https://planetdetroit.org/2022/03/experts-weigh-in-on-how-to-fix-and-pay-for-detroits-flooding-problems/

CLIMATE GREAT LAKES INFRASTRUCTURE STORIES WATER

Experts weigh in on how to fix and pay for Detroit’s flooding problems

March 19, 2022 7min read

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Experts weigh in on how to fix and pay for Detroit’s flooding problems

 The Great Lakes Water Authority has said it could take anywhere $5 billion to $20 billion to upgrade the regional stormwater system enough to reduce basement flooding.


In 1972, Milwaukee had the good fortune to be sued by the state of Illinois. At the time, Milwaukee and several nearby cities were sending an estimated 200 million gallons annually of combined sewer overflow (CSO) – a mix of untreated or partially treated sewage and stormwater – into Lake Michigan during heavy rains.

The fortunate part was that the lawsuit came at a time when abundant federal funds were available to pay for water infrastructure. And so 55 percent of Milwaukee’s so-called “Deep Tunnel” – a series of underground retention basins that hold untreated sewage and keep it from flowing into the lake – was covered by the federal government. The project was rolled out in three phases, starting in 1993; it’s been referred to as the “backbone” of the city’s now widely-praised sewer system. The deep tunnel can sequester 520 million gallons of water, enough to fill up the U.S. Capitol Rotunda 53 times.

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Milwaukee continues to deal with heavy rainstorms and flooding, similar to other Great Lakes cities where the climate crisis is increasing the intensity and volume of rainfall. But the tunnel made a substantial difference. 

“It brought us down from having 50 to 60 [sewage] overflows a year to two or three,” Breanne Plier, manager of sustainability at the Milwaukee Metropolitan Sewerage District (MMSD) told Planet Detroit. 

Milwaukee plans to reinforce its stormwater capacity by adding 740 million additional gallons worth of storage in the form of green stormwater infrastructure (GSI) – including tree planting and bioretention swales or vegetated depressions that catch rainwater and slowly release it back into the groundwater or storm sewers–as part of its “2035 Vision.”

Milwaukee’s experience could offer a roadmap for Detroit, according to Sanjiv K. Sinha, a senior vice president at the consulting firm Environmental Consulting & Technology. “By rolling together green infrastructure and traditional stormwater infrastructure quickly, [Detroit] could tap into economies of scale that reduce the overall cost [of infrastructure projects],” Sinha told Planet Detroit.  

Detroit suffered its second “500-year flood” in a decade on June 26, 2021 when parts of the metro area received more than six inches of rain in a single night, backing up sewers and sending water and sewage into thousands of basements. Although it’s impossible to know how many gallons of water backed up from overloaded sewer systems and streets into homes, roughly 10 billion gallons of sewage flowed into local waterways following the storm.

Like Milwaukee, Metro Detroit has already spent a lot of money to address its CSO problem. A study commissioned by the Erb Family Foundation found that the region invested more than $2 billion to build nine CSO facilities that collectively treat 97% of wet weather events. The number of uncontrolled CSOs in the region has declined from 310 to 76 annually since 1988.

But with an accelerating climate crisis bringing more intense storms and flooding to eastern and midwestern cities, the region will need to act quickly to mitigate future disasters. A flooded basement can cost a homeowner tens of thousands of dollars, and at least 80,000 households called the city’s flood complaint center last June.

Billions of gallons, billions of dollars

Staving off further economic damage from flooding could require adding millions, if not billions, of gallons of additional capacity to the Great Lakes Water Authority (GLWA)’s regional system.  “You’ve got to match the spatial scale of the solution to the spatial scale of the problem,” said Bill Shuster, a professor and chair of civil and environmental engineering at Wayne State University.

Shuster notes that over the last few decades the regional sewer system has expanded its service area without adding sufficient capacity, while rising levels in the Great Lakes and broken pipes stressed existing infrastructure.  

GLWA, which oversees much of the region’s sewer and water treatment infrastructure including the troubled Conner Creek Pump Station and Freud pumping stations whose partial failure contributed to the June flooding, has said it could take anywhere $5 billion to $20 billion to upgrade the regional stormwater system enough to reduce basement flooding. A GLWA statement emailed to Planet Detroit said the agency plans to invest $3.4 billion in water and wastewater improvements over the next ten years, which includes rebuilding the Conner Creek Pump Station and replacing the Freud station. 

City solutions

Detroit Mayor Mike Duggan has proposed expanding sewer capacity on the far east and west sides of the city to avoid basement flooding by sending combined sewage directly into the Detroit River during major storms as opposed to the city’s sewer system. But that would come at the expense of surface water quality and potentially drinking water quality.

And DWSD Director Gary Brown suggested separating sanitary and storm sewers, which could cost around $2.2 billion.

But while sewer separation might reduce sewage backups in basements, Shuster said there’s no guarantee it would totally prevent them unless significant capacity to the overall system is added. Another problem is “rainfall-derived inflow and infiltration,” a term that refers to stormwater moving into aging, leaky pipes and creating backups.

As a short-term fix, the city is investing in backflow valves to prevent basement backups. The department is piloting a cost-sharing program in affected neighborhoods that will pay homeowners $6,000 per household to install the devices.

Jefferson Chalmers resident Blake Grannum is considering installing the valve after experiencing multiple floods in the past decade. On June 26, she once again had several feet of water in her basement, the largest among several backups she experienced last summer.

“We’re constantly cleaning,” Grannum said. “Every single time you flood, you have to spend money, not just replacing the things that you’ve lost, but having to get it cleaned so that you can at least breathe properly.”

https://planetdetroit.org/2022/03/experts-weigh-in-on-how-to-fix-and-pay-for-detroits-flooding-problems/