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

What do we know?

The Blue Earth County Board of Commissioners voted Tuesday to demolish the Rapidan Dam and replace the County Road 9 bridge, following multiple assessments of both structures.

The board’s resolution directs staff to obtain funds from federal and state sources for the bridge replacement and to work with FEMA to demolish the dam. The county also wants to work with the U.S. Army Corps of Engineers to restore the Blue Earth River channel.

background

On June 24, high water levels from heavy rains and debris accumulation caused the dam to breach laterally, destroying an Xcel Energy substation.

In the days that followed, the waters eroded the western side of the river bank along the dam. Eventually, a house on the bank collapsed into the river and the nearby Dam Store was destroyed.

Erosion also continued to cut into the bank near the County Road 9 bridge, which lies directly south of the dam.

Dam history

The Rapidan Dam, built in 1910, once provided half of Mankato’s energy.

By 2024, the dam had significantly exceeded its design life. Structural engineers say concrete in dams can last 50 to 100 years, but maintenance is critical. Flood events in 1965, 2010, 2019 and 2020 caused significant damage, and Blue Earth County considered demolishing the dam as early as 2000.

Federal inspectors concluded two years ago that the dam was in poor condition. The county council had been weighing its options for the dam in recent years.