Scientific Investigations Map 3070
Prepared in cooperation with
St. Johns River Water Management District
South Florida Water Management District
Southwest Florida 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 2008. Potentiometric contours are based on water-level measurements collected at 589 wells during the period September 15-25, 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 ConditionsMeasured values of the potentiometric surface ranged from 11 feet below NGVD29 near Fernandina Beach, Florida, to 127 feet above NGVD29 in Polk County, Florida. Rainfall totals during the wet season were above average from record-setting rainfall produced by Tropical Storm Fay during the period August 18-24, 2008. This event was preceded by several months of below-average rainfall which resulted in the average water level of the network in September 2008 being only about 4 feet higher than the average in May 2008. Seasonal differences in network average water levels generally range from 4 to 6 feet. For 581 wells with previous measurements, September 2008 levels ranged from about 2 feet below to about 20 feet above May 2008 water levels. The greatest increase in water levels was observed in Hardee County.
For 568 wells with previous measurements, September 2008 levels ranged from about 7 feet below to about 11 feet above September 2007 water levels. The average water level of the network in September 2008 was about 3 feet higher than the average in September 2007.
Additional ReferenceLong-term hydrographs of ground-water levels for continuous and periodic wells are available at: http://waterdata.usgs.gov/fl/nwis/gw
Kinnaman, S.L., and Dixon, J.F., 2009, Potentiometric surface of the Upper Floridan aquifer in the St. Johns River Water Management District and vicinity, Florida, September 2008: U.S. Geological Survey Scientific Investigations Map 3070, 1 sheet.
For additional information, contact:
U.S. Geological Survey