The function of large wood in a river for salmon habitat could be compared to the game Plinko, from the TV show “The Price is Right.”
With the wood structures as the bounce points and the water as the chip, water slows as it moves downstream, making it easier for salmon to swim upstream to spawn.
But because of floodplain loss and deforestation along the lower Elwha River, those structures have disappeared.
To re-establish the benefits of large wood for salmon, the Lower Elwha Klallam Tribe has been installing engineered logjams (ELJs) in river mile 3.
“That’s really the issue up here—the management of velocity and stream energy—because this is probably the most impacted reach of the Elwha River in terms of floodplain constrictions,” said Mike McHenry, a habitat biologist for the tribe.
The latest restored section of the Elwha River has been impacted by removal of riparian forest plus development upstream, such as the city of Port Angeles’ water intakes and well, a state fish hatchery, and a temporary sediment treatment plant that was built to mitigate the effects of the river’s dam removal project between 2011-2014.
“With that infrastructure, we lost a lot of the historic floodplain where the river’s energy was originally distributed,” McHenry said. “Now it’s funneled, creating a firehose effect. We’ve got super high velocities coming through this reach and ELJs are designed to break that up.”
The tribe installed 18 ELJs in one-third of a mile in 2024, bringing the tribe’s overall logjam count to nearly 100 in the three decades the tribe has been building them.
“When you increase the density of ELJs in a river like this, you really force some pretty dramatic habitat changes,” McHenry said. “You increase the number of pools, dramatically increase the number of side channels, and as a result, there is an interactive effect between the jams.”
This area of river now has multiple channels where the water can spread out as well as forested islands that serve multiple purposes.
When there were historic levels of wood in the river, it was common that islands would form downstream of stable logjams, McHenry said.
On the upstream end of an island, a scour hole develops, creating a pool 9- to-15-feet deep where adult fish—such as chinook, coho and steelhead—like to hang out. The pools also are deep enough to source the groundwater, which helps keep the river’s water temperatures cool.
Another feature of forested islands is that gravel and sediment settle along the margins and tail end of the logjams, creating areas optimal for spawning, said Jamie Michel, the tribe’s habitat program manager.
“You’ve got a lot of great habitat in and among the wood for juvenile fish, and the adults can hang in the deep pools,” he said. “You’re increasing the complexity in it and the logjams are designed to collect additional wood, allowing the river to rearrange itself every time there is a flood of significance.”
After more than 30 years of salmon restoration and dam removal, salmon have returned to the Elwha, but the work is not over. There are areas along the river where habitat restoration is still needed.
“This system is unique, with much of the watershed being in Olympic National Park, but once you leave that, you still have that legacy of land clearing, floodplain development and loss of all that large wood that would have otherwise contributed to channel complexity,” Michel said. “We’ll just continue to watch the evolution of the river and see where additional restoration might be appropriate, when an opportunity arises.”
Engineered logjams were installed in the Elwha River in summer 2024 to enhance salmon habitat. Photo: Natural Systems Design; Story: Tiffany Royal
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