Full pool is the 560-foot mark where water begins to flow over the dam spillway if no gates are lowered.

Normal lake elevations are usually at some point less than full pool and are seasonally variable. How full the lake stays is largely up to mother nature. A full pool elevation is not normal except for possibly a few weeks in the spring. The lowest normal elevations usually occur in the fall and early winter months after a long, hot summer. For example, normal October elevations are nearly two feet below full pool. Highest lake levels typically occur in the spring after the seasonal rains.

It simply has to rain in the lake's watershed for Lake Springfield's water levels to remain at or close to normal. During hot, dry spells, however, Sugar and Lick Creeks - which are the primary sources feeding the lake - can dry up into a series of disconnected pools and contribute little or no water to the lake. In a typical summer, naturally low levels of rainfall, combined with high demand and increased rates of evaporation, cause the lake's level to drop at a rate of about six inches per month.

To supplement the supply available from Sugar and Lick Creeks, CWLP constructed a pumping station in the South Fork of the Sangamon River in the 1950s. When the lake level drops below its average in any given month, the utility can pump water from the South Fork to the lake providing there is a sufficient flow rate in the South Fork.

As a hedge against the possibility of a spring drought, the utility tries, whenever possible, to maintain the lake's winter level at no less than six inches below full pool. Keeping the level a little lower than 560 feet helps protect facilities from the potential for ice damage in the winter.

The lowest water level ever recorded at Lake Springfield since it was first filled in 1935, occurred during the 1953-55 drought when the lake dropped to 547.44 feet. The highest level occurred during a storm event in December 1982 when the lake crested at 564 feet.

How is the Lake Springfield's water level measured?

When at full pool, the lake's elevation is 560 feet above sea level. (The official elevation, as provided by the United States Geological Service is 559.35 feet above sea level, but the utility uses the "CWLP datum" of 560 feet.)

CWLP uses two methods to measure the lake's level. The first, a continuous, high-tech option, bounces sonic waves off the surface of the lake. The second employs a low-tech measuring stick. Surprisingly, this method, in use since the lake was built in 1935, provides the most accurate reading.

This measurement is taken in the basement of Lakeside Power Plant, which contains a series of pumps used to direct lake water to the filter plant. A tunnel joining the basement to the lake allows the basement's pumping chamber to fill to the exact level of the lake at the intake tower outside. Water Division operators dip a marked stick into the water to read its depth every two hours. Because there is no wave action in the basement, they are able to get a precise measurement, which is used as the official reading.
 

Lake Levels
(With Comparative Levels for the Previous Year)

Last update: 10/10/08

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