Henry Grabar poses an interesting question: what if the Deep Tunnel project, one of the largest civil engineering feats in the world, does not solve flooding and stormwater issues in the Chicago region?

What if Chicago took a wrong turn in 1972 when, in the spirit of civic grandee Daniel Burnham (“Make no little plans”), it opted to build the world’s largest sewers instead of making all possible efforts to keep rainwater out of them? Scott Bernstein, the founder of the Center for Neighborhood Technology, says that the Deep Tunnel imposed a massive opportunity cost because the city and the district did little else to adapt. The MWRD spent billions on what engineers call “gray infrastructure” (pipes, tanks, pumps) and virtually nothing on “green infrastructure”: rain barrels, detention ponds, green roofs, porous pavements, and other adaptations that would have kept water out of the system…

The project proceeded regardless. Even with downsized reservoirs and a longer time frame, Chicago’s ambition captured the attention of civil engineers around the world. Today, most U.S. cities whose combined sewer overflows are governed by consent decrees with the EPA are working on Chicago-style digs. St. Louis, which has the fourth-largest sewer system in the country, is under a consent decree to commit $4.7 billion to ending its overflows through deep tunnels…

While engineers’ penchant for megaprojects endures, some American cities are preaching deterrence. If Chicago built a bathtub, Philadelphia is trying to transform itself into a sponge with park space, street trees, and permeable pavement. The city is spending $2.4 billion to implement the nation’s largest green infrastructure plan, an experiment that positions it as the anti-Chicago. The city thinks keeping water out of the system will save billions of dollars compared to a rejected tunnel proposal—and that green initiatives will produce positive externalities, like improving air quality and creating verdant streets.

In Chicago, meanwhile, the MWRD has committed to creating just 10 million gallons of green infrastructure capacity under its EPA consent decree. Compare that to neighboring Milwaukee, a deep-tunnel city that now believes its green infrastructure will, by 2035, surpass the capacity of the tunnels and hold up to 740 million gallons of rain where it falls.

Hindsight may always be a little tricky in these cases as we have the advantage now of being able to see the Deep Tunnel project in action. Does it actually accomplish its goals? Was all the spent money worth it? At the same time, a project of this magnitude should have generated plenty of discussion and at least a few alternative options.

If Deep Tunnel does not work as intended or does not solve all of the flooding and stormwater problems, I wonder if it could be used in other ways. I’m thinking of other major infrastructure projects that have been reversed or reused, like urban highways that are torn out (like in Boston or San Francisco) or former railroad lines turned parks or recreation areas (think the High Line). Some other options for the Deep Tunnel:

1. Underground roads. With Elon Musk’s Boring Company working on underground roads plus Chicago’s legacy of Lower Wacker Drive, perhaps traffic could be rerouted deep underground.
2. Underground freight movement. Given Chicago’s railroad bottleneck, this could be an interesting solution.
3. An underground park and recreation area. It would certainly be unique. Think a combination of spelunking, rock climbing, and exploration.
4. A military installation and testing area.