HYDROGEOLOGIC PROPERTIES OF DIFFERENT GEOMORPHIC SETTINGS IN A SMALL DISTURBED WATERSHED, WESTERN NORTH CAROLINA

Understanding hydrologic properties and processes in small, disturbed watersheds in western North Carolina has become increasingly important to water resources and quality management. Gribble Gap, a 0.44 km² headwaters basin extensively logged decades ago, is part of hydrologic research station recently established by the North Carolina Department of Environmental and Natural Resources and Western Carolina University. This study examines the hydraulic properties of slope flowpaths to explore water routing in the basin, which is similar to many in the mountains of Western North Carolina.

This study examined various hydrogeologic properties within a first-order headwaters stream system including: (1) the spatial variability of near surface saturated hydraulic conductivity (K_SAT) values in different geomorphic slope positions, (2) the relationship between grain size and geomorphic position, (3) the spatial variability of K_SAT above and below the water table at and near streams. Transects included soil descriptions and K_SAT measurements, at depths of 10-40 cm, every 3 m for 15 m at 4 slope positions. Hvorslev slug-tests and constant-head permeameter tests were performed downstream at nested wells (n=40), where the headwaters stream meets a colluvium dominated valley floor. Soil moisture sensors and a rain gage were positioned at the downstream sampling location. Surface and sub-surface waters were analyzed for major ions.

K_SAT values, to date, ranged from 10^-3 to 10^-4 cm s^-1 along the footslope and backslope transects. The average K_SAT value for all footslope measurements (9.3x10^-4 cm s^-1) is higher than the average K_SAT value for all backslope measurements (5.4x10^-4 cm s^-1) suggesting that the valley location is more likely to have deeper flow paths. K_SAT values ranged from 10^-4 to 10^-5 cm s^-1 below the water table with the lowest values occurring in the deeper wells, 6-8 m deep. The stream, Gribble Gap Creek, is losing in this reach, likely in response to the increased depth to bedrock. Variation in water chemistry, coupled with physical data, indicate complex flow paths. Future work will determine if properties are similar to various other similar locations in order to obtain increased knowledge on the hydrology of western North Carolina.