The potentiometric surface, or height of groundwater in feet using survey datum NGVD 1929, is measured in wells throughout the District. One hundred sixty-seven of these wells are measured monthly and 70 wells are fitted with continuous recording instruments. The majority of the water levels are collected from wells completed in the Upper Floridan aquifer. Water levels are also collected from wells completed in the intermediate aquifer system (the eastern portion of the District) and the surficial aquifer system.
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When groundwater levels are contoured on a potentiometric surface map, the water level elevation is represented and the regional groundwater flow direction can be determined. Within the District, the regional direction of groundwater flow in the Upper Floridan aquifer is toward the Gulf of Mexico (northeast to southwest).
The District uses groundwater levels for evaluating long-term trends, detecting areas of water resource concerns, and developing management strategies. This information is useful to geologic consultants, well drillers, water plant operators, the agricultural community, and the general public.
The Floridan is a carbonate (limestone) aquifer that varies in degree of confinement but is continuous throughout the District. It is the primary source of this area's drinking and irrigation water. The Floridan aquifer system is represented by the Upper Floridan aquifer, mid-Floridan confining unit, and Lower Floridan aquifer. In the District, the mid-Floridan confining unit is generally poorly defined, as is the presence of the Lower Floridan aquifer. Nearly all wells for all water use types produce water from the Upper Floridan Aquifer in our region.
Water levels in the Floridan aquifer system fluctuate in response to climatic conditions and pumpage. In more than two-thirds of the District the total fluctuation is less than 15 feet. The lowest fluctuation is found along the Gulf coast where the water levels remain just above mean sea level. Higher fluctuations occur along the river corridors where the aquifer is influenced by the river's response to flooding and drought. The most dynamic fluctuation is seen in the Alapaha River basin in Hamilton County where the water table may fluctuate over 35 feet.