A 1980s federal law gives the U.S. Army Corps of Engineers the authority to dredge the Cowlitz River of the sediment still flowing from the last Mount St. Helens eruption, but agency leaders say it does not have the federal funding to start dredging and the threshold to begin hasn't been met.
A spokesperson for the Army Corps of Engineers’ Portland District told The Daily News last week that dredging the Cowlitz River wasn’t “a realistic expectation” due to costs, as well as other municipalities’ presumptions that the nation’s remaining large rivers’ tributaries would also be dredged.
Kerry Solan, another spokesperson for the agency’s Portland District, has since clarified.
She said the Corps has the legal authority to dredge the Cowlitz River due to a 1985 budget passed by Congress and its “unique need” for flood risk management. However, this specific flood risk project hasn’t received a Congressional appropriation.
Solan also said the threshold for dredging the Cowlitz River has not been met, based on the agency’s annual sediment monitoring.
Still, the river has experienced minor flooding amid storms in recent weeks, and Cowlitz County leaders say the sediment buildup is worsening the flood risk.
The Corps is preparing to raise the level of the Toutle sediment dam to help fix the issue, but local leaders say dredging is also necessary.
The Corps of Engineers has managed the sediment building in the Cowlitz River — and its costly ongoing impacts — since Mount St. Helens’ 1980 eruption, which sent 1 million Olympic swimming pools’ worth of debris into the upper Toutle Valley and into nearby rivers flowing downstream.
The sediment continues to flow, raising the river bed. In 2008, the Corps dredged the last 5.7 miles of the Cowlitz River, but hasn’t since.
Kelso City Councilman and former Weyerhaeuser engineer Mike Karnofski said the Cowlitz River is too unique to compare to the nation’s other large river tributaries.
“To me, it doesn’t set a precedent if they would dredge,” he said, “because there’s no other river in the United States that’s filling with silt from a volcano.”
Sloan said the benchmark to start dredging the Cowlitz River is when data shows that areas are not, or soon will not, meet their mandated “levels of protection.”
The level of protection corresponds to the risk of flooding based on a model showing a 1% chance of flooding any given year, or noted as 1 in 100 years.
Along the Cowlitz, “flood” is defined as the river overtopping the levees, said Ben O’Connor, who is a Corps hydrologist working in the Mount St. Helens area.
The standard level of protection in Castle Rock is 1 in 118 years; Kelso is 1 in 143 years; and both Longview and Lexington are 1 in 167 years, according to the latest Corps sediment report.
As of 2024, Kelso and Longview were at a comfortable 1 in 500 years or more, Lexington around 1 in 236 years and Castle Rock at 1 in 135 years, said O’Connor.
However, David Vorse, longtime Castle Rock public works director, said he expects that to soon change. Vorse said he believes the Corps’ August reports, likely to be released in 2026, will show the city is nearing the benchmark to start dredging.
“We fully anticipate when we do see those reports in March, we’ll be really, really close to — or under — those levels of protection,” he said.
Vorse also said he understands the risks dredging has on the river’s ecology, especially for fish populations. But there are no options, he added, now that the Cowlitz River has so much sediment, it is flowing past the sediment retention dam.
On top of the levees, the heart of communities’ protection is the giant dam that runs across the North Fork Toutle River valley. The structure was built in 1989 to allow sediment to sink out of the slowed water to the riverbed, stopping it from flowing downstream.
Since it was built, sediment caught by the structure has raised the miles-long valley floor by about 100 feet, Solan said in May.
Now, the dam has gone from catching 80% of passing sediment to only catching 20% since it was last raised in 2013, a Corps spokesperson said in March.
The Corps has started the process to raise the crest, but the actual work isn’t set to start until this summer, and could stretch into fall 2027, while communities downstream fear more flooding in the years to come.
Still, the project may provide more safety than just a higher crest. O’Connor said the last raise in 2013 not only prevented more sediment from flowing downstream, it also allowed the river to erode more sediment than it was depositing.
A June listing for the project on the federal government’s contracting website said it is estimated to cost between $25 million and $100 million.
This comes as the Corps faces budget shortfalls.
The agency saw at least $1.5 billion in cuts from the Trump administration this year, with blue states like Washington taking especially big hits.
“We want to do the best with the money the taxpayers give us,” said Solan on Friday, adding the agency’s priorities are “life safety and making the taxpayers dollar go as far as it can in addressing this issue.”
