The rush of rock and gravel cascading down from Mount Rainier’s melting glaciers is making a mess of man-made infrastructure in the park.
Roads, trails, bridges and buildings are costing millions to repair, and they’re expected to cost many million more as climate change intensifies.
But the large volume of sediment coming down the mountain also is upsetting the equilibrium between rivers and the park’s oldest living species — giant Western red cedar, Douglas fir and hemlock trees that have helped keep the rivers in their banks for thousands of years.
In some river drainages, most notably the Carbon River in Mount Rainier National Park’s northwestern corner, the riverbed is so loaded with sediment the entire mainstem of the river is flip-flopping across the valley, seeking new routes well away from its historic territory.
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In places, the Carbon has inundated acres of old growth trees, leaving them standing dead in what National Park Service geomorphologist Paul Kennard calls “ghost forests.”
“The river beds are building up, and in the Carbon it’s happening at an alarming rate,” Kennard said. “It gets to be where the bed of the river is much higher than the surrounding forest.”
For centuries, the roots of the big trees and their giant fallen trunks created effective barriers to the water, he said, forcing the rivers to turn aside and find easier paths.
“That’s beginning to unravel here at the Carbon,” Kennard said. “We’re beginning to think that, where for centuries there’s been a balance between the river and the forest, now the river is winning. And the forests are being decimated by the river.”
Kennard characterizes the longstanding struggle as “The War of the Woods.”
He and a group of other geologists, summer interns and graduate students he’s recruited from across the country have turned the upper Carbon River valley into an outdoor laboratory, where they’re working to better understand the balance between the erosive forces of a river and the ability of a forest to hold it in place.
Kennard and his band, who sometimes call themselves “river rats,” hope their findings will help them understand the mechanics of how forests control sudden river-channel shifting, or “avulsions,” erosion, debris flows and flooding — not only on the Carbon but throughout the park and elsewhere.
In many areas of the park, Kennard said, river bottoms are higher than the surrounding forest, and the presence of large trees at the river’s edge is all that prevents catastrophic flooding.
That’s a big threat to roads, trails and bridges, but it also threatens forest habitat that supports endangered species, including spotted owls and marbled murrelets, and salmon and bull trout.
Mount Rainier’s forests have never been commercially logged, and some stands are estimated to be as much as 1,000 years old.
More than two-thirds of the old-growth forests in Washington have been cut since the 1930s, according to the U.S. Department of Agriculture, which makes the park’s stands increasingly valuable as ecological refuges.
The work of Kennard and his river rats already has shown results. Thanks in part to their findings, park managers are better able to figure out where wandering rivers pose the biggest threats and how to design more effective flood protection structures.
Taking cues from the old-growth trees, they’ve found that in many cases, natural timber does a better job than concrete or rock in keeping rivers in their channels.
Another plus for the cash-strapped park: Wood flood-control structures generally are cheaper.
On the Carbon, four massive engineered log jams not only provide flood protection but also are fish friendly. Like icebergs, most of the structures are below the surface, with logs buried 15 feet or more below river bottoms.
As climate change intensifies, more effective, environmentally sensitive ways of controlling rivers are of increasing interest beyond park borders.
On the Nisqually and White rivers particularly, Pierce County and downstream towns are concerned about the increasing amount of sediment leaving the park and clogging the downstream rivers, increasing flooding risks.
In the upper Carbon valley, the river is winning the war of the woods.
“This forest, which took centuries to create, was destroyed in just years,” Kennard said. “Now there’s going to be a tremendous lag.
“We’re going to be in this intermediate area where we don’t get the benefit of a robust forest,” he said. “The river’s going to be extremely dynamic, and it’s going to take centuries to get the trees back here.”