FLORIDA GEOLOGICAL SURVEY


is the level to which water will rise in cased wells drilled into the aquifer, and is likened to the level of water in a vertical pipe that taps a city water main. Water can be taken from an artesian aquifer and the piezometric surface lowered without dewatering the aquifer. Only when the piezometric surface is lowered below the top of the aquifer is the aquifer dewatered. The quantity of water that can be withdrawn without dewatering the aquifer depends upon the ability of the aquifer to transmit water and the rate of recharge to the aquifer.

                 HYDRAULICS OF AQUIFERS
   When a well that taps the Floridan aquifer begins to discharge water, the piezometric surface surrounding the well is lowered. A cone, centered at the discharging well, describes the shape of the lowered pressure surface in the vicinity of the well. This lowered pressure surface near a well or a group of wells in a producing field is referred to as the cone of depression or cone of influence. This cone of depression is graphically portrayed by the cones developed in the piezometric surface of the Floridan aquifer in the vicinity of the well fields in the Panama City area, as shown in figure 13.
   In the initial stages of development the cone of depression is small in diameter and depth. As discharge from the well continues the cone spreads out. The lowering or drawdown of the pressure surface at the well continues until the amount of water being discharged is balanced by an equal amount being transmitted through the aquifer to the well. This balance can be achieved by a decrease in natural discharge or an increase in natural recharge.
   When pumping stops the pressure surface begins to recover, rapidly at first, then at a progressively slower rate. With no further pumpnC, in the vicinity the pressure surface will eventually recover to the initial level.
   The response of an aquifer to pumping from one well or a group of neighboring wells in terms of the rate and extent of drawdown in the pressure surface, and the quantity of water that the aquifer will produce is related to the hydraulics of the aquifer at that location. The principal hydraulic properties of an aquifer are its ability to transmit and to store water.
   An artesian aquifer, such as the Floridan aquifer in the Econfina Creek basin, functions as a conduit through which water moves from the areas of recharge to the areas of discharge. The aquifer's ability to transmit water is expressed in terms of its coefficient of transmissibility. It is the quantity of water, in gallons per day, that will flow