CONTROLS ON TURBIDITY AND TOTAL SUSPENDED SOLIDS CONCENTRATIONS IN ALLEN'S CREEK, AN UNDEVELOPED, MOUNTAINOUS WATERSHED, WESTERN NORTH CAROLINA

Few data sets are as important and widely used in the management of riverine ecosystems as those generated by water quality monitoring programs. In western North Carolina (WNC), determination of temporal changes in suspended sediment concentrations and loads is particularly important as sediment is often considered the most significant threat to aquatic biota. In 2007 an intensive water quality monitoring program consisting of five extensively instrumented sites was initiated in the Allen’s Creek Watershed in Haywood County, North Carolina. Allen’s Creek, characterized by high gradients (>0.05 m/m), boulder bed materials, and local exposures of bedrock, feeds a reservoir that serves as the drinking water supply for the Town of Waynesville. The watershed encompasses an area of approximately 21.9 km², and is currently undeveloped with no permitted point source discharges, allowing it to be classified as a WS-I watershed. More than 95 % of the basin is forested. Thus, the watershed provides an excellent setting to assess water quality in a relatively undeveloped basin. This study focuses on the turbidity and the concentration of total suspended solids during floods of various magnitudes and frequencies at three sites within the basin, including the main stem of Allen’s Creek and two tributaries (Cherry Cove and Old Bald Creek). Peak discharge during precipitation events ranged from 0.4 to 3.44, 0.75 to 1.53, and 0.02 to 1.07 m³/s on the three sites, respectively. Turbidity values during base flow were below or near detection (<2 to 5 NTU), and exhibited maximum values of 59 NTU, 44 NTU, and 99 NTU, respectively during floods. TSS values were also extremely low; for example, more that 90 % of the 1052 samples collected at the Allen’s Creek site over a full range of flow conditions exhibited TSS values below 30 ppm. Only 2.3 % of the samples exhibited TSS values above 100 ppm. Systematic correlations between turbidity, TSS, and discharge were not observed within the data set, suggesting factors in addition to flow magnitude controls sediment loads. Preliminary analyses suggest these include storm intensity, total precipitation, and season.