By: Caitlin Federici

A warming climate has led to drastic swings in the water levels of Lake Michigan. Warmer temperatures lead to more evaporation and record-low water levels.[1] Colder temperatures mean reduced evaporation and greater ice cover resulting in record-high water levels.[2] While climate change causes the earth’s climate to trend warmer on average, these trends do not always manifest in a linear fashion. For instance, when warm air from the tropics moves too far north, it can disrupt the balance of the polar vortex sending blasts of arctic air much farther south than it would otherwise reach.[3] In Chicago, an unstable polar vortex equates to frigid winters and rising levels in Lake Michigan; multiple consecutive years of such instability can produce record-high water levels.[4]

Additionally, climate change has brought more frequent and intense storms to Chicago in recent decades. Five of Chicago’s top ten wettest years dating back to the mid-1800s occurred in the last 22 years.[5] For a massive city constructed upon a sprawling swamp, this much rainfall disrupts the delicate balance of the water system surrounding the city. The consequences of these trends may prove catastrophic for Chicago.

One of the most pressing concerns for city residents is sewage disposal. Over the years, Chicago has undertaken many engineering projects to remedy the issue of human waste. First, engineers lifted the city out of the swamp by propping it up on colossal steel stilts and created an underground combined sewer system designed to process both waste and storm runoff through the same pipes.[6] The discharge from this system was released into the Chicago River.[7] At the time, the Chicago River flowed into Lake Michigan–the city’s source of drinking water.[8] To protect Lake Michigan from contamination, engineers built a system of canals to reverse the flow of the river away from the lake. [9] They also installed a lock system to prevent the bodies of water from mingling. [10]

The combined sewer system still exists today. When this system is overwhelmed, runoff and sewage flood into the Chicago River and bubble up through drains in city basements.[11] The Deep Tunnel was designedto solve this problem. This 20-billion-gallon system was designed to store excess sewage and runoff until it could be processed.[12] While this helps reduce flooding events, it was not designed to contain the volume of runoff from heavier storms Chicago now experiences.

From 2004 to 2014 the Chicagoland area received $1.8 billion in subsidized disaster aid, loans, and insurance payouts to cover urban flood damage.[13] The Chicago Tribune reports that “only hurricane-ravaged areas of coastal Louisiana, New York, and Texas received more federal flood aid during [that same] decade.”[14] Furthermore, this price tag only includes damages from flooding events that earned a disaster declaration signed by the president.[15] Thus, the true cost of Chicago’s urban flooding problem is likely much higher than the recorded $1.8 billion.

Chicago’s low-income communities suffer the brunt of the damage from the city’s failing sewer system.[16] Data from a 2013 storm that caused urban flooding across the city showed the damage was concentrated in low to middle income communities on the South and West side.[17] Similarly, data of 311 calls made during a string of storms in 2019 showed that although flooding reports were received from all 77 communities in Chicago, over a third came from just eight “low-income, predominantly African-American neighborhoods on the South and West sides.”[18]

In downtown Chicago the Harbor Lock system protects the area from catastrophic flooding. If the river rises beyond the trigger level—3.5 feet above ground level—the lock gates open to release excess water into Lake Michigan.[19] This, of course, must only be done in emergencies as the sewage in the river will contaminate Chicago’s drinking water. Still, it protects Chicago’s infrastructure from irreversible damage.

To be effective, the water level in the lake must remain below the trigger level in the river. If the lake level exceeds that of the river, opening the lock gates would force a rush of water from the lake into the city. When both the river and the lake are at exceedingly high levels, there are no solutions.

Such an event occurred in May 2020 when Lake Michigan was at record-high levels and the city experienced record rainfall over a 3-day period.[20] Water levels in the river rose 5-6 feet in a matter of hours.[21] As the city flooded, lock operators had no choice but to keep the gates locked.[22] The river rose more than a foot beyond the trigger level before small gushes of water could be safely released into the lake.[23] This led to more than 1,500 residential reports of flooded basements.[24]


Individual communities offer solutions to a city-wide problem

While Chicagoans can contribute to healing the global climate crisis, we cannot solve the issue alone. Unfortunately, this likely means Lake Michigan’s water levels will continue to fluctuate rather aggressively and the city will continue to experience more frequent and intense rainstorms. Luckily, there are steps we can take to reduce the amount of runoff that lands in our sewer system.

Some low-lying communities that experience the most frequent flooding have begun implementing their own innovative solutions.[25] One such solution calls for installing rain gardens. Rain gardens are a cheap option as it only requires lowering the edge of the street curb enough to draw runoff from the street into a garden at the front of a yard.[26] Another solution calls for diverting runoff into basins with trees and native plants.[27] Not only do both of these options reduce the amount of runoff that enters the sewers, they also reduce the amount of tap water used to water outdoor plants.

Installing permeable pavement is an option that would be most beneficial if implemented during larger construction projects but would also serve individual homeowners who wish to reduce runoff in their neighborhoods. Unlike normal concrete, permeable pavement is porous, allowing it to soak up large volumes of water.[28] The rainwater then soaks into the surrounding soil rather than flowing into the sewer.[29]

Although these solutions hold promise for mitigating Chicago’s flooding problem, they are not substitutes for the large-scale, systemic change Chicago needs to make to its sewer system. The Deep Tunnel, though almost complete, does not adequately protect the city from flooding. It is certainly not prepared to withstand the intensifying weather patterns facing the Midwest. So far, the proposed solution is to expand the already-insufficient Deep Tunnel project, but this only serves to store sewage until it is processed without processing it at a faster rate. Once these additional tunnels are full, Chicago will face the same flooding risks it faces now.

According to the EPA, sewer separation is highly effective at reducing or eliminating overflow events that lead to urban flooding.[30] Both full and partial sewer separation are effective.[31] Large urban centers such as Minneapolis and St. Paul have completed sewer separation projects resulting in significant reductions in overflow events and water quality improvements.[32] Additionally, the EPA recommends merging such projects with other infrastructure projects that are already planned to mitigate the costs of separating the system.[33]

As mentioned, the Deep Tunnel project is still underway. Construction crews are already under our streets manipulating the sewer system. Although the Deep Tunnel is almost complete, it has failed Chicagoans time and again at preventing overflow events. Perhaps it’s time City and State officials reconsider whether completion of the Deep Tunnel project is the best allocation of taxpayer dollars or whether an option such as sewer separation is a more sustainable solution.


[1] Dan Egan, A Battle Between a Great City and a Great Lake, New York Times (July 7, 2021), [].

[2] Id.

[3] Rebecca Lindsey, Understanding the Arctic polar vortex, (Mar. 5, 2021), [].

[4] Egan, supra note 1.

[5] Chicago’s Precipitation Records, Nat’l Weather Service, (last visited Sep. 24, 2022) [].

[6] Egan, supra note 1.

[7] Id.

[8] Id.

[9] Id.

[10] Id.

[11] Id.

[12] Id.

[13] Michael Hawthorne & Morgan Greene, Flooding in the Chicago Area has been so bad in the past decade that only places ravaged by hurricanes sustain more damage, Chicago Tribune (May 10, 2019), [].

[14] Id.

[15] Id.

[16] Id.

[17] Id.

[18] Id.

[19] Egan, supra note1.

[20] Id.

[21] Id.

[22] Id.

[23] Id.

[24] Id.

[25] Hawthorne & Greene, supra note 6.

[26] Soak Up the Rain: Rain Gardens, EPA, (last visited Sep. 24, 2022) []

[27] Hawthorne & Greene, supra note 6.

[28] Soak Up the Rain: Permeable Pavement, EPA, (last visited Sep. 24, 2022) []

[29] Id.

[30] U.S. Env’t Prot. Agency, 832-F-99-041, Combined Sewer Overflow Management Fact Sheet (1999).

[31] Id.

[32] Id.

[33] Id.