"This water is moving very fast. It’s moving at faster than 40,000 cu ft per second, which is probably in the neighborhood of 10 to 15 miles per hour, and there is a lot of debris in the water," said Jeffrey Johnson, director of public works with the City of Mankato. Officials believed the water had crested as of 10:30 a.m. June 25 and no further damage to the dam had yet been discovered.

While the earthen abutment will need to be rebuilt, local officials were cautiously optimistic that further damage could be avoided if the rain lets up. Equipment was not available over the weekend to begin immediate repairs of the abutment as the water was still rising, and efforts were focused on protecting the dam. More storms were predicted over the coming days. 

“Water found the path of least resistance on the west side of the dam,” said Ryan Thilges, county engineer and public works director for Blue Earth County. He also said a small parks building was damaged by the water flowing west of the dam, as was a substation providing power to about 600 area homes.

Officials said they would continue to monitor the situation as water continued to flow around the dam.

"We’re working with the [U.S. Army] Corps of Engineers and the National Weather Service on some models so that we can have a better idea of what’s going to happen," Johnson said. "It’s not a catastrophic failure, it’s slowly failing, so I think that’s a good situation to be in."

The Federal Energy Regulatory Commission will also be involved in assessing the damage. The Corps' national dam assessment rated the Rapidan Dam as being in poor condition in April 2023, classifying its hazard potential as "significant." The dam is now owned by Blue Earth County and is one of many former hydroelectric dams that has not produced energy for years, causing the county to require other funding for repairs and upkeep of the dam. 

The county said, in a press release, that the flow of water peaked June 24 at 34,800 cu ft per second, and had lowered to 33,000 cu ft per second as of June 25. Rapid liquefaction of dam embankments in Michigan and Nebraska was found to be the cause of similar failures by the Association of State Dam Safety Officials.

Rail Bridge Partially Collapses

On the Big Sioux River, a Burlington Northern Santa Fe cargo-only railroad bridge between North Sioux City, S.D., and Sioux City, Iowa, partially collapsed at about 11 p.m. June 24.

"That is the main bridge going into Iowa that a lot of commodities and different materials move on throughout the state," South Dakota Gov. Kristi Noem (R) said in a press conference. "It was a big loss for us. That'll impact us for many, many months to come."

The bridge was closed before the river peaked at about 44.9 ft.

“We have been monitoring the region through our increased track inspections and had not been operating over the bridge at North Sioux City as a precaution, given conditions,” said Kendall Sloan, a spokesperson for BNSF. 

She said the middle span of the bridge collapsed and that all trains are being rerouted via Creston, Iowa. 

“We will continue to monitor and inspect conditions in the area and execute recovery operations as needed,” she said. 

More than a dozen Corps river gauges in the area have already broken all-time records, some by as much as 7 ft.