ANALYSIS OF WATER-LEVEL-LAKE JACKSON


time. Thus, if similarities can be established between lake-level
fluctuations and variations of other hydrologic parameters, the
probable range of the past lake-level fluctuations may be inferred.

 COMPARISON OF LAKE LEVEL AND GROUND-WATER LEVEL

 Although lakes and ground-water bodies differ in many ways,
the two have at least one important factor in common. Both derive
their water from rainfall. Thus, if the recharge area for the
ground-water body is in the general area of the lake, the fluctua-
tions of the two must follow the same long-term trend.
 The recharge area for the limestone aquifer underlying Lake
Jackson though not precisely delineated is known to be widespread.
As indicated by rainfall records for Quincy, Monticello, and Talla-
hassee, the variations in rainfall at Lake Jackson would apply
to a broad area. Therefore, the long-term water-level fluctuations
of Lake Jackson should be similar to those of wells 7 and 115.
Although the hydrograph for Lake Jackson shown in figure 6 is
not entirely similar to those shown for wells 7 and 115, the
graphs do follow the same over-all trends.
 The fluctuations of the ground-water levels between 1933 and
1947 are smaller than those for subsequent years (fig. 6). Thus,
though records of lake-level fluctuations prior to 1950 are lacking,
the graphs of ground-water levels suggest that the fluctuations of
Lake Jackson between 1933 and 1947 were much less pronounced
than those for subsequent years. A longer period of record is
needed for comparison, in order to establish which set of fluctua-
tions might be considered the more unusual.

 COMPARISON OF LAKE LEVELS AND RAINFALL

 Extreme levels of natural water bodies normally result from
 successive years of greater-than-average or less-than-average rain-
 fall rather than from a gross excess or deficiency of rainfall in any
 one year. The cumulative effect of two or more years of rainfall
 can be appraised by use of a moving average of rainfall.
 The moving average is computed by averaging rainfall data for
 a specified number of consecutive years, progressively discarding
 data for the first year of the period as data for each successive
 year is included. Thus, in a sense, the period represented by the
 average moves through the entire period of record. Figure 12
 shows the moving average of rainfall at Tallahassee for 3-year