Rapidan Dam failure: County makes decision on future of dam

RAPIDAN TOWNSHIP, Minn. (FOX 9) - A county board has voted on the future of the Rapidan Dam in southern Minnesota after a partial failure of the dam back in June.

What do we know?

The Blue Earth County Board of Commissioners voted Tuesday to remove the Rapidan Dam and replace the County Road 9 bridge. The decision follows multiple assessments of both structures.

The board's resolution directs staff to secure funding from federal and state sources for the bridge replacement and to collaborate with FEMA on the dam removal. The county is also looking to work with the U.S. Army Corps of Engineers to restore the Blue Earth River channel.

Background

On June 24, amid high water levels from heavy rains and accumulating debris, the dam suffered a side breach, destroying an Xcel Energy substation.

Over the ensuing days, water rushing around the side of the dam ate away at the west side of the river bank. Ultimately, a home along the bank fell into the river and the nearby Dam Store was demolished.

The erosion also continued to cut into the bank closer to the County Road 9 bridge, which is just south of the dam.

Dam history

The Rapidan Dam, constructed in 1910, at one time supplied half of Mankato's energy.

By 2024, the dam was well past its lifespan. Civil engineers say concrete can last 50 to 100 years in dams, but maintenance is key. High water events in 1965, 2010, 2019, and 2020 did significant damage and Blue Earth County started considering removing the dam as far back as the year 2000.

Federal inspectors deemed it to be in poor condition two years ago. The county board had been weighing its options for the dam in recent years.