Blame It on the Rain

Snaking under Chicago’s streets is a web of tunnels that engineers began digging 40 years ago. They cover more than 100 miles and plunge 300 feet belowground in places—all to prevent storm water and sewage from overflowing into the city’s three major rivers and, ultimately, Lake Michigan. Right now most of the tunnels just hold the storm water, but over the next 15 years, they will all flush into giant manmade reservoirs capable of holding billions of gallons. Water managers will cut the ribbon on the second of three reservoirs this summer.

But a cloud of uncertainty will loom over the celebration: Can a system devised four decades ago be able to handle what climate change brings?

Before the tunnels existed, Chicago’s rivers were so gross that architects would design buildings with windows facing away from the reeking eyesores. Only 10 fish species existed within them in the 1970s; water managers now count more than 70. Today, the nonprofit Friends of the Chicago River is even installing osprey nests, and people rent kayaks and take boat tours (see “Cry Us a River”).

Rainwater currently drains into storm sewers, then flows into the tunnels, along with wastewater from sewage pipes. From there, it either waits for treatment plants—some of the biggest in the country—to process it, or flows into reservoirs. However, when rainfall exceeds the tunnels’ capacity, which happens about 40 times a year, the sewage overflows into the rivers and backs up into basements. And when the rivers rise too high, water managers have to open the locks that prevent river water from flowing into Lake Michigan, the source of drinking water for seven million people.

The Tunnel and Reservoir Plan, known informally as the Deep Tunnel project, was designed to capture and keep all the stinking, polluted water in reservoirs until treated. The first, the Gloria Alitto Majewski Reservoir, opened in 1998 and holds 350 million gallons. When Thornton, a quarry 25 miles south of the city, comes online this summer, it’ll hold 7.8 billion gallons. The third, McCook Reservoir, will keep an additional 10 billion gallons; the first section is scheduled to open in 2017. The entire $3.5 billion project, one of the largest in the world, is projected to finish in 2029.

Even though Deep Tunnel isn’t yet operating at full capacity, it’s already helping to keep sewage out of waterways. Water managers estimate that together the reservoirs will save more than $1 billion in damages and alleviate flooding for millions of people. When complete, the system will be able to handle 17 billion gallons of water. That’s huge, but still might not be enough.

The Great Lakes region is already seeing intense storms more frequently due to climate change, and models predict it’ll only get worse. Greenhouse gases are making the atmosphere warmer, allowing it to hold more water before it rains. The number of storms that dump 2.5 inches of rain on the region in 24 hours could increase 50 percent by 2039, and as much as 160 percent by the end of the century.

So a coalition of environmental groups, including NRDC (disclosure), is pushing for measures to enhance Deep Tunnel to anticipate the changing climate, even as the project moves forward.

“If you look around at major cities in the country, Chicago had so much foresight, spent tremendously less, and received tremendously more than almost any other,” says David St. Pierre, executive director of the Metropolitan Water Reclamation District in regard to other efforts to keep storms from flooding cities. The system has done a great job dealing with the Chicago’s old weather patterns, he says—but to stand up to climate change, the city will need more green infrastructure, such as permeable pavement and green roofs that prevent water from getting into the drainage system in the first place.

That’s what NRDC argued when it filed suit against the Water Reclamation District in 2011, saying the city agency needs to look further at how well the tunnel plan will prevent sewage overflows under Chicago’s increasingly rainy climate forecast. (That lawsuit and another that could force the agency to act are currently tied up in court.)

Green infrastructure would be one way to do that. Bigger tunnels are another, says Ann Alexander, an attorney for NRDC. “You can build a bathtub as big as you want, but if you’re trying to fill it with a drinking straw, you’re going to have a problem.”

Hydrologist Marcelo Garcia at the University of Illinois says that climate change will prevent the project from ever keeping the city’s storm runoff completely at bay. “Make no mistake, given what the weather is throwing at us, making Chicago completely flood-proof is a little bit utopian,” he says. “We shouldn’t fool ourselves.”

Despite its shortcomings, Deep Tunnel is largely seen as an effective way to keep Chicago from reverting to its marshy past, and if Chicago hadn’t started work when it did, the project would be stretching before us, with a hefty bill attached. The solution may not be perfect—and still could be better—but it’s giving the city a shot a healthy, fish-friendly, and clean-water-drinking future. Boat tour, anyone?