REPORT OF INVESTIGATIONS NO. 48


outflow in excess of ground-water and surface-water inflow from
the tributary area. If such inflow were zero-and it probably was
minimal during these relatively dry years-the decline of 2.0 feet
per year would be a measure of the ground-water outflow.
 During years 1957-61, 1964-65, the lake rose an average of
3.1 feet per year. Precipitation at Quincy, Monticello, and Talla-
hassee during these years averaged 5.6 feet. Evaporation and
transpiration again may be assumed to be 4.2 feet per year. Thus,
only 1.4 feet of the 3.1 feet average yearly rise may be attributed
to the difference between precipitation and evaporation. The
remaining 1.7 feet of the rise represents the difference between
gound-water and surface-water inflow from the tributary area and
ground-water outflow. In other words, inflow from the tributary
area apparently was greater than ground-water outflow through
the lake bottom by an amount equivalent to 1.7 feet per year.
 The relative distribution of inflow from the tributary area
between surface-water inflow and ground-water inflow cannot be
determined. The small lakes and ponds within the tributary area
are influenced by the same factors that cause Lake Jackson to
fluctuate, and they contribute inflow to Lake Jackson only at the
height of unusually wet periods. In addition their combined surface
area is small relative to that of Lake Jackson. Therefore, the
drainage of surface water from lakes and ponds would not be likely
to noticeably affect the average yearly rise of Lake Jackson.
 The preceding analysis of the lake-level rise due to rainfall
shows that at times during and immediately after storms, surface-
water runoff contributed substantially to the water-level rise of
Lake Jackson. This effect does not appear to have exceeded from
I to 1.5 feet per year during the wettest years (fig. 11). Thus,
during wet years ground-water inflow may have exceeded ground-
water outflow.
 Ground-water outflow during dry years was equivalent to a
 lake-level decline averaging at least 2 feet per year, and it could
 be about the same during wet years. If so, ground-water inflow
 contributed substantially to the over-all lake-level rise during the
 wet years.
 The years of net rise all occurred after the lake was almost
dry in 1957, when one active sink reportedly was filled with dirt.
Therefore, ground-water outflow during years after 1957 may have
been less than indicated by data for preceding years.
 This possibility is partly substantiated by data given in table 2.
 During years 1952-53 and 1962-63 the lake was declining from