Editor’s note: This story is part of the Republican Eagle’s 2019 Progress Edition. This year we take readers “Behind the Scenes” of the sometimes hidden work of organizations around the area. Find the rest of the stories at Behind the Scenes.
CANNON FALLS - A three-year renovation project and an emergency evacuation plan are recent developments designed to ensure the safety of anyone who lives or works downriver of Byllesby Dam.
Although the dam, built in 1910-11, is very safe, according to Josh Peterson, senior water resources engineer, it needs some upgrades.
With the dam and its working parts being more than a century old, Peterson said a three-part renovation is underway. The first part, involving new crest gates with hydraulic cylinders on the spillway, has been completed and cost $7.5 million.
"We have to maintain the pool flat," Peterson said. "Whatever water comes into us, we have to pass that much downstream. If the river is at a certain flow rate, every gate here is open to that flow rate."
Before the new gates, heavy rain or flooding would back up in the reservoir, raising the lake level, "because we didn't have the capacity to pass the water," Peterson said. "Now we have that capacity."
The second phase of renovation was to make repairs across the face of the spillway and other maintenance issues. Those fixes cost $4 million and have been completed.
The third phase is a powerhouse upgrade. The turbines and generators inside the powerhouse are original equipment, Peterson explained.
"We are replacing it and rejuvenating the building," he said. "Overall, the powerhouse will be a $14 million project."
The work on the powerhouse, scheduled to start next year, will require shutting down the hydroelectric plant for some time. It should reopen in 2121.
The overall cost of the three projects is estimated at $25.5 million.
Peterson said officials considered other alternative to the renovation. Permanently shutting down the hydroelectric portion of the dam would have been one possibility, however, they would still have to pay to maintain the dam, but not have the revenue. Removing the dam completely would also be possible, but the cost to do that would be "tens and tens of millions of dollars," Peterson said. "It was not financially feasible."
Peterson said all of this work is to make sure that the dam is safe. Then, strict regulations require operators to perform daily inspections, monthly walkthroughs and reports to federal inspectors, and yearly inspections with federal regulators. The dam has round-the-clock monitoring and alarms systems.
"Cannon Falls has been working on an updated action plan," Peterson said. "In the unlikely event that there were ever a dam failure, we want people to be informed and know what to do."
Jeff McCormick, Cannon Falls chief of police, is one of many involved in discussions about an evacuation plan in case of a disaster at Byllesby Dam.
"We have looked at a lot of different things," McCormick said. "Dam flooding is not common in the United States, and when it does occur, it is usually related to bad weather. We have to plan for that catastrophic event that could happen on a sunny day with no warning. That's where we are right now."
One part of the plan divides Cannon Falls into zones which would help an evacuation process. Signs would direct people to follow evacuation routes. One problem, at this point, is that the Minnesota Department of Transportation would need to approve any signs that were placed on the state roads going through Cannon Falls. McCormick plans to have further discussions with MnDOT about this issue.
An evacuation plan is different for people who live in various areas. For example, McCormick explained that people in Red Wing would have about two hours before water from a dam failure reached the city. That would be time to barricade roads and direct people to safe areas.
Cannon Falls, on the other hand, would have about seven minutes, so safety measures need to be in place in advance.
"How do you get people to evacuate to safe locations?" McCormick asked. "The way to do that is to have information already in place."
An evacuation plan must consider the many people who would be using it. For example, if signs are color-coded, what about people who are color-blind? How many languages should be used on the signs? What languages best fit the people who would be using a particular area? These are questions that the committee has been discussing.
"The stuff that we are planning for is the worst case scenario," McCormick said. "We don't ever expect it to happen, but we've got to plan for it."
McCormick said Dakota County's investment in the dam have already made a huge difference, especially during high-water events. He said the trip gates used to go off in the middle of the night and the river would rise three feet.
"With the control gates, Josh will tell me he is going to drop it 6 inches, and I know we are going to get a 6-inch rise here," McCormick said. "It has been great."
McCormick said the resurfacing projects at the dam "help build on what was already a structurally sound dam. I am not worried about it dissolving in the middle of the night."
"Dam safety is our number one priority," Peterson said. "Everything we do is extensively reviewed for any safety issue. There are no compromises here."