RAPIDAN, Minn. — Authorities say the Rapidan Dam, under intense pressure from days of torrential rain and collected debris, is in “imminent failure condition.”

“There was some debris that got up against the dam, and that caused the water to find a new path around it and cut over to the west over to where The Dam Store is and the residence that’s down there,” said Chief Deputy Paul Barta of the Blue Earth County Sheriff’s Department on Monday. “And it basically eroded away the west side of the dam and created a new path through there. It’s taken a substation for the power plant into the river.”

Heavy rains cause high water levels on the Blue Earth River at the Rapidan Dam near Mankato, Minn., Monday, June 24, 2024. Officials say the dam is threatened with “imminent failure.” (AP Photo/Mark Vancleave)

Barta said authorities have notified residents downstream from the dam about the potential danger. Rapidan is approximately 10 miles southwest of Mankato. The Blue Earth River flows through the dam and meets the Minnesota River near Mankato.

“We’re deeming it as an imminent threat, just because none of us are hydrologists and don’t really know; there’s a lot of variables with this,” Barta said. “It’s pretty significant.”

A Blue Earth County press release said, “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.”

Officials in Mankato, North Mankato and Blue Earth and Nicollet counties say they are monitoring the dam situation closely, but say they are confident the flood-control system will protect the two cities if the dam fails.

The river at Mankato was at about 28 feet Monday and the levee system is built to protect up to 39.5 feet. Officials said that if the entire dam at Rapidan goes out it would add up to a 2-foot surge in the river level, which would still leave more than 9 feet of capacity for the flood wall system.

‘My childhood go down the river’

At The Dam Store Monday morning, Louise Henderson, longtime family friend of siblings and store owner David Hruska and Jenny Barnes, was among those helping clear out what they could from the house located next to the store.

“The house is in grave danger and we’re trying to get everything out,” Henderson said.

The riverbank alongside the store and house was being eaten away rapidly by the powerful flows of water.

Henderson, who lives atop the hill near the dam, said she heard transformers at an electric substation at the dam begin to pop loudly and then heard steel twisting as the substation was swept into the river. That caused power outages in Good Thunder and other areas.

She said support has been strong. “The number of people helping out has been phenomenal.”

Henderson said that when she got to the highway bridge behind the dam early this morning and saw the scene she was hit hard.

“I was watching my childhood go down the river. This is where I grew up. My family has been here for generations.”

Her great-grandfather started the dam store in 1910 to feed those building the dam.

Amy Strand also grew up near the dam and was one of hundreds of people who parked atop the east hill from the dam and walked down to look at the devastation. The county had blocked the highway bridge behind the dam at both ends.

“I’m worried about if the whole dam breaks up and what would happen to the bridges and people downriver,” she said.

No forced evacuations

If the situation were to worsen, Barta said they’d increase efforts to notify residents and businesses downstream. They cannot, however, force anyone to evacuate.

“In the state of Minnesota, law enforcement cannot mandate an evacuation,” he said. “We cannot tell people they are required to leave their private property. People have the individual right to make the assessments if they want to stay or leave. So we make a recommendation, but we can’t force them.”

The debris that gathered near the dam made an already dicey situation even worse, causing the river to backup and reroute itself around the dam, perilously close to the beloved Dam Store.

The jam caused power outages early Monday. Xcel Energy’s outage map showed 579 impacted customers in the Mankato, Lake Crystal and Good Thunder service areas as of 10:30 a.m.

Debris remains packed hard against the dam, but Barta said it would be too dangerous to attempt to remove it.

“Trying to clear some of that stuff out can be just as problematic as trying to let let some of it wash away,” he said. “We’ve been fortunate none of it’s been been breaking up and flowing down river. Trees and things like that haven’t created an issue yet.”

The city of North Mankato has declared a flood emergency, closing the Lookout/Lee Boulevard intersection beginning at 9:30 a.m. to allow crews to build the temporary earth wall levee in this area.

Dam has been center of attention

In recent years the dam has been at the center of intense scrutiny and emotions as to its future.

Blue Earth County, which owns the dam, has been weighing whether to repair the dam, built in 1910, or to remove it.

Many wanted to save the dam because of its historic and social value. But others said removing dams to return rivers to their natural state more environmentally sound. And some argued removing the dam could allow for creation of a man-made white water rapids that would draw tourists.

Both options carried a big price tag. In 2022 the cost of repair was set at $15 million, with a staggering $82 million price tag to remove it. Much of the cost of getting rid of the dam was to properly remove and dispose of the huge amount of sediment that has filled in behind the dam over more than a century.

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