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

A 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 now been told to evacuate - as officials continue to monitor whether the Rapidan Dam will fully give in.

The structure is located on the Blue Earth River, where it's been for the past 114 years. Footage shows a house being swept up in the torrent of river water let loose by the damage.

Debris started accumulating there Sunday following abnormally high rates of rainfall, placing the more than century old barrier 'in imminent failure condition.'

By 10:36 am, 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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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 raised 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 

'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. 

'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 - of which there are more than 28,000 - to evacuate, though the warning was meant more for those in low-lying areas of the river valley.

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.

ric 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. 

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. 

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.

The Rapidian 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. 

'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 4 a.m. 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.' 

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