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LAKE LEVELS

 
Lake Level Table
Photos of South Fork
Channel Dam & Pump Station
Photos of
Measuring the Lake Level
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What is a normal lake level? Lake Springfield is full when the water surface is at the nominal pool elevation of 560 feet above mean sea level. If the lake is 1.5 feet below full pool, the lake elevation will be registered as 558.5. CWLP Water Division employees take great care to track lake levels and to maintain optimum levels to ensure there will always be a sufficient quantity of water available to meet the city's drinking water needs and the Electric Division's condenser cooling requirements.

How CWLP Measures the Lake Level (click to open)
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, the second 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 Station, 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, operators are able to get a precise measurement, which is used as the official reading.

See photos of the lake level being measured.

Check our table of weekly lake level readings.


How CWLP Maintains the Lake Level (click to open)
At Lake Springfield . . .
Full pool is the 560-foot mark. Above this point, water will flow into the dam spillway even if no dam gates are lowered.
Average lake elevations vary according to the season. Highest average lake levels typically occur in the spring after the seasonal rains. The lowest average elevations occur in the fall and early winter months after a long, hot summer. For example, average October elevations are more than two feet below full pool.
It simply has to rain "normally" in the lake's watershed for Lake Springfield's water levels to remain at or above their monthly or seasonal averages. 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, can 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 dam and 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—providing there is a sufficient flow rate in the South Fork—raise the dam, causing water from the South Fork to back up into a channel from which the water can be pumped into the lake.

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. In winter, keeping the level a little lower than 560 feet helps protect docks and other facilities from the potential for ice damage.

Excessively high or low lake levels can threaten power and water plant operations. When the water is too high, there is the danger it will flood the low-service pumps located in the sub-basement of Lakeside Power Station. If this were to occur, these pumps—which draw water into both the power and water plants—would be put out of commission. If the lake water level were to drop to 13 feet below full pool, it would be too low to reach the low-service pumps, thus putting the power and water plants out of commission. The highest lake water level ever recorded at Lake Springfield since it was first filled in 1935 occurred during a storm event on April 12, 1994, when the lake crested at 564.5 feet. Intensive sandbagging efforts at the Lakeside Power Station helped protect the low-service pumps from being flooded. The lowest water level ever recorded was 547.44 feet, which occurred on December 29, 1954, during the drought of 1953-55. The return of heavy spring rains in 1955 prevented the lake level from dropping to the magic level of 13 feet below full pool at which power and water service to Springfield customers would have been disrupted.

See photos of the South Fork channel dam and pumping station.

Links to more information about lake levels, as well as related topics, can be found in the left-hand column of this page.

 

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