies have shown that erosion and sedimentation have altered soil characteristics of the landscape. Water flow paths through this watershed have likely been changed through intensive land use, subsequently affecting runoff generation mechanisms operating within the system. The study's purpose is to examine the relationship between water flow paths and catchment runoff through responses of soil moisture and discharge to precipitation events within the Gribble Gap watershed.

To determine water pathways through a slope within the watershed, the response of soil moisture to precipitation events was examined using soil moisture sensors along a hillslope transect perpendicular to a stream. The sensor locations were placed at the ridge top, shoulder, and toe of the hill slope. Weekly groundwater level measurements were taken at a well located at the toe slope. Antecedent precipitation index (API) was calculated using precipitation data measured in a clearing at the bottom of the catchment and discharge was measured in a flume at the mouth of the catchment.

Preliminary data suggests a threshold in precipitation that triggers an increase in discharge in the watershed, without considering antecedent wetness. Previous studies characterizing the soil texture at depths of the moisture sensor locations help explain the moisture responses, and identify a potential mechanism for the precipitation threshold in our preliminary data. This weak precipitation-discharge threshold relationship is indicative of a change in the catchment system once this threshold is surpassed, which could be the result of saturated lateral subsurface flow.

A weak precipitation-discharge relationship without considering antecedent wetness suggests quick flow pathways are operating within the watershed to generate runoff regardless of existing soil moisture. These pathways may be the result of erosion and sedimentation triggered by intensive land use. Historic erosion of the top soil in the upper slopes of the catchment has left limited storage above a restrictive clay layer. This may result in saturated lateral water flux developing more quickly than in an undisturbed location, making runoff generation in these areas less dependent on antecedent wetness.