To protect Boise paper, engineers weigh limit to dam flows

Minnesota's northern border lakes and rivers are at record levels, and with more rain in the forecast, dam engineers are contemplating an unusual move.

If as the National Weather Service expects three inches of additional rain falls on the already flooded area near the U.S.-Canada border by Monday, engineers at the International Falls Dam may close a few spillways to restrict flows from Rainy Lake into the Rainy River.

That might help protect operations at the Boise paper mill in International Falls, where water blasting through spillways and water wheels at the dam threatens its massive generators.

If the generators are flooded, the entire facility will be shut down for weeks, substantially cutting flows through the dam at the worst possible time, said Matt DeWolfe, an engineering adviser to the International Lake of the Woods Watershed Board.

When torrential rains pushed water past flood stage engineers cranked the area dams that control water levels on Rainy Lake and Rainy River wide open. Thousands of gallons a second gush from the lake into the river flowing to Lake of the Woods.

• Endless rain, flood threats dampen business bottom lines • 'Water just about everywhere you look': Rain closes city park, streets in Mankato

• Updraft: 2014 is the wettest year on record so far

With more rain in the forecast, and a 65-year-old flood record already shattered, engineers for the International Joint Commission, which regulates dams along the border, had to think of a solution.

In a test, engineers closed just two of the 15 spillways which stretch from the Boise powerhouse to generators on the Canadian side for two hours on Tuesday. DeWolfe said it worked, drawing down the river by a few inches.

"It's an exchange," he said. "For a few hours or a day of diminished flow, we protect our flow capacity over the whole summer."

DeWolfe said they determined that restricting the dam temporarily might bring down the Rainy River enough to keep the Boise powerhouse going. Until they tried it on Tuesday, they were just guessing.

"We've never had a situation like this," DeWolfe said. "So we didn't know if it would work."

As a result of the test, if thunderstorms blow in, dam operators will have options. But slowing the flows on the river with water this high is a risk because holding back water in Rainy Lake is bad news for people there.

There are 75 homes surrounded by sandbags. Two structures on the Rainy River were recently lost. If any part of the dam's flow is slowed down, the lake will undoubtedly rise.

"Every inch this lake goes up is a peril for someone," International Falls Mayor Bob Anderson said.