Blue Earth County to remove Rapidan Dam

The dam west of Mankato that failed during major flooding in June will be removed, ending a years-long local debate over what to do with the aging infrastructure.

The Blue Earth County Board voted Tuesday to remove the dam, rather than fix or replace it.

Commissioners argued against replacing the dam, saying it would cost far more to keep it than remove it altogether. Getting rid of the dam also frees up recreational opportunities along the Blue Earth River.

“Mother Nature came out and showed us we have to push this thing along,” Commissioner Vance Stuehrenberg said.

The county has for years discussed what to do with a dam after a 2019 flood badly damaged the facility. Blue Earth County officials have since assessed whether it was worth repairing enough so that it could generate electricity again.

A 2021 study estimated repairs at $15 million and removal at $82 million, but county officials said Tuesday that fixing the dam and the river channel back to pre-disaster levels would cost far more than removing it. Another massive flood would likely damage the dam once more, engineers told the board.

Major storms rolled through the area in June, causing the dam to partially fail when the west bank of the river flooded over, demolishing a nearby house and destroying a longtime local business.

Engineers stabilized one of the dam’s supports after the floods but the dam was damaged, as was a nearby bridge on County Road 9. The board voted Tuesday to replace the bridge.

Both projects are intertwined as the Blue Earth River’s flow could further erode the bridge’s support, making it likely the bridge would fall. Though the bridge only sees about 600 cars a day, area farmers and truckers use it to transport goods to market.

“We know that doing nothing is too high of a safety and economic risk,” board chair Kevin Paap said.

County Engineer Ryan Thilges said federal aid could be used to help remove and replace the bridge and dam, though further steps and studies will have to happen. It’s too early to tell when those projects will take place, according to officials.

The Rapidan Dam was built in 1910. The facility was operated back then by the Northern States Power Co., according to the Blue Earth County Historical Society, and was constructed using a novel method at the time. Builders used hollow reinforced concrete to increase the structure’s durability.

It used to generate electricity but was damaged by massive flooding in 1965. The county took over the dam in 1970 and later restarted electricity operations in 1984.

Blue Earth County officials made emergency repairs in 2010, as well as further fixes in 2010 and 2017. But a series of floods and ice damage in 2019 and 2020 forced the county to take the dam offline.

Commissioners told staff last year to surrender the dam’s operational license, but that process was paused after the disaster damage in June.