The Rapidan Dam, how we got here

water flowing over and around a dam

By Jake Richards, IT Specialist Individual Placement / AmeriCorps Member placed at Minnesota Department of Natural Resources, Division of Parks and Trails


As of late June 2024, if you live in Minnesota, you have probably noticed the seemingly never-ending rainfall we have received over the past few months. The entire state has been blanketed in rain since mid-April, enough to break yearly drought conditions from the abnormally dry 2023-24 winter and the lingering overall drought since 2021. With this rainfall, many of the state’s waterbodies have recovered from historic lows seen in fall 2023, however some of them have maybe recovered a bit too much….

One of these major recoveries is the Blue Earth River. Located in south-central MN, the Blue Earth River flows north from the southern border of Faribault County, up to Mankato where it then joins the Minnesota River. It is by volume the largest tributary of the Minnesota River, making up almost half of the larger river’s flow at the confluence point, meaning when it’s at full strength it is a powerful river. This power led to residents of Mankato to want to harness it for electricity, resulting in the construction of a hydroelectric dam southwest of the city, the Rapidan Dam.

A small river winds through woods, four Canada geese stand in the shallows along the flat river bank.
Blue Earth River, MPCA

First constructed in 1910, the Rapidan Dam is a concrete gravity dam used to generate electricity for the surrounding areas. At its peak it generated 6 MW of power and was surrounded by the Rapidan Park and Campground along with a Café Store of the same name, which had gained local notoriety as a popular place to visit. The dam had been evaluated for its viability routinely, having been deemed potentially unsafe multiple times with the most significant being in 1972 and again in 2002. The dam continued generating power until a flooding incident in 2019 damaged its equipment and put the dam up for evaluation once more. After a 2022 public survey where repairing the dam had overwhelming support, an engineering survey was conducted, and plans were made to get the dam operational again. Even with these plans however, the National Inventory of Dams gave the Rapidan a rating of “poor” and cited the conditions of the dam having “significant hazard potential”. The dry conditions of the early 2020’s had covered up the issues the dam was facing and once the calendar turned to 2024 and the weather warmed, we now know something had to give.

This “give” occurred on June 24th, 2024, after a stretch of heavy rainfall blanketed the area for multiple days. Debris started to gather behind the dam and caused the river to back up, the dam was preemptively declared to be in “imminent failure conditions.” Dam operators notified local authorities as conditions worsened and evacuations started to commence. The night of the 24th the western side of the dam failed, and water poured around the structure, quickly eroding the riverbank. The story is still developing and while authorities have stated the expected damage will be mostly environmental, only time will tell the extent of damage this failure will cause.

water flowing over and around a dam
Rapidan Dam post 6/24/24 failure, Wikimedia Commons