By Fiona Skeggs
The upper Quinault River in Washington is always changing. In February, you’ll be scrambling over rocks and dodging areas of soft, wet sand that was about 8 feet lower in October, the high winter flow having deposited new material on the floodplain. In December, you’d have been swimming.
Still, water levels in rivers across the Pacific Northwest are at historic lows. Valleys once covered in thick vegetation are now barren, rocky landscapes. Extensive logging over the decades has increased erosion, flooding events are more frequent and fish spawning habitats are dwindling. The loss of plants and trees in the watershed has allowed rivers to widen and engulf much of the historic floodplains that once protected communities downstream.
These vast expanses of water are also rising in temperature. Glaciers are melting. In Olympic National Park, the Anderson Glacier retreated to less than 10% of its original length between 1927 and 2009. And by 2015, it had disappeared entirely, according to the National Park Service. Without the injection of cold water, summer temperatures are soaring to levels lethal to aquatic life.
While it won’t reverse glacial retreat or climate change, engineered log jams provide one solution for restoring rivers and woodlands to a more natural state, reducing the risk of flood and returning the habitat to prelogging times.
WHAT IS AN ENGINEERED LOG JAM?
All across the riverbank, clusters of vertical wooden posts dot the valley. Arranged like a skittles at the end of a bowling lane, the upright poles are connected by horizontal beams and surrounded by fallen trees, roots and driftwood. Small boulders and pebbles are sprinkled on top. Some stand alone on the dry riverbank; some are islands with water flowing past on either side.
The occasional flash of green indicates a log jam considered stable enough to support growth, and the wide, flat post tops provide the perfect perch for a hungry eagle. These giant wooden structures are engineered log jams, but what are they for?
WHY ARE THEY NEEDED?
Large areas of forest around Lake Quinault, Washington, were logged in the early 1900s to provide timber for building materials and clear land for settlements. Bill Armstrong, biologist for the Quinault Indian Nation, said more than 99% of old mature woodland in the upper Quinault Valley has been lost.
The removal of trees and their stabilizing web of roots from the valley led to increased erosion of the riverbank, widening of the water channel, flooding and a decrease in suitable spawning habitat for sockeye salmon.
By restoring the floodplain of the Quinault River and replanting vegetation, Armstrong hopes to protect the communities of Lake Quinault, and the road that runs the perimeter of the lake, from flooding. He said by restoring the floodplain and substrate along the river, they will be able to slow the erosion or perhaps stop it altogether.
WHAT DO THEY DO?
Engineered log jams help split the flow of water and confine channels to certain locations.
Armstrong said before restoration efforts started, the floodplain was a desolate gravel bar lacking any signs of vegetation. He said during the winter, when river levels are at their highest, the water would span the entire floodplain as one wide, continuous expanse of water.
After the log jams were installed, the water channel split, meandering around the structures and taking multiple paths through the floodplain. Armstrong said the aim is to reduce the width of the channel to an average of about 150 feet.
Armstrong said the log jams are designed to mimic and restore the process lost in the logging of old growth. He said large trees used to line the riverbank, and the root balls, some up to 60 feet wide, grew under the riverbed to naturally create channels and islands. The root balls died off with the removal of the trees, so the river had no obstructions and flowed as one unstoppable force, eroding the riverbank as it went.
The log jams allow sediment and wood to accumulate and create new areas on the floodplain, which over time will become established with vegetation and trees. The deadwood and debris also slow the water flow.
Mike McHenry, fish habitat manager for the Lower Elwha Klallam Tribe, said by slowing the river, water pools form behind the jams, which contain cooler water for the salmon to rest and hide in during the hot summer months. He said the log jams are also vital in restoring fish habitat as they cause gravel to accumulate, creating areas of substrate suitable for spawning salmon.
HOW ARE THEY BUILT?
A crane and pile driver installed the 40-foot vertical logs 30 feet below the surface. Construction varied depending on the condition of substrate under the riverbed. Armstrong said on a good day, they’d drive 20 posts if the ground was soft, some days they’d only drive six.
“Sometimes they go down to a couple inches,” he said. “Sometimes they don’t go down at all.”
The installation took two months. Construction started in August 2008, and 13 log jams emerged over the summer. To date, there are just under 50 log jams. Armstrong said a few were washed away by the river, but generally they’ve held well.
He said during the first year of construction a big storm came through in early September, and the river went from low, summer flow to almost full, winter flow in one day.
“The whole project area was underwater,” he said. “They had to move all the pile driver, the crane, all the heavy equipment out.”
Armstrong said they didn’t lose any material, but it was a race against time to move the logs that hadn’t been assembled yet out of the water’s path and the danger of being swept downstream.
Once the log jams are stabilized with sediment and substrate, Armstrong and his team plant trees on top of the jams to further stabilize the accumulated debris and encourage growth.
“We usually wait a year or two,” he said. “Then we come out and plant conifer, alder and black cottonwood.”
It takes around 10 years for young trees and vegetation to colonize an area and a further 50 to 80 years to fully mature. Armstrong hopes the log jams will one day become small, forested islands that the river will naturally flow around.
“As far as forests go, that’s our target,” he said, pointing to the dark green canopy of Douglas fir and Sitka spruce behind him, “to restore as much of these older trees and old forest structure throughout the valley bottom as we can.”
Fiona is a science and environmental journalism graduate student at Medill. You can follow her on Twitter at @fiona_skeggs.