The Rattlesnake Dam has seen 115 summer solstices, but this was its last.
On Monday, crews started preparing the slopes east of Rattlesnake Creek for the construction of a bypass channel of that will eventually funnel water around the Rattlesnake dam, leaving it high and dry so it can be removed.
The project to remove the now inoperable dam, built in 1904, and restore Rattlesnake Creek has been a multi-year effort by the City of Missoula’s Water Division and Parks and Recreation Department, Trout Unlimited, and Montana Fish, Wildlife, and Parks – with the support of more than 20 entities, including numerous local businesses, individuals, and organizations.
Last month, crews tore down a few of the smaller outbuildings. Last week, Idaho-based Aqua Terra Restoration, which got the contract to do the construction work, pre-positioned its bulldozers, excavators and other heavy equipment down near the dam. Now, the real work begins.
With the last of the spring runoff coming down, the creek’s flows have dropped enough that water is no longer blasting through the rectangular hole in the middle of the dam. Some daylight can be seen through the top of the hole.
But the water is still a little higher than planned. Work was originally scheduled to start the first week of July, said Rob Roberts, Trout Unlimited dam project manager, but Aqua Terra either finished other projects early or a few fell through.
“It’s a little earlier, probably by a week or two,” Roberts said. “The water is on the higher side of normal, which is always a contingency. But there’s plenty of work that can be done outside of the channel.”
Aqua Terra’s owner, Arlin Grimes, has an idea of what to expect. Having lived in the upper Rattlesnake valley, he’s returning to his childhood stomping grounds to remove the dam and re-naturalize an area that was dominated by the dam the entire time he was growing up.
“Arlin’s local knowledge, fisheries background, and decades of experience in construction and stream restoration are sure to produce a project Missoula can be proud of,” Roberts said.
On Monday, the crews were beginning to dig into the eastern embankment, taking out trees and topsoil, screening it to pull out the rock and gravel. That will probably continue through the week.
On Tuesday, they’ll start draining the reservoir to dry things out, because the side channel will be built right through the middle of the reservoir.
The side channel is designed to hold 100 cubic feet per second, but Rattlesnake Creek is currently flowing at about three times that rate. So it’ll take another week or two for the creek to drop low enough to be diverted. Then the crews will have to build a temporary road over the bypass channel to reach the dam to begin cutting it up.
Because the concrete in the dam is clean, the Department of Environmental Quality said it could be cut and buried on site, saving 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.
Project work is expected to continue into the fall with final revegetation efforts by the end of October. Residents can visit the project overlook by taking a short walk or bike ride on the Rattlesnake Greenway. The dam site and overlook are about .8 miles from the trailhead at the north end of Duncan Drive. Visitors to the site should use caution as construction work begins.
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.
Visitors to the site should use caution as construction work begins. The dam site and overlook are about .8 miles from the trailhead at the north end of Duncan Drive. Residents can visit the project overlook by taking a short walk or bike ride on the Rattlesnake Greenway.
A webcam has been installed to allow daily glimpses of the progress. See the latest photo at here.