FLORIDA GEOLOGICAL SURVEY


 The presence of highly mineralized water in the Floridan
aquifer may also be used to indicate the direction of movement of
water. Assuming that at some time much of the aquifer of central
Florida contained salt water, then the area in which the water now
contains little or no salt (chloride), would be better flushed with
fresh water than areas containing high amounts. The chloride con-
tent is generally higher at shallow depths near the coast than in the
interior, shown in figure 44. However, water of low chloride content
is present several hundred feet deep in local areas near the coast.
Data from a few scattered deep wells indicate that fresh water
extends to about 1,500 feet below sea level in much of the interior
of central Florida from Marion County to Highlands County.
Figure 44 and other data from the deep wells indicate that salt
water has been flushed from the aquifer in much of the interior.
Therefore, the total mineral content of the water in the Floridan
aquifer in the interior of Florida is due to solution of limestone
and not due to mixing with salt water. If recharge occurred only
in the Green Swamp area, then the concentration gradient should
increase in all directions from that area. Figure 45 shows that
the concentration gradients do not increase immediately away from
the Green Swamp but instead show a decrease over much of central
Florida. The areas of low mineral content and areas of under-
saturation generally coincide (figs. 43 and 45). This supports the
implication that recharge is not confined to the Green Swamp area.

 ANALYSIS OF THE HYDROLOGIC SYSTEM

 The Green Swamp area is considered to be a self-sustaining
hydrologic unit because most of its water supply is derived from
rain that falls directly on the area. Water is imported from outside
the area only in the vicinity of Dade City (see figs. 5, 11, 35, 36).
Inflows in the vicinity of Dade City affect only the lower reaches
of the Withlacoochee River.
 The amounts of water in the various parts of the hydrologic
system and losses of water as the result of natural processes, are
evaluated for the Green Swamp area.

 RAINFALL, RUNOFF, AND WATER LOSS

 Runoff is the residual of precipitation after all the demands of
 nature have been met. These demands taken collectively are called
 water loss. A simple definition for water loss is: Water loss equals
 precipitation minus runoff adjusted for change in storage and for