Potentiometric surfaces of the Upper Floridan Aquifer in the St. Johns River Water Management District and vicinity, Florida, Available data between May 1976 - September 2002, plus Predevelopment 1936.

***NOTE: FOR MORE RECENT POTENTIOMETRIC SURFACE DATASETS, CHECK THE FOLLOWING DATA DOWNLOAD PAGE: http://fl.water.usgs.gov/Orlando/PotMap/index.html***

A POTENTIOMETRIC SURFACE is defined as an imaginary surface defined by the level to which water rises in a tightly cased well constructed in a confined aquifer (alternatively, the level water rises due to the pressure in the rock).  Groundwater levels decline when wells are pumped and rise when pumping is reduced.  Water levels also respond to recharge from rainfall, droughts, and seasonal changes in water demands for drainage, irrigation, public supply, and industry.  In areas of increased groundwater pumping, water levels have declined over time.  When pumping ceases or is reduced substantially, water levels can recover to former levels.  Potentiometric surface contours are generalized on a regional scale to portray water levels in a dynamic hydrologic system taking due account of the variations in hydrogeologic conditions such as well-depth differences, non-simultaneous measurements of water levels, variable effects of pumping, and changing climatic influence.  The potentiometric contours, thus, may not conform exactly with individual measurements of water level.  Potentiometric surfaces maps for the St. Johns River Water Management District (and vicinity) are produced by the U.S. Geological Survey bi-annually in May and September; corresponding to the end of the dry and wet season, respectively.  The original data was provided by the U.S. Geological Survey on mylar District staff and/or private contractors digitized the contours from these mylars.

The potentiometric surface is important in monitoring effects of groundwater withdrawals, determining recharge areas, monitoring the possible travel of contaminates, placement of consumptive use wells, and is an important variable in a variety of hydrogeologic models and modeling goals.  Comparison of historic potentiometric surfaces maps area an important measure of the effects of rainfall and consumptive use/agricultural withdrawals on the aquifer.  Additionally, the potentiometric surface is important in calibrating models and predicting the effects of consumptive use, land use change, and climate on the aquifer levels.

The available point & line (contours) features depict the potentiometric surface of the Upper Floridan aquifer in the St. Johns River Water Management District and vicinity for the corresponding season/year.  Potentiometric contours are based on water-level measurements collected at a number of wells in May or September, during the end of the dry or wet season.  The shapes of some of the contours have been 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.  Potentiometric 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.  Groundwater withdrawals locally have lowered the potentiometric surface.  Ground water in the Upper Floridan aquifer generally flows from potentiometric highs to potentiometric lows in a directions perpendicular to the contours.