Local leaders say dredging the Cowlitz River for the first time in about 18 years would prevent flooding along the waterway filled with debris from the last Mount St. Helens eruption — particularly as the roughly 36-year-old sediment retention dam near Toutle is weakening.
Millions of tons of sediment from the 1980 eruption continue to flow down the Cowlitz each year, raising its bed after the debris enters the river from the Toutle River's North Fork. That makes the Cowlitz more prone to floods in Cowlitz County, said Scott Neves, director of the county Department of Emergency Management.
“I can't dump a 5-gallon bucket of sand in my bathtub and expect to have the same amount of water capacity in that bathtub,” he said.
Despite repeated requests — including one by local leaders in the fall — the U.S. Army Corps of Engineers say they cannot dredge a tributary to a major river due to budget constraints, despite more local rain and floods expected early this week (though now mostly in Oregon according to latest forecasts).
“If we start doing one, then we have to do it for everybody,” said John Morgan, a spokesperson for the Army Corps of Engineers’ Portland District, “and then everybody's going to want dredging.”
After initial dredging of the Cowlitz in the 1980s, the last time the river was dredged was in 2008, said Morgan.
In 2024, local lobbying succeeded in gaining federal approval to dredge the Cowlitz near its mouth, but only to keep the Columbia River's 43-foot deep federal navigation channel operational — a channel that moves tens of billions of dollars in goods each year.
While Morgan explained the impacts of sediment in the river similarly to the local officials, he said the Army Corps simply cannot afford to dredge because of the precedent it stands to create.
The agency currently maintains over 25,000 miles of waterways as well as 400 ports and harbors across the country, costing an average of $1.7 billion a year. The agency was also hit with at least $1.5 billion in cuts earlier this year.
“It's just not a realistic expectation,” Morgan said. “We really do have to limit how much we can do because it's expensive. It's a very expensive proposition.”
In October, Cowlitz County Commissioner Steve Rader and Washington state Sen. Jeff Wilson, R-Longview — alongside more than a dozen other officials around the county including mayors, county commissioners and state representatives — sent the Army Corps a letter asking it to dredge from the mouth of the Toutle River, down the Cowlitz to the Columbia, among other requests.
The commander of the Portland District, Col. Larry Caswell, responded in November. That letter, obtained by The Daily News, said the agency was aware of sandbars in the river but that levees along the lower Cowlitz were up to legal standards. It did not address dredging on the Cowlitz.
Rader said he has discussed the issue with the offices of Sens. Patty Murray, Maria Cantwell, and Rep. Marie Gluesenkamp Perez, D-Skamania, and he is headed to Washington, D.C., in February to talk to the Army Corps about the issue.
The problems caused by sediment in the river became clear by the morning after Mount St. Helens’ 1980 eruption when a ship ran aground in the Columbia River’s deep water navigation channel, which sediment had filled from 32 feet deep to just 12 feet.
The blast sent about 1 million Olympic swimming pools worth of debris into the area around the North Fork Toutle River. That’s slowly eroded at a rate of about 6 million tons each year on average, according to the U.S. Geological Survey.
But the problem of sediment in the Cowlitz has only grown worse in recent years due to a delayed raise of the roughly 36-year-old dam that captures the sediment back on the North Fork Toutle River.
The structure has become less and less effective as it fills, switching from catching about 80% of passing sediment to allowing 80% to pass, an Army Corps spokesman said in March.
Rader and Neves said they can see the river filling with sediment.
“If you just take a look at the river,” said Neves, “we have literal islands in the middle of the Cowlitz River that have never existed there, and they've been there so long that there are actually trees growing on them.”
Officials from local cities echo similar frustrations.
Chris Collins, Longview public works director and assistant city manager, said the area is more prone to catastrophic flooding due to the sediment.
"There's just not enough room in the river,” he said.
Devin Mackin, Kelso public works manager, said the sediment has increased the chances of flooding by raising the water table.
“With the amount of sediment in there, it does raise with the groundwater table a little bit,” he said. “If the Army Corps did come through and remove some of that sediment, that would help that groundwater table to lower.”
And David Vorse, longtime Castle Rock public works director, said the sediment is worsening flood conditions each year.
“We're overdue,” Vorse said about major flooding, “and because we now have a capacity issue within the basin, when we get hit, it's going to have more dramatic effects than we have seen in the past.”
Cowlitz County, and the rest of the Pacific Northwest, are set to be slammed by another atmospheric river early this week, with local officials are warning of more potential flooding.
“In my 44 years of being here,” Vorse said on Friday, “I don't know that I can recall seeing 5-plus inches of rain in 24 hours.” Some places in the area saw as much as 19 inches of rain, according to the U.S. Forest Service Friday.
And Vorse said this week’s rain leaves the region particularly vulnerable to flooding from the next storm.
“Now everything is pretty well saturated, so there's no holding capacity in the ground,” he said. “So if we continue to get rains, it's going to immediately get into the river, and that's going to make the impacts more severe.”
