MANKATO — When a dam breaks, it takes more than bulldozers and blueprints to repair the waterway. It demands engineering inventiveness, bureaucratic patience and millions of dollars.
The Blue Earth County Board of Commissioners on Tuesday was presented with the comprehensive removal plan of the Rapidan Dam and restoration of the Blue Earth River channel, following a request for an analysis and cost estimate on Aug. 27, 2024. The report from Barr Engineering included high-level preliminary estimates to complete those actions.
Barr presented findings from extensive investigations, including geotechnical studies, hydraulic modeling and environmental assessments. The project centers on removing the damaged dam and replacing the adjacent bridge, with total estimated costs approaching $90 million, the $1.47 million planning and design of the Rapidan Dam’s removal found.
Civil engineer Jim Herbert said key project components include complete dam removal, channel stabilization and west bank restoration. The current plan involves constructing a new bridge before dam removal, a sequence necessitated by funding timelines and federal regulatory requirements.
Investigations revealed challenging site conditions, with bedrock located 30 to 45 feet underground and characterized as “highly erodible.” Engineer Tom MacDonald told the board that hydraulic modeling demonstrated extreme water velocities in the current configuration, with 100-year flood events potentially generating water speeds up to 30 feet per second through the dam breach area. These conditions necessitate substantial rock armoring, estimated to cost about $30 million.
The project faces multiple regulatory challenges, primarily from federal agencies such as the Federal Energy Regulatory Commission and the Federal Emergency Management Agency. Despite the dam’s current non-operational status, these agencies continue to require comprehensive reviews and approvals.
The county received a $5 million federal grant from the Federal Highway Administration’s Emergency Relief Program to assess and repair flood-damaged roads and bridges, which also requires a certain amount of federal oversight. County officials expressed frustration with the prolonged regulatory process.
“At some point, do we say we don’t care about the federal funding anymore? What do we need to do to get this thing done on our own? We have to do all kinds of extra work to make it stronger, because it’s there. What’s that number compared to what is waiting for our funding, funding that we don’t know if we’re ever going to get. We can’t afford to do this on our own,” County Board Chairman Kip Bruender said. “And we can’t put that on the taxpayers in the county.”
Herbert emphasized the necessity of comprehensive review to ensure public safety and environmental protection.
“When we met with the county and agencies, they all recognized this as a unique situation, and their playbook doesn’t really address the way this happened. So they all said, we’ll work with you any way we can. But they also are held by their own playbook and the guidelines, so nobody is allowed to stray outside their mechanism of payment of approvals,” he said. “That’s what we’ve seen as kind of the biggest hurdle about this.”
Engineers also have explored alternative — and cheaper — approaches, including partial dam removal, bridge relocation and different channel configurations.
Coordination with multiple agencies remains complex, involving bi-weekly meetings and extensive documentation. County Engineer Ryan Thilges said there have been talks with the Minnesota Department of Transportation about the possibility of applying for an extension on the timeline of funding distribution.
“There is risk in the interim condition between the bridge being constructed and the dam removal and channel stabilization being completed. And again, the reason that we’re in the position of having to do the bridge ahead of the dam removal is because of the funding timeline for the bridge construction,” Thilges said. “Again, due to the uncertainty associated with all the federal agencies we have to coordinate with for dam removal, we’re not certain that we would fall within a desired timeline to extend those funds. So we want to make sure we don’t lose the opportunity to use those funds.”
The project’s next steps include obtaining an environmental assessment worksheet, conducting a third-party technical review and continuing negotiations with federal and state agencies. A public information meeting will be scheduled for later this summer. Demolition is scheduled to begin in mid-2027 and conclude by the end of 2028.