Hydrology and Water Budget for a Forested Atlantic Coastal Plain Watershed, South Carolina

Increases in timber demand and urban development in the Atlantic Coastal Plain over the past decade have motivated studies on the hydrology, water quality, and sustainable management of coastal plain watersheds. However, studies on baseline water budgets are limited for the low-lying, forested watersheds of the Atlantic Coastal Plain. The purpose of this study was to document the hydrology and a method to quantify the water budget of a first-order forested watershed, WS80, located within the USDA Forest Service Santee Experimental Forest northeast of Charleston, South Carolina. Annual Rainfall for the 2003 and 2004 periods were 1,671 mm (300 mm above normal) and 962 mm (over 400 mm below normal), respectively. Runoff coefficients (outflow as a fraction of total rainfall) for the 2003 and 2004 periods were 0.47 and 0.08, respectively, indicating a wide variability of outflows as affected by antecedent conditions. A spreadsheet-based Thornthwaite monthly water balance model was tested on WS80 using three different potential evapotranspiration estimators [Hamon, Thornthwaite, and Penman-Monteith (P-M)]. The Hamon and P-M-based methods performed reasonably well with average absolute monthly deviations of 12.6 and 13.9 mm, respectively, between the measured and predicted outflows. Estimated closure errors were all within 9% for the 2003, 2004, and seasonal water budgets. These results may have implications on forest management practices and provide necessary baseline or reference information for Atlantic Coastal Plain watersheds. KEY TERMS: Runoff; hydrologic-modeling; hydrologic-monitoring; Thornthwaite water-balance; water table, evapotranspiration. Harder Scott V, Devendra M. Amatya, Timothy J. Callahan, Carl C. Trettin, and Jon Hakkila, 2007. Hydrology and Water Budget for a Forested Atlantic Coastal Plain Watershed, South Carolina. Journal of the American Water Resources Association (JAWRA) 43(3):563-575. DOI: 10.1111 ⁄ j.1752-1688.2007.00035.x