REPORT OF INVESTIGATIONS NO. 48


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 JAN FEB MAR APR MAY JUN JUL AUG SEPT OCT NOV DEC

 EXPLANATION
 Period of complete record


 Figure 9.-Months for which water-level recorder chart record for Lake
 Jackson was complete.

 The tendency for the lake-level rise to be smaller than monthly
rainfall for amounts less than about 0.6 foot may be due partly to
evaporation and ground-water outflow and partly to mechanical
lag of the water-level recorder. If the recorder is following a down-
ward trend, the water level must rise about 0.01 foot before a trace
of the rise is recorded. This effect is a cumulative one if only the
rises are considered as has been done on this analysis. The total
effect is appreciable for months having several rises.
 The tendency of the lake-level rise to exceed rainfall when
monthly rainfall is greater than about 0.6 foot is probably due to
surface-water inflow from the more intense storms during the
month.
 The data shown in figure 10 are plotted on a cumulative basis
in figure 11. Monthly values of each parameter were summed in
chronological order for months when the data were complete.
(See fig. 9).
 The over-all slope of the graph in figure 11 shows that measured
rainfall generally exceeded the recorded rise of the lake level. As