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.
The table below shows water level readings taken at Lake Springfield over the past year.
For comparative purposes, it also includes readings for the same date in the previous year,
as well as the average levels for each month (as recorded from 1936 through last calendar year).
During periods of normal to above-normal lake elevation, readings will be recorded no more than once
per week (usually on Friday). If declining levels become a concern, readings will be posted more frequently.
Lake Springfield's full pool level is 560 feet above sea level. When water rises above that elevation,
it will overflow the gates of Spaulding Dam. The highest level ever recorded at Lake
Springfield was 564.5 feet (4.5 feet above full pool) on April 12, 1994. The lowest level ever
recorded since the lake originally reached full pool in May 1935 was 547.44 feet (12.56 feet below full pool)
on December 29, 1954. For more information about the importance of maintaining an adequate water
level in Lake Springfield, see How CWLP Maintains the Lake Level.
All readings are taken at the CWLP Plant Complex, 3100 Stevenson Drive. The table below shows the last 2 years of reads.
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.
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 1953-1955.
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.