Estimating groundwater recharge in lowland watersheds

Abstract

Abstract:Little attention has been given to the role of groundwater in the hydrological cycle of lowland watersheds. Our objective in this study was to estimate total recharge to groundwater by analysing water table response to storm events and the rate at which water was transferred into the shallow aquifer. This was conducted at three sites in a rural watershed in the lower Atlantic coastal plain near Charleston, South Carolina, USA. A novel version of the water table fluctuation method was used to estimate total recharge to the shallow aquifer by comparing hourly data of water table position following storm events and measuring water table recession behavior, rather than subjective graphical analysis methods. Also, shallow aquifer recharge rates (vertical fluxes) were estimated using Darcy's Law by comparing static water levels in a water table well and in a shallow piezometer during dry periods. The total annual recharge estimated ranged from 107 AE 39 mmÁyr -1 (5-10% of annual precipitation) at a poorly drained topographic low area to 1140 AE 230 mmÁyr -1 (62-94% of annual precipitation) for a moderately well-drained upland site. The average aquifer recharge rate was 114 AE 60 mmÁyr, which is similar to previous estimations of base flow for the ephemeral thirdorder streams in this watershed. The difference in the two methods may have been caused by processes not accounted for in the Darcy flux method, soil moisture deficits, and average evapotranspiration demand, which is about 1100 mmÁyr -1 for this region. Although other factors also can affect partitioning of recharge, an integrated approach to inspecting easily gathered groundwater data can provide information on an often neglected aspect of water budget estimation. We also discuss the effects of land use change on recharge reduction, given a typical development scenario for the region.

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

“…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. Since both watersheds in the current study comprise poorly drained soils and are almost 35 times smaller in drainage area than the one studied by Callahan et al (2012), we anticipated even lower groundwater recharge possibly in the order of 2-3 % of incident precipitation.…”

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].…”

“…Similarly, the ET g rate at a forested site in a floodplain system of the Congaree National Park in the upper (inner) coastal plain of South Carolina, USA, ranged from 0.2 to 4 mm·d −1 [66]. This was based on an assumed value for specific yield of the soils and sediments of 0.07 [25,39]. For comparison, an eddy covariance method estimated the ET to be about 7 mm·d −1 for a coastal forest in eastern North Carolina USA [56].…”

“…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].…”

“…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.) [25]. 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.…”