Construction of new Lake Bronson dam structure to begin this month

By Anna Jauhola
As a part of the summer programs, Lake Bronson State Park Manager Tim Williamson gave an update on the progress of the dam replacement project on Saturday, June 14.
Four people from the public attended the presentation.
Williamson gave a brief history of the original dam’s construction, which was a Works Progress Administration project. It was built to dam the Two Rivers to provide a better water source for downstream towns, specifically Hallock, which took its water from the river.
“According to the Bronson family records, Maggie Bronson had to be carried out of her home in 1937 because she refused to leave. She was on the second floor at that time, and it took the first floor flooding to convince her to leave the family home,” he said.
The Bronson’s home was also a boarding house and stopping place along the stage coach route though the area. Its foundation can be seen on the lake bottom.
Eventually, the reservoir became a recreational lake when rural water dug in lines across to the west side of the county, and Hallock no longer took its water from the Two Rivers.
While construction of the original dam began only one week after receiving federal funding in 1936, it took four years after receiving money to start construction of the new dam, Williamson said. He shared more details of why there was such a need for replacing the original dam.
Each day, park staff had to check the water level and the dam structure. If the water level was over 20.10 feet, that puts staff into a level one stage emergency, which is above flood level. If it went above 21.7 feet on the old measurement, that was a critical danger downstream.
“The dam was actively falling apart in front of us for the past 20 years,” Williamson said. “We’ve been filling it with dirt and backfilling it on occasion.”
During flood situations, they’d monitor the dam every two to four hours. If the dam outlets were plugged up with trees, the water would have scaled the structure, gone up and over, and carved out all the soil holding the back half of the dam, collapsing it within six to eight hours, he said. Such an event happened in 2006. Williamson showed photos of Anderson Brothers Construction building earthen dikes along County Road 28 over the dam and said they pulled out trees caught in front of the dam to keep water flowing. In that year, the Lakeside Campground flooded all the way to the shower house.
“The spillway was undersized and did not have the capacity to pass a 100-year or 500-year flood,” Williamson said.
The dam was deteriorating also because water was working its way underneath the structure during high water events over the last 15 to 20 years. During a high water event, the ground on the south side of the dam was spongy, Williamson added.
“Regularly on the lakeside of the dam, we would walk and observe,” he said. “We’d find points where you could see something looked different in those rocks.”
This is an area they’d found sinkholes, which park staff had to fill in to help prevent the dam from further deteriorating. He added that in recent years, which have been unusually dry, the relief wells have had no water in them, which isn’t good when that pressure is needed should there be a 3-inch rainfall.
“The pressure you’d need on the back half of the dam wasn’t there to support water movement. So the dam was just as dangerous in drought as it would be if it was like spring flooding,” Williamson said.
Testing in the relief wells showed there were air gaps forming in the soils, and one of the signs showing air gaps was the riprap on the lakeside caving in. It wasn’t uncommon to find rocks were about a foot lower than normal, so park staff would backfill that spot and report it to state dam safety.
The dam has been deemed “unsafe” by the Minnesota Department of Natural Resources since 1978. He said the bike trail that was built in the early 2000s was one of the things that prolonged the life of the dam because it added stability. The giant relief wells were installed in the early 1990s when the lake was last drained, and major gate repair was done in 2008 to include newer engines that operated the gates.
Now that construction has begun on the new dam, which is a labyrinth weir, the majority of the project should be completed by the end of 2026. The weir structure will allow water to flow over the top without any gates to operate, and a boom structure will catch major debris, preventing it from clogging the flow over the dam.
The massive amounts of dirt that have been moved to carve out the area for the new dam will be used as backfill when the old dam is removed and to create a parking lot in its place. Ames Construction worked on building the new spillway and demolishing the old dam throughout November, December, January and February, with brief pauses due to cold temperatures. Even now, Ames Construction is continuing to shape the spillway and preparing the lakeside portion of the project. The first half of the cutoff wall was dug and completed in March and early April.
“Here in June, they are starting the process of putting in the new dam,” Williamson said.
Final project completion is scheduled for July 2027.
Throughout the project, park staff, Barr Engineering and Ames Construction have been on the lookout for artifacts or historical items, and worked with the Minnesota Historical Society. That work is ongoing.
Currently, the lake is down to river status, so there is still water in the basin of Lake Bronson, however, Williamson reminded everyone the lake bed and surface is closed throughout the project.
Williamson noted that Ames Construction and Barr Engineering have been great companies to work with.
“It’s been an interesting partnership,” Williamson said.
A reminder — Lake Bronson State Park is still open for visitors and camping is available at Two Rivers Campground on the east end of the park. The majority of trails are open for hiking, biking and horse riding. And park staff has a slate of programs set for the summer, typically on Saturdays and Sundays. For more information, call the park office at 218-754-2200 or visit the park.