REPORT OF INVESTIGATIONS No. 41


   There are about 80 named lakes in the basin, most of which are in southeastern Washington County. Deer Point Lake, a fresh-water reservoir covering 4,700 acres, is the largest. Porter Lake has a surface area of 930 acres and is the largest natural lake.
   The major uses of water within the basin are for the manufacture of paper products, for public and domestic supplies, and for recreation. Prior to February 1964 no surface water was being withdrawn and ground water was being used at the rate of 25.2 mgd. Of this amount, 22.7 mgd came from the Floridan aquifer. The International Paper Company was the largest user of water, using about 13.5 mgd from the Floridan aquifer and about 1.5 mgd from the water-table aquifer. In February 1964 this company started receiving water from Deer Point Lake at the rate of about 30 mgd. Ground-water use in the Panama City area was reduced to about 11 mgd.
   The first well in the Floridan aquifer was drilled in 1908. Later, as the demand for water increased, more wells and well fields were developed and water levels were lowered. By the end of 1963, when water was being withdrawn at the rate of about 25.2 mgd, pumping levels had been lowered as much as 200 feet near the centers of major well fields. Pumping from the paper company well field, consisting of 21 wells, was discontinued in February 1964 and water levels in this field recovered 163 feet within 51 days.
   The Deadening lakes in southeastern Washington County offer considerable recreation potential. However, they lose water to the ground at a high rate causing wide fluctuations in stage and this prevents their full potential from being realized. The Washington County Development Authority has proposed a plan to divert water from Econfina Creek to stabilize these lakes at an elevation of 70 feet. The diversion from Econfina Creek would be at a point just downstream from Tenmile Creek where the minimum flow was estimated to be 30 mgd. The proposed plan calls for a detention reservoir on Econfina Creek to raise the water level and make gravity flow through a diversion canal possible. The storage in this reservoir, added to the natural flow of the creek, would provide a minimum flow of 40 mgd which would supply about 0.7 of a foot of water per month on the 5,000-acre lake area.
   Water leaks from the lakes to the Floridan aquifer at a rate proportional to the head between the lake surfaces and the piezometric surface of the aquifer. If the lake levels are maintained at a constant elevation, the head that will be established depends on the ability of the Floridan aquifer to transmit water away from the area.
   If diversion from Econfina Creek is at a rate of 30 mgd, the stream