Fixing a vulnerable section of retaining wall along the Boardman River between Park and Union Streets in downtown Traverse City could cost north of $2.4 million, with the city facing the risk of a catastrophic sewer failure if it doesn’t address the problem. The proposed fix could reshape the Front Street alley – notably removing alley parking in the 100 block – but also offer opportunities to soften the waterfront, create more wildlife habitat, and improve direct public access to the river.

Consulting firm SmithGroup gave a presentation to Traverse City Downtown Development Authority (DDA) board members Friday and will appear before city commissioners Monday to share recommended solutions for fixing the retaining wall in the 100 and 200 alley blocks of Front Street. Bob Doyle of SmithGroup said that in the last decade, as water levels have risen, the soil underneath the wall has been “scoured out,” creating a three-foot gap between the bottom of the wall and the bottom of the Boardman River. The scouring is now extending beyond the wall footing, leaking in soil from behind and leading to “pavement failure, sidewalk failure, (and) disappearing signs” in the alleys.

Of greater concern is a large 24-inch sanitary sewer main that sits directly on the top of the river wall foundation and is a “key sewer within the City of Traverse City” that also serves portions of nearby townships, Doyle said. Some 30 sewer lines connect to the main from Front Street businesses – connections that are nearly a century old in the 100 block – that are “also settling and cracking and failing” as the soil settles around the wall, Doyle said. That movement is allowing sewage to get into the Boardman and groundwater to infiltrate the sewer main. When big storm events hit, “the sewer is already full of groundwater” and failures can occur like those seen downtown in 2020, Doyle said.

According to City Director of Municipal Utilities Art Krueger, the sewer main is at risk and must either be protected or relocated. “If the wall footing were to tip or move due to the lack of supporting soil beneath, it would likely cause a catastrophic failure of the sewer main allowing raw sewage to discharge directly into the Boardman River,” he wrote in a memo to city commissioners.

SmithGroup modeled a number of potential solutions and weighed options against factors like cost, further hardening of the riverfront (something the DDA wants to avoid), impact on downtown businesses, and flooding risks. The consulting firm ultimately landed on two different proposed fixes for the 100 and 200 blocks. In the 100 block, the company recommends removing the retaining wall entirely and rerouting the sewer main further south under the alley. The project would require eliminating parking spaces on the north side of the alley in the 100 block.

While businesses would lose some parking, Doyle said there would also be benefits to owners in removing the wall and relocating the sewer main, including the city replacing the aging sanitary leads coming from the businesses. The firm is also recommending installing a sloping green lawn down to the river complete with native vegetation and stepping stones, and leaving the lower wall piling in place within the river to provide fish habitat. The “softer” waterfront would provide direct public access down to the Boardman for fishing and other recreational uses – instead of being blocked off by a hard vertical wall – and offer riverbank habitat for wildlife.

Doyle noted that the public has identified softer, more accessible waterfront as a priority during input sessions for the Lower Boardman River Unified Plan. “There's also I think a longer-term interest in making sure the river makes an inviting place for pedestrians so that the area behind the buildings is shared by vehicles and pedestrians, which could increase traffic along there,” he said. “Hopefully we would bring the level of traffic and shopping up.” Downtown leaders have also had discussions about eventually building a river walk promenade that could serve as a placemaking project in the same alleys affected by the retaining wall.

Doyle said there was “no room to do a softer solution” in the narrower 200 alley block, so SmithGroup is instead recommending driving a sheet pile into the earth on the river side of the retaining wall. Concrete would be pumped between the sheet pile and wall and fill under the footer, completely filling the gap. The sheet pile would protect the wall from further scouring; rip rap could also be placed into the river to provide fish habitat. The sanitary leads in the 200 block were replaced roughly a decade ago, so those lines are in good condition, according to SmithGroup.

Consultants pegged the project at a rough “ballpark” cost of $2.4 million, noting that the estimate only includes the basic infrastructure repairs and not additional amenities like the green space in the 100 block, lighting, stepping stones, and boardwalks. Those add-ons could drive the final price tag significantly higher, as could engineering once detailed plans are created. Mayor Jim Carruthers pointed out that city waterfront projects often “end up being a lot more than we planned,” saying the project “could double in price, easy.”

How exactly the repairs will be funded – and who will foot the bill – still remains to be seen. City staff have already applied for one grant for the project and will likely pursue others. DDA Board Chair Gabe Schneider said the repairs are likely to resurrect old philosophical debates about what role the DDA should play in funding downtown infrastructure projects – typically through tax increment financing (TIF) funds – versus the city bearing those costs. Schneider said he believed the DDA should contribute more to amenities like lighting, stepping stones, and boardwalks that beautify downtown projects, rather than fund the underlying infrastructure. “I do think that will be part of our conversation going forward,” he said. The DDA and city split the costs for the $65,870 contract to hire SmithGroup to analyze the retaining wall, with the DDA solely paying another $13,320 for the hydraulic modeling of solutions.

DDA CEO Jean Derenzy reiterated that downtown “infrastructure is owned and controlled by the City of Traverse City” and that city commissioners will have final say over funding, engineering, permitting, and construction plans. When it comes to determining next steps to address the retaining wall, “that’s going to be up for discussion with the city,” Derenzy said.