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Floridan aquifer
The Floridan aquifer system, composed of the Upper and Lower Floridan aquifers, is a sequence of Paleogene carbonate rock which spans an area of about 100,000 square miles (260,000 km2) in the southeastern United States. It underlies the entire state of Florida and parts of Alabama, Georgia, Mississippi, and South Carolina.
The Floridan aquifer system is one of the world's most productive aquifers and supplies drinking water for nearly 10 million people. According to the United States Geological Survey, total withdrawals from the Floridan aquifer system in 2000 were ranked 5th highest of all principal aquifers in the nation at 3,640 million gallons per day (Mgal/d) (13.8 million m3/d; 11,200 acre⋅ft/d). Of the total, 49% (1,949 Mgal/d; 7.38 million m3/d; 5,980 acre⋅ft/d) was used for irrigation, 33% (1,329 Mgal/d; 5.03 million m3/d; 4,080 acre⋅ft/d) was used for public water supply, 14% (576 Mgal/d, 2.18 million m3/d; 1,770 acre⋅ft/d) was used for industrial purposes, and 4% were domestic self-supplied withdrawals. The Floridan aquifer system is the primary source of drinking water for most cities in central and northern Florida as well as eastern and southern Georgia, including Brunswick, Savannah, and Valdosta.
In 1936, geologist Victor Timothy (V.T.) Stringfield first identified the existence of the Floridan Aquifer in peninsular Florida and referred to the carbonate units as the "principal artesian formations." In 1944, M.A. Warren of the Georgia Geological Survey described an extension of this system in south Georgia and applied the term "principal artesian aquifer" to the carbonate units involved. In 1953 and 1966 Stringfield also applied the term "principal artesian aquifer" to these rocks. In 1955, Garald G. Parker noted the hydrologic and lithologic similarities of the Tertiary carbonate formations in southeast Florida, concluded that they represented a single hydrologic unit, and named that unit the "Floridan aquifer". With additional information collection, more zones of high and low hydraulic conductivity have been identified. As a result, the name Floridan Aquifer has evolved into "Floridan aquifer system", which contains the Upper and Lower Floridan aquifers.
Withdrawals from the Floridan aquifer system began in 1887 when the City of Savannah, Georgia, began to supplement surface water withdrawals from the Savannah River with groundwater. At that time artesian heads in the system were 40 feet (12 m) above land surface and no pumps were needed; by 1898, it was estimated that between 200 and 300 wells had been finished in South Georgia, and by 1943, about 3,500 wells had been completed in the six coastal counties of Georgia. By around 1910–1912, development of the Floridan aquifer system had already occurred in Fernandina and Jacksonville and south along the east coast of Florida, as well as from Tampa south to Fort Myers on the west coast. Over time, the number of wells increased, as did the finished depths, as demand increased. Industrial supply for pulp and paper mills became a large proportion of the water withdrawn starting in the late 1930s. In the 1950s, all municipal, domestic, and industrial supply (except cooling), and about half of agricultural supply in Orlando, Florida had been converted to groundwater from the Floridan aquifer system. Groundwater withdrawals from the Floridan aquifer system increased steadily from 630 Mgal/d (2.4 million m3/d; 1,900 acre⋅ft/d) in 1950 to 3,430 Mgal/d (13.0 million m3/d; 10,500 acre⋅ft/d) in 1990. Permitting and regulations enacted during the 1990s curtailed the year-on-year increases in withdrawal; however, withdrawals in 2000 increased to 4,020 Mgal/d (15.2 million m3/d; 12,300 acre⋅ft/d) due to extreme drought conditions between 1999 and 2001 that prevailed over much of the Southeastern United States. Much of the increase was due to increased agricultural demand.
The Floridan aquifer system spans an area of about 100,000 square miles (260,000 km2) in the southeastern United States and underlies all of Florida and parts of southern Alabama, southeastern Georgia, and southern South Carolina. The Upper Floridan aquifer contains freshwater over much of its extent, though is brackish and saline south of Lake Okeechobee.
The Floridan aquifer system crops out in central and southern Georgia where the limestone, and its weathered byproducts, are present at land surface. The aquifer system generally dips below the land surface to the south where it becomes buried beneath surficial sand deposits and clay. In areas depicted in brown in the image at the right, the Floridan aquifer system crops out and is again exposed at land surface. These regions are particularly prone to sinkhole activity due to the proximity of the karstified limestone aquifer to land surface. Some of the fractures/conduits within the aquifer are large enough for scuba divers to swim through.
The carbonate rocks that form the Floridan aquifer system are of late Paleocene to early Oligocene age and are overlain by low-permeability clays of Miocene age (upper confining unit) and surficial sands of Pliocene and Holocene age (surficial aquifer system). In west-central Florida, north Florida, and along the updip margin of the system, the limestone crops out and the aquifer system is unconfined. Where low-permeability clays of the upper confining unit are present and substantial, the system is confined and groundwater is contained under pressure. The upper confining unit is particularly thick in Coastal Georgia and South Florida; downward leakage of water through the upper confining unit in these areas is minimal and the Floridan aquifer system is thickly confined. Low permeability limestone rocks of Paleocene age (e.g. Cedar Keys Formation) form the base of the Floridan aquifer system. The Floridan aquifer system ranges in thickness from less than 100 feet (30 m) in updip areas where the rocks pinch out to more than 3,700 feet (1,100 m) in southwestern Florida. Recharge, flow, and natural discharge in the Floridan aquifer system are largely controlled by the degree of confinement provided by upper confining units, the interaction of streams and rivers with the aquifer in its unconfined areas, and the interaction between fresh and saline water along the coastlines.
Where the Floridan aquifer system is at or near land surface (areas shaded brown in image above), clays are thin or absent and dissolution of the limestone is intensified and many springs and sinkholes are apparent. Transmissivity of the aquifer in karstified areas such as these is much higher owing to the development of large, well-connected conduits within the rock (see image at right). Springs form where the water pressure is great enough for the groundwater to flow out on the land surface. More than 700 springs have been mapped in Florida. Wakulla Springs in Wakulla County is one of a number of major outflows of the aquifer with a flow rate of 200–300 million US gallons (0.76–1.14 million cubic metres; 610–920 acre-feet) of water per day. A record peak flow from the spring on April 11, 1973, was measured at 14,324 US gallons (54.22 m3) per second – equal to 1.24 billion US gal (4.68 million m3; 3,800 acre⋅ft) per day.
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Floridan aquifer
The Floridan aquifer system, composed of the Upper and Lower Floridan aquifers, is a sequence of Paleogene carbonate rock which spans an area of about 100,000 square miles (260,000 km2) in the southeastern United States. It underlies the entire state of Florida and parts of Alabama, Georgia, Mississippi, and South Carolina.
The Floridan aquifer system is one of the world's most productive aquifers and supplies drinking water for nearly 10 million people. According to the United States Geological Survey, total withdrawals from the Floridan aquifer system in 2000 were ranked 5th highest of all principal aquifers in the nation at 3,640 million gallons per day (Mgal/d) (13.8 million m3/d; 11,200 acre⋅ft/d). Of the total, 49% (1,949 Mgal/d; 7.38 million m3/d; 5,980 acre⋅ft/d) was used for irrigation, 33% (1,329 Mgal/d; 5.03 million m3/d; 4,080 acre⋅ft/d) was used for public water supply, 14% (576 Mgal/d, 2.18 million m3/d; 1,770 acre⋅ft/d) was used for industrial purposes, and 4% were domestic self-supplied withdrawals. The Floridan aquifer system is the primary source of drinking water for most cities in central and northern Florida as well as eastern and southern Georgia, including Brunswick, Savannah, and Valdosta.
In 1936, geologist Victor Timothy (V.T.) Stringfield first identified the existence of the Floridan Aquifer in peninsular Florida and referred to the carbonate units as the "principal artesian formations." In 1944, M.A. Warren of the Georgia Geological Survey described an extension of this system in south Georgia and applied the term "principal artesian aquifer" to the carbonate units involved. In 1953 and 1966 Stringfield also applied the term "principal artesian aquifer" to these rocks. In 1955, Garald G. Parker noted the hydrologic and lithologic similarities of the Tertiary carbonate formations in southeast Florida, concluded that they represented a single hydrologic unit, and named that unit the "Floridan aquifer". With additional information collection, more zones of high and low hydraulic conductivity have been identified. As a result, the name Floridan Aquifer has evolved into "Floridan aquifer system", which contains the Upper and Lower Floridan aquifers.
Withdrawals from the Floridan aquifer system began in 1887 when the City of Savannah, Georgia, began to supplement surface water withdrawals from the Savannah River with groundwater. At that time artesian heads in the system were 40 feet (12 m) above land surface and no pumps were needed; by 1898, it was estimated that between 200 and 300 wells had been finished in South Georgia, and by 1943, about 3,500 wells had been completed in the six coastal counties of Georgia. By around 1910–1912, development of the Floridan aquifer system had already occurred in Fernandina and Jacksonville and south along the east coast of Florida, as well as from Tampa south to Fort Myers on the west coast. Over time, the number of wells increased, as did the finished depths, as demand increased. Industrial supply for pulp and paper mills became a large proportion of the water withdrawn starting in the late 1930s. In the 1950s, all municipal, domestic, and industrial supply (except cooling), and about half of agricultural supply in Orlando, Florida had been converted to groundwater from the Floridan aquifer system. Groundwater withdrawals from the Floridan aquifer system increased steadily from 630 Mgal/d (2.4 million m3/d; 1,900 acre⋅ft/d) in 1950 to 3,430 Mgal/d (13.0 million m3/d; 10,500 acre⋅ft/d) in 1990. Permitting and regulations enacted during the 1990s curtailed the year-on-year increases in withdrawal; however, withdrawals in 2000 increased to 4,020 Mgal/d (15.2 million m3/d; 12,300 acre⋅ft/d) due to extreme drought conditions between 1999 and 2001 that prevailed over much of the Southeastern United States. Much of the increase was due to increased agricultural demand.
The Floridan aquifer system spans an area of about 100,000 square miles (260,000 km2) in the southeastern United States and underlies all of Florida and parts of southern Alabama, southeastern Georgia, and southern South Carolina. The Upper Floridan aquifer contains freshwater over much of its extent, though is brackish and saline south of Lake Okeechobee.
The Floridan aquifer system crops out in central and southern Georgia where the limestone, and its weathered byproducts, are present at land surface. The aquifer system generally dips below the land surface to the south where it becomes buried beneath surficial sand deposits and clay. In areas depicted in brown in the image at the right, the Floridan aquifer system crops out and is again exposed at land surface. These regions are particularly prone to sinkhole activity due to the proximity of the karstified limestone aquifer to land surface. Some of the fractures/conduits within the aquifer are large enough for scuba divers to swim through.
The carbonate rocks that form the Floridan aquifer system are of late Paleocene to early Oligocene age and are overlain by low-permeability clays of Miocene age (upper confining unit) and surficial sands of Pliocene and Holocene age (surficial aquifer system). In west-central Florida, north Florida, and along the updip margin of the system, the limestone crops out and the aquifer system is unconfined. Where low-permeability clays of the upper confining unit are present and substantial, the system is confined and groundwater is contained under pressure. The upper confining unit is particularly thick in Coastal Georgia and South Florida; downward leakage of water through the upper confining unit in these areas is minimal and the Floridan aquifer system is thickly confined. Low permeability limestone rocks of Paleocene age (e.g. Cedar Keys Formation) form the base of the Floridan aquifer system. The Floridan aquifer system ranges in thickness from less than 100 feet (30 m) in updip areas where the rocks pinch out to more than 3,700 feet (1,100 m) in southwestern Florida. Recharge, flow, and natural discharge in the Floridan aquifer system are largely controlled by the degree of confinement provided by upper confining units, the interaction of streams and rivers with the aquifer in its unconfined areas, and the interaction between fresh and saline water along the coastlines.
Where the Floridan aquifer system is at or near land surface (areas shaded brown in image above), clays are thin or absent and dissolution of the limestone is intensified and many springs and sinkholes are apparent. Transmissivity of the aquifer in karstified areas such as these is much higher owing to the development of large, well-connected conduits within the rock (see image at right). Springs form where the water pressure is great enough for the groundwater to flow out on the land surface. More than 700 springs have been mapped in Florida. Wakulla Springs in Wakulla County is one of a number of major outflows of the aquifer with a flow rate of 200–300 million US gallons (0.76–1.14 million cubic metres; 610–920 acre-feet) of water per day. A record peak flow from the spring on April 11, 1973, was measured at 14,324 US gallons (54.22 m3) per second – equal to 1.24 billion US gal (4.68 million m3; 3,800 acre⋅ft) per day.