TRAVERSE CITY — Fixing an aging wall along the Boardman River in Traverse City isn’t likely to happen soon.
Bob Doyle, a principal and landscape architect for SmithGroup, said water has undercut the wall and soil behind it. That poses a potential risk to a major sanitary sewer main built on the wall’s foundation.
But it’ll take time to come up with the funding — previous estimates put the cost for SmithGroup’s recommended fix at $2.4 million. City Manager Marty Colburn said he and Art Krueger, the city Department of Municipal Utilities director, are looking for funding sources.
It also could take some time to hear from the public about just how to fix the wall along the two downtown blocks where it needs it.
Commissioner Brian McGillivary pointed out that a Downtown Development Authority-led committee is working on a unified plan for the Boardman River, from the Union Street Dam to the river mouth, with a draft expected soon.
McGillivary argued that settling on a fix would short-circuit that process, especially one that would create as much of a change as what SmithGroup suggests — he acknowledged the input process for the project may have to move quickly.
Doyle agreed, having previously told McGillivary the need to fix the wall is serious but not overly urgent.
“I think it’s prudent to move forward with looking at how this may be fixed and how it might be funded,” Doyle said. “Do we think that it needs to be fixed tomorrow? No. Do we think it needs to be fixed in the short term? Yes.”
A monitoring program that would use devices to track any shifting of the wall would give the city some assurance, Doyle said — that would also include watching for any new sinkholes, but some have formed under pavement, making detection difficult.
High Lake Michigan water levels are partly to blame for washing out the dirt below the river wall, which dates back to the 1930s, documents show. It’s made of numerous vertical concrete slabs sitting at the edge of a flat concrete base that’s held up by wooden pilings driven dozens of feet underground.
Water has washed away the dirt under and behind the base, causing sinkholes to open along the alley, as previously reported.
Adding urgency to any fix is the fact that, also resting atop the base is a major sewer main. Any shift of the base could cause a catastrophic failure of the sewer main and pollute the river.
SmithGroup proposes removing the wall between Union and Cass streets and rerouting the sewer line for a stretch of that same block, documents show. In its place a slope would be built with riprap along the water’s edge. The old wall footing potentially could be left to serve as fish habitat.
For the block between Cass and Park streets, contractors would drive sheet piling into the river right in front of the wall footing and pour concrete into the space below the footing and behind the new sheet wall.
Doyle said that’s the best bet to stop any future erosion, and modeling shows it would only increase flood elevations a little, and only within the project site.
That same fix for both blocks would increase flood elevations upstream, requiring every property owner between the Union Street Dam and the project site to agree to the change through a Federal Emergency Management Administration process, Doyle said.
It’s quite a hurdle, Doyle said. And it would complicate one alternative Commissioner Tim Werner suggested. He wanted to leave the wall and sewer main in place on both blocks, using the sheet piling-and-concrete fix for both as well while lowering the top of the wall between Union and Cass streets.
Werner also suggested separating the wall repair and sewer main relocation projects, at least along the Union-to-Cass stretch. That would let the city move forward and revisit whatever riverside changes are necessary later.
Colburn told Mayor Jim Carruthers he’ll work on a timeline for what needs to be done next, including coordinating with the Lower Boardman River Leadership Team.
Doyle suggested a two-track approach where the city moves forward in looking for funding.
“While that process is underway, we can begin to engage the public this summer about the entire unified plan, and then specifically, about this particular area,” he said.