Hydrology and Water Budget for a Forested Atlantic Coastal Plain Watershed, South Carolina¹

Abstract

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.

Hurricane impacts on a pair of coastal forested watersheds: implications of selective hurricane damage to forest structure and streamflow dynamics

“…These topographic and soil characteristics indicate a high surface water detention capacity and slow surface water drainage. The climate is mild and wet, with an average temperature of 18.3 • C, and an average annual precipitation of 1370 mm (Dai et al, 2013;Harder et al, 2007).…”

“…Soon after Hurricane Hugo, WS77 underwent a salvage harvest, where high-valued damaged or fallen trees were removed from the watershed -WS80 however was left untouched. Additional descriptions of the site, field measurements and past studies are detailed in Dai et al (2013), Harder et al (2007), Amatya et al (2006), Amatya and Trettin (2007), and Amatya and Radecki-Pawlik (2007).…”

“…WS77 and WS80 were calibrated using streamflow data between 1969 and 1976, followed by a series of prescribed burning experiments on WS77 from 1977 through 1981 (Richter et al, 1982(Richter et al, , 1983. Data collection resumed in November 1989, following Hugo, and has continued until the present (Amatya et al, 2003Miwa et al, 2003;Sun et al, 2000;Harder et al, 2007;Dai et al, 2013). Streamflow rates on both watersheds (WS77 and WS80) were estimated using a compound weir instrumented with stage recorders.…”

“…Infiltration losses for this study were considered to be minimal based on Harder et al (2007), who reported that deep seepage or infiltration losses are negligible in coastal forest systems. Additionally, recent work by Callahan et al (2012) on a proximal but larger watershed yielded about 5-10 % of annual precipitation lost to groundwater for a moderately well drained upland site.…”

“…Differences in water table position has been shown to be a primary cause for variability in the relationship between rainfall and runoff (Epps et al, 2013;La Torre Torres et al, 2011;Harder et al, 2007;Young and Klawitter, 1968). This high variability is probably responsible for the low R 2 values found by MOSUM analysis, although using rainfall measurements from the relatively distal Santee headquarters rain gauge (refer Fig.…”