A balance of protection: How the MWRD manages waterways
The MWRD prides itself on protecting the waterways and improving the quality of water in its service area. The MWRD controls 76.1 miles of navigable waterways, which are part of the inland waterway system connecting the Great Lakes with the Gulf of Mexico. The Chicago Area Waterway System (CAWS) is comprised of waterways, dams, locks, and port facilities that includes the Chicago River and its north and south branches (including Bubbly Creek), the North Shore Channel, Chicago Sanitary and Ship Canal, Cal-Sag Channel, Calumet River, Lake Calumet, Wilmette Pumping Station and Sluice Gate, Chicago River Controlling Works North and South (CRCW), O’Brien Lock and Dam, Lockport Control Works and Lockport Powerhouse and Lock, and the Grand and Little Calumet rivers. The MWRD also monitors water quality in area waterways outside of the CAWS, including the Des Plaines River and some of its tributaries, Salt Creek, and the West Branch of the DuPage River.
The majority of the CAWS is comprised of manmade canals. The rest are formerly natural streams that have been dredged, straightened, widened, realigned, and otherwise modified to facilitate the conveyance of the MWRD’s treated water, commercial navigation and flood control. The MWRD controls the flow and water level in the CAWS to achieve efficient drainage in dry and wet weather, prevent discharges to Lake Michigan and ensure safe passage of commercial and recreational navigation. In order to maintain water quality, the MWRD diverts water from Lake Michigan.
How are CAWS levels set?
Under normal conditions, the lake is usually several feet above the level of the CAWS. This allows lake water to flow into the Chicago River, North Shore Channel and the Calumet River. The goal is to allow vessels to pass freely under bridges and yet stay afloat – not too high, not too low. The MWRD manages the level of the CAWS through four control structures, three of which are connected to Lake Michigan, including the Wilmette Pumping Station to the north, T.J. O’Brien Lock and Dam on the south, CRCW in downtown Chicago and the fourth is the Lockport Powerhouse.
Where does the water exit from the CAWS?
The Lockport Powerhouse, located in Lockport, Ill., was built by the MWRD in 1907 and marks the southern point of the MWRD-managed CAWS. The Powerhouse is located right before the Chicago Sanitary and Ship Canal connects with the Des Plaines River. The facility is an integral part of the MWRD's work to manage the CAWS to reduce the risk of flooding throughout the MWRD service area. The Lockport Powerhouse (Lockport) enables the MWRD to control the levels of the waterways and provides financial benefits from hydroelectric power generation. The water flowing through the facility is harnessed by two turbines to provide a safe and environmentally friendly hydroelectric energy source that is sold back to Commonwealth Edison. Lockport has generated more than $1 million worth of electricity almost every year for the last 20 years.
Chicago Area Waterway System—Normal Condition
How does the MWRD manage water levels in anticipation of storms?
MWRD waterway control operators work around the clock to monitor severity and duration of storms to draw down the elevation of the waterways. The MWRD continuously monitors the weather with real-time radar and rain gauges. When a storm is predicted, the water level in the CAWS is lowered by closing the gates at the three lakefront intakes and increasing flow through the hydroelectric generators and sluice gates at Lockport. To determine the amount of draw down, the MWRD analyzes forecasts, the geographical area of the approaching storm and the availability of storage in the MWRD’s Tunnel and Reservoir Plan (TARP) facilities. It can take several hours to lower the CAWS water levels and the process starts well in advance of a storm.
Chicago Area Waterway System—Moderate Storm Condition
During a storm, approximately half a billion gallons of water can be released from the CAWS at Lockport every hour. The water levels at the three intake control locations and throughout the CAWS are monitored along with the rainfall intensity and amounts at various locations in the metropolitan area. Monitoring these dynamic conditions allows the waterways control center operators to adjust the discharge at Lockport. When the discharge is maximized at Lockport, rainfall is continuing, and water levels continue to rise, the MWRD would have the discretion to discharge excess floodwater to the lake. In many cases, the water level in the CAWS will rise higher than the lake level at one or all of the three lakefront control locations, but threatening flood levels are not attained. Therefore, the floodwaters can be contained within the CAWS without having to discharge polluted overflows to the lake.
Chicago Area Waterway System—Severe Storm Condition
Depending on the severity of a storm, it may become necessary to open gates at Wilmette Pumping Station, CRCW and/or O’Brien Lock and Dam to relieve high water elevations and to prevent overbank flooding of the CAWS. There are several factors the MWRD uses to determine whether or not to release floodwater to the lake. These factors include the rate the water level is rising at each lakefront control location, whether the rainfall intensity is continuing or beginning to decrease, and the storm conditions on the radar.
Most occurrences of floodwater discharges to the lake do not occur at all three locations and last less than 24 hours. Whenever these occur, water departments and park districts are notified to protect the water supply and beaches. The discharges are also reported to the Illinois Environmental Protection Agency and posted on mwrd.org. Consistent with the MWRD mission of protecting Lake Michigan from pollution, every effort is made to minimize the amount of floodwater discharged to the lake during extreme storms.