ANALYSIS OF WATER-LEVEL-LAKE JACKSON


 I J.*. *

 g** a 0

 :** .*

0 0.2 0.4 0.6 0.8 1.0
 MONTHLY RAINFALL


1.2
FEET


1.4 1.6 1.8 2.0


Figure 10.-Plot of monthly rainfall estimated for Lake Jackson
 cumulation of all rises of the lake level during the month.


versus the


mentioned above, this tendency may be due to the use of nonrepre-
sentative rainfall data, mechanical lag of the recorder, loss of water
from the lake by evaporation, or by ground-water outflow during
storm periods.
 The breaks in the slope of the graph are generally related to
rising and declining trends of the lake level. Periods of increasing
slope, which correspond to rising trends of the lake level, indicate
that surface-water inflow probably contributed appreciably to the
lake-level rise during these periods. This interpretation is consis-
tent with the fact that rising trends of the lake level are related
to periods of greater-than-average rainfall when maximum surface
runoff occurs.
 Urbanization alters the pattern of runoff from an area and may
 alter the total yield of the area. The effect of progressive urbani-
 zation would be manifested in a cumulative relation involving