HYDROLOGICAL PROPERTIES AND NEAR-STREAM GROUNDWATER RESPONSE AT MULTIPLE CATCHMENT SCALES, WESTERN NORTH CAROLINA

The Western Carolina Hydrological Research Station was designed to characterize near-stream hydrological processes at different scales within the southern Appalachians. The research station is a series of nested basins which we have used to examine the change in near-stream sediment properties with scale and how these properties impact groundwater-stream water interaction. The area has variably been logged once or twice in the last 150 years, and many hillslopes are gullied and have experienced topsoil loss, both of which are documented in a 1938 map. In areas that have experienced multiple periods of deforestation, colluvial/ alluvial fans lie downslope of the gullies. These fans are cut by channels and locally, water tunnels through the deposits and becomes channelized downstream.

Groundwater wells are monitored at a colluvial/alluvial fan (Gribble Gap; ~0.4 km²), a slightly larger colluvial/alluvial valley (Long Branch; 2.8 km²) and an alluvial valley (Cullowhee Creek; 65 km²). These near-stream deposits typically lie in a thin veneer over saprolite, which we interpret from cores to be within 2 m of the surface. We have measured groundwater levels on an approximately weekly basis over the last four years in ~50 near stream wells, examined soil cores from each of the sites, tested saprolite hydraulic conductivity using well slug tests, and measured hydraulic conductivity of near-surface (< 1 m) deposits with a field constant-head permeameter.

In a preliminary analysis, average hydraulic conductivity in the saprolite at depth and average hydraulic conductivity in the overlying sediments increases downstream in the alluvium relative to upstream colluvial/alluvial sites. Despite differences in the surface materials at each site, the weekly groundwater record for three selected streamside wells appears similar, with the Gribble Gap site having slightly higher variability in groundwater levels than the other two sites over the four years of monitoring. All of the hydraulic heads in these wells increased in January 2013 after a relative drought in the first 2 years of monitoring. Work will continue to characterize these sites and extend the insights from this highly monitored station to other similar environments throughout the southern Appalachians.