The Rapidan Dam, built in 1910 by Consumers Power Company (now Xcel Energy) to generate hydroelectricity, has served the 2,430-square-mile Blue Earth River watershed for over a century. The 456-foot-long and 87-foot-high hollow Ambursen buttress dam consists of a powerhouse with integral intakes, a spillway section including five tainter gates, and the east and west non-overflow sections and abutments.
After a flood in 1965 damaged hydroelectric operations, Blue Earth County took ownership of the dam and reservoir lands in 1975. While hydropower generation was redeveloped in the 1980s, the dam has faced persistent structural issues and costly repairs, primarily due to repeated flooding and erosion.
Despite temporary risk reduction from emergency repairs and subsequent projects over the years, a catastrophic flood following historic rainfall in June 2024 led to debris accumulation and the river overtopping the dam, causing failure of the west abutment. This triggered riverbank erosion, property damage, and power outages, leading the county board to pursue dam removal. Barr is currently collaborating with local, state, and federal agencies to assess the overall damage and develop plans for the dam removal, river channel restoration, and west abutment and slope reconstruction.
Barr created a HEC-RAS 2D model to guide the design by determining channel velocities and shear stresses. But designing the removal and restoration presents several complex challenges. A nearby upstream bridge was also significantly damaged by the flood. Its replacement is being designed by others on a separate timeline from the dam removal. The initial river restoration concept included a mile of heavily riprapped channel that was necessary to protect the bridge foundations but also carried a high price tag. In coordination with the bridge design team, county staff, and regulatory agencies, Barr developed other options for the channel restoration to lower the overall cost. The bridge design was revised by the bridge design team to incorporate deep drilled shaft foundations extending below the anticipated channel scour elevation, addressing the highly erodible nature of the area’s Jordan sandstone and allowing the mile of channel riprap to be significantly reduced from the design. Significantly reducing channel riprap will allow for natural channel development.
In addition, Barr conducted a geotechnical investigation to support the west abutment and slope reconstruction. The investigation will also inform property restoration, public outreach and park re-establishment conceptual design, and water access along the west embankment and slope.
The design phase of the Rapidan Dam removal project is currently underway. Its success will depend on the ongoing interdisciplinary coordination between the county, design teams from multiple consultants, and the numerous federal and state agencies involved in the project's permitting and funding.
