RAPIDAN, Minn. — Authorities feared Monday that an aging hydroelectric dam on the Blue Earth River in southern Minnesota, under immense pressure from days of torrential rain and floating debris, was in “imminent failure condition.”
The Blue Earth River flows north through the Rapidan Dam and meets the Minnesota River downstream near Mankato. Early Monday, the combination of the raging water and debris plugging spillways caused the river to divert around the west side of the dam and rapidly erode the bank, destroying an Xcel Energy substation and threatening a longtime store and restaurant popular with anglers and other dam visitors.
But later Monday, Eric Weller, the Blue Earth County emergency management director, said authorities believed the dam’s western bank would likely erode more, but didn’t expect the concrete dam itself to fail.
Earlier, Blue Earth County Chief Sheriff’s Deputy Paul Barta said authorities had notified a handful of residents downstream from the dam about the potential danger. Rapidan is approximately 10 miles southwest of 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.”
According to Blue Earth County, “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 said they were monitoring the dam situation closely, but added that they are confident the flood-control system would protect the two cities even if the 114-year-old dam failed.
The Blue Earth 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 went 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 floodwall system.
‘My childhood goes down the river’
At the Dam Store on 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 shopkeeper’s house located next to the dam.
“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 the 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 Monday morning and saw the scene it hit her 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. It now serves visitors to a riverside county park.
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 would 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 back up and reroute itself around the dam, perilously close to the Dam Store.
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 some of it wash away,” he said. “We’ve been fortunate none of it’s been breaking up and flowing downriver. Trees and things like that haven’t created an issue yet.”
The city of North Mankato declared a flood emergency, closing the Lookout/Lee Boulevard intersection to allow crews to build the temporary earth wall levee in this area.
Future of the dam
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 or 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 is more environmentally sound. And some argued removing the dam could allow for creation of a man-made whitewater 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.
