STORM EVENT FLOW AND RUNOFF-RAINFALL PATTERNS IN A THIRD-ORDER COASTAL PLAIN WATERSHED

Turkey Creek and Quinby Creek are third-order watersheds, each are about 5,000 hectares in area, and located mostly within the boundaries of the Francis Marion National Forest on the Lower Coastal Plain of South Carolina, northeast of Charleston. The Turkey Creek watershed is predominantly forested public land managed by the USDA Forest Service; the majority of the Quinby Creek watershed is forested, however 34% of the area is privately owned. An analysis of the potential effects of land use change on annual stream outflows of Turkey and Quinby Creek is ongoing, involving observations of stream flow dynamics and characterization of watershed spatial data. Aerial photography and information on topography, soils, land use, hydrography and vegetation are being compiled. The Turkey Creek watershed was monitored by the US Geological Survey for rainfall and stream outflows from 1963 to 1984, and in December 2004 the gaging station was re-established less than 1 km upstream of the decommissioned gage. First- and second-order watersheds within and adjacent to Turkey Creek watershed have also been monitored continually by the US Forest Service's Southern Research Station since the mid-1960s. The water budget for one first-order watershed was recently calculated for the years 2003 and 2004. It was found that during the wet year 2003, the runoff-rainfall ratio was nearly 0.5, whereas for the dry year 2004 it was 0.1. The thirteen-year (1964-76) average annual runoff-rainfall ratio for the Turkey Creek watershed has been estimated as 0.25. Historical instantaneous stream flow data are being analyzed to understand storm event outflow as affected by seasonal rainfall patterns, and storm volume, intensity and duration. We will present results on the hydrograph characteristics including runoff-rainfall ratios for Turkey Creek for various storm events and will discuss the possible impacts of land use change in the Quinby Creek watershed and similar Coastal Plain watersheds.