Minnesota's Rapidan Dam at risk of 'failure' amid severe flooding

As southern Minnesota battles an onslaught of rain and severe flooding, the fate of the Rapidan Dam hangs in the balance, with officials saying the dam is in "imminent failure condition."

The Rapidan Dam, built in 1910, is located on the Blue Earth River, which begins in Iowa and runs outside Mankato, Minnesota, about 85 miles southwest of Minneapolis.

The Blue Earth County Sheriff's Office reported the dam was in precarious standing amid the overflow of the river, which has caused "erosion and slope-cutting" to the dam as well as a buildup of debris in the area.

The sheriff's office reported a "partial failure" of the dam on the west abutment on Monday.

"We do not know if it will totally fail or if it will remain in place, however, we determined it was necessary to issue this notification to advise downstream residents and the correct regulatory agencies and other local agencies," the office wrote in an alert on Facebook Monday.

"Public Works, Emergency Management and Sheriffs Offices are implementing steps outlined in the Rapidan Dam Emergency Action Plan for Imminent Failure of the Dam including notification of potentially affected residents, impacted regulatory agencies and other local agencies," the office said.

On Monday, river levels peaked at 34,800 cubic feet per second and have lowered to 33,000 cubic feet per second as of Tuesday while officials continue assessment and evaluation of the dam.

An Xcel Energy substation, which supplies power to 600 customers, was swept downriver during the overflow Monday, according to the company.

"Our teams have been working diligently since floodwaters knocked out the Rapidan substation this morning to bring power back to homes and businesses in the area — more than 170 Xcel Energy employees arrived at the scene to assist," Ryan Long, president of Xcel Energy–Minnesota, said in a press release Monday.

"We know people depend on electricity, especially during warm days and severe weather," Long said, adding, "We urge residents to stay safe as our crews work by avoiding any damaged electrical equipment and following all flooding precautions."

In April 2023, the National Inventory of Dams gave Rapidan Dam a "poor condition" rating with the hazard potential classification as "significant."

Minnesota has faced over 18 inches of rain over the last few weeks, affecting 40 counties, Minnesota Gov. Tim Walz said during a press conference Monday, warning forecasts for more rain could lead to further damage.

"We're making sure, first and foremost, people are safe, protecting property and protecting public infrastructure," Walz said.

Walz signaled he would request a presidential disaster declaration if the damage in the state reached the federal threshold.

Blue Earth County Road 9 bridge that crosses the river remains closed to traffic for public safety, according to the Blue Earth County Sheriff's Office update on Tuesday.

At this time, the department has not issued any mass evacuation plans.