“This is an unprecedented opportunity to understand how rivers function,” said Wilcox, an assistant professor of geosciences at the University of Montana. “Other people have to do this in lab models, so this is a great natural experiment.”
Wilcox leads a research team studying how the Clark Fork and Blackfoot rivers will react to flowing freely for the first time in a century, and what happens to their unleashed silt, sand, gravel and rocks.
Researchers don't know whether the sediment will make the riverbed more sandy or gravelly, or whether it will flush quickly and spread out for hundreds of miles downstream.
Geoscientists in Washington state and other areas with upcoming dam removal projects are watching the Clark Fork to see what happens, Wilcox said.
The U.S. Environmental Protection Agency “has scour models, but I'm trying to find out if the EPA predictions are correct” for the Clark Fork, he said. “I'm trying to learn if we can apply what we learn here to dam removals and river management elsewhere.”
The Upper Clark Fork Basin is the nation's largest Superfund site, covering a 120-mile swath of western Montana from Milltown to Butte and Anaconda.
It's also one of the most complicated Superfund projects, involving the removal of a dam and 2.2 million cubic yards of toxic mining wastes at the confluence of two rivers - while minimizing the environmental impact and preparing to restore the confluence to its natural state and redevelop it as a public park.
In addition to physical changes in the river, various researchers are looking at biological and chemical changes as the Clark Fork's ecosystem is allowed to reclaim its natural state 100 years after humans drastically altered it with a dam and metals-laden sediments.
“We're trying to understand the whole river” as it perpetually widens, narrows, deepens and becomes shallow while carrying its historic load, moving sediment both gradually and in big pulses determined by the water's force, Wilcox said.
The Clark Fork's sediment accumulated on the bottom of Milltown Reservoir over the past century, as the river hit slack water at the upper end of the reservoir and then the dam, causing the sediment to settle in a confined area rather than moving continually downstream.
The load will start shifting Friday when the dam breaching releases 300,000 cubic yards of uncontaminated material from the mouth of the Blackfoot River where it joins the Clark Fork, creating muddy waters for several months.
That will be followed over the years by 3 million more cubic yards of sediment from the Clark Fork River upstream of the area where mining wastes are being removed from behind the dam.
The sediment load is not expected to contain toxic materials, the worst of which are being removed as part of the Superfund cleanup.
Watch a video about the history of the Milltown DamWilcox and several of his students have spent the past month measuring the channel depths and topography, sediment samples and other factors on the Clark Fork and Blackfoot rivers upstream and downstream of the dam. They would have started sooner, but the rivers were largely frozen.
Using surveying, sonar and global positioning system equipment, they will monitor where the sediment goes, how fast it moves and how it changes the aquatic environment as it scours out, fills in, and reshapes the riverbed and banks downstream.
Their research will compare data from 2004, from just before the dam breaching and for the next decade in an effort to chart the impact of releasing the two rivers.
Wilcox, who joined the university this fall after working for the U.S. Geological Survey, said he was astounded to find that nobody was studying the Clark Fork's geomorphology - or how water and other forces of nature change the landscape - as the dam breaching approached.
“It was incomprehensible that no one was doing this work,” he said. “So much attention has focused on the reservoir and the dam that it's taken away from the concern about how the river's going to be affected downstream.”
Wilcox and one of his students, Doug Brinkerhoff, took last-minute measurements Thursday, using surveying equipment to measure the Clark Fork's channel depths over a two-mile stretch below the dam.
A spring snowstorm made for chilly conditions as Wilcox, wearing a dry suit, waded and paddled through the water and probed the depths of the channel bed, while Brinkerhoff recorded measurements on shore along Bandmann Flats.
Wilcox will next take measurements in the fall, after the initial sediment from the dam breaching and the larger load from the spring runoff move downstream.
How quickly the sediment moves, how much it scours and where it ends up depends on how much snow the basin receives and how fast it melts over the years.
Snowpack in the Upper Clark Fork Basin is at
97 percent of normal, but a cool spring has lowered runoff rates.
Water flowed past the dam Thursday at about 1,250 cubic feet per second, about half of the 2,200 to 2,300 cubic feet per second that is typical for late March, so that will lower the muddy surge that follows the breaching.
The breaching, which may last about an hour, is projected to immediately raise the river level about 3.5 feet just below the dam, 2.5 feet at Pine Grove an hour after release, 1.5 feet at Deer Creek an hour and a half after release, 1 foot in downtown Missoula two hours after release and a few inches at the Bitterroot River five hours after release.
During the peak flow period in late May to early June, an average spring peak flow of 15,000 cubic feet per second is projected to pass through the breach.
The dam breaching, removal of mining wastes and release of clean sediment will have major changes on the river's aquatic life.
The initial sediment load is expected to kill a large number of fish, insects and other organisms, but fish will be able to migrate upstream again and the ecosystem is expected to recover in three to five years.
State fisheries biologists, who have studied the dam's impact for the past decade, are monitoring the sediment's impact on nearly 500 caged and radio-tagged fish in the Clark Fork above and below the dam site.
None of the fish has died since they were placed in cages or had telemetry devices implanted in early March.
Dave Schmetterling, a Montana Fish, Wildlife and Parks fisheries biologist, and his team will track the fish's mortality and movement each day until the end of high water in July.
Another 30 fish will be tagged after the breaching to monitor their passage through the new river channel and the bypass channel, where boulders have been placed to create resting and hiding places.
The river's current flow rate is below normal and the breaching was timed to occur before peak spring runoff, so fish will be able to swim upstream easily through the gap where the old Milltown powerhouse was located.
Schmetterling said fish migration may be a concern when spring runoff increases the volume and velocity of water flowing through the powerhouse gap, but he said boulders placed in the gap should help fish to pass.
Reporter John Cramer can be reached at 523-5259 or at johncramer@missoulian.com
Public can view dam breaching from bluff overlook
The Milltown Dam breaching can be viewed from the bluff overlooking the confluence of the Clark Fork and Blackfoot rivers.
The overlook will be open to the public.
The breaching is tentatively scheduled for 11:30 a.m. Friday, March 28.
To reach the overlook from Highway 200, turn on Speedway, turn on Deer Creek Road, pass the Canyon River Golf Course, pass the shooting range, go up the hill and park along the road at the crest of the hill. Signs mark the short trail to the bluff.
Parking is limited, so car-pooling is encouraged.
Please follow the posted signs. The area surrounding the trail is private property.
The trail may be slippery and snow-covered and the bluff cold and windy.
The breaching also can be viewed on the Milltown webcam at www.clarkfork.org or www.envirocon.com
Missoulian
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