The closed Blue Earth County Road 9 bridge next to the flood-damaged Rapidan Dam is unsafe to reopen and the county will pursue federal funding to remove it and build a new one.
That means it will likely be a few years before a new bridge is in place.
Meanwhile, at least some county commissioners appear to be in favor of removing the dam on the Blue Earth River, pursuing federal and state funds to help pay for removal and river restoration work.
“It’s tremendously complex,” Karl Jensen of the U.S. Army Corps of Engineers, said of working through the federal and state agencies and making decisions on the dam and bridge. Corps officials as well as those from the Minnesota Department of Transportation met with commissioners at a work session Tuesday.
The 114-year-old dam south of Mankato was damaged as floodwaters last month carved around the west end, eroding land and causing a home to wash into the river and leading to the demolition of the landmark Dam Store.
County Engineer Ryan Thilges told the board they have four options on the dam: repair the current dam and fill the large void left by the new river channel, build a new dam, leave the dam in place as it is while improving the eroded riverbank or remove the dam.
He said the board will need to make a decision about the dam because that would affect the design of the new bridge.
Commissioners had no enthusiasm for repairing the dam or building a new one.
“We’re down to remove or leave the dam,” Board Chair Kevin Paap said.
A Minnesota Department of Natural Resources representative said leaving the old dam in place means it would continue to act as a weir, funneling water to the west and eroding the bank further.
Commissioner Vance Stuehrenberg said that if the county leaves the current dam up it faces liability issues if people go onto it.
“Removing it seems the only option,” he said.
Jensen said that if the county wants to, the Army Corps could begin a study of the dam and river with an eye toward restoring the river’s ecosystem, which means allowing fish and other aquatic life to be able to travel up and down the river.
That could be done with the dam removed, or if it stays in place there could be options for utilizing the new channel around the dam for fish to swim through. But the water now coming around the dam is at a relatively high speed, which probably keeps most fish from being able to go upstream.
But such a feasibility study usually takes about three years. Then, if they were to undertake a project, the corps would have to get authorization and funding from Congress.
The county is also likely to seek funding from the Federal Emergency Management Agency for removing the dam. Federal funding would cover 75%, with 25% coming from local/state funding.
Federal bridge funding likely
The highway bridge just upriver of the dam was built in the early 1980s. The piers of the bridge are on bedrock, but the bedrock is sandstone, which can erode fairly easily under strong water flows.
A thick layer of sediment behind the dam had held the piers in place and prevented water from churning at the base of the piers. But much of that sediment washed down the river when the new channel was created.
Thilges said inspections of the bridge show it cannot be safely reopened to traffic. He said trying to repair and rebuild the piers with the bridge standing wouldn’t be feasible.
He said an early estimate for the cost of a new bridge is more than $18 million.
Kristine Elwood, of MnDOT, said the county is eligible for federal Highway Administration emergency funding to remove and replace the bridge. She said the feds would cover 80% with the state likely to cover the other 20%. There’s also a chance the federal agency would cover all the costs.
She said if the county wanted to add a wider bridge with a bike lane, the county would have to cover that added cost.
Elwood said the county has two years from the time of the flooding to get all federal authorizations and the funding. She said the board needs to begin making decisions and keep the process on schedule.
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