FLORIDA GEOLOGICAL SURVEY


mean daily underflow would range from about 20 to 80 cfs. If the
impoundment occurred during a dry period, then the piezometric
surface would rise from 89 to 100 feet, the gradient would increase
from 2.6 to 13.6 feet per mile, and the estimated mean daily
underflow would range from about 40 to 150 cfs.
 Seepage and evaporative losses from the shallow reservoir
indicate that the amount of water that would be available for
release during dry periods such as that in 1962 would probably be
small. The position of the reservoir with respect to contributing
recharge to the heavily pumped portions of the Floridan aquifer is
poor. However, benefits derived from the reservoir would be
increased base flow of the upper Withlacoochee and Hillsborough
rivers and reduction of flood crests.

EFFECTS OF WATER IMPOUNDMENT IN SOUTHEASTERN
 CONSERVATION AREA ON GROUND-WATER LEVELS

 The primary purpose of a plan for water impoundment in the
Southeastern Conservation Area (Johnson, 1961), also designated
the Lowery-Mattie Conservation Area (Corps of Engineers, 1961),
is to maintain and to increase recharge to the Floridan aquifer.
The three pools that would comprise the Southeastern Conservation
Area proposed by Johnson would cover about 46 square miles, with
pool levels ranging from 133 to 134.5 feet above msl. The pools
would overlie an area of high piezometric levels in the Floridan
aquifer. In this area, water normally seeps downward from the
nonartesian aquifer through a bed of clay (aquiclude) into the
underlying Floridan aquifer. Here, the water level in the
nonartesian aquifer and in surface-water bodies are above the
piezometric surface of the Floridan aquifer. The difference in levels
is caused by relative differences in the permeabilities of the
nonartesian aquifer, of the Floridan aquifer, and of the aquiclude.
The rate of seepage through the aquiclude is directly proportional
to the difference between the water levels; therefore, raising the
water table or lowering the piezometric surface will increase the
rate of seepage.
 In order to evaluate the importance of the three conservation
 pools, a comparison was made of seepage rates during wet and dry
 periods in the vicinity of Lake Lowery with seepage rates that
 would occur had the pools been at the proposed levels. The average
 vertical permeability of the aquiclude was estimated and used as
 the basis of computations of seepage rates for existing hydraulic


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