FROM THE VICE PRESIDENT
Campus research efforts now expend more than $67 million annually.
A rundown of science stories during the past year
THE OUTER LIMITS
New University research center studies the edge of human endurance.
THE ROOTS OF SOCIAL INEQUALITY
Digs in British Columbia offer a groundbreaking view of hunter-gatherer societies.
Research reveals another public health threat from asbestos contamination.
A young UM researcher studies flying rhinoceros beetles in Taiwan.
The Milltown Dam removal allows trapped sediments to travel.
How do prey species react when predators are returned to ecosystems.
THE NEW NOTE-TAKING
UM develops new software to aid college students.
A UM legal scholar reveals Constitution's original intent.
FLIP THROUGH CURRENT ISSUE
Cover: Jeff Cincoski, a triathlete and UM employee, puts a research bike through its paces in a 100-degree, temperature-controlled room at the Montana Center for Work Physiology and Exercise Metabolism.
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Milltown Dam removal releases sediments
By Patia Stephens
|UM geosciences Assistant Professor Andrew Wilcox carries a McNeil sediment sampler through the Clark Fork River west of Reserve Street in Missoula. Wilcox has observed widespread deposition of sediment released by the removal of Milltown Dam in that stretch of river.
On his faculty Web site, Assistant Professor Andrew Wilcox recruits prospective students with the following quip: “The University of Montana is a fantastic place to study river systems. … Montana also has great geography for studying rivers – there are a lot of nice ones around here, and some screwed-up ones, too.”
It’s a humorously apt description of a place that has both some of the most pristine bodies of water in the world and some of the most polluted, thanks to its legacy of resource extraction.
The Clark Fork River, named for explorer William Clark, is the main drainage for Western Montana’s northern Rocky Mountains and a main tributary of the huge Columbia River. The Clark Fork and its own main tributary, Silver Bow Creek, are recovering from a century of mining for copper and other metals in Butte and Anaconda. In 1908 a massive flood flushed millions of tons of mining and smelting waste down the two waterways. These heavy-metal residues – mainly arsenic, cadmium, copper, lead and zinc – traveled more than 100 miles until they hit Milltown Dam. The dam had been built only a few months earlier at the confluence of the Clark Fork and Blackfoot rivers just east of Missoula. There the toxic sediments stayed – most of them, anyway – earning the 120-mile stretch between Butte and Missoula the dubious honor of being the nation’s largest Superfund site.
The Clark Fork River Superfund Site was established in 1983 after dangerous levels of arsenic were discovered in Milltown wells and traced to sediments that had collected in the 180-acre reservoir behind the dam. Two decades later in April 2003, the U.S. Environmental Protection Agency and the Montana Department of Environmental Quality issued a plan recommending removal of Milltown Dam. The plan also called for removal of approximately 2.2 million of the 6.6 million cubic yards of contaminated sediments in Milltown Reservoir. After thousands of public comments, the EPA’s proposal to remove the dam and sediments was finalized in December 2004.
A railroad spur was built to haul the sediments back upstream for disposal at Opportunity Ponds near Anaconda, and excavation began in October 2007. When Milltown Dam was officially breached in March 2008, the Clark Fork and Blackfoot rivers flowed together unimpeded for the first time since the 100-year-old timber crib dam was built. While more than 2 million cubic yards of the most contaminated sediments have been removed, that leaves some 4 million behind. Where will the sediments go? How much has been flushed downstream since the dam was breached? How will it affect the river and its denizens, both in the short and long term?
Those are questions Wilcox and his students have attempted to answer. Wilcox, who researches and teaches in UM’s Department of Geosciences, is a fluvial geomorphologist, meaning he studies river flow, sediment transport and channel evolution. He arrived at UM in August 2007 just in time to cobble together a few small grants and begin studying the removal of Milltown Dam. He received another, larger grant of $180,000 from the National Science Foundation in summer 2009.
Across the country, dam removal is a relatively new and burgeoning industry, and the science surrounding it is in its infancy. In the West, at least eight dams are scheduled for removal in coming years, and debates are under way concerning others. Removal of Montana’s Milltown Dam and its contaminated sediments is the biggest project of its type ever undertaken. Wilcox hopes information gleaned from the project will help inform discussion, planning and execution of other dam removals.
“When tens of millions of dollars are being spent on sediment removal from Milltown,” Wilcox says, “we can see why having better tools for modeling and predicting sediment transport is important.”
Wilcox has had no trouble recruiting undergraduate and graduate students from the geomorphology classes he teaches to work on the research project. Together, they’ve used sampling devices suspended from bridges on the Blackfoot and the Clark Fork to capture sediment flowing into and out of the reservoir. The researchers have measured channel and sediment depths and collected sediment samples from the riverbed and banks between the dam and where the Clark Fork joins the Bitterroot River west of Missoula. They’ve collaborated with UM geochemistry Professor Johnnie Moore to measure heavy metal content in the sediments, allowing them to “fingerprint” the source of downstream deposits based on their geochemical signature.
Wilcox’s sampling, combined with measurements by the U.S. Geological Survey, reveals that hundreds of thousands of tons of sediment have moved through the gap – far more than anticipated. An initial large “pulse” of sediments occurred after the breach in 2008, followed by a smaller pulse during this spring’s high-water event. Some of the sediment has contained heavy metals. Much of it has been deposited, at least temporarily, along the riverbed and banks of the Clark Fork – especially where the river slows and spreads near Kelly Island, west of Missoula’s Reserve Street and the city’s levees. Some of the sediment, presumably, has traveled more than 100 hundred miles downstream to settle behind the next major obstacle – Thompson Falls Dam.
With so many organizations involved in facets of the dam removal – the Environmental Protection Agency; the Department of Environmental Quality; UM; Fish, Wildlife & Parks; Envirocon; Atlantic Richfield; the Clark Fork Coalition; and private monitoring consultants, to name a few – there’s bound to be some controversy. Wilcox wrote a guest editorial for the Missoulian last November to reject a statement about the Clark Fork’s water quality that was incorrectly attributed to him.
“I am not a toxicologist,” he wrote. “I would not make human health recommendations.” In his opinion piece, and again in this interview, he said the EPA has found that the Clark Fork’s water quality is within health standards. “My students and I spend a lot of time in the Clark Fork. I’m not concerned about our health.”
Wilcox is more concerned with the sediments’ effects – negative and positive – on the riverbed and the creatures that live in it, such as the threatened westslope cutthroat trout and bull trout.
“Even if the sediment doesn’t have contaminants, it could have effects like suffocating the gravels that fish spawn in,” he says. “That is the most significant effect we’ve seen on the river. The space between rocks where bugs and juvenile fish hang out has been filled with sand and fine sediments.”
But that development may be temporary – and to a certain extent, it may also be natural.
“Rivers need sediment,” he says. “A river bed without sediment is coarse and ‘armored’ – static and locked into place.
“We know that this dam removal will create long-term benefits to the river by restoring natural processes and habitat – allowing sediment to move and fish to migrate. Part of what makes rivers natural is that they are dynamic. They erode their banks. They erode their beds. They move from side to side.”
Wilcox’s research also has shown dramatic changes to the Blackfoot River, the revered stream made famous by Norman Maclean’s book “A River Runs Through It.” Sediments deposited in the lower Blackfoot by dam backflow already have been flushed out, restoring riffles and pools to the river after a hundred years without them. Now the fish that can once again migrate upstream from the Clark Fork to the Blackfoot have a more natural habitat to welcome them.
Where policymakers and the public might prefer a sure thing, Wilcox takes the view of a scholar and scientist.
“Removing dams is an experiment,” he says. “There’s a lot we don’t know and a lot we can learn. We need to embrace uncertainty and be open to learning.”
For more information, e-mail email@example.com.
|(Top) Milltown Dam was built in 1907 by copper-mining tycoon William A. Clark to supply hydroelectricity to his sawmills in nearby Bonner. The dam trapped nearly 6 million cubic yards of contaminated sediment from upstream mining activity. (Middle) A coffer dam side channel is breached in March 2008, allowing the Clark Fork to flow freely past Milltown Dam for the first time in a century. (Bottom) This area of Milltown Reservoir, which is upstream from the dam removal, shows effects of river erosion.
|UM researchers walk on a sandbar made up of sediments once trapped behind Milltown Dam. The sandbar is several miles downstream from the former dam site.
|A bedload sampler is dangled into the Clark Fork River to capture the sediment flowing downstream.