ANALYSIS OF GROUNDWATER-SURFACE WATER INTERACTION IN A HEADWATERS STREAM SYSTEM IN THE SOUTHERN APPALACHIANS, CULLOWHEE, NC. PART B: HYDROLOGY IN DIFFERENT HYDROGEOMORPHIC SETTINGS

Understanding groundwater - surface water interaction (GSI) is important to development of sustainable water resource management practices. A new hydrologic research station has been established at Western Carolina University as part of the Resource Evaluation Program of the North Carolina Department of Environment and Natural Resources. The primary objective of this research station is to document GSI in different hydrogeomorphic settings. The purpose of this study is to determine basic groundwater patterns and a physiochemical fingerprint for GSI to identify the hyporheic zone along the stream system continuum.

Head levels and different physiochemical measurements were taken from 12 nested well sites (~40 wells total), at three different hydrogeomorphic reaches within the Cullowhee Creek watershed (62 km²) (see Part A for hydrogeologic setting). Head levels were taken at least weekly over one month. Groundwater and surface water samples were measured for carbon, nitrogen and sulfur content, pH, electrical conductivity, and temperature. Estimation of the patterns at the groundwater - surface water interface can be applied by this multi-scale approach and by combining all information gathered for data analysis.

Head level data show groundwater patterns are strongly controlled by valley topography, where local relief is up to 200 m. All three stream reaches are fed by groundwater, at least on one side of the stream. Strong upward flow gradients, up to 0.3, are present at the middle reach, Long Branch, where the stream is adjacent to the valley side. Adjacent to the stream at each reach, the shallow, intermediate, and deep wells show similar and quick responses to storms. Of the physiochemical parameters tested, temperature proved to be the most effective means of distinguishing groundwater from surface water. During October 2010, Cullowhee Creek (downstream) had a 10 °C temperature difference with groundwater, compared with 6 °C at Long Branch, and 4 °C at Gribble Gap. These data indicate that stream water at the upstream Gribble Gap reach is dominated most by groundwater. To appropriately quantify the interaction of groundwater and stream water in the different hydrogeomorphic settings, a multi-method approach must be utilized over an extended time and coupled with physical data.