NorthWestern replacing flood-damaged power lines in Missoula conservation area

While the Clark Fork River has retreated from the Tower Street Conservation Area, it’s likely to return this spring, giving NorthWestern Energy crews a narrow window to complete the first phase of their work. (Martin Kidston/Missoula Current)

Crews with NorthWestern Energy are racing to beat this year’s high water to replace and reroute a key transmission line felled by last year’s flooding in the Missoula Valley.

While the Clark Fork River has retreated from the Tower Street Conservation Area, it’s likely to return this spring, giving power crews a narrow window to complete the first phase of their work.

“The water has already come up, but the plan is to get in here before we get more flooding,” said Steve Clawson with NorthWestern Energy. “Once we get the structures up, we’ll move out until the place dries up before coming back in July and start running the wire.”

Last may, the Clark Fork River washed over the conservation area and inundated surrounding homes. The river’s scour also toppled key infrastructure supporting a main feeder line, allowing it to drop into the river.

That occurred in May, prompting NorthWestern Energy to repair the system once the water retreated. But even then, the utility began looking for a long-term fix to what’s expected to be a reoccurring event under climate change and the ever-advancing spring runoff.

“It went down and we started looking at our options of rerouting this system,” said Joe Wulf, a senior engineer with NorthWestern. “These new structures are designed to handle the full flow of water, and they’re designed to handle a certain footage of scour.”

Those new structures include six steel towers perched on heavy concrete pads embedded several dozen feet into the ground. The pads themselves will likely stand above the worst possible flooding and hold up as moving water erodes the earth around them.

The power line handles 161,000 volts of electricity and feeds a broad area of the Missoula and Bitterroot valleys. The entire project spans around 2,500 linear feet and crosses the Clark Fork River further east than the old lines.

“The (pads and towers) are significantly more powerful from the standpoint of their ability to withstand flooding and erosion and those types of things,” said Wulf. “We move several hundred amps through the line daily. It supports the Target Range area clear down into the Bitterroot as well. It’s an important feeder for us.”

Joe Wulf, a senior engineer with NorthWestern, said the new structures will likely stand above the worst possible flooding and hold up as moving water erodes the earth around them. (Martin Kidston/Missoula Current)

Once the structures are in place and the line is drawn and energized, crews will decommission and remove the old lines and their wooden poles. With heavy equipment moving through the conservation area, the project will also require its share of reclamation.

Clawson said the utility is working closely with the city’s Conservation Lands Program on the project and its eventual cleanup.

“We should be in and out with the tree planting and reclamation work by the fall,” said Clawson. “A lot of the trees look broken off, but that’s by design for habitat, and a lot of trees are down, but that was also by design for habitat.”

It was last July when Morgan Valliant, the city’s conservation lands manager, noted the reach of the flooding in what’s generally a sandy inland wood.

The high water washed away much of the infrastructure in the Tower Street Conservation Area, including trails, signs and fencing. Much of it has since been replaced, though rerouting the transmission lines will bring some changes to the area.

“We’ve been able to save some of the trees in the process,” said Clawson. “Those will be relocated and planted. The vegetation will be what they (the city) want to see in here, and what they want the park to look like. The idea is to keep this park as pristine as possible.”