Minnesota's Rapidan Dam in 'imminent failure condition' after heavy flooding, residents warned

A dam in south central Minnesota failed Monday morning - leading to fears of flooding for at least 45,000 residents in the valley below. 

Citizens in low-lying areas of the Minnesota River Valley have now been told to evacuate - as officials continue to monitor whether the Rapidan Dam will fully give in.

The 114-year-old dam on the Blue Earth River is about 90 miles southwest of Minneapolis. Aerial footage shows a house just a few feet away from the tributary being completely engulfed by the floodwaters.

It was later revealed an Xcel Energy substation located at the dam was actually washed away. It supplied power to some 600 customers, local law enforcement said.

Debris started accumulating there on Sunday following abnormally high levels of rainfall. It left the century old dam 'in imminent failure condition,' officials said.

By 10:36 am Monday, the river had eroded earth around the west side of the dam near the south side of Mankato to the point where water was sent cascading over the concrete, with accumulating flooding now putting the city of 45,140 at risk.

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The Rapidan Dam in south central Minnesota failed Monday morning - spurring fears of flooding for nearby residents

Citizens in low-lying areas of the Minnesota River Valley have been told to evacuate - as officials continue to monitor whether the 114-year-old dam on the Blue Earth River will fully collapse. An Xcel Energy substation was turned into debris and washed away

In an alert issued Monday as footage showed parts of the dam in ruins, Blue Earth County Emergency Management stated, 'We do not know if it will totally fail or if it will remain in place.

'However,' the agency added, 'we determined it was necessary to issue this notification to advise downstream residents and the correct regulatory agencies and other local agencies.'

In the meantime, debris knocked loose by the torrent of water continues to rush downstream, as power outages have also been reported in surrounding areas.

The Blue Earth County Sheriff's Office Monday morning said they were aware of such outages and were working to address them, though did not provide specifics on the amount of homes affected. 

In their own statement, the National Weather Service described how the failure is set to cause the portion of river that cuts through Mankato to crest just below major flood state Tuesday morning.

Twenty other cities - such as Fairmont - also sit in the flash flood radius, as water has already washed out a large portion of the dam, which for years has spurred questions about its structural integrity.

Gov. Tim Walz and state emergency response officials cited such scrutiny upon issuing their own statement Monday morning, as nearby roads are in danger of being overflowed.

'I know the structural integrity of the dam has been a question for a long time,' Gov. Walz said of the longstanding structure, constructed in 1910 by the Ambersen Hydraulic Construction Company.

Officials are warning residents downstream about the risk of wayward debris and rising water levels, which have already washed out a portion of the dam and several buildings nearby

Le Sueur County residents - of which there are more than 28,000 - are being told to evacuate, particularly those living in low-lying areas of the river valley

'The removal of the dam has been a question that's been up there.' 

He and other officials are warning residents downstream about the risk of wayward debris and rising water levels, which have already washed out a portion of the dam and several buildings nearby, photos show.

They're telling Le Sueur County residents to evacuate, specifically those in low-lying areas. 

Parts of Mankato near Blue Earth River fit this criteria, and are expected to bear the brunt of the flooding as it hits a forecasted tipping point Tuesday.

Until then, the NWS has issued a flash flood warning for thousands living downstream until 4:30pm, though no official evacuation order has been given.

That said, in Minnesota, local law enforcement cannot mandate an evacuation - with the decision to issue such an order ultimately left up to Walz himself. 

He has already mobilized the state's National Guard, a historic move made by his office on Sunday upon being met with the first signs of the prospective failure.

Eric Weller, Blue Earth County emergency management director, told the Star Tribune over the phone late Monday morning that the 'The dam could fail,' and that everyone deemed to be and danger have been notified. 

Parts of Mankato near Blue Earth River fit this criteria, and are expected to bear the brunt of the flooding as it hits a forecasted tipping point Tuesday

He added that despite the absence of an official order, several have already vacated their homes after the dam was 'breached,' and that anyone in danger has already been urged to consider leaving. 

Again not providing specifics, he said those not warned were likely not in danger, though things could change as the extent of the crisis is again measured on Tuesday.

Officials, in the interim, are preparing for the worst - as swelling water was seen cutting through the west side of the dam Monday, causing debris to accumulate in the river.

Authorities are monitoring bridges for County Road 33 and County Road 90 to see if those debris will continue to pass downstream and plague motorists, ready to close the roads if needed.

In the afternoon, nearly 20 road closures were announced, including Highway 60 in Windom Highway 99, near the Minnesota River bridge in St. Peter.

Footage filmed overhead shows homes near the west side of the dam set dangerously close to the torrent of water, which as of writing continues to send more water than usual downstream toward towns like Mankato, not to mention the debris.

Pieces of county infrastructure are among of the debris currently being sent downriver, officials said - as they continue to keep tabs on the unfolding event.

Before it happened, the generators at the dam supplied enough power for up to 3,000 residences in the surrounding area.

The number of them left without power has yet to be aired.

A 2021 assessment of the dam's structural integrity found that it would soon need to be repaired or replaced - undertakings that would be costly. Such a venture would also take at least four years, officials said - citing how three years would be spent solely planning the move

The City of North Mankato, meanwhile, issued a statement revealing how  officials are building a levee as a precaution and to protect the lower part of the city - clarifying Monday afternoon that no evacuations or preparations from residents are needed at this time.

North Mankato City Administrator Kevin McCann said the work is merely being done out of an abundance of caution, explaining in a statement, 'Even before [the water would] get to this dirt, it'd have to rise up four feet.

'So, we're well protected,' he went on, adding if the dam were to break, water levels would rise six inches to - at the very worst - two feet.

'As we continue to monitor river levels and the situation at Rapidan Dam, the current river level is 28 ft. and our levee system is built for a river capacity of 39.5 feet,' McCann said in a statement at around 1pm ET.

'According to Blue Earth County officials, if Rapidan Dam becomes compromised, they estimate that there would be a up to a 2 feet surge in the river level. 

'This reamains[sic] a developing situation and the City of Mankato is confident the levee system will hold and there are no areas currently in the City of Mankato that are under evacuation orders. 

'For your safety, do not go around barriers of any closed areas.'

The Rapidan Dam was constructed between 1908 and 1910. It measures in at 87 feet high and 475 feet long, and is made entirely of concrete. 

Officials are currently implementing the opening stages outlined in the Rapidan Dam Emergency Action Plan, a guidance outlining how to respond to such a failure and help potentially affected people kept on the backburner. 

As it stands, the current river level is 28 feet - dangerously close to the capacity of the dam's levee system, 39.5 feet.

No action has been taken since - aside from the county last year saying it had begun the process to release its licensure exemption under federal energy laws, as the damage over the years was to declare it not reliable enough to provide hydroelectricity

A 2021 assessment of the dam's structural integrity found that it would soon need to be repaired or replaced - undertakings that, in both cases, would be costly.

Such a venture would also take at least four years, officials at the time said - citing how three years would be spent solely planning the designing stage.

A completely new dam would take ten years, the county found - before asking the community for feedback to determine the next course of action.

No action has been taken since - aside from the county last year saying it had begun the process to release its licensure exemption under federal energy laws, as the damage over the years was to declare it not reliable enough to provide hydroelectricity.

Such an approval would put the dam under control of the state's Department of Natural Resources, but prior to the disaster, no such move was made. 

'We are continuing to monitor the status of the dam with local officials,' said Homeland Security and Emergency Management Director Kristi Rollwagen Monday. 

'We were made aware of the situation about 4am this morning. We're also looking at the communication cell towers in the area and working to get resources down there to support cellular communications.

'Right now the integrity of the dam is intact, but we will continue to monitor it and be aware of what's going on.' 

Such an approval would put the dam under control of the state's Department of Natural Resources, but prior to the disaster, no such move was made. the state's various agencies, as of Monday afternoon, 'are in close contact with Blue Earth County... regarding the dam['s] future effect on Mankato

Gov Walz added how the state's agencies, as of Monday afternoon, 'are in close contact with Blue Earth County and other local officials regarding the dam['s] future effect on Mankato.

'Emergency management is on the ground and acting quickly to ensure the safety of Minnesotans as the situation develops,' he said. 

'No changes to the dam structure are being proposed at this time,' the country added in an informational release issued later in the day. 

'Surrendering the exemption simply means that the FERC would no longer have regulatory authority over the dam.'

DailyMail.com has reached out to Walz's office for more information. 

This is a developing story; please check back for updates.