Streamflow characteristics of a naturally drained forested watershed in southeast Atlantic coastal plain
Information about streamflow characteristics e.g. runoff-rainfall (R/O) ratio, rate and timing of flow, surface and subsurface drainage (SSD), and response time to rainfall events is necessary to accurately simulate fluxes and for designing best management practices (BMPs). Unfortunately, those data are scarce in the southeastern Atlantic coastal plain, a highly urbanizing region characterized by poorly drained low-gradient forested landscape where runoff is dominated by shallow SSD and saturation excess overland flow. In this paper we evaluate these characteristics using four years (2005-08) of streamflow data measured on a 72 km2 naturally drained forested watershed on the Francis Marion National Forest in coastal South Carolina. The calculated average event peak flow rate, time to peak, event duration, SSD as % of streamflow, and R/O ratio were 4.2 m3 sec-1 km-2, 14.6 hrs, 13.9 days, 29%, and 20%, respectively, for 12 events with rainfall amount varying from 153 mm to 34 mm. The events were similar to those from the historic data (1964-73) indicating a hydrologic recovery of forest since its regeneration after Hurricane Hugo in 1989. The average drainage response time to the rain was 7.8 hours. Results suggested that the runoff and peak flow rate of storm events are dependent upon both the rainfall and its intensity as well as the antecedent conditions described better by initial water table positions than the initial flow rate. These results, as a baseline reference, may have implications for regional water and water quality management assessments including the restoration efforts.