REPORT OF INVESTIGATIONS NO. 48


Figure 12.-Three-year moving average of rainfall at Tallahassee, Florida.


periods, the average being plotted at the end of the last year of the
period represented.
 Although the rainfall graph (fig. 12) and the water-level
graphs for Lake Jackson and wells 5 and 7 (fig. 6) differ in
detail, in a gross sense the graphs are similar. The rainfall record
for Tallahassee was used to compute the moving average because
the period of continuous record for this station was appreciably
longer than that for either Quincy or Monticello.
 The rainfall graph suggests that the 3-year periods preceding
1948. 1956, and 1965 were periods of hydrologic significance. The
graph further suggests that the level of Lake Jackson was higher
in 1965 than at any time during the preceding 75 years. The same
conclusion is indicated by moving average graphs for 4- and
10-year periods. The graph for 5-year periods shows the average
for the period ending 1948 to be slightly higher than that for 1965.
 Lake Jackson was dry during the early part of 1957, coincident
with the low shown on the graph of rainfall. The lake is quite
shallow, however, and leakage through its bottom may vary. Thus,
the lake could have been dry during less severe drought periods
than 1954-56. Sellards (1914, p. 129) reported the lake to be "dry,
or nearly so, in the early spring of 1907." He also mentioned the
existence of two active sinks in the lake bottom. Local residents
report that the lake was dry in 1932, 1935, and 1936. Thus, inter-
preted in light of this information, the rainfall graph indicates
that the lake may have been dry a number of times.