ANALYSIS OF WATER-LEVEL-LAKE JACKSON


ANALYSIS OF THE YEARLY CHANGE OF THE LAKE LEVEL

 The level of Lake Jackson declines because of evaporation from
the water surface, transpiration by aquatic vegetation, and ground-
water outflow. The lake level rises because of precipitation on the
water surface and inflow from the tributary area. Whether there
is a net decline or a net rise for a given period depends on the
degree of balance between these different factors. Separate analy-
sis of years of net decline and of years of net rise provides a
broader basis for understanding the behavior of the lake.
 During years 1950-56, 1962-63, the lake level declined an
average of 2.2 feet per year (table 2). Evaporation from the water
surface as computed from table 1 was 4.2 feet per year, and it is
arbitrarily assumed that any transpiration by aquatic vegetation
was the same. Yearly rainfall at Lake Jackson may be assumed
equal to the average of rainfall at Quincy, Monticello, and Talla-
hassee, which during these particular years (table 2) was 4 feet
per year. Thus, the net decline that may be attributed to the
difference between precipitation and evaporation was only 0.2 foot.
The remaining 2.0 feet of the decline represents ground-water

 TABLE 2.-NET YEARLY CHANGE IN WATER LEVEL OF LAKE
 JACKSON, 1950-65
 [Minus (-) indicates decline; plus (+) indicates rise]

 Average lake Net yearly Estimated rain-
 Year level, in feet change, in feet fall*, in inches

 1950 92.5 -1.7 45.1
 1951 90.2 -1.9 54.1
 1952 88.8 -2.3 46.1
 1953 86.4 -1.4 60.9
 1954 83.0 -5.0 30.4
 1955 79.1 -3.2 41.8
 1956 76.9 -1.8 51.7
 1957 .... +2.2 66.3
 1958 80.2 +2.4 52.9
 1959 83.4 +5.0 73.7
 1960 87.2 +3.2 64.8
 1961 89.1 +0.2 51.8
 1962 88.4 -1.0 47.9
 1963 87.3 -1.6 51.3
 1964 88.8 +4.7 92.0
 1965 94.2 +3.9 73.4


Quincy, Monticello, and Tallahassee.


*Average of rainfall at