Photo By Tony Thompson
Each fall at the CWLP Water Plant, a day is set to transition Lake Springfield to what is called “winter operations.” Winter operations protocol, which began November 3 this year, established the target elevation of the lake to be 559.60 feet above mean sea level (MSL). At Lake Springfield, full pool is the 560-foot mark.
Whenever possible, CWLP Water Plant Operators seek 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 and wave damage.
In recent years the lake has remained full enough to be at or close to full pool that going to winter operations has involved releasing a substantial amount of water over the course of a week or so to lower the lake. This year, however, the lake elevation has been around 558 feet above MSL since mid-September so no release of water was needed to move to winter operations. As a hedge against drought, the return to summer operations with a target of full pool at 560.50 MSL, is planned to resume in April.
More on Lake Levels
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 typically more than two feet below full pool.
It simply has to rain "normally" in the lake's 265-mile 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 to nine 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 full pool or lower, 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.
The highest lake water level ever recorded 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. These pumps have since been abandoned and replaced to the new Low Service Pump Station located northeast of the Lakeside Station to a more secure and less flood prone facility.
The lowest water level ever recorded was 547.44 feet, which occurred on December 29, 1954, during the drought of 1953-1955. The return of heavy spring rains in 1955 prevented the lake level from dropping to 13 feet below full pool at which power and water service to Springfield customers would have been disrupted due to the location of the low service pumps at that time and the inability to draw in water.
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