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.
Frequently Asked Questions
Will the low lake level cause a reversal of the Chicago River? No, the MWRD gate structures will not allow a reversal of the river under any circumstance with the exception of major storm events when the CAWS is full to capacity and needs relief. This has happened an average of once a year over the past ten years.
What impact will the low lake level have on the MWRD’s operation? If the lake level continues to decline, the MWRD would not be able to take in any diversion water. This would cause the dissolved oxygen to decrease in the main stem of the Chicago River or the downtown area. We would need to coordinate a schedule with the USACE and the Port Authority to allow a refreshing of the main channel. This schedule may cause a suspension of river traffic for a certain time frame. It would not be prolonged or stop traffic altogether. It would also cause the MWRD to receive the authority to maintain the level of the CAWS at a higher level than the lake in order to maintain navigation. This should not restrict the operation of the locks at the main stem or at the O’Brien Lock system.
Are we in a crisis? We are not in a crisis at this time nor do we anticipate being in a crisis this year even if the drought should continue. However, a prolonged drought could eventually result in significant water management developments within the region. It certainly highlights the value of water and the need to respect our use. Every citizen should certainly do their best to conserve water and use it wisely not wastefully.
Will the low lake level cause water quality problems in Lake Michigan? No, there is no reason to expect water quality problems in Lake Michigan due to lower lake levels.
There have been media reports declaring the CAWS will reverse during the low lake level. Again, this is not the case. It is also important to note that historically lake levels seem to swing in a sinusoidal curve over a twenty year period. In 1964, lake levels were at the current level and peaked in 1984 and have now returned to 1964 levels. This has been the trend over the past 100 years.
For an accurate news report, please visit the Fox 32 News website at http://www.myfoxchicago.com/story/20548616/drought-wont-affect-chicago-river-much-after-all.
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