FLORIDA GEOLOGICAL SURVEY


1,800 feet below the land surface, owing to the southwestward dip of the
aquifer.
 The Floridan aquifer is thickest, 1,300 feet, in north-central Santa
Rosa County and thinnest, 800 feet, at the Perdido River near Perdido
Bay. The thickness of the Bucatunna Clay Member has not been in-
cluded in the above figures.
 The water in the Floridan aquifer is under high artesian pressure.
The artesian pressure head in wells drilled into the upper limestone of
the FIoridan aquifer in southeastern Santa Rosa County is about 50 to
70 feet above sea level (fig. 33). At low land-surface elevations, 50 to
several hundred gallons per minute by natural flow are obtained from
this aquifer; but the water is more mineralized than that from the sand-
and-gravel aquifer. Because suitable water of low mineral content usu-
ally is available near the surface, little use is made of the water from the
upper limestone in this area.

 MOVEMENT OF WATER
 Ground water in the sand-and-gravel aquifer moves from high to low
 elevations. Ground-water levels usually correlate with land-surface ele-
 vations. Thus, in the two counties, the general areas of ground-water
 recharge can be delineated on topographic maps. Recharge is greatest
 where the land is relatively flat. Water percolates downward to the wa-
 ter table and then moves laterally toward the places of discharge.
 The lower permeable beds in the sand-and-gravel aquifer are re-
 charged by percolation of water from upper permeable beds through
 and around beds of clay or sandy clay. The percolation results from
 differences in the hydrostatic heads within the permeable beds.
 The sand-and-gravel aquifer is recharged by local rainfall, which in-
 filtrates to the water table. The aquifer is discharged by pumping;
 evapotranspiration; and seepage into streams, swamps, bays, and the
 Gulf of Mexico.
 Data at Gulf Breeze were used to calculate the amount of recharge
 received by the upper part of the sand-and-gravel aquifer for different
 periods of time. Gulf Breeze was selected because the surface material
 contains little clay, the water table is near the surface, and the direct
 overland runoff is slight. In addition, no lateral movement of fresh
 ground water to or from other areas is possible because Gulf Breeze is
 on a peninsula. Thus, recharge from rainfall at Gulf Breeze would be as
 great as anywhere in the area.
 The highest percentage of recharge from rainfall, about 92 percent,