Minnesota dams mostly held up in June flooding, but old structures need repair

Historic June flooding knocked out a small dam in northeast Minnesota and battered two larger ones, creating dramatic scenes like the tree-clogged Rapidan Dam in the roaring Blue Earth River near Mankato.

The state dodged major consequences, but the episodes drew a national spotlight to what is a common problem in Minnesota and elsewhere: old and creaky dams that are costly to fix, replace or remove.

"Most of these projects were built in the [1930s], so they're either nearing the end of their life cycle or have reached the end of their life cycle," said Jason Boyle, who oversees Minnesota's dams as the state's top safety engineer. "Some might have been designed not up to current standards."

Boyle said Minnesota has addressed nearly all of the dams in shaky condition that would be the most dangerous if they collapsed. Failures, however, are not unheard of: State records show 26 dams or related infrastructure have failed in minor and significant ways from 2010 to 2023.

Boyle's department also has a list of 73 state and locally owned dams in need of $33.6 million in work, mainly to boost safety. At the top of that list is a Nest Lake dam near Spicer, but there are needs across the state. The Coon Rapids Dam in the Twin Cities metro ranks No. 9.

State lawmakers have approved money for dam projects, though inconsistently in recent years. And independent groups have mixed reviews of Minnesota's infrastructure.

"Now that we know so much more about hydrology and flooding, that's probably a pretty common problem is just having the ability to safely pass a flood," Boyle said.

Failed dams

The Rapidan Dam has not fallen despite water at one point spilling over the top of the dam and a partial breach of its west abutment. The Woolen Mill Dam in Faribault also required some emergency work because of high flood waters.

But Sullivan Lake roughly 25 miles north of Two Harbors practically emptied after high water broke a small 124-year old dam built of wood, stone and dirt.

Flooding from spring snow melt or heavy rains is a common issue for partially or fully breached dams, state records show. Most are not major or dangerous incidents and often involve small structures, though a few have raised public concern.

In 2012, massive rains took out a section of a canal that feeds Minnesota Power's hydroelectric station in Carlton. That sent water into the St. Louis River and drained Forbay Lake, said Nora Rosemore, manager of the company's renewable business operations.

The utility activated an emergency action plan during the flooding, but the large Thomson Dam otherwise withstood the rains. The utility has since fortified its infrastructure.

Minnesota lagging

Overall, Boyle said, Minnesota is "doing OK" on dam safety. For instance in the past decade, the state upgraded six "high-hazard" dams that it oversees, he said. That classification means a failure could kill people or cause significant property damage.

Minnesota has 1,150 dams, according to a federal database; 55 are high hazard. Lawmakers have approved more than $23 million since 2020 for the state-owned Lake Bronson Dam in Kittson County, which Boyle said is the only state-regulated high-hazard dam that's in poor condition. The state is reviewing proposals to replace the dam's spillway.

"It's definitely safe under normal conditions or even reasonably expected conditions," Boyle said. "It would be the extreme conditions where it would be a concern."

Still, lawmakers have passed few infrastructure bonding bills in recent years, leaving many other projects in limbo. That includes, notably, flood mitigation work.

In 2023, a historically large $2.6 billion infrastructure bill included just $4 million for dam safety repair and reconstruction, and $500,000 for the city of Gaylord to help replace the Lake Titlow Dam. That $4 million is enough to cover the state's share of eight dam projects on the lengthy priority list, which does not include private dams in need of repair or federally owned ones.

Roughly 37% of Minnesota's dams are privately owned. About 10% are owned by the federal government, which also regulates some it does not own, namely hydroelectric dams like Rapidan and Thomson.

Dams in Minnesota were often built for flood control, fish and wildlife management, and recreation. Few were for hydroelectric power or holding waste from mining, known as tailings.

In 2022, the American Society of Civil Engineers gave Minnesota a "C" grade for its dam infrastructure. The group cited the age of dams and a long list of needs, even as officials have worked to reduce the project backlog.

That's not solely a Minnesota phenomenon. Everett Taylor, Utah's dam safety engineering manager and treasurer for the national Association of State Dam Safety Officials (ASDSO), noted the feds announced in late June $185 million for high-hazard dams across the country from the 2021 bipartisan infrastructure law. That included $2 million for Minnesota.

ASDSO largely rates Minnesota well compared to its model policies for factors like permitting and plans for responding to emergencies. But the state mustered only a 67% for its safety enforcement efforts.

Boyle said Minnesota's score was lower because the state does not have penalties to deter dam safety violations nor the authority to recover costs from dam owners for emergency steps through legal action.

Work to do

Not every dam on the priority list kept by the Department of Natural Resource (DNR) has safety problems. The state can fund other work, including to help fish passage. Plans to remove dams for safety issues can also face local opposition.

The DNR wants to demolish a dam in Hinckley on the Grindstone River, for example, but officials there have fought the idea in part because of recreation opportunities on the reservoir the dam created. One hurdle for Blue Earth County to remove the Rapidan Dam was a 2021 study that estimated demolition would cost $82 million.

No project on the DNR's list comes near that price tag — at least now — though a dam on the Pike River in St. Louis County listed in poor condition needs $4 million for "expensive repairs."

The top DNR priority is $250,000 for the Nest Lake dam in Kandiyohi County that has an old, leaning wall on a channel downstream of the "low-hazard" dam, Boyle said.

The Coon Rapids Dam, which Three Rivers Park District operates, is one of two "significant-hazard" structures near the top of the DNR's priority list. More than a decade ago, lawmakers approved $16 million to replace gates on the dam. Now, $2 million is needed to repair cracked and damaged concrete, district spokesman Tom Knisely said.

Knisely said the structure is in good enough condition that it's not urgent to address.

Boyle said the need to upgrade Minnesota's dams will persist.

"Dams will continue to age," he said, "and new dams will be added to this list as they continue to age."