Seasonal and annual variations in the potentiometric surface of the Floridan Aquifer in Duval County, Florida, 1960-77

Potentiometric levels of the Floridan aquifer in Duval County, Fla., are constantly changing in response to gains of water to the aquifer, primarily by recharge from rainfall; and losses from the aquifer, primarily by withdrawals from hundreds of wells. Seasonal variations of the potentiometric level in one well at Jacksonville was 4.2 feet during 1976. During the 18 year period from 1960 to 1977 the mean annual decline of potentiometric levels in the county was about 8 feet because of a large increase in withdrawals and to a lesser extent a decline in average annual rainfall in recharge areas. Maps of the potentiometric surface in 1960 and 1977 indicate that the greatest decline was more than 20 feet in the south-central part of the county. The decline was less than 5 feet in the western part of the county. (Kosco-USGS)