There have been some inaccurate media reports pertaining to the impact of low Lake Michigan levels on the Chicago River, and the Metropolitan Water Reclamation District of Greater Chicago (MWRD) would like to explain how it is not possible for the Chicago River to reverse course on its own.
The MWRD controls the level of the Chicago Area Waterway System (CAWS) through four control structures – three of which are connected to Lake Michigan and the fourth is the powerhouse in Lockport. The MWRD has an allowance of 305 cubic feet per second (cfs) to draw water from the lake; 270 cfs is for discretionary diversion to maintain water quality in the channels and 35 cfs is for navigation purposes.
CAWS levels are regulated under the Code of Federal Regulation and overseen by the US Army Corps of Engineers (USACE). These levels are set according to the Chicago City Datum (CCD) point that is a gauge at the downtown or mainstream lock. The MWRD’s normal operating levels are between -0.5 feet to -2.0 feet CCD. This allows vessels to pass freely under bridges and yet stay afloat – not too high, not too low. Before a storm event, the MWRD generally lowers the CAWS to -3.0 feet. This still allows for navigation traffic in the CAWS.
The lake typically is several feet above the CAWS level. This allows for discretionary diversion to flow into the main channel and the Calumet system. The MWRD pumps diversion flow from the lake into the North Shore Channel at Wilmette. The current lake level is -2.55 feet, and we are operating the CAWS at -2.91 feet. We strive to maintain a minimum of 6 inches differential between the lake and the CAWS.
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