ANALYSIS OF GROUNDWATER-SURFACE WATER INTERACTION IN A HEADWATERS STREAM SYSTEM IN THE SOUTHERN APPALACHIANS, CULLOWHEE, NC. PART A: PHYSICAL SETTING IN DIFFERENT HYDROGEOMORPHIC REACHES

Currently, minimal data document groundwater-surface water interactions (GSI) in Western North Carolina. A new hydrologic research station has been established at Western Carolina University as part of North Carolina’s Resource Evaluation Program in the Department of Environment and Natural Resources. The overall objective of the station is to define groundwater–surface water interaction in different hydrogeomorphic settings of a small stream system to better guide management decisions.

The purpose of this study was to determine the physical hydrogeologic setting of three reaches of a small basin in different geomorphic zones. Data were collected in order to describe the hydraulic and physical properties within three distinct reaches: Gribble Gap Creek (0.44 km²) – a colluvial reach, flows into Long Branch (4.39 km²) – a colluvial-alluvial reach, which flows into Cullowhee Creek (62 km²) – an alluvial reach. Four cores, 6 to 9 m in depth, were taken adjacent to channels and were described for texture, color, and carbon, nitrogen, and sulfur content. A constant-head permeameter and the Hvorslev slug-tests were used to determine hydraulic conductivity (K) profiles at each reach above and below the water table. These data were collected at nested sites perpendicular and parallel to the stream at each reach.

Core data suggests that depth to saprolite increases downstream from about 1.2 m at the colluvial reach to 1.4 m at the alluvial reach. On average, sediments increase in grain size and variability downstream. Hydraulic conductivity data (n=60), in both vadose and saturated zones, show analogous trends; overall, K ranges from 10^-3 – 10^-6 cm s^-1. Cullowhee Creek, the alluvial reach, shows the greatest lateral variability in K within the vadose zone. Below the water table, K is most variable at Long Branch, ranging from 10^-3 – 10^-6 cm s^-1, and least at Gribble Gap (10^-4 – 10^-5 cm s^-1). The hydrogeologic setting, described here, directly affects groundwater flow and the interaction with stream water (see Part B). In sum, the sediments and their hydraulic traits vary by geomorphic setting; this information can be applied to similar settings within the Southern Appalachian Mountains.