Groundwater availability in the Atlantic Coastal Plain of North and South Carolina

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

“…Proponents of new pumping may refer to geological information and argue that the groundwater systems are separated, when in fact, the systems are hydraulically connected. This has been shown for the Gordon aquifer, where limestone is underlain by sands in other nearby areas of this combined system, located inland from the coast [30,31]. In the absence of data, it is a mistake to assume that pumping from a deeper stratum does not involve the extraction of water from shallower units and to conclude that the surface wetland or shallow-water table environment will not be affected.…”

“…Figure A1 shows a hydrogeological cross-section model of the coastal plain subsurface for South Carolina [31]. A geological formation beneath the uppermost principal aquifer may have a different lithology (in this case, sand versus limestone) and different geological formation names (e.g., the Gordon aquifer, within the Black Mingo Formation, also known locally as the Santee Limestone).…”

“…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 evapotranspiration (PET = 1135 mm) [29], facilitates the formation of excess saturated soil conditions, on average, during and after rainy periods. The shallow water table in these systems is the surficial aquifer, in which undifferentiated fine-grained sands of the Pleistocene Epoch (Wando Formation and Silver Bluff beds) are deposited on semi-consolidated marine sediments in coastal South Carolina of the Chicora Member of the Williamsburg Formation (also known as the Santee Limestone) of the late Paleocene [30,31]. See Figure A1 for an idealized geological cross-section of this region.…”

“…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).…”

HydroClimATe: hydrologic and climatic analysis toolkit

“…Climate variability influences the timing and volumes of inflow and outflow components of hydrologic budgets (for example Hanson and others, 2003;others, 2007, 2009;Faunt, 2009;others, 2009, 2012;Campbell and Coes, 2010;Heilweil and Brooks, 2011). Influences on surface water include the distribution, timing, and amount of runoff-producing precipitation, which leads to changes in surface-water deliveries in agricultural and municipal areas, as well as streamflow for ecosystems.…”