Posted on March 17, 2025
DredgeWire likes this article and offers this relevant dredging history:
Mount St. Helens Eruption and Dredging:
On May 18, 1980, Mount St. Helens erupted, causing the deadliest and most economically destructive volcanic event in U.S. history, with 57 deaths and widespread destruction.
Ellicott Dredges’ Role:
Ellicott Dredges, a company specializing in dredging equipment, was instrumental in the post-eruption cleanup, particularly in clearing the Cowlitz River, which was heavily impacted by ash and debris.
Canonie construction mobilized two Ellicott dredges. They took just five weeks to move and mobilize the 500 ton “Marialyce Canonie“, a 2250-hp, 24-inch dredge 2800 miles from Baltimore. The “Marialyce Canonie” was an Ellicott® Brand “SUPER-DRAGON®” dredge. The two dredges and other supporting equipment required a fleet of more than 60 trucks to make the move.
Quick Cleanup:
Ellicott Dredges’ equipment and expertise allowed for the rapid clearing of ash and debris from the Cowlitz River, which was vital for restoring the area and minimizing further damage.
Impact:
The cleanup efforts by Ellicott Dredges were essential in restoring the region after the devastation caused by the eruption.
Nearly 45 years after Mount St. Helens’ eruption sent almost 90 billion cubic feet of debris into the upper Toutle Valley, millions of tons of sediment still pour down into the Cowlitz River each year.
And that flow is causing costly problems for towns along the way.
Updating Toutle’s roughly 36-year-old sediment retention dam has been delayed, leaving nearby cities to find their own solutions to drinking water needs, and maintaining deep draft levels at ports.
Kelso is looking to update its water system due to impeding sediment, while Castle Rock and and Longview have changed their systems in light of the blast, and the U.S. Army Corps of Engineers continues to monitor sediment levels.
The problem
The issue starts when mountain runoff carries ashen remains of what was the volcano’s peak into the North Fork Toutle River and down to the Toutle. From there, the lower Cowlitz River ferries an average of nearly 3 millions tons of sediment through Castle Rock, Kelso and Longview before much of it dumps into the Columbia on its way to the Pacific Ocean.
That 3 million tons is 10 times greater than pre-eruption levels, and it causes damage by burying cities’ water intake systems and filling-in deep water ports’ berths.
The U.S. Army Corps of Engineers has long managed the issue. It constructed the sediment retention dam in 1989 on the North Fork of the Toutle River, and still spends between $400,000 and $600,000 a year monitoring the problem, said Corps’ spokesman Jeffrey Henon.
But the structure has become less and less effective as it fills, switching from catching about 80% of passing sediment to allowing 80% to pass, said Henon.
While work to refurbish the structure again is planned, it has been delayed, said David Vorse, Castle Rock Public Works director.
And — with the Corps spread thin managing an almost endless number of project around the country including most of the Columbia River hydropower system — the burden of dealing with Mount St. Helens’ sediment has increasingly fallen to cities along the rivers’ path.
Kelso plans for new water system
That management can be a costly task, said Kelso City Councilperson Mike Karnofski, who used to run utilities for Weyerhaeuser’s local operations and now budgets for upgrades to the city’s water system.
The city switched from drawing water directly from the Cowlitz River to a Ranney Collector Well system in 1979, said Kelso Public Works Manager Devin Mackin. Ranney wells collect naturally filtered groundwater using pipes that extend out under a riverbed horizontally from a main vertical shaft.
The switch was planned to create a more consistent water supply, not as vulnerable to seasonal changes in water level, contamination and natural disasters.
But, when the mountain blew one year later, fine sediment deposited on the riverbed began to slow the percolation of water into the intake pipes. That problem has not gone away and it’s not cheap to deal with.
“We do not have a precise cost estimate for managing the silt and sediment in the Cowlitz River because the expenses are too extensive to accurately track, and the silt buildup itself is not systematically monitored,” Mackin said.
To combat the issue, the city has needed to dredge above the intakes, buy water from Longview and even refurbish the system.
The last of that trio alone cost the city about $1 million last year, said Karnofski. And the continuing expense is significant enough that it has led the City Council to budget for maintenance and an eventual replacement years into the future.
The current system has about five to eight years left, said Karnofski. After that, the city will have to build a new water system.
Longview dredging costs
Longview gets its water from groundwater wells near the Mint Farm Regional Water Treatment Plant.
That approach started in 2013 specifically to avoid costly and frequent sediment related maintenance, said Chris Collins, Longview Public Works director and assistant city manager.
“It was to the point where the plant was needing a full rebuild, which would have cost $40 million over the course of nine years, and our new plant was $32 million,” Collins said. “So it made that decision pretty easy.”
And while the approach hasn’t always been universally popular, it has been consistent and helped the city avoid issues that come from getting water directly from the Cowlitz or from a Ranney well system under it.
But, as Port of Longview director of external affairs Dale Lewis will tell you, that doesn’t mean the city totally dodged the bullet.
Last year alone, the port spent more than half a million dollars dredging about 200,000 cubic feet of Mount St. Helens’ sediment from the mouth of the Cowlitz and nearby port berths.
“We dredge almost every year,” Lewis said. “The amount of dredging at the docks varies by year but is almost always needed since the eruption of the Mount St. Helens.”
The recently passed 2024 Water Resource Development Act authorized the Corps to start dredging the mouth of the Cowlitz River to support navigation and not just flood risk, said Henon, the Corps’ spokesman. That could reduce some of the cost the port has taken on.
Castle Rock issues
“When the Mountain blew, the log debris that came down the river literally wiped out the intake structure to the water treatment plant,” said Vorse in Castle Rock.
When the city rebuilt, they put their water intake on the upper Cowlitz River — above where the Toutle and all the Mount St. Helens’ sediment it carries meet the river.
Vorse, who started his job the year after the eruption, said the system they built in the aftermath still provides water to many communities around the area.
Despite that combination of lucky location and ambitious engineering, even Castle Rock hasn’t come out totally unscathed.
Water cleaned by the city’s wastewater treatment plant is supposed to be released by a set of diffuser pipes back into the river, but it’s buried in 3 feet of sediment at all times.
“Again, it’s a sediment issue that has impacted all three of the communities along the river at some level,” he said.
