Turkey Creek—A Case Study of Ecohydrology and Integrated Watershed Management in the Low-Gradient Atlantic Coastal Plain, USA

Abstract

Water yield, water supply and quality, wildlife habitat, and ecosystem productivity and services are important societal concerns for natural resource management in the 21 st century. Watershedscale ecohydrologic studies can provide needed context for addressing complex spatial and temporal dynamics of these functions and services. This study was conducted on the 5240 ha Turkey Creek watershed (WS 78) draining a 3 rd order stream on the Santee Experimental Forest within the South Carolina Atlantic Coastal Plain, USA. The study objectives were to present the hydrologic characteristics of this relatively undisturbed, except by a hurricane (Hugo, 1989), forested watershed and to discuss key elements for watershed management, including water resource assessment (WRM), modeling integrated water resources management, environmental assessment, land use planning, social impact assessment, and information management. Runoff coefficients, flow duration curves, flood and low flow frequency curves, surface and ground water yields were assessed as elements of the WRM. Results from the last 10 years of interdisciplinary studies have also advanced the understanding of coastal ecohydrologic characteristics and processes, water D. Amatya et al. 793 balance, and their modeling including the need of high resolution LiDAR data. For example, surface water dynamics were shown to be regulated primarily by the water table, dependent upon precipitation and evapotranspiration (ET). Analysis of pre-and post-Hugo streamflow data showed somewhat lower but insignificant (α = 0.05) mean annual flow but increased frequency of larger flows for the post-Hugo compared with the pre-Hugo level. However, there was no significant difference in mean annual ET, potentially indicating the resiliency of this coastal forest. Although the information from this study may be useful for comparison of coastal ecohydrologic issues, it is becoming increasingly clear that multi-site studies may be warranted to understand these complex systems in the face of climate change, sea level rise, and increasing development in coastal regions.

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

“…There are also perennially wet locations adjacent to streams, and at least one significant spring mouth (Blue Spring, Echaw Creek, Berkeley County, SC, USA) was found during an investigation for potential GDE sites in the FMNF [28], in addition to at least one of the deeper partially-infilled solution depressions. While most of these features receive direct rainfall or shallow surface runoff from adjacent uplands, the presence of a shallow water table in this landscape, where the long-term average annual precipitation (1370 mm) is higher than the long-term annual potential [25,26].…”

“…The sandy-loam texture of the soils and sediments is also an important factor. Some cases in point are studies of the water table response in three locations in the coastal plain region [26,39], and data have indicated that the specific yield of the surficial aquifer sediments was 0.1 or less, such that 5 mm of water loss by evapotranspiration (ET) can cause the water table depth to drop by at least 5 cm [40][41][42]. A comparable study in a drier climate, that used water table hydrograph data to understand groundwater recharge, found that the management of eucalypt stands in Australia can affect the water balance, but that the landscape position in that region was more important [32,33].…”

“…Figure 3 is the U.S. National Wetlands Inventory map for the Francis Marion National Forest and surrounding region, which shows the widespread condition of depressional wetlands and a landscape with a shallow water position. [25,26].…”

“…Figure 4 shows a conceptual diagram that illustrates how changing the water table position may affect a riparian zone or depression wetland [35]. Based on field visits, interpretations of geological surveys [31,36,37], and water-level data from piezometers in the region (Figure 2) [26,38], we estimate that, for the most part, this area does not have truly perched groundwater conditions and thus downward drainage is not limited geologically, but rather by the small downward hydraulic gradients in this flat, highwater-table landscape. Considering an example site with a shallow water-table, if there is an annual one meter water table fluctuation and then a relatively sudden half-meter decrease in the water table elevation due to groundwater withdrawal or tree harvesting, the relative impacts on the vegetation and habitat may be larger than in locations where the average water table is significantly deeper (>3 m).…”

“…Surface hydrology is complex in the low gradient terrain of the lower coastal plain due to a series of beach, back-barrier, river, and swamp depositional facies that influence the surface topography. The coastal plain of the southeastern U.S. contains a substantial diversity of wet to damp habitats, such as frequently-inundated swamps (both riverine and nonriverine), seasonally-inundated wetlands, and shallow water table conditions, yet only occasionally flooded forests in the uplands of pine stands [18,19,26,27]. Approximately 45% of the FMNF are riparian or wetland systems with bottomland hardwood species such as bald cypress (Taxodium distichum) and pond cypress (T. ascendens), blackgum (Nyssa sylvatica), water or swamp tupelo (N. aquatica), pond pine (P. serotina), red maple (Acer rubrum), and sweetgum (Liquidambar spp.)…”