November 9, 2016
The City of Detroit has a combined sewage and rainwater sewer system that becomes overwhelmed by heavy downpours. Water is flushed into the same pipes that lead to the city’s sewage treatment plant during rainstorms. The DFC Strategic Framework recommends changing the way the city thinks about infrastructure by encouraging Detroiters to use landscapes as infrastructure.
The City of Detroit is solving one of its major problems with the help of one of its other problems. Detroit is experiencing combined sewer overflow, a messy, and often downright dangerous event that happens every time it rains too much. But by leveraging the abundant city-owned vacant land, Detroit may have found a way to alleviate at least some of the overflow.
Detroit, like many cities its size, has a combined sewage and rainwater sewer system. This means that when it rains, water is flushed into the same pipes that lead to the city’s sewage treatment plant. But when it rains too much, this system can be overwhelmed, leading to massive discharges of untreated sewage into the waterways around the city. These sewer overflows are one of the largest polluters of the Great Lakes and also often flood residents’ basements with sewage. The raw sewage, filled with bacteria, chemicals, and prescription drug waste, is also causing dangerous algae blooms in Lake Erie.
In cities like Chicago and Milwaukee, which have partial or fully combined sewer systems, there are epic underground caverns and reservoirs to tackle the overflows. And though this is not foolproof, it is not even an option at all for Detroit: The economically struggling city does not have the means to construct multi-billion dollar tunnels nor the time needed to dig one of these systems—Chicago’s deep tunnel has been under construction since 1975.
So Detroit is turning to a more grassroots approach. One of the major issues of rainwater in any city is that so much of the ground is impermeable, forcing the water into drains instead of just soaking into the earth. As the City of Detroit controls nearly half of the land within the city limits, it has decided to actively ensure this land is permeable. Aside from simply breaking up many square miles of surface pavement, the city is working with communities to build bioswales, rain gardens, and marshlands.
Joan Nassauer, a landscape architect and University of Michigan professor, has already implemented a set of aggressive water retention prototypes. Working with a team of university researchers, she devised a system that is now in a pilot phase. After the Detroit Land Bank demolishes homes, the Detroit Water and Sewerage Department excavates the large holes formerly occupied by the houses’ basements, fills them with sand and stones, and tops them with hardy, short plants. Each resulting bioretention garden collects stormwater from the street, stopping it from entering the overburdened drains.
For Nassauer, the gardens presented quite a design challenge: Her experiences taught her that green infrastructure in financially-stressed neighborhoods is successful and accepted by the community when it looks well-kept. So the gardens had to be low maintenance without looking wild. Moreover, an overgrown garden might create visibility and safety concerns. The plant varities Nassauer selected—such as St. John’s wort, bergamot, coneflower, yarrow—are all showy but short: They remain visually appealing without growing too tall and requiring attention. Four test sites were built in Detroit’s Warrendale neighborhood; each can hold over 300,000 gallons of storm water per year.
In legacy cities like Detroit, Nassauer said, there’s simultaneously an “opportunity to design super-efficient green infrastructure and immediately make people’s neighborhoods better places….” But much hinges on political will: In Detroit, Nassauer’s challenge to coordinate among institutions was greatly aided the mayor’s office and political climate. “There are political forces and a lot of citizen energy [going] toward taking Detroit to a new level of desirability for a place to live and work,” she said.
Along with Nassauer’s prototypes, the city’s flood mitigation plan is heavily based on the 2012 report Detroit Future City. Among other things, the report recommended changing the way the city thinks about infrastructure. Rather than focusing on hard infrastructure—roads, sewers, bridges—the report encouraged “landscapes as infrastructure.” The benefits of the plan are varied, but one of the main advantages is the community-based nature of improvements. Not only can the public see the improvements, but they are able to enact their own changes within the system. Multiple nonprofits have taught residents how to construct rain gardens, while other groups already working in vacant lots to cultivate land for food production. More formal projects by the city include permeable sidewalks and streets, improvements that can be made when streets are already in need of repair.
Click here to read the full article in The Architects Newspaper.