FLORIDA GEOLOGICAL SURVEY


fall- Water also moves from the sands downward to the Floridan aquifer but the amount diminishes toward the southwest because the aquiclude becomes thicker. Movement within the Floridan aquifer is generally southward with some water flowing into the channel of Econfina Creek by way of artesian springs.
   The transmissibility of the Floridan aquifer varies within the basin, and is lower than the transmissibility of this aquifer in most other areas in Florida. Coefficients of transmissibility range from
9.000 to 30,000 gpd/ft.
   The water in the lakes and streams differs little in mineral concentration from rain water because of the relative insolubility of the surface materials. Two areas of exception are where Econfina Creek receives artesian spring flow and near the mouth of streams that empty into salt-water bays.
   The mineral content of water from the water-table aquifer generally ranges from 10 to 50 ppm, and that of water from the secondary artesian aquifer from 80 to 150 ppm. The mineral content of water from the Floridan aquifer is higher than that from the other two aquifers. Mineral concentrations in water from this aquifer show increases in all constituents from the northern part of the basin to the southwest.
   Some salt-water intrusion was detected in the water-table and the secondary artesian aquifers adjacent to the bays and Gulf. The confining clay layer overlying the Floridan aquifer in the coastal and bay area is sufficiently impermeable to prevent leakage of water from the overlying aquifers. Water in the Floridan aquifer in the southern part of the basin is apparently a mixture of fresh water and residual saline water.
   Streamflow to the bays is at an average rate of about 960 mgd which for a vear would amount to 40 percent of the average annual rainfall of 58 inches. About 650 mgd flows through Deer Point Lake into North Bay, and another 30 mgd flows into North Bay below Deer Point Dam. East Bay receives a flow of about 210 mgd and West Bay about 70 mgd. Most of the streams have sufficient flow to be a potential water supply. During periods of minimum flows there is more than 10 times as much fresh water flowing into the-bays than is being withdrawn in the basin. Econfina Creek, by far the largest stream in the basin, has an average flow of 355 mgd.
   Low runoff from the southern part of the basin results from poor drainage features of the flat-woods forest. Drainage in the sinks and lakes division is mostly internal. High base flow due to seepage from the porous sands causes high runoff in the sand hills division.