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Rattlesnake Dam removal poised to begin; creek to flow freely after 115 years

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Posted at 4:02 PM, Mar 09, 2020
and last updated 2020-03-09 18:02:23-04

Only one more month until work begins on a project to allow Rattlesnake Creek to flow free for the first time in 115 years.

Rob Roberts of Trout Unlimited and Missoula City Conservation Land Manager Morgan Valliant have appeared before the Missoula City Council a number of times in the past year or more explaining plans to remove the Rattlesnake Dam.

But when they spoke to the Public Works Committee on Wednesday, it was probably their last appearance in the City Council chambers before April when the initial work begins.

In April, crews will begin removing the old dam outbuildings, including the caretaker’s cabin, in preparation to move the large demolition equipment onsite in late June. After a groundbreaking ceremony to kick things off, the crews will construct a side channel in July using pneumatic hammers – no explosives – to allow the creek to bypass the dam.

“At that point, that project will be moving full steam from July to the beginning of October,” Roberts said. “The actual demolition of the structures will go pretty fast.”

Because the concrete structure is clean, it will be cut in such a way that the Department of Environmental Quality allows the concrete to be buried on site, which saves money.

That should be complete by August, allowing the team to reconstruct the stream channel so the creek is flowing naturally by mid-October. The team has a hard deadline because the construction permits require all water-related work to be finished by Oct. 15.

“Communication, getting the word out is important. This will be a significant disturbance to the site,” Roberts said. “Many who have been involved in these kinds of projects know that, about midway through, it looks like a bomb went off. You have to deconstruct to construct, that’s just the way it works.”

Over the winter, the project team has used the city greenhouse to sprout almost 2,000 plants from seeds collected in the Rattlesnake corridor. The starts, along with 10,000 willow cuttings, will be planted in the spring and mostly the fall to revegetate the project area.

The city will be calling for volunteers to help with the planting work. Roberts anticipates that everything could be done by Thanksgiving. The project area will be fenced temporarily to ensure the new banks, wetland and plants aren’t disturbed while they become established.

But that doesn’t mean the public won’t be able to see what’s going on. Valliant said the city would be building a few new trails and overlook points with interpretive signs and kiosks to allow people to monitor the progress.

“We’ve already started work on the east-side trail and built a construction overlook that’s going to have some temporary signs about the project so the public will be able to come up and watch this thing happen,” Valliant said.

rattlesnake-dam-1.jpg<div class="Figure-credit" itemprop="author">Martin Kidston/Missoula Current file photo
The concrete dam will be removed and Rattlesnake Creek restored to natural conditions.

All told, the project will cost around $2 million, including about $400,000 that has already been spent on planning and design. Of the total, the demolition and stream restoration work, not including revegetation, costs about $800,000.

Most of the funding for this year’s work, almost $1.4 million, comes from federal, state and private grants. Even the Federal Emergency Management Agency is chipping in some money because removing the dam diminishes Missoula’s risk of flooding, should the dam have failed.

As the area recovers in the future, Missoulians will be able to see priceless ecological and recreational benefits.

“One of the biggest benefits is reconnecting Rattlesnake Creek for about 15 miles upstream. That has not been the case since 1901,” Roberts said.

Roberts said it could help threatened bull trout move up from the Clark Fork River to spawn in the source lakes in the Rattlesnake Recreational Area, even though lower stretches of the creek are degraded by surrounding homes and roads.

The area under the former reservoir will be turned into about 4 acres of wetland, which will contribute to the biological diversity of the area. And once the new plants are established and the fencing removed, the riparian area will provide cover and linkage for wildlife traveling through.

“The Rattlesnake corridor is a major wildlife migratory corridor, it always has been,” Valliant said.

City councilman Brian Von Lossberg said none of this would have happened if the city hadn’t taken action to acquire Missoula’s water system from Mountain Water two years ago. It was a struggle prompted by economic factors, but this project is another benefit, von Lossberg said.

“This was the other opportunity, to do this kind of ecological restoration work that public ownership brought to the table,” von Lossberg said. “Generations of Missoulians will be bringing their families and their kids to these areas and telling the story and learning about the story.”

Contact reporter Laura Lundquist at lundquist@missoulacurrent.com .