Open-File Report 2008-1085
Prepared in cooperation with
St. Johns River Water Management District
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IntroductionThis map depicts the potentiometric surface of the Upper Floridan aquifer in the St. Johns River Water Management District and vicinity for September 2007. Potentiometric contours are based on water-level measurements collected at 554 wells during the period September 15-27, near the end of the wet season. Some contours are inferred from previous potentiometric-surface maps with larger well networks. The potentiometric surface of the carbonate Upper Floridan aquifer responds mainly to rainfall, and more locally, to ground-water withdrawals and spring flow. Potentiometric-surface highs generally correspond to topographic highs where the aquifer is recharged. Springs and areas of diffuse upward leakage naturally discharge water from the aquifer and are most prevalent along the St. Johns River. Areas of discharge are reflected by depressions in the potentiometric surface. Ground-water withdrawals locally have lowered the potentiometric surface. Ground water in the Upper Floridan aquifer generally flows from potentiometric highs to potentiometric lows in a direction perpendicular to the contours.
Summary of Hydrologic Conditions
Measured values of the potentiometric surface ranged from 14 feet below NGVD29 near Fernandina Beach, Florida, to 126 feet above NGVD29 in Polk County, Florida. The average water level of the network in September 2007 was about 2 feet higher than the average in May 2007 following below-average rainfall. Seasonal differences in network average water levels generally range from 4 to 6 feet. For 535 wells with previous measurements, September 2007 levels ranged from about 8 feet below to about 26 feet above May 2007 water levels. The only exception was one measurement that was 26 feet above the May 2007 water level. Historical data indicate that such fluctuations have previously occurred. For 520 wells with previous measurements, September 2007 levels ranged from about 12 feet below to about 10 feet above September 2006 water levels. The average water level of the network in September 2007 was about a foot lower than the average in September 2006.
Additional ReferenceLong-term hydrographs of ground-water levels for continuous and periodic wells are available at internet site: http://waterdata.usgs.gov/fl/nwis/gw
Kinnaman, S.L., and Dixon, J.F., 2008, Potentiometric Surface of the Upper Floridan Aquifer in the St. Johns River Water Management District and vicinity, Florida, September 2007: U.S. Geological Survey Open-File Report 2008-1085, 1 sheet.
For additional information, contact:
U.S. Geological Survey