FLORIDA GEOLOGICAL SURVEY


basin is equated to that leaving the basin, plus or minus changes in
basin storage.
 The budget equation was the basis of the expression for
determining the water-loss equation in the foregoing discussion of
rainfall, runoff, and water loss. The water-budget equation may be
expressed in greater detail as

 P = R + ET + U + AS, + SS
 where: P is precipitation
 R is streamflow
 ET is evapotranspiration
 U is ground-water outflow
 AS, is change in surface-water storage
 (+ for net gain; for net loss)
 AS, is change in ground-water storage
 (+ for net gain; for net loss)
 Precipitation (P) and streamflow (R) are factors of the budget
equation that can be measured directly. The other factors are not
measured directly but are derived from observed or deduced data.
Ground-water outflow (U) in the Green Swamp area is the net
amount of water that moves out of the basin by subsurface flow
through both the nonartesian and Floridan aquifers.
 The amount of water leaving the nonartesian aquifer by
 horizontal underflow is an insignificant factor in the budget where
 the water-table divides coincide with the surface-water divides. In
 the Green Swamp area, the divides on the eastern boundary do not
 coincide and a small quantity of water leaves the area via the
 nonartesian aquifer.
 The amount of water leaving the area via the Floridan aquifer
 was estimated by using the hydraulic coefficients of the aquifer
 and piezometric maps.
 The gain or loss of water by storage changes (AS, and ASg) in
 an area such as the Green Swamp may be a significant quantity for
 short periods. However, by using selected long-term periods, the
 effects of storage changes are minimized. The change in surface-
 water storage (AS,) is indicated by change in stage of lakes, stream
 channels, and swamps in a basin. In this analysis, the open water
 surfaces were considered to be a small percentage of the total
 drainage area, and estimates for storage changes in the nonartesian
 aquifer were used for an overall storage change including AS,.
 The change in ground-water storage (AS,) is the net change in
 ground-water stage multiplied by the specific yield for (or storage


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