FLORIDA GEOLOGICAL SURVEY


southeast of Polk City on top of the piezometric high (see figs. 5 and
35). The lake has no surface inlet and no surface outlet except at
extremely high stages, and in 1962 its surface area ranged from
56.6 to 51.2 acres. It is nearly devoid of vegetative growth;
consequently, transpiration losses are negligible. A map of Lake
Helene showing depth contours is given in figure 50. The depth-
contour map for Lake Helene is taken from a report by Kenner
(1964): This map shows the locations of the water-stage and
rainfall recorder and the raft in mid-lake supporting an anemometer
and a water-surface temperature recorder.
 Figure 51 is the hydrograph of the daily stage of Lake Helene
from March 31, 1961, to December 31, 1962. The evaporation
station was established December 13, 1961. Computations of the
evaporation data for the 1962 calendar year have been summarized
and used to help define the annual water budget.
 Pumpage of water from Lake Helene to irrigate the surrounding
 citrus groves contributes to water loss from the lake. A pumping
 station capable of pumping 1,800 gallons per minute was installed
 in 1962 and operated intermittently during the year. The volume
 changes due to pumpage from the lake were computed from the
 recorded changes in stage and stage-volume relations. These
 computations were verified by records of the approximate periods
 of pumpage and the rated capacity of the pump.
 Nearly all the gains of water in the lake were derived from
 rain that fell directly on the water surface. The lake stage increased
 approximately the same amount as the recorded depths of rainfall
 during light to moderate rain storms. However, during a few heavy
 rain storms the lake stage increased slightly more than the depth
 of rain, indicating runoff from land. The increase in lake stage
 during these periods is equivalent to the total gain for rain falling
 directly on the lake and from runoff. Net seepage to or from the
 lake caused a gain in volume at times and a loss at other times.
 The water-budget equation for Lake Helene may be expressed
 as follows:
 V = P + R +Se- E-Pu
 where:
 AV is change in lake volume
 (+ for increase; for decrease)
 P is precipitation on lake
 R is runoff from land
 Se is seepage
 (+for net gain; for net loss)


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