CS1A - Concurrent Session 01A: Lighting Strikes Twice at Rapidan Dam

Abstract Description: The Rapidan Dam, a hydroelectric structure built in 1910, underwent emergency repairs in 2001 due to extensive erosion and undermining of its sandstone foundation (author presented at the 2003 ASDSO Conference). Emergency repairs resulted in the placement of 2,350 cubic yards of concrete to save and stabilize the dam. Despite these efforts and subsequent repair projects, the dam faced another significant challenge in June 2024 when high flows overtopped the dam due to near-record rainfalls and accumulated debris, leading to erosion and breach of the west embankment. This breach caused substantial damage, including the destruction of an Xcel Energy substation and the collapse of a nearby home.

In the wake of the breach, Blue Earth County swiftly mobilized to address the situation. The county's response included immediate measures to ensure public safety and provide a media narrative. They coordinated with federal and state agencies to secure funding and for technical support for the dam's removal. Barr Engineering Co. provided post-breach technical assistance and was formally selected by Blue Earth County in January 2025 to lead the dam removal process.

Key technical challenges include addressing sediment loss, removing the dam components, focusing on stabilizing the abutment areas and downstream slope to prevent further erosion, and designing a new stable and sustainable river channel. The removal plan includes careful consideration of environmental impacts and community needs. The County anticipates incorporating historical features into a nearby park and creating a regional river use park with attractions to draw visitors to the area.

Collaboration with multiple project partners including federal agencies like FERC, FEMA, the U.S. Army Corps of Engineers, and the Minnesota DNR, has been ongoing for months and was crucial in moving the project forward.

The presentation will provide an up-to-date status of the Rapidan Dam removal project with a focus on the County response and media coordination, dam removal, channel and embankment design, and agency coordination and permitting.