FLORIDA GEOLOGICAL SURVEY


the water-budget analysis of the Green Swamp area for the period
1959-61. Yearly summaries of the budget factors are presented in
table 18.
 Surface runoff is directly dependent on rainfall and varies
through a wide range as shown by comparison of the wet years of
1959 and 1960 with the dry year of 1961. On the other hand, the
ground-water outflow from the area varied little from the wet to
dry years. Though the difference is small, the ground-water outflow
was more during the dry year than during either wet year. The
increase in ground-water outflow during 1961 was caused primarily
by increased pumpage from the Floridan aquifer in the area along
the southern and western boundaries of the Green Swamp area.
The net loss in ground-water storage during 1961 also was greatest
along the boundaries reflecting the drawdown effects caused by the
pumpage.
 The 3-year average evapotranspiration loss was 36.8 inches from
the Green Swamp area as shown in table 18. Evaporation from
Lake Helene in 1962 amounted to 53.1 inches (table 12). Compari-
son of these values indicates that exposure of the water surface by
impoundment in reservoirs would increase the evaporation loss by
about 16 inches per year per unit area in the Green Swamp. Other
studies indicate that the increased evaporation loss would be less
than 16 inches. Estimates by Kohler and others (1959) indicate
that the average annual lake evaporation in central Florida is 49
inches. From table 14 the evapotranspiration loss for two represen-
tative basins averaged about 40 inches for the 3-year period. Based

TABLE 18. Summary of water-budget factors in Green Swamp area, 1959-61


 Note. ET = P S-R- U
 *Negligible
 *Ground-water outflow for 1959 and 1960 assumed to be same as for November 1959 and
that for 1961 assumed to be the average for twb periods (table 17).


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