REPORT OF INVESTIGATIONS No. 42


 E is evaporation from lake
 Pu is pumpage from lake
 The monthly water budget for Lake Helene for 1962 is shown in
table 12. The total loss from evaporation was 53.10 inches as shown
in column 12. Seepage to or from the lake was variable as shown
by the monthly amounts in columns 10 and 11. Net seepage for the
year was 6.64 inches from the lake.
 The items of inflow and of outflow for Lake Helene were
determined independently. Computed values of change in volume
(column 16) are the algebraic sums of the items of inflow and items
of outflow for each month. These values compare closely with the
observed values of change in storage shown in column 17.
 Average annual lake evaporation in this part of central Florida
for a 10-year period (1946-55) has been estimated to be about 49
inches (Kohler and others, 1959, pl. 2). Evaporation losses from
Lake Helene for 1962 exceeded Kohler's estimate, based on a
10-year average, by about 4 inches. Records from several
evaporation pan stations show that evaporation amounts are
generally higher during dry years. Thus, the measured evaporation
from Lake Helene during 1962, a dry year, may be higher than for
an average year.

 COMPARISON OF EASTERN AND WESTERN BASINS

 Geology and topography, the two predominant factors affecting
the water budget of the Green Swamp area, are somewhat different
in the eastern and in the western parts of the area. The effects of
these factors on the components of the water budgets have been
determined by the selection of representative basins in each part
for defining the budget equation.
 The drainage basins east of State Highway 33 are intercon-
nected by swamp channels (see fig. 5) and flood runoff from each
basin may not be representative of that originating within the
basin. However, the sum of the discharges measured at Big Creek
at station 3, Little Creek at station 5, and Withlacoochee River at
station 36 represents approximately the natural streamflow from
the combined drainage basin of 208 square miles. Small amounts
of water may be exchanged with other basins at interconnecting
points designated as C-4, C-5, C-6, and C-7 in figure 5. The amount
and duration of flow through these openings are considered to be
insignificant in comparison with the total amounts measured at
the three gaging stations. In the following analysis of the water


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