Upper Floridan Aquifer

The Upper Floridan aquifer underlies most of the Coastal Plain of Georgia, southern South Carolina, extreme southeastern Alabama, and all of Florida (Miller, 1986). This aquifer is one of the most productive in the United States and a major source of water in the region. During 2010, about 803 million gallons per day (Mgal/d) were withdrawn from the Upper and Lower Floridan aquifers in Georgia, primarily for irrigation, industrial, and public-supply uses (Lawrence, 2016).

The Upper Floridan aquifer predominately consists of Eocene- to Oligocene-age limestone, dolomite, and calcareous sand. The aquifer is thinnest along its northern limit (map on Home page) and thickens to the southeast, where the maximum thickness is about 1,700 feet (ft) in Ware County, Georgia (Miller, 1986). The aquifer is confined throughout most of its extent, except where it crops out or is near land surface along the northern limit and in karst areas in parts of southwestern and south-central Georgia.

The Coastal Plain of Georgia has been divided informally into four hydrologic areas for discussion of water levels —the southwestern, south-central, east-central, and coastal areas. This subdivision is a modification of that used by Peck and others (1999) and is similar to that used by Clarke (1987).

Southwestern area

All or parts of 16 counties, including the Albany-Dougherty County area, constitute the southwestern area. In this area, the Upper Floridan aquifer ranges in thickness from about 50 ft in the northwest to about 475 ft in the southeast (Hicks and others, 1987). The aquifer is overlain by sandy clay residuum, which is hydraulically connected to streams. Since the introduction of center-pivot irrigation systems around 1975, the Upper Floridan aquifer has been widely used as the primary water source for irrigation in southwestern Georgia (Hicks and others, 1987).

South-central area

Seven counties constitute the south-central area. In this area, the Upper Floridan aquifer ranges in thickness from about 300 to 700 ft (Miller, 1986). Lowndes County is a karst region that has abundant sinkholes and sinkhole lakes that have formed where the aquifer crops out and the overlying confining unit has been removed by erosion (Krause, 1979). Direct recharge from rivers to the Upper Floridan aquifer occurs through these sinkholes at a rate of about 70 Mgal/d (Krause, 1979).

East-central area

Four counties constitute the east-central area. In this area, the Upper Floridan aquifer can be as thick as 650 ft in the southeast or absent in the north.

Coastal area

The Georgia Environmental Protection Division (GaEPD) defines the coastal area of Georgia as a 24-county area that includes 6 coastal counties and the adjacent 18 counties—an area of about 12,240 square miles (mi2; Clarke, 2003). In the coastal area, the Upper Floridan aquifer may be thin or absent in the north (Burke County) and about 1,700 ft thick in the south (Ware County; Miller, 1986).

The coastal area of Georgia has been subdivided by GaEPD into three subareas—northern, central, and southern—to facilitate implementation of the State’s water-management policies. The northern subarea is northwest of the Gulf Trough (Herrick and Vorhis, 1963), a prominent geologic feature that is characterized by a zone of low permeability in the Upper Floridan aquifer that inhibits flow between the central and northern subareas. In the northern subarea, pumping from the aquifer primarily is for agricultural use, and no large pumping centers are located in the area. The central subarea includes the largest concentration of pumping centers-Savannah, Brunswick, and Jesup-in the coastal area. The southern subarea is separated from the central subarea by the Satilla Line, a postulated hydrologic boundary (Applied Coastal Research Laboratory, Georgia Southern University, 2002). In the southern subarea, the largest pumping center is located immediately south of the area at Fernandina Beach, Nassau County, Florida.

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