Posted on August 26, 2024
As water levels continued to rise the last week of June, the St. Paul District activated its Emergency Operations Center to assist the state of Minnesota and surrounding communities with the summer flood risk.
Community support
Nearly 50 district employees were activated to assist in the planning, coordination, staging and delivery sites, and technical oversight of sandbag operations at locations from Minnesota to Wisconsin.
The EOC provided 175,000 sandbags, two 4-inch pumps and technical assistance to communities impacted by the flooding while supporting Blue Earth County officials responding to the Rapidan Dam breach.
Rapidan Dam support
As flows continued to rise on the Minnesota River, water broke through the west embankment of Rapidan Dam and took out one side of the small hydro plant. Rapidan Dam is located 12 miles upstream of Mankato, Minnesota, on the Blue Earth River, a tributary of the Minnesota River.
The non-federal dam was built in early 1910s and through the years developed sedimentation. The Corps performed repairs in the early 2000s.
To assist county and state officials in their decision making, geotechnical engineers inspected site conditions and hydraulic engineers performed inundation modeling to assess the impacts of a partial and/or full breach on downstream entities.
“Hydraulic engineers used tools available for Blue Earth River and Rapidan Dam such that we can begin to understand the implications/ risks. Blue Earth River flows to the Minnesota River with confluence at the upstream end of Mankato,” said Heather Henneman, hydrologic engineering section chief.
District engineers recommended Mankato levee closures be installed, reassuring the community downstream should the Rapidan Dam experience total failure while the Minnesota River was cresting
Lock and Dam closures
The Mississippi River was at peak river levels driven by high precipitation that resulted in major flooding on the Minnesota River basin, with moderate contributions from the other key tributaries.
As a result, Locks and Dams 2 and 3 experienced the highest peaks, with Lock and Dam 2 surpassing peak elevations experienced last spring by about a foot. Locks and dams 1 and 3 closed to commercial navigation from June 29 through July 2.
