REPORT OF INVESTIGATioNs No. 41


                     DEER POINT LAKE
   Deer Point Lake (fig. 1) was formed on November 17, 1961, by construction of a salt-water barrier across North Bay at Deer Point. The lake was planned to serve as a source of fresh water and to provide recreational facilities. It covers 4,700 acres, most of which was formerly a part of North Bay, and stores approximately 32,000 acrefeet of water at a level of 4.5 feet above mean sea level, the elevation of the dam.
   The lake is stabilized at an elevation of 5.0 feet above mean sea level. The potential fresh water supply is approximately 650 mgd, the average flow through the lake to North Bay. In February 1964 the only withdrawal from Deer Point Lake was the 30 mgd by the International Paper Company.
   A study of the lake hydrology in the period immediately before and for several months after the dam was constructed (Toler, Musgrove, and Foster, 1964) was made to determine the rate of freshening and the effect the lake would have on the water-table aquifer.
   Figure 27 shows the rate of freshening of the lake in terms of the number of times the inflow of fresh water would have filled the lake. Plotted in this manner, the graph enables a prediction of the rate of freshening of any similar lake if the volume and concentration of lake water and inflowing water are known (Toler, Musgrove, and Foster, 1964). When the barrier was completed on November 17, 1961, the lake was about half full and the chloride concentration was about 7,400 ppm. Flow over the spillway began on November 29, 1961, and the chloride concentration had been reduced to 3,700 ppm. In midFebruary 1962 the chloride concentration was about 200 ppm.
   When the barrier was completed, water levels in the lake and in the water-table aquifer adjacent to the lake rose rapidly, as shown in figure 28. An immediate effect of the rise in the lake level was to reverse the water-table gradient near the lake so that water moved from the lake into the aquifer. This is evidenced by the rise in chloride content in water from well 015-535-232, 45 feet from the lake. Water in wells 100 feet or more from the lake showed no change in chloride content. When the water table adjusted to the new lake level, the water movement was again toward the lake and the high chloride water was flushed from the aquifer.

                           SUMNL4-RY
    In general, the hydrologic system through which'water moves in the Econfina Creek basin is similar to most basins in northwest I ?