Detroit going green to help slow flooding during heavy rains

National

A retention pond at a stormwater park near the new Stellantis Detroit Assembly Complex on the city’s eastside is shown June 30, 2021. The park is a greenspace reconfigured to filter rainwater runoff before it flows into sewer systems. (AP Photo/Corey Williams)

DETROIT (AP) — Massive amounts of green are being spent to find “green” ways to prevent basements, yards, streets and freeways in Detroit from flooding during heavy storms like one last month.

Of $100 million pumped each year into infrastructure upgrades for the city’s aging water and sewer systems, $10 million goes toward installing detention ponds, bioswales, rain gardens and permeable pavement. Called green stormwater infrastructure, the features hold and slowly release rainfall into sewers, lessening flooding that has plagued Detroit and other older cities for decades.

“It’s not the end-all-be-all, but it is a type of intervention that reduces wet weather flows into the system or delays them,” cautioned Palencia Mobley, deputy director and chief engineer for Detroit’s Water and Sewerage Department.

City officials say 6 inches (15 centimeters) of rain that poured down in the area June 25-26 was the most at one time in 80 years. Like a funnel beneath a swiftly flowing faucet, the volume of water moved faster than it could be pumped out or pushed through sewers to water treatment plants.

Water pooled in streets and yards as debris clogged sewer grates. Untreated water pushed up through basement drains. Motorists were stranded on freeways. New vehicles in one auto plant lot were nearly submerged.

Democratic Gov. Gretchen Whitmer soon would declare a state of emergency for the city and surrounding Wayne County.

Near William M. Davis’ home in a west side neighborhood where Detroit’s water department recently installed sloping bioretention gardens in boulevard medians water rose in the basements. But Davis believes the $8.6 million project that was designed to manage more than 37 million gallons (140 million liters) of stormwater each year helped lessen the flooding. Rain and snowmelt seep through the soil into box-shaped chambers that store the flow before releasing it into the sewer system.

“We still have problems … but it’s going in the right direction,” Davis said.

Herbert Hollis saw water rise high enough to reach the pilot on the water heater in his basement. Hollis, 73, said the area always has had flooding, but this time “the water did go down” more quickly.

At the new Stellantis Detroit Assembly Complex on the city’s east side, underground storage and adjacent stormwater parks helped alleviate the flow of around 12 million gallons (45.4 million liters) of water, according to the automaker. But a retention pond at another part of the complex was not able to release water due to the loss of power at a nearby city pumping station. Flooding to a shipping yard damaged 25 vehicles.

Green infrastructure typically is more cost-effective when designed to manage smaller, more common storm events, said Anika Goss-Foster, CEO of Detroit Future City, which provides education programs and technical assistance on green infrastructure practices.

“In Detroit, we have suffered two so-called 500-year storm events in the span of seven years,” she said. “And this latest flood in June demonstrated again the critical need to invest in our aging stormwater management systems to address serious flooding issues that are unfortunately becoming more and more common and will disproportionately impact low-income people who do not have the resources to recover from repeated flooding events.”

Other cities with green infrastructure include New Orleans, which used $141 million in federal funds for the GentillyResilience District. It features a water garden designed and a network of vacant lots, streets and alleys that also capture stormwater.

To help combat flooding in Atlanta’s historic Fourth Ward, city leaders decided against using more pipe and concrete and instead built a detention pond, water wall, splashpad and skatepark. The $23-million Historic Fourth Ward Park also kickstarted the city’s 22-mile (35-kilometer) Beltline Greenway, which has spurred economic development.

“It was going to be a big dumb gray tank,” Mobley said. “They turned it into a stormwater park. You don’t know that that’s what it’s doing. They have beautiful flowing walkways and something that looks like a waterfall. But it’s functional infrastructure in the midst of a neighborhood.”

A savannah-like look with wildflowers, other plants and grass walking paths is envisioned for a park in one west side Detroit neighborhood prone to seasonal flooding.

The program attached to Rouge Park is expected to cost about $30 million over five years and manage 95 million gallons (360 million liters) of stormwater each year. Initial plans had a large tunnel being erected along the nearby Rouge River to handle untreated sewage discharges, but that would have been costly, Mobley said.

“We were given the opportunity (by the state) to try to use stormwater management to reduce combined sewer overflows,” she said.

Copyright 2021 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

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