Ann Arbor investigates failure of stormwater system at West Park; residents concerned about floods

Daniel Marano, who lives on Maple Ridge just west of the park, appeared before the Ann Arbor City Council this past week and expressed concerns about what he described as "a severe flooding problem" he believes is linked to failure of the park's stormwater system.

The park was closed from March to October 2010 so stormwater and recreational improvements could be completed.

"Almost a year to the day, we have had two major floods that have destroyed property," Marano said. "I have a bill here for several thousand dollars for a car. There are neighbors of mine who are out of town this week who have sustained serious property damage. And there's the real possibility of danger to human beings, neighborhood pets and small children."

Marano said he awoke one morning earlier this month after heavy rains to find about a foot of water in his car, while other neighbors found about a foot of water in their basements.

"You can see lines — a foot, 18 inches — on garages for a few of the homes next to me, all clearly a result of flooding that has never happened there before," he said. "And it seems impossible to somehow not be linked to the construction or the failures going on in West Park."

Marano said residents have suffered from "these monsoon rains where several feet of water appears out of nowhere and lasts for about an hour or so." He said that's followed by "a catastrophic emptying of the entire street" where the storm drains open up and, "like two giant toilet bowls or bathtub drains," the street drains in a matter of minutes.

"The first time this happened was last Aug. 10, 2010. When we reported it to the city, we were met with derision," Marano said. "One neighbor in particular who reported it was told, 'Well, it's raining heavily outside.' We were aware of that then and we're aware of it this week. This is a lot more than just standard, extreme runoff and backing up of sewers."

Mayor John Hieftje and other members of the City Council say Marano and other residents who have complained raise legitimate concerns.

Hieftje said the city is looking into the problems right now, but he called it "a complicated engineering issue" and said it's going to take time to resolve.

Council Members Mike Anglin and Carsten Hohnke, who represent the 5th Ward, said they're hopeful the city can provide residents with more answers soon.

"It's very stressful for the people who live up in there, as it would be for any of us, so I hope that we can continue to make sure this moves as quickly as possible," Anglin said.

Sue McCormick, the city's public services administrator, offered an update on the status of the West Park problems in an Aug. 5 memo to interim City Administrator Tom Crawford.

In addition to other park improvements, construction was performed on the Allen Creek Drain within West Park last year with the goal of improving stormwater quality in the drain. McCormick said the work was partially paid for with federal stimulus funding.

The plans were designed by Beckett & Raeder Inc. and included the installation of eight swirl concentrator units to remove suspended solids from stormwater prior to reintroducing it into the system — both on the north and south branches of Allen Creek near the park's west side.

The project also included “daylighting” the stormwater runoff from North Seventh Street, allowing it to travel over the surface of the park through a series of wet meadows instead of through the underground pipes. McCormick explained in her memo that was intended to reduce the likelihood of flooding upstream of the park.

But during construction, flooding was experienced upstream of the work area during one of the several large storms experienced last summer, McCormick said.

"In addition, in October of 2010, after the stormwater work had been completed, one of the swirl concentrators on the north branch collapsed, creating a sinkhole near the northwest corner of the park," she said. "Subsequent investigation revealed that the remaining swirl concentrators on the north branch were in various stages of failure as well."

In response, McCormick said weir plates that served to divert flow into the swirl concentrator units were removed due to concerns about their effect on upstream flooding.

She said the swirl concentrators were taken offline prior to the collapse of the swirl concentrator unit in October. Currently, she said, the weirs are still removed, leaving the below-ground sewer system to function essentially as it did prior to the 2010 construction — with the exception of the overland flow aspects of the project.

"The inclusion of the overland flow reduces the amount of flow in the storm sewer pipes, and actually lessens the chance of flooding upstream of the park as compared to conditions prior to construction of project," McCormick said.

The city has engaged the engineering consulting services of Orchard Hiltz & McCliment to analyze the failure of the swirl concentrator units and to also evaluate the original design and propose any necessary changes in order to make sure that properties upstream are not affected by the changes. Based on OHM’s initial analysis, McCormick said it's believed the failure of the swirl concentrator units was caused primarily by a "manufacturing defect."

"In addition, we have also concluded that the weirs in the diversion manholes were designed and installed too high, and that insufficient analysis was performed initially to verify the effects of the weirs," she said, adding OHM is expected to make further recommendations for redesigning or replacing the weirs.

In the meantime, the city's staff is still working with Site Development Inc., the general contractor on the project, to have discussions with AquaShield Inc. and L.F. Manufacturing, which manufactured the swirl concentrator units.

McCormick said it's the city’s intention to recover all costs from the analysis, redesign and replacement of the units, as well as any changes that need to be made to the rest of the system, from the manufacturer, the original design engineering firm and possibly others. She said the city is hoping all necessary repairs will be identified and constructed early in the 2012 construction season, and West Park should be restored to its full public use afterward.

McCormick offered an overview of current contracts relevant to the project:

• Orchard Hiltz & McCliment — $125,000 (expected final cost of evaluation and recommendations report; further design costs to be determined following discussions with the manufacturer of the swirl concentrator units)
• Beckett & Reader, Inc. — $344,870 (preliminary study, design, construction inspection and construction management)
• Site Development Inc. — $1,580,877 (current value of construction contract, including change orders)

In addition to the failure of the stormwater system, Hieftje said he can't help but question whether climate change is at work.

"What used to be a 50-year storm is occurring every five years now it seems," he said. "We just have more intense rain events than we had historically. It all comes down at once."

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