June 12, 2019

Our Wet, Wet, Wet, Wet, Hot, Wet World

By now many of you may have heard that the month of May was the wettest on record for northern Illinois since we started measuring rainfall in 1871, outstripping the prior record May for rainfall, which occurred just last year. Cook County recorded 8.25” of rain in May, roughly 20 percent of the total annual rainfall in one month!  

During the month of May, the Metropolitan Water Reclamation District’s Tunnel and Reservoir system intercepted nearly 13.6 billion gallons of combined sewer overflows (CSOs). That’s sewage and waste water from our homes, businesses, and industries combined with rain washing over city streets collecting salt, oil, pet poop, brake dust, and fertilizer from lawns and gardens that otherwise would have flowed directly into nearby rivers and streams, polluting them significantly.

From January through May 31, the Tunnel and Reservoir system captured 42.56 billion gallons of combined sewer overflows. Think about that: if that amount of water covered the surface area of Chicago, we’d be wading in 10.5” of stormwater mixed with sewage. Remarkably, given the record rains, there have been NO REVERSALS of CSOs to Lake Michigan since October 2017.

Annual-Reversal-by-Site-_2019.jpgConsider this: even though our region has been breaking rainfall records, we’ve avoided reversals to the lake, the Albany Park diversion tunnel has saved that area from flooding, and CSOs are down in number. The reason? The first phase of the McCook Reservoir, which can capture and hold 3.5 billion gallons of CSOs, went online in December 2017. 

Thanks are due not only to huge pipes and tunnels, but also to the heroic efforts by MWRD staff to lower water levels in the Chicago Area Waterways system in advance of storms to give the system as much capacity as possible to capture stormwater. During the late May storms, the gates releasing water at MWRD’s Lockport Powerhouse were open as wide as possible and the flow recorded there was 20,000 cubic feet per second (cfs). By comparison, Chicago can legally withdraw only 3,200 cfs/day of freshwater from Lake Michigan. 

Here's a fascinating fact: one cubic foot of water weighs 62.5 lbs. Thus, the flow of 20,000 cfs at Lockport equaled 625 tons of water per second flowing through the Powerhouse gates. The high flows on the Chicago Waterways also brought commercial barge traffic to a standstill in recent months. Beginning on May 7th, the US Coast Guard halted barge traffic on the Illinois River (which receives flows from the Chicago Waterways).

And our soils are soaked! The soil moisture in Cook County is now higher than 99 percent of the historical record, according to NOAA and the National Weather Service. Saturated soils mean much less capacity to absorb rain when it comes.

The Great Lakes have responded to this record-setting weather as well. According the Army Corps of Engineers, which tracks Great Lakes water levels, Lake Erie and Lake Superior reached new monthly mean high water levels in May, and Lake Ontario surpassed its all-time record high level this week. As of the first week of June, Lake Michigan is 13” above its average level and is expected to continue rising through this summer. Lake Michigan is currently just 2” below its all-time record height for June, set in 1986.

Burnham_Harbor_May.jpg

Sidewalks typically well above water are now submerged along harbor's edge at Chicago's Burnham Harbor. Photo courtesy of Chicago Park District.

What’s to be done with all this water? First, expect the unprecedented. Predictions for the climate crisis in northeastern Illinois include more intense, less predictable rain and snowstorms. These are likely to be our new normal. Consider this conundrum: warmer air here in Illinois means more water evaporates and coalesces into violent storms, while warmer air in the Arctic destabilizes the jet stream, leading the Great Lakes to freeze over and lake levels to rise when the ice melts. Cook County sits at the crux of these forces, with all the variability that entails. 

Second, let’s do everything we can to give the land more absorptive capacity. We should install rain gardens, bioswales, permeable pavement, and green roofs everywhere we can to capture rain and keep it out of the sewers. But we may also need to un-finish our basements and expect them to take on water now and then—the way things used to be. (A harsh reality, I know, but we live in a flat, wet world. There’s no downhill to move water away from us.) Finally, let’s get creative about ways to capture (and reuse) rain. Let's think about repurposing rail tank cars for stormwater capture next to big box stores and warehouses. Let's install community cisterns block by block and re-green vacant lots as wetlands. Let's convert parkway patches into prairie grass stands. Bring your ideas to your local representatives and push for action. Folks, we need all hands on deck because we’re taking on water!