Just two months ago, the Clark Fork River deposited a large amount of sand and silt in the Tower Street Conservation Area and knocked down a main transmission line across the river.
While debris was still scattered across the forest floor on Monday, crews with NorthWestern Energy were busy lifting the transmission line to its proper place above the river, and replacing the power poles felled by the floodwaters.
“We had two transmission line structures that were damaged,” said Butch Larcomb, public relations officer for NorthWestern. “The 161,0000 kilovolt is a major line. Keeping that transmission line in good condition is real important. It helps boost reliability.”
It was early May when emergency officials in Missoula County issued evacuation notices to residents in the Tower Street area. A heavy snowfall and early runoff sent the Clark Fork River surging over its banks.
The floodwaters inundated low-lying neighborhoods, washing away several structures and toppling one of the main transmission lines through Missoula. Still, the company said, customers never lost power.
It wasn’t until last week that the soils dried enough to bring in the heavy equipment needed to repair the system. NorthWestern didn’t have a cost estimate on the damage.
“It is one of our main transmission lines in Missoula, but because we have multiple lines, we didn’t see any outages to customers associated with it,” said Gary Palm, the operations manager for NorthWestern’s Missoula division. “But it is part of our reliability for the whole Missoula area.”
The force of the river, which flowed at 51,000 cubic feet per second and reached a 100-year record by mid-May, also worked to reshape the river channel.
The full impact of that hydrological work is still becoming evident as the water subsides, and NorthWestern is considering future flood events and their impact on Missoula’s power grid.
“We’re having initial talks within the company about the idea of maybe relocating the line, said Larcomb. “But we don’t have a specific proposal. We do realize it’s a flood-prone area and we should consider that.”
Morgan Valiant, the city’s conservation lands manager, noted the water’s depth in what’s now a sandy inland wood. The evidence of the flow, marked by moss and forest debris four feet up the listing trees, also represents the river’s natural floodplain where the water coursed two months ago.
Most of the infrastructure in the Tower Street Conservation Area washed away, including trails, signs, asphalt and fencing. The area remains closed to the public, though the city is working to reopen the area.
“We pretty much lost all of our trails and we’ve got to do a lot of work in the parking lot,” said Valiant. “Our work is happening at the same time as NorthWestern Energy and we hope to get both our projects moving forward in concert so that when one is complete, the other is complete.”
That should happen in about three weeks, though changes in the river channel have already reshaped the park.
“Where I’m standing was probably pushing chest deep in some spots,” said Valiant. “That’s one of the things that really shifted this year – all these little side channels have started to form.
“It was a smaller side channel and now it has turned into a pretty decent-sized stem of the Clark Fork River, and it might hold water for the majority of the season, where before it would hold it just for a few months.”