On the evening of January 16, 2011, a soaking-wet Sunday in northwest Oregon, the Sandy River, engorged by snowmelt and hurricane-level rainfall, leapt its banks. The river tore through neighborhoods on the slopes of Mount Hood, devoured cars and trucks, and left hundreds without power or phone service. Lolo Pass Road was transformed into the Sandy’s new channel.
If any good came of the catastrophe, it was this: As the flood hurtled along, it uprooted dozens of trees and swept them downriver, where they eventually lodged against the pilings of a construction site at which the state was replacing two aging bridges. The massive raft of splintered, waterlogged debris couldn’t be used for much, but it was perfectly suited for one purpose – the creation of salmon habitat.
The Freshwater Trust, a non-profit river restoration group, was ready to put the logs to productive use. Since 2010, the Trust – on behalf of a coalition of agencies, private interests and non-profits together called the Sandy River Basin Partners – had been working to restore the Salmon River and Still Creek, two streams that eventually flow into the Sandy (itself a 56-mile-long tributary of the Columbia). For nearly a century, salmon and steelhead in the Sandy watershed had been partly impeded by Marmot Dam and Little Sandy Dam. To the delight of river advocates, the dams were removed in 2007 and 2008. Yet the fish still faced a major barrier to recovery: Decades of Army Corps meddling in the name of flood control had left rivers straightened, lined with dikes and berms, and purged of woody debris. “They lost the habitat diversity and complexity that salmon thrive on,” says Mark McCollister, habitat restoration director at the Freshwater Trust.
The theft of riverine wood especially harmed the fish. It’s hard for modern-day boaters, accustomed to smooth water, to imagine just how much woody debris once cluttered Northwestern rivers. Settlers and surveyors in the late 1800’s described miles-long logjams comprised of hundreds of thousands of pieces – not branches, but trees up to fifteen feet in diameter. The enormous snags made travel hazardous or impossible. Even the mighty Columbia was chockfull of immense trees.
As a result of the Army Corps’ clearing, along with widespread timber harvest, that natural wreckage has mostly vanished from contemporary rivers. That’s good news if you’re a rafter who doesn’t want to see your inflatable craft punctured. But if you’re a fish? Not so much. As any angler who’s ever cast behind a logjam can attest, in-river wood scours out deep pools in which adult salmon and steelhead rest on their way upriver. Spring Chinook salmon, which enter rivers long before spawning in the fall, are particularly reliant on those holes for shelter through hot summers.
Equally important are the services that debris provides for young fish. “If you’re a fish that’s a few inches long and you’re in a river that’s flowing at one to three meters per second during a flood, you’re not going to be able to hold your position (in a main channel),” David Montgomery, author of the indispensable King of Fish: The Thousand-Year Run of Salmon, pointed out in a 2012 lecture. By deflecting floodwaters into slower side channels and floodplains, woody debris helps those vulnerable juveniles take shelter during high flows. And by sapping rivers of their kinetic energy, logjams allow gravel and cobble to settle out, creating the substrate that salmon need to build redds and lay eggs.
Creating logjams has been a crucial part of the restoration strategy for the Still and the Salmon. Each artificial jam that’s been installed, says McCollister, contains between 15 and 40 pieces of wood, obtained from private landowners, federal agencies, and the Oregon Department of Transportation (ODOT), which clears “hazard trees” from roads. Nonetheless, logs have remained the limiting resource in restoring rivers to their original states. “You look at the Northwest and there are trees everywhere, but one of the hardest parts of the projects is finding enough wood,” says McCollister.
That’s what made the 2011 flood such a windfall. ODOT spent weeks clearing the jam from the construction site; as the agency removed trees from beneath the bridge, it donated the largest ones to the Freshwater Trust, which placed them in the Salmon later that year. "Floods are still pretty traumatic for the natural area," Freshwater Trust spokesperson Adrian McCarthy told The Oregonian two weeks after the disaster, “but we can make the best of it.”
Once formed, logjams, pools and side channels have a nearly instantaneous impact. “You don’t have to excavate anything to create a side channel – it’s so easy to pop these rivers back into their floodplain,” says Greg Wanner, supervisory fish biologist at the Mount Hood National Forest. “As soon as we take out a berm and let water go down a side channel, juvenile fish key in. These channels haven’t had water in them in 50 years, and we see salmon and steelhead the next day.”
Wanner adds that it’s too early to say whether the restoration efforts – which included opening up around 7,000 feet of side channels in 2013 alone – are actually increasing production or merely redistributing existing fish. Smolt surveys should provide definitive answers in years to come. And he says there’s still much to be done: perhaps another five years of work on Still Creek, and another eight on the Salmon.
Still, McCollister is confident: “We know where we are, where we want to be, and how we’re going to get there,” he says. Sometimes, all fish need is a fallen forest.
Ben Goldfarb is an editorial intern at High Country News. He tweets @bengoldfarb13.