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

A small watershed in Cullowhee, NC is planned to be established as a hydrologic research station as part of the NC Department of Environment and Natural Resources, Groundwater Resource Evaluation Program. This site is being developed in collaboration with and on the property of Western Carolina University. A primary objective of this station is to document groundwater-stream water interaction (GSI) in streams of different scales in different geomorphic settings.

The purpose of this study is to characterize GSI and stream hydrology along the continuum of an increasingly higher order stream system and determine the relations between GSI, watershed hydrology, and geologic controls (see PART A). A nested study design was implemented that targeted processes at various spatial and temporal scales in three reach types: colluvial, colluvial-alluvial, and alluvial. Hydrologic data types collected at each reach include stream discharge, stream bed/subsurface temperatures from longitudinal surveys and vertically nested loggers, hydraulic head data from stream-side and in-channel wells, and channel surface and subsurface water physicochemical, nutrients, and major metals data.

GSI varies with the size of the hyporheic zone that in turn appears to be controlled by alluvial sediment volume and stratigraphy. The hyporheic zone tends to have a small vertical dimension in upstream reaches with low amounts of coarse grained alluvium underlain by a confining clay layer. The vertical dimension of the hyporheic zone is significantly larger in downstream reaches with a higher depth to bedrock and greater volume of coarse alluvial sediment. Electrical Conductivity (EC) is a sensitive indicator of hyporheic zone shape and exchange. The use of endmember EC values of groundwater and surface water permit the relative position of a water sample within the hyporheic zone to be estimated. Hyporheic exchange varies temporally depending on stage conditions and changes in bed topography. This study enhances the ability to identify GSI conditions and to further investigate hydrogeomorphic controls on GSI in headwater streams in the southern Appalachians.