Did dams fail? No, but they ‘overtopped’About 1 a.m. on June 21, as historic rains continued to pound the Northland, Ginger Kulaszewicz’s alarm went off. This was no ordinary alarm, but one of six given by Minnesota Power to Thomson residents set to go off only if the company’s Thomson Dam was failing.
By: Brandon Stahl, Pine Journal
About 1 a.m. on June 21, as historic rains continued to pound the Northland, Ginger Kulaszewicz’s alarm went off. This was no ordinary alarm, but one of six given by Minnesota Power to Thomson residents set to go off only if the company’s Thomson Dam was failing.
“I was told that if that alarm goes off, you have 15 minutes to get to higher ground,” Kulaszewicz said.
By the time she got out of her home, she said she had to cross her street through several feet of high rushing water. She made it to safety, but her home was severely damaged by the flood.
Five weeks later, her story raises questions: Did the Thomson Dam fail? What part did the dam play in the flooding at Thomson, and other areas along the St. Louis River, such as Duluth’s Fond du Lac neighborhood? And what can be done, if anything, to prevent that type of flooding from happening again?
Q: Did the Thomson Dam fail?
A: No, according to Minnesota Power, which owns and operates the dam, along with several others along the St. Louis River.
While dramatic aerial photos taken by a Minnesota Department of Transportation engineer on June 21 show water overtopping parts of the Thomson dam and contributing to the flooding in the township, that doesn’t mean the structure failed.
In fact, said officials with Minnesota Power, the overtopping was supposed to happen.
“Some people may view that and say, ‘Doesn’t that mean there was a failure?’” said Amy Rutledge, Minnesota Power’s communications manager. “The overtopping is a part of the design, the way our system is designed to make sure that we maintain the integrity of those dams and that they don’t fail. … It’s a sign it’s working, and that there’s a lot of water in a short amount of time.”
Dam failures are when the structures actually break down or give way. Had that happened, the flooding along the river would have been catastrophic, said Bonny Carlson, Minnesota Power’s renewable business operations manager.
The overtopping happened over spillways that are designed to pass water and alleviate dam pressure during high-water events, she said.
“In normal flows we would never be that high, to overtop,” Carlson said. “But in historic floods like this, (the dam) is designed to still maintain its integrity, even though it’s overtopping. It did what it was supposed to do.”
Q: So why did Minnesota Power’s alarms go off, indicating the dam failed?
A: The alarms – also called “the dam failure warning system” – weren’t supposed to go off that day, though in retrospect it was good they did.
Minnesota Power officials thought the alarms would only go off in the event of a dam failure, said Nora Rosemore, the company’s Hydro Operations superintendent. But during the floods, the alarms were also triggered by the significant overtopping of a section of dam, causing high water levels flowing into a pond behind Kulaszewicz’s home.
“In hindsight, it probably has a bad name,” Pat Mullen, Minnesota Power’s vice president of marketing and corporate communications, said of the dam failure warning system. “But the good news is that it was activated.”
Q: Did any of Minnesota Power’s structures or dams fail?
A: Yes. Forbay Lake, which fed into the Thomson Hydro Station, is now a dry lake bed. That’s because at about 10:30 p.m. on June 20, an earthen dike got so saturated with water that it gave way, Carlson said. That created a new river through Jay Cooke State Park and that river, at the very least, exacerbated road damage on Highway 210. It might have completely washed parts of the road away.
“We do have indications that 210 had already failed,” Mullen said. “But this was certainly a contributing factor to it.”
The Thomson Hydro station is out of commission after suffering damage from the flood, including seeing its basement flooded with water. It’s still out of commission and, with roads still washed out in Jay Cooke, can only be accessed by ATV.
Minnesota Power has begun a legal assessment to determine what financial liability the company has for the damage caused to Highway 210 and Jay Cooke, Mullen said.
Q: Did the Forbay Lake failure contribute to other flooding down the river, including in the Fond du Lac neighborhood?
A: Minnesota Power officials say no. The Fond du Lac dam never overtopped, nor did they see a larger wave of water come through after the Forbay Lake dike failure.
“Once it hit the bigger flow, the bigger river, it really wasn’t that much water,” Carlson said. “By the time it hit the Fond du Lac dam, that even spreads it out.”
Q: Are any state or federal agencies investigating the dams’ response to the flooding, and will the results of that investigation be public?
A: Oversight and licensing of Minnesota Power’s dams along the St. Louis River is handled by the Federal Energy Regulatory Commission, but a large portion of its records on Minnesota Power’s dams are considered classified for security reasons and won’t be released.
A spokeswoman for FERC said Minnesota Power submitted a report on how the dams responded to the flooding by its July 18 deadline, and that report is now under review.
“We’ll now look at the report and determine any next steps,” said the FERC spokeswoman.
FERC would not release inspection records on Minnesota Power’s dams before the floods. But the spokeswoman did say that during most recent inspections of the dams, “no dam safety deficiencies were noted that would require immediate remedial actions.”
Q: Did the rain and floods cause any structural problems to the dams?
A: “There were no visible dam failures from the flooding at all,” Mullen said. “The structure of the dams appear to have held fine.”
Minnesota Power’s crews are still making repairs to the Thomson Hydro Station, and the company is seeking proposals for how to repair the Forbay Lake dike and put safeguards in place so the dike won’t fail again, the company said.
But generally, said Mullen, “everything worked the way it should. What we learned is how effectively we were able to respond to the needs of the system as everything is going on and making sure it wasn’t any worse than it was.”
Q: Did Minnesota Power ever plan for a rain event like the kind we had in June?
A: “We do plan on rain events of this proportion and are prepared for it,” Rutledge said, “because FERC requires our dams/infrastructure to be built to a certain standard that will withstand the type of high flows we saw during the event and even higher.”
The water that flowed through Minnesota Power’s dam system was the highest it has ever been in recorded history.
“We do build to really big floods,” said Hydro Operations superintendent Rosemore. “But we now have a new worst-case scenario to plan for.”
Q: Besides the six alarms that went off in Thomson Township, did Minnesota Power alert residents about flooding?
A: The company’s protocol during potential floods is to alert the National Weather Service and emergency responders like police and fire departments, which Rutledge said did happen during last month’s floods.
Otherwise, Minnesota Power said the company’s employees weren’t on the ground letting people know that areas could potentially flood. As to whether the company should have alerted individual residents, or will do that in the future, Rutledge and Mullen said it isn’t feasible to notify everyone along the St. Louis River and reservoir system.
“That’s really the role of emergency response folks,” Rutledge said. “(The National Weather Service) is the agency that can alert a large population.”
Added Mullen: “The plan is really to keep the integrity of our system, using our people to make sure the integrity of our system is holding, and using the Weather Service as the notification process.”
Q: Can Minnesota Power build higher walls on the Thomson Dam spillways to prevent future flooding?
A: They could, but there’s the cost to consider to ratepayers for that – and also what would happen to areas north of river in the event of another rainfall that could produce flooding.
“It’s a balancing act,” said Mullen. “If you have less overtopping, you would have water backing up (and) affecting some residents upstream, too. It’s not as easy as saying you should let more water go, or have more water stay.”