June 16, 2020

On the Water Front: A Wet May, a Rising Lake, and Flooding Again

By now most of you know that Chicago and Cook County recorded the wettest May on record—9.51” recorded at O’Hare—a full 1.26” over the previous record set in…wait for it…May 2019. That’s a total of 156 billion gallons of water if it had been evenly distributed across the expanse of Cook County. 

However, these rains weren't only restricted to Cook County—the entire Lake Michigan watershed experienced a wet spring, raising the already high lake level even further. As of this week, Lake Michigan is six inches higher than at this point last year, and just two inches shy of its all-time record height, set back in 1986. Now, the Army Corps of Engineers warns Lake Michigan will continue rising through September.

Look at what this rain meant to Tracey Vowell, who owns Three Sisters Garden, a small farm near Kankakee:

Seems we are getting into monsoon season a tad early, with 7 inches having fallen on this tiny farm [in the last week]. Here is what goes through my chef turned farmer mind as the rain gets really out of hand.

Gallons of water needed to make an inch of water on an acre of land: 27,154
Pounds in a gallon:  8.4
Size of my farm: 10 acres
Inches fallen: 7
Pounds of water to hit my little postage stamp farm in the last week: 15,966,552

You guys see my van picking up pallets of empty water bottles somewhere, know that we are about to start offering bottled rainwater.

The historic rains of May 14–15 (4.21") and 16–17 (3.67") caused widespread basement backups, overbank flooding in some places, viaducts under water, and prompted one constituent to write me:

“Why is it after every storm we hear again that the rainfall amounts were unprecedented, and that that somehow explains yet again the discharge of wastewater into Lake Michigan, the source of drinking water for millions and millions of people? Why is it that every underpass under Lake Shore Drive floods after every torrential rain? When will it be the case that the City of Chicago is able to manage the storms that inevitably come instead of once more passing the buck—or, better, telling citizens that the answer is to defer their five-minute drop-in-the-bucket showers?

“Don't get me wrong, I'm all for doing my part. But I can't help asking: just what precisely does the MWRD do, when the situation from one spring and summer to the next simply never seems to change?”

All good questions, sir. Here’s my attempt to provide an answer:

There are several aspects to what we’re experiencing with these more intense rainstorms and resultant flooding in Chicago and Cook County: global factors and local elements that meet in a demonic—rather than harmonic—convergence. Chicago's flooding problem is not new. To understand the unique challenges we face and how we've landed where we are, let’s look at our history.

First, blame the glaciers. Our water story in Chicago begins roughly 15,000 years ago when the Wisconsonian glacier extended this far south and not much farther. The weight of the glacier, however, essentially flattened the landscape and compacted much of the soil, so that a nearly impervious layer of clay lies a foot or more below the surface, retarding the ability of water to infiltrate.

The scene, then, is that of flat land, clay soils, a soggy, mucky, wet place with a burgeoning populace dumping all manner of human, animal, and industrial waste into the sluggish, sleepy, slow-moving Chicago River—a river that flowed into Lake Michigan, thus delivering sewage, waste from stockyards, tanneries, and more directly into the city’s drinking water supply.

What followed was a series of epic engineering solutions that span decades from their conception to their construction. In considering them, my motto is: all problems started out as solutions. The solution to the problem of Chicago’s contaminated drinking water was to dig a canal and reverse a river—to use water from Lake Michigan to flush Chicago’s waste away from the lake and deliver it into the Mississippi River system via the Des Plaines tributary. Chicago did it—dug the Sanitary & Ship Canal between the south branch of the Chicago River and the Des Plaines River, built a lock at the mouth of the Chicago River, and beginning in January 1900, reversed the flow of the Chicago River sending raw sewage mixed with stormwater towards St. Louis (people there weren’t happy) and beyond. As Chicago became a great metropolis, two more man-made canals—the North Shore Channel and the Cal-Sag Channel—completed the bold reversal, protecting the city’s drinking water supply from sewage and establishing a route for commercial barge traffic to travel between the Mississippi and the Great Lakes.

Now let’s get really local. Chicago and most older cities have combined sewers, meaning the same pipe laid down the middle of the street 70 years ago to convey used water from your home (toilets, dishwashers, showers, laundry machines) also fill with stormwater flowing down street drains carrying surface contaminants like salt, oil, bits of brake dust, dirt, leaves, pet poop, etc.

Most sewer pipes under city streets are sized to handle a five-year storm—basically the amount of rain in a storm with a one-in-five chance of happening each year. When these pipes fill up, as pipes do especially in heavy rains, they’re designed to overflow directly into a nearby river or stream. That’s called a combined sewer overflow (CSO). CSOs were very common and people realized that they were also seriously bad for river health because they dump all sorts of pollutants from street surfaces mixed with raw sewage into area waterways. Yuck.

Chicago dreams big—again. Beginning in the late 1960s, engineers at the Metropolitan Sanitary District conceived of a Tunnel and Reservoir Plan (TARP) to dig a huge underground storage tank in four sections and three large reservoirs to capture these CSOs and keep them from discharging into Chicago’s waterways both to prevent pollution—the EPA was in its infancy in the early 1970s, as were a host of aspirational clean water and air acts—and, later, to reduce flooding. Again, Chicago embarks on a multi-billion dollar, multi-year project to solve the problem of CSOs. The four sections of the “Deep Tunnel” burrowed 300 ft. below Chicago rivers, generally 33-ft. in diameter, were completed in 2006 and can hold 2.3 billion gallons of stormwater overflow. The water diverted into these tunnel sections is pumped to wastewater treatment plants when they have capacity to treat it and much of the pollution is removed. So it is that the treated wastewater discharged into the waterways today is much cleaner than the bodies receiving it. As a result of these and other measures, the Chicago waterways now boast more than 70 species of fish where once there were none.

Work on the reservoirs is still underway but 2 1/3 of the three planned reservoirs are completed. (Sections of the Deep Tunnel connect to the reservoirs, so they become massive holding tanks for stormwater overflow that also gets pumped to treatment plants and treated.) The existing reservoirs can hold a total of 13.75 billion gallons of stormwater overflow. Essentially, they’re an effort to compensate for the build-out of our urban environment and the flatness of the landscape (nowhere to pump water away from us).

Almost to your questions, sir!

We built this magnificent system; why doesn’t it work?

I think there are several factors now: climate change, aging infrastructure, and the nature of urban growth. Regarding climate change, it’s getting hotter and it’s getting wetter. May 2020 (9.51” total) has been wetter than May 2019 (8.25”), which was declared the wettest May on record when it broke the monthly rainfall record that had been set in—you guessed it!—May 2018 (8.21”). The storms we are seeing are the local manifestation of profound changes in the global climate that in other places manifest themselves as wildfires, sea-level rise, drought, and desertification. To all appearances, these grim phenomena are with us to stay, and we will have to adapt.

Not only are we experiencing more rain, but we are also experiencing more intense rain events. These storms are more localized and less predictable—in 2014 the weather stations at Midway Airport recorded 10 inches more rainfall than the station at O’Hare Airport. As a result, intense storms are overwhelming the capacity of the local sewer system even to convey the stormwater to the larger interceptors and to the tunnel drop shafts and reservoirs. These more intense rain events—see accompanying chart of one that occurred in August 2014—are our new normal. Four inches of rain spread out over 24 hours, the system can handle. Four inches of rain dumped in one hour, no system can handle. We see sewers backing up into basements and localized flooding as a result.

Oak Lawn_Burbank 8_22_2014.jpg

Another factor that influenced the storms of May 14–17: the ground was already saturated from rains two days’ prior. When we get one rain after another, the ground gets soaked, the water cannot seep through that clay layer left by the glaciers, and the ground acts like an impervious surface itself. It’s full, too, and can’t take on more. Hence seepage into basements from cracks in foundations and water flowing through window wells. That’s bad luck for the soil conditions and weather to converge this way, but it happens.

One could argue that the MWRD is doing a much better job of managing stormwater than it used to. Over the last three decades, the number of reversals to Lake Michigan has gone down significantly, and the number of combined sewer overflows, too, has dropped substantially. Regional and local flood-control projects have made a visible difference in their targeted areas. (If you aren’t happy with the sewage reversals to Lake Michigan and localized flooding that you have been seeing, you would be absolutely horrified by the number of reversals and floods we would have suffered without having these projects in place.) But there’s no denying the fact that the stormwater-management infrastructure built in the 1920s, 1950s, and 1970s, has been overtaken by the swiftness and violence of climate change, and that the current infrastructure has not solved all the flooding problems that Chicago and Cook County face.

Volume of MWRD Reversals to Lake Michigan by Site.jpg

Some measures have endeavored to address the current situation. The Water Reclamation District passed a Watershed Management Ordinance in 2014 establishing minimum standards for retention and detention of stormwater on new development and redevelopment in Cook County. It’s one effort to mitigate the impact of future flooding.

What’s to be done? Return to the land some of its ability to absorb water (peel back some of the concrete skin we’ve laid over the landscape). Deploy every tool in the green infrastructure toolkit—install permeable parking lots, green roofs and rain gardens, bioswales and wetlands—and invent some new ones (repurposing old rail tank cars to capture rain off the roofs of big box stores, installing large community cisterns, turning vacant lots into localized stormwater retention). We need to patch leaky pipes and compel new development to capture and hold rain where it falls. And we need to change our expectations that our streets and basements should never take on water. (Years ago, people didn’t have finished basements so when they took on water, it wasn’t such a damaging event.) We need to slow the flow of rain into the sewers or endeavor to keep it out altogether.

In other words, we cannot continue to think of these solutions as though there is a finish line where we have "done enough." We need to do what we can to adapt to climate change, mitigate its effects, and make our region more like a sponge. A worthy goal, don’t you think?