The Rapidan Dam in Minnesota has become vulnerable after recent flooding on the Blue Earth River, prompting officials to warn Monday that the dam is on “imminent risk of collapse.”
The Blue Earth County Sheriff's Office said the river had breached the dam's banks and debris was accumulating in the water. It declared a “condition of imminent failure” and notified people who might be affected.
“We do not know if it will fail completely or if it will remain in place, however we have determined that this notification is necessary to notify downstream residents and the correct regulatory agencies and other local agencies,” the sheriff's office said.
The dam is located outside the city of Mankato, about 85 miles southwest of Minneapolis.
By Monday afternoon, the sheriff's office reported a “partial breach” of the levee on the west levee.
“The dam is still intact and no mass evacuations are planned,” the sheriff said on Facebook. “Part of the river flow has been diverted to the western side of the dam and water continues to flow.”
The Xcel Energy substation at the dam, which supplies power to about 600 customers, was swept away Monday morning. The utility company said its crews were working to replace the destroyed substation and restore power.
“The river was already high and moving rapidly due to recent heavy rainfall when it turned around the dam near the substation and began flowing over the bank,” the company said in a statement.
Minnesota Gov. Tim Waltz said at a news conference Monday morning that the state has received about 18 inches of rain over the past couple of weeks, leaving the ground completely soaked and the water with nowhere to go. He said more rain is likely on the way.
“With that in mind, the resources that are being deployed are strategically placed there,” Waltz said. “We're first and foremost making sure people are safe, property is protected and public infrastructure is protected.”
Waltz said flooding has so far affected about 40 counties, some of which have declared a state of emergency. The governor said he would request a disaster declaration from the president if damage assessments reach a level that requires federal assistance.
The Rapidan Dam was built in 1910 as an energy source and is managed by the county. According to the county's website, frequent flooding for more than a century has caused significant damage to the structure.
A 2021 assessment concluded the dam must be repaired or replaced, both of which would be costly. However, the county says on its website that doing nothing would “create public safety concerns and result in significant liability.”
Repairing the dam will take four years, three of which will be in the planning and design phase. But the county says it will take 10 years to build a completely new dam, which includes removing the dam and rerouting the river.
The county said it is seeking feedback from the community to determine what steps to take next.
Last year, Blue Earth County said it began the process to release its license waiver under the Federal Energy Regulatory Commission because damage has hindered the dam's ability to provide hydropower. The approval would put the dam under the control of the Minnesota Department of Natural Resources.
“No changes to the dam’s structure are proposed at this time,” the country said in an informational release. “Withdrawal of the waiver simply means that FERC will no longer have regulatory authority over the dam.”