Characterization of Storm Flow Dynamics of Headwater Streams in the South Carolina Lower Coastal Plain¹

Abstract

Hydrologic monitoring was conducted in two first-order lower coastal plain watersheds in South Carolina, United States, a region with increasing growth and land use change. Storm events over a three-year period were analyzed for direct runoff coefficients (ROC) and the total storm response (TSR) as percent rainfall. ROC calculations utilized an empirical hydrograph separation method that partitioned total streamflow into sustained base flow and direct runoff components. ROC ratios ranged from 0 to 0.32 on the Upper Debidue Creek (UDC) watershed and 0 to 0.57 on Watershed 80 (WS80); TSR results ranged from 0 to 0.93 at UDC and 0.01 to 0.74 at WS80. Variability in event runoff generation was attributed to seasonal trends in water table elevation fluctuation as regulated by evapotranspiration. Groundwater elevation breakpoints for each watershed were identified based on antecedent water table elevation, streamflow, ROCs, and TSRs. These thresholds represent the groundwater elevation above which event runoff generation increased sharply in response to rainfall. For effective coastal land use decision making, baseline watershed hydrology must be understood to serve as a benchmark for management goals, based on both seasonal and event-based surface and groundwater interactions.(KEY TERMS: surface water ⁄ groundwater interaction; runoff; watershed management; streamflow; coastal watershed hydrology; first-order stream; hydrograph separation; South Carolina.)

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

“…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.…”

“…Storm runoff varies widely, from none to over 70 % of rainfall (Epps et al, 2013), which is believed to be related to soil water and depression storage. In low-gradient forested watersheds, we anticipate an even greater coupling of transpirative and soil water dynamics in runoff generation processes (Amatya et al, 1996;Slattery et al, 2006;Sun et al, 2010;Amatya and Skaggs, 2011;Dai et al, 2011;Skaggs et al, 2011;Tian et al, 2012).…”

Curve Number Derivation for Watersheds Draining Two Headwater Streams in Lower Coastal Plain South Carolina, USA

“…Previous work within these study watersheds determined breakpoint water table elevations for measures of outflow and runoff at each of these watersheds above which runoff generation increased sharply. These breakpoints were in the range of 3.25–3.5 m above sea level at UDC and 8.5–8.97 m above sea level at WS80 (Epps et al ., ). Figure demonstrates that the trend in CNs plotted by antecedent water table elevation approximately intersects the CN‐II and mean storm event CN lines within these water table elevation ranges at each of the watersheds.…”

“…(Left) Upper Debidue Creek ( UDC ) Watershed and (Right) Watershed 80 (WS80) Delineations and Monitoring Networks, Including Outflow and Rainfall Gages, and Water Table Wells ( WR 66/P1 and Well H, respectively) (Epps et al ., ).…”

Coastal Forests and Groundwater: Using Case Studies to Understand the Effects of Drivers and Stressors for Resource Management

“…The potential connection between the shallow aquifers and the deeper, regionally-confined aquifers, that in-part support many large communities, is poorly understood. Although variable shallow water table dynamics driven by the interaction between rainfall and the water table dominate the streamflow as saturation excess runoff in these coastal forests [28,39,41,45,[47][48][49], earlier hydrological water balance studies on forest watersheds within the Francis Marion National Forest, based on field measurements [39] and model validation studies [50,51], assumed a negligible interaction between shallow and deep aquifers or no deep seepage losses. However, recent work investigating shallow groundwater recharge in the lower coastal plain estimated an average annual recharge rate to the water table aquifer of about 10% of the total precipitation [26].…”