REPORT OF INVESTIGATIONS No. 40


occurred from a one-day rain on October 10, 1959. The 7.5-inch rainfall
on this day (at Pensacola Beach) caused a rise in the water table of
2.54 feet by the next day, equivalent to 7.0 inches of water computed by
using a coefficient of storage of 0.23. The loss by evapotranspiration in
one day was estimated as 8 percent. Later that month on the 28th, a
rain of 4.15 inches caused a rise in the water table of 0.92 foot. On the
assumption that the coefficient of storage remains a uniform 0.23, this
rise accounts for about 61 percent of the rain. These short-term recharge
values were obtained by comparing the amount of ground water taken
into storage if all the rain percolated to the water table to the amount of
water actually taken into storage.
 The average annual amount of recharge from rain may be computed
 by determining the amount of rain that falls on an area and computing
 the amount of seepage from that area. The average water level near the
 center of the peninsula at Gulf Breeze is 4.5 feet above sea level. This
 gives a hydraulic gradient of about 9 feet per mile toward Pensacola Bay
 and toward Santa Rosa Sound. Using this gradient and the rate of move-
 ment of water through the sand, the average ground-water seepage into
 either Pensacola Bay or Santa Rosa Sound would be about 305,000 gpd
 per mile length of the peninsula. The total seepage into Pensacola Bay
 and Santa Rosa Sound would be about 610,000 gpd per mile length of
 the peninsula. The average rainfall at Pensacola from 1950 through 1961
 was 61.6 inches. The average rain falling on a one-mile length of the
 peninsula (which is about 0.95 square mile) was about 2,770,000 gpd.
 The average daily seepage of fresh ground water represents the annual
 amount of recharge from rainfall and is about 22 percent of the total
 rain or 13.6 inches of rain. The figures do not take into account the loss:
 by pumpage of ground water and the loss by evapotranspiration after
 the water reaches the water table. The amount of water removed by
 these processes would increase the recharge to possibly 25 to 28 percent
 or about 15 to 17 inches of rain.
 A graph of monthly rainfall at Pensacola and graphs of the water
 levels in an artesian well and in two nonartesian wells, drilled into the-
 sand-and-gravel aquifer, are illustrated by figure 33. Wells 054-726-1
 and 054-726-2 are at Oak Grove in northern Escambia County, and are-
 about 6 feet apart. Well 055-726-1 is 0.6 mile north of these two wells.
 Relatively permeable and impermeable beds and changes in water levels-
 caused by rainfall are shown in figure 33.
 Well 054-726-1 was drilled to a depth of 206 feet and is screened from
 201 to 206 feet in a permeable sand bed. Although the top of the bed is
 190 feet below the surface, the water in the well rose to within 83 to 90