ANN ARBOR—On the former sites of vacant Detroit homes, University of Michigan researchers and their partners have built innovative gardens that help manage stormwater while removing neighborhood blight.
The four new "bioretention gardens" are designed to capture and hold stormwater in a subsurface layer of gravel while beautifying the Cody Rouge area on Detroit's west side. The just-completed gardens are expected to achieve an average annual stormwater volume reduction of 300,000 gallons per site, for a total of 1.2 million gallons, and should help reduce street flooding during big storms.
The pilot project shows how vacant properties can become green infrastructure that enhances neighborhood quality of life while improving water quality in the Detroit River and the Great Lakes, said project leader Joan Nassauer, a professor of landscape architecture at the U-M School of Natural Resources and Environment.
"Nature and the residents of Warrendale win with these new gardens," Nassauer said. "This project's innovative approach uses Detroit's vacant property demolition process as an opportunity to construct high-efficiency stormwater management and storage and to transform the sites of abandoned houses into beautiful flower gardens."
Research for the project was funded by $285,000 from the U-M Water Center with support from the Erb Family Foundation. The gardens were constructed and instrumented for data gathering with a $500,000 investment by the Detroit Water and Sewerage Department on land owned by the Detroit Land Bank Authority. Collaborators in the project include the Cody Rouge Community Action Alliance and the Warrendale Community Organization.
"Projects like these are going to be extremely important as we move forward in the city. They allow us to make use of vacant land and to make it more productive, while at the same time eradicating blight in the neighborhoods," said Palencia Mobley, deputy director/chief engineer at the Detroit Water and Sewerage Department.
The Warrendale neighborhood is part of the Cody Rouge area, which is in the Rouge River watershed. The Rouge flows into the Detroit River, which empties into western Lake Erie. Heavy rainstorms sometimes overwhelm Detroit's wastewater treatment plant, resulting in events called combined sewer overflows, in which both stormwater and untreated sewage are released into waterways.
Cross-section of one of four "bioretention flower gardens" under construction in Detroit's Cody Rouge neighborhood. The gardens will soak up and store storm water to help reduce overflows during large storms. Image credit: Tetra TechSeveral efforts to use green infrastructure to help manage stormwater and reduce combined sewer overflows are underway in Detroit. Green infrastructure uses vegetation and soils to soak up and store stormwater.
Each of the Cody Rouge bioretention gardens is roughly 25 feet on a side. They sit in shallow, depressed areas planted with flowering shrubs and perennials to provide valuable neighborhood amenities.
Beneath the surface of each garden is a 30-inch-thick layer of engineered soil and a 2-foot-thick layer of gravel beneath the soil. The gardens are designed to capture stormwater from the street and allow it to soak into the ground slowly over 24 to 72 hours, said Dan Christian, a senior water resource engineer at Tetra Tech.
As a safety feature, the gravel layer contains a perforated PVC underdrain pipe. This pipe collects any stormwater that does not infiltrate and sends it to the city's combined sewer system. A valve in the pipe allows engineers to control discharges to the combined sewer system to ensure that the site is drained and ready for the next rain event, Christian said.
"I am overjoyed when I look at these projects and think about what they're doing," Mobley said. "One thing that we have in this city is land. We have tons and tons of land. And being able to make that land productive is going to be an amazing benefit for us in the future. So I hope that we can continue to do these types of projects and that we can inspire others to do them, as well."
About $1.15 million from a new $3 million Erb Family Foundation grant to the U-M Water Center, announced in September, will allow Nassauer's interdisciplinary team to assess the performance of the Warrendale bioretention gardens over time, to monitor the acceptance and understanding of those structures by neighborhood residents, and to develop new green infrastructure design concepts tailored specifically for use in Detroit.
The grant will also allow the team to distill green infrastructure knowledge from all disciplines into advice for decision makers.
"This new grant will enable us to make essential measurements of green infrastructure social and environmental performance over time and use what we learn to offer design and planning innovations that will contribute to improving the quality of life for neighborhoods in Detroit and other cities," Nassauer said.
The new Erb grant will also fund a study of Detroit River hydrology and water quality.
The bioretention gardens were designed in Nassauer's U-M lab and were built on properties owned by the Detroit Land Bank Authority and managed by the Detroit Water and Sewerage Department. DWSD's green infrastructure program consultant, Tetra Tech, led the technical design and implementation of the gardens. Tooles Contracting Group led the construction.
"I do think these projects have the ability to inspire hope," Mobley said. "And they reinforce a message to residents: We haven't forgotten about you. You're important. You matter."
The pilot research project was led by Nassauer and by Natalie Sampson of the Department of Health and Human Services at U-M Dearborn. Additional collaborators include U-M faculty members Amy Schulz of the School of Public Health, Margaret Dewar of the A. Alfred Taubman College of Architecture and Urban Planning, Alicia Alvarez of the Law School, Noah Webster of the Institute for Social Research, and Allen Burton and Catherine Riseng of the School of Natural Resources and Environment. Shawn McElmurry of the Department of Civil and Environmental Engineering at Wayne State University also participated.