RAPIDAN TOWNSHIP, Minn. – On Monday, officials in southern Minnesota announced it The Rapidan Dam had been breached and is in an “imminent state of failure.”
Residents in low-lying areas of the Minnesota River Valley are advised to closely monitor the situation and prepare for the possibility of evacuation.
The National Weather Service says the failure is expected to cause the Minnesota River at Mankato to rise just below major flood status Tuesday morning.
What is the history of the Rapidan Dam?
The Rapidan Dam is located on the Blue Earth River in Rapidan Township, approximately 14 miles south of Mankato.
When it opened in 1910, the dam doubled the power capacity of Mankato’s electrical system, according to the Blue Earth County Historical Society.
The dam was built using hollow reinforced concrete.
The dam was owned and operated by Northern States Power Company until 1970, when it offered the dam and surrounding 750 acres to Blue Earth County “as an ecological corridor of wildlife habitats, recreational areas and nature trails,” says the county’s historical society .
However, in 1972, the historical society said the county government ruled that the dam should either be rebuilt or demolished because the dam would cause “significant damage” to surrounding areas if it collapsed.
To address safety concerns, engineers added more concrete reinforcement to the Rapidan Dam in the 1980s. The National Society of Professional Engineers called the renovations “one of the best engineering feats of 1986.”
Emergency repairs were carried out in 2002 after it was discovered that the dam’s foundation had been extensively undermined.
Blue Earth County says the Rapidan Dam has experienced periodic flooding over the years, with the second highest flood on record occurring five years ago in 2019. That flooding caused “significant damage to the structure and serviceability of the dam “, and that has not led to the ability to produce energy since then, according to the province’s website.
A 2021 study identified two viable solutions for the dam: repair or removal.
From 1999 through 2022, a report found that the dam actually lost Blue Earth County more than half a million dollars.
Blue Earth County officials formed the Future of Rapidan Dam to “identify community needs and concerns and use their input” to make the best decision on what to do with the dam.
A dam repair feasibility report commissioned by the province in 2021 estimated it would cost at least $15.1 million to repair the dam. However, the county reports that it will likely lose more than $4 million on the dam over 40 years. Removing the dam was estimated to cost at least $65.2 million.
In August 2022, Blue Earth County presented the final brief, which showed that the majority of people surveyed supported repairing the dam.
Because both options involved significant costs, they were ultimately not implemented.
In March 2023, Blue Earth County initiated the process of surrendering Federal Energy Regulation Commission license exemptions for the Rapidan Dam, as the dam no longer generates hydroelectricity.
