Minnesota bridge on verge of collapsing following torrential rain, flooding

A bridge near a Minnesota dam is on the verge of crumbling into the Blue Earth River following a barrage of heavy rain and flooding.

The County Road 9 bridge, a roughly 40-year-old bridge near the Minnesota city of Mankato, may topple over if the weather doesn’t subside to allow proper structural reinforcements to take place. 

Heavy rain and flooding have pummeled the Midwest for days with Blue Earth River’s water levels rising dramatically, testing the structural integrity of the Rapidan Dam.

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The dam has already suffered a partial failure, which resulted in a house along the Blue Earth River near the dam falling into the river, and the dam store nearby being demolished. The Rapidan Dam is located about 14 miles south of Mankato in Southern Minnesota.

"Unfortunately, we’re at the mercy of Mother Nature at this point," Ryan Thilges, the public works director for Blue Earth County told reporters Tuesday. He was flanked by Minnesota Gov. Tim Walz and other officials who went to the dam to get an update on flood conditions and recovery efforts.

Thilges said that the bridge’s piers are piled through sediment and sit atop of sandstone bedrock, and not driven into the bedrock. The gushing water has washed some of the sediment away, putting the bridge’s stability at risk.

"All of the lateral stability for the piling was achieved through the sediment that was in place, that had been impounded in the river basin over the life of the dam," Thilges said. 

"So as we're seeing dramatic levels of river head cutting, as the river's lowering itself down and washing away tremendous amounts of sediment, we're losing stability."

He said the water is flowing too fast to take measurements of the sediment in the river or at the pier. Locals use the bridge to commute across the dam from rural patches of land to nearby towns.

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"Right now, again, we believe it's approximately 50 percent exposed. And as the river level continues to decrease and cut the riverbed elevation down, we're very concerned about the potential for partial or full failure of the bridge," Thilges said. "With that being said, the bridge has been closed since the dam began to overtop Monday morning and we'll continue to keep it closed for public safety."

Officials say they began shoring up the west pier of the County Road 9 bridge last week with loose stones -- known as rip rap -- as an emergency mitigation strategy to avoid further exposure at the base of the pier. The riprap remains in place and the bridge remains closed as officials continue to monitor it for stability.

Walz said he fears the bridge will collapse and will need to be replaced. He gave locals assurances that it would be built back should the worst case scenario come to pass. 

"The one thing I think Minnesotans should be reassured about… we will rebuild. The cost will be shared by all of us," Walz said. "So, the burden will not fall on these county commissioners."

Last week, the governor’s office announced that the Federal Emergency Management Agency (FEMA) approved a federal disaster declaration for 22 counties in Minnesota impacted by flooding. State funding provided by the Minnesota Legislature will also be provided to help communities, Fox 9 reports. 

The dam partially failed after heavy rain last week pushed water around the west side of the structure instead of through the gates of the dam.

Construction of the Rapidan Dam was finished in 1910. While it was built to generate electricity, it has been damaged by several rounds of flooding in recent decades. An April 2023 assessment conducted by the National Inventory of Dams found Rapidan to be in poor condition, and officials have been studying the possibility of removing it.

Editor's note: This story has been updated for accuracy.

The Associated Press contributed to this report.