Blugolds seek answers and predictions in Minnesota dam failure

One of those earth scientists is Ella Gould, a senior environmental geography major at the University of Wisconsin-Eau Claire. Gould and a handful of other students are part of a team led by Dr. Zach Hilgendorf, assistant professor of geography and anthropology at UW-Eau Claire, and Dr. Phillip Larson, director of earth sciences at Minnesota State University, Mankato.

Both Hilgendorf and Larson are graduates of the UW-Eau Claire geography program, Larson in 2008 and Hilgendorf in 2015.

“This is my third project in collaboration with Dr. Hilgendorf and the Mankato team, but this dam study is by far the most extensive project,” Gould says.

Historic rains and flash flooding caused the Blue Earth River to push itself around the side of the 115-year-old dam. The river now flows roughly 300 feet to the west of its former location.

Hilgendorf and the team arrived on-site within a week of the disaster, thanks to special emergency funding from the National Science Foundation. The NSF Rapid Response Research grant program allows real-time data collection in swiftly changing situations like this natural disaster, data that Gould and the team have been gathering via drone photo and video surveillance of the waterway for just over a year.

As she enters her final semester as a Blugold geography major, Gould says she’s grateful for this important project that aligns with her specific geographic and geomorphological interests.

“I’ve always been really interested in water systems,” says the Amery native. “Implementing a dam on a river system does change things a lot, as would the removal of a dam. The chance to work on a project like this has really helped me narrow my path in graduate school and a future career.”

Key factors and details of the disaster

In the year since the Rapidan Dam collapse, much has been learned about the natural and human-made factors that contributed to the massive flood and erosion at the dam. Part of the ongoing efforts in the study, Hilgendorf says, is to shine a light on the potential for similar failures elsewhere, giving communities information to help avoid this type of outcome on their waterways.

A summary of the events and current situation at and around the dam:

• The dam was built in 1910 and because of age and damage from previous flooding, a 2023 assessment rated it in “poor condition.”
• Historic rains of 8-9 inches in the region around and upstream from the dam took place from June 22-24, 2024.
• The flood gates were unable to fully open to release the waters, due to decades of fine-grade sediment jamming the mechanics of the structure, along with large amounts of debris stacking up against the dam in those two days of flooding.
• With nowhere else to go, the raging waters pushed their way to the west of the dam, taking with them several riverside structures, an Xcel Energy substation and nearly 220,000 cubic meters of sediment flushed downstream in the first five days. That is the equivalent of 87 Olympic swimming pools, an amount of erosion that has nearly doubled in the months since the event.

“This was not a true ‘failure’ of the dam in the structural sense,” Hilgendorf says. “The mechanics of the flood gates did not work properly, but the basic structure held. It’s what we call an avulsion — the sudden redirection of a river into a new course. The water just forced its way around the dam.”

Other dams in the Upper Midwest, Hilgendorf says, share similar disrepair to the Rapidan Dam, with two other major failures in the region during the weeks surrounding the event in Mankato.

“Within a month, we saw dams fail at Manawa here in Wisconsin and at the Nashville Dam in southern Illinois,” Hilgendorf says.

“One compounding reality is that major rainfalls are becoming more and more frequent, bringing historic amounts of rain. With the average age of dams in the region at 60 years, these aging structures were simply not built to withstand those types of flooding events.”

Hilgendorf believes that more dam failures will be seen, citing recent data from the National Inventory of Dams that assessed 30% of dams in the U.S. to be in the category of “significant/high” risk for failure.

“The recreational, water management and energy production that dams offer communities is a huge benefit, but there can also be a cost to altering the landscape,” Hilgendorf says.

According to Hilgendorf, dam reservoirs provide great fishing and boating, but their waters can bring challenges. Stagnant waters in reservoirs can become unhealthy for fish when suspended sediment darkens the water, causing heat retention and reduced oxygen levels. Reservoirs can also become too high in certain nutrients that promote algae blooms which also reduce oxygen levels in the water.

“We hope our study will help to quantify the impact of dams on river systems and help communities weigh the benefits and risks as they examine the health of their own waterways,” Hilgendorf says.

Career-shaping student research opportunities

As Gould prepares to graduate in December, she is helping to onboard two new Blugold student researchers to the Rapidan project. Jordan Clay, a senior environmental geography major from New Prague, Minnesota, and Nick White, a senior ecology and environmental biology major from Ellsworth, have joined the dam project and are excited to help move the study into the next phases.

“It’s pretty crazy to see this place,” Clay says. “I’ve been looking at all the photos, but they do not do it justice at all. The area of damage is so much bigger than I expected when you see it person — it’s hard to imagine what happened here.”

Clay has a strong interest in fluvial geomorphology, the study of how rivers and streams shape the landscape, and the chance to add this type of research to her undergraduate experiences was exciting.

White says he is grateful for the interdisciplinary nature of this research team and having the chance to learn more about geography and technology at work in this study. He says he also looks forward to the potential to bring his biology knowledge to use in examining the ways the ecosystem is responding to the outcome of the dam failure.

“I’m hoping to look into the biological impacts of all this,” White says. “One idea I have had is to track changes in the fish and other aquatic species, as well as plant life along the banks. With all the various expertise on this project, it reinforces that multiple perspectives and viewpoints make it easier to approach a big problem like this dam failure.”

Another Blugold-to-Mankato grad school plan in the works

As she noted, Gould has worked with the Mankato earth science team on a couple other recent projects, one in the Duluth area and one in the Upper Peninsula of Michigan.

“I’ve worked with Dr. Phil Larson a few times now, and on this dam project, and Andy Brown from MSU’s EARTH Systems Lab is our large drone operator in the field,” Gould says. “I’ve gotten to know them well, along with some of the MSU graduate students. I’m happy to say my grad school decision is made and next spring I’ll be starting the MSU master of science program in geography.”

For Hilgendorf, the student experience in all his collaborative projects is a top priority. Also a graduate of the MSU master’s degree program under Larson, Hilgendorf is thrilled to see another Blugold move on to that program.

“Ella will be the fourth recent graduate of UWEC to move on to Phil’s program — it’s a strong connection between our campuses. Ella is well prepared and I know she will do very well,” Hilgendorf says.