HYDROGEOLOGIC TRAITS AND SETTING OF HEADWATERS STREAM BOUND BY ALLUVIAL AND COLLUVIAL DEPOSITS WITH A DISTRUBANCE HISTORY TYPICAL OF THE SOUTHERN APPLACACHIANS: A CASE STUDY

Downstream water quality has been shown to be influenced by small but numerous headwater streams, which are largely unregulated. Long Branch (4.4 km² area) is bound by alluvial and colluvial deposits in a setting typical of the Southern Appalachians. The site is part of the Western Carolina Hydrologic Research Station (WCHRS; wchrs.wcu.edu). The purpose of this study is to determine the primary controls on groundwater traits, groundwater and stream water interaction, and impacts of land use on hydrology of the Long Branch site.

Site infrastructure includes 17 shallow groundwater wells, a stream staff gage, and a rain gage. Data collected includes ground penetrating radar (GPR) cross-sections, soil and sediment hydraulic conductivity, stream water-stream bed temperature surveys, stream discharges, temperature and level logger data, soil-sediment descriptions, and vegetative traits from remote sensing imagery.

The south side of Long Branch is incised into the distal end of a fan underlain by a mix of sediments typical of southern Appalachian debris flow dominated fans. The upper 1.5 m of sediments range from clay loam to loamy gravels. GPR surveys show a persistent cobble-rich layer at depths ranging from 0.5 to 1.5 m. Measured hydraulic conductivity values range from 10^-3 to 10^-6 cm s^-1. Fine-grained sediments near the fan surface support a shallow water table (<20 cm) with a patchy wetland and gleyed soils even though the Long Branch is incised about 1 m deep. Temperature surveys of the stream water and stream bed (~15 cm depth) show zones of high groundwater flux into the stream bed/banks along the study reach, with more influence from the fan side, which has cooler groundwater, than the side with a small floodplain at the base of the opposing valley slope.

Remote sensing imagery shows human disturbance of the riparian vegetation has decreased greenness, which is reflected by less diurnal variation in water table levels. Recent construction, a large building in a cut-fill site (~4 ha), changed the slope hydrology contributing to Long Branch by disrupting shallow groundwater flow paths and increasing storm runoff. The knowledge from this study and the future work provides a strong basis for estimating the hydrologic traits of similar settings and can help provide an improved basis for planning and management decisions.