Water resources of the Ochlockonee River area, northwest Florida

Abstract

The Ochlockonee River area comprises about 1,420 square miles in the panhandle of northwest Florida. In 1975, the population of the area was about 48,000. Water use averaged 11.4 million gallons per day; about half was pumped from wells and half from streams. The area receives 57 inches of precipitation per year on the average. Much of this water enters the surficial sand aquifer, seeps to streams, or enters the underlying water-bearing zone of the upper confining unit and the Floridan aquifer. The water-bearing zone of the upper confining unit is used for rural domestic supplies and is also important because the water it stores is a source of recharge to the underlying Floridan aquifer. The Floridan aquifer underlies all of the Ochlockonee River area and, except for the city of Quincy, is the principal source of municipal water supply. Well yields range from as little as 20 gallons per minute in Gadsden County to as much as 4,500 gallons per minute in Leon County. The transmissivity of the Floridan aquifer ranges from about 170 feet squared per day in the southern part of the area to 5,100 feet squared per day in the northern part. Storage coefficients calculated from two aquifer tests are 2 x 10-4 and 2.6 x 10-4. At Tallahassee, directly east of the Ochlockonee River, transmissivity is as high as 130,000 feet squared per day. The Floridan aquifer is recharged by downward leakage of water from the surficial sand aquifer and from the water-bearing zone of the upper confining unit. The Floridan aquifer is also recharged directly by rainfall in northern Leon County and in southern Georgia where it is near or at land surface. Ground water moves toward the southeast from the potentiometric high in southwestern Gadsden County and south from Leon County toward Wakulla Springs, located about 10 miles south of Tallahassee. The potentiometric surface of the upper part of the Floridan aquifer ranges from about 50 feet higher than that of the middle and lower part of the Floridan aquifer in southwestern Gadsden County to about 10 feet higher near Midway in eastern Gadsden County. The aquifer discharge in the basin area is by wells and by natural discharge through seeps and springs along the Ochlockonee River and at Ochlockonee Bay. Water levels in the Floridan aquifer fluctuate in response to seasonal and long-term variations in rainfall. Hydrographs do not show evidence of any long-term water-level declining trend. Saline water (more than 1,000 milligrams per liter of dissolved solids) occurs naturally within the Floridan aquifer throughout the Ochlockonee River area at depths ranging from 200 to 600 feet below sea level. The depth below which dissolved solids in water exceed 500 milligrams per liter in the Havana area ranges from 200 to 250 feet below sea level; in the Quincy area, from 400 to 450 feet below; and in the Greensboro area, from 200 to 250 feet below. Concentrations of dissolved solids in water pumped from wells tapping the Floridan aquifer in the Ochlockonee River area range from 60 to 1,370 milligrams per liter; chloride from 0 to 630 milligrams per liter; sulfate from 0.0 to 280 milligrams per liter; and fluoride from 0.0 to 1.3 milligrams per liter. Streamflow originating in the Ochlockonee River area in Florida averages about 1,000 million gallons per day; minimum discharge during dry periods is about 285 million gallons per day. Stream yields range from 0.90 to 2.62 cubic feet per second per square mile. Quincy Creek, at State Highway 267 at Quincy, the primary source of water for the city of Quincy, yields an average flow of 19 million gallons per day, has a 7-day 10-year low flow of 2.8 million gallons per day, and contains water of acceptable quality. The chemical quality of most streams in the basin is acceptable for most uses. Dissolved-solids concentration is generally less than 135 milligrams per liter; pH ranges from 5.3 to 7.3 units; color from 20 to 90 platinum-cobalt units; and turbidity from 3 to 85 Jackson turbidity units. Variations in chloride concentration in water from the Ochlockonee River (5.2 to 140 milligrams per liter) are influenced by discharge of food processing waste and municipal sewage plant effluent to the river. The three large lakes in the basin range from 4,000 to 7,000 acres in surface area. All are now used primarily for recreation. Dissolved-solids concentrations of water from the lakes range from less than 20 to 50 milligrams per liter. A major flood occurred in 1975 when the Ochlockonee River near Havana reached the third highest stage of record and the peak flood at the Sopchoppy River exceeded that for the period of record (11 years in 1975); no significant damage occurred.