When Mount St. Helens erupted May 18, 1980, the upper North Fork of the Toutle River was buried in up to 600 feet of volcanic debris.
Forty-three years later, the resurfaced river cuts through a barren sediment plain and spills over a dam holding back millions of cubic yards of silt, before regaining anything close to its pre-eruption look.
The sediment retention dam built to help protect downstream communities from flooding contributes to the ongoing buildup of gravel and sand.
Unlike its counterpart to the south, there’s been limited restoration work on the North Fork, but Mother Nature appears to be taking matters into her own hands.
‘Nature’s River Restorers’
When researcher Colin Thorne visited the Toutle River last summer, he was “amazed” to see parts of the sediment plain turning green. The reason? Beavers moving from tributary streams into the main stem, said Thorne, professor emeritus of physical geography at the University of Nottingham, England.
“I think they’re telling us something. Maybe it is time we can start restoration work on the North Fork Toutle,” he said. “It really brings a lump to your throat. … These are nature’s river restorers.”
Where beavers go, salmon are likely to follow.
Beavers create slow water and deep pools that provide opportunities for juvenile salmon to grow, hide from predators and make their way down to the ocean to complete their life cycle, Thorne said.
The sediment retention structure has hampered efforts to improve salmon runs in the upper reaches of the North Fork. Fish headed upstream cannot get through the structure, which also contributes to the sediment buildup.
In 1989, the U.S. Army Corps of Engineers built a fish collection facility about a mile downstream of the sediment dam, where salmon are collected, then trucked and released into tributaries upriver to spawn.
The beavers have begun moving from tributaries to wall-based channels — river channels running along the base of the valley wall, rather than through the middle of the sediment plain, Thorne said. The channels are shady with cooler, spring-fed water containing food and nutrients for fish from insects, leaves and other debris falling off overhanging trees, he said.
“The wall based channels have a lot of potential for becoming salmon and lamprey habitat,” Thorne said.
While he hasn’t gotten a close look at the channel on the south side, the north side is definitely “greening up” and improving habitat, Thorne said.
These changes may have been aided by grade-building structures, or engineered log jams, installed by the Army Corps 13 years ago to study if they help block sediment from moving downstream.
“We want to find out, are they what made this area good enough for the beaver to make a foray into it?” Thorne said. “Is it just a coincidence or did the engineered log jams set the table for the beaver by encouraging willows and alders to grow? Because that’s what beaver like to eat.”
With or without human intervention, it will be decades before the entire watershed recovers, but evidence of natural progress is an encouraging sign for researchers and conservationists.
For the Lower Columbia Fish Enhancement Group, which has worked to restore the South Fork Toutle area for years, investing in the North Fork is “problematic,” said Shauna Hanisch-Kirkbride, managing director.
The large amount of sediment flowing off the mountain into the North Fork and the bureaucracy surrounding the sediment retention structure creates uncertainty, Hanisch-Kirkbride said.
“We’ve been hesitant to get real involved until the future of it is real clear,” she said. “Plus my organization is plenty busy with the South Fork.”
Creating Habitat
The South Fork, which branches off just east of Toutle, bounced back much quicker because it was not hit as hard by the eruption and doesn’t have the sediment retention dam.
Although the 1980 eruption killed a lot of fish in both forks of the Toutle, the longer term impact was habitat destruction, Hanisch-Kirkbride said. The effort to recover some economic value from the damaged trees by salvaging them denuded the watershed, making things worse ecologically, she said.
It’s difficult for plants to grow in the sediment, which is not rich soil, Hanisch-Kirkbride said. The river is warmer and moves faster, in part because of a lack of natural wood in the water, she said.
“Those things combined don’t make good fish habitat,” Hanisch-Kirkbride said.
Restoration includes putting wood in the water to help slow it down and create areas for seedlings to establish, Hanisch-Kirkbride said. The trees provide shade and nutrients, eventually die and fall into the water, perpetuating a cycle that’s currently lacking, she said.
After the Lower Columbia Fish Enhancement Group’s work in Bear, Harrington and Little Cow creeks and Little Cow Springs a few years ago, steelhead and coho salmon now spawn there, said Brice Crayne, project manager.
Fish responded really quickly to the changes, Hanisch-Kirkbride said.
“What’s impressive there is if you build it they will come,” she said.
The group is now taking “little bites at a time” off a long-term project to restore habitat along a 17-mile stretch of the South Fork, after working with a team of experts to complete the design in 2021, Hanisch-Kirkbride said. The project will likely take 20 years to complete, depending on funding, she added.
“It is a big and bold project,” Hanisch-Kirkbride said. “To really create change and affect habitat; thinking big helps.”
Last year, the group received $5 million from the state’s Salmon Recovery Funding Board to implement the project’s first phase over the next four years. This includes restoring habitat by adding wood and excavating channels along 2.82 miles of the South Fork Toutle River.
Some of these methods could eventually be used in the North Fork Toutle but it’s “a very different setting,” Hanisch-Kirkbride said.
Shifting From Sediment
The amount of silt trapped by the sediment retention structure varies from year to year but adds up to about 3 million cubic yards annually, according to the Army Corps of Engineers. That would be enough to fill 50 million standard full-size pickup trucks, which each hold 2.5 cubic yards of material.
Since it was built in 1986, the dam has trapped about 125 million cubic yards of sediment out of its estimated capacity of 258 million cubic yards. That capacity is after two planned crest raises totaling 23 feet.
While the Corps’ grade-building structures successfully slowed the river and blocked sediment from moving downstream, sediment will bury the structures after the 10-foot crest raise scheduled for next year, said John Morgan, Corps spokesperson.
While the Corps’ focus has been addressing the sediment, the agency is among more than a dozen participating in the Spirit Lake-Toutle/Cowlitz River System Collaborative, aiming to address the watershed as a whole.
The group formed in 2021 to allow for easier discussions and agreements among federal, state and local stakeholders about the future of the water systems impacted by the 1980 eruption.
Thorne, who has done research at Mount St. Helens on and off since 1984, got involved in the collaborative to help in any way he could, he said.
Until recently, the Toutle and Cowlitz rivers have been managed as a hazard, which they still are, Thorne said. However, there is now opportunity to help make the Toutle River more productive like it used to be, he said.
“That’s where the collaborative can really help,” Thorne said. “By bringing forward partnerships between different players, interest groups with the common aim of restoring the ecology of the river to support the economy of the community.”
