A consequential debate is unfolding along the lower Columbia River. The U.S. Army Corps of Engineers has proposed a new long-term plan to manage dredged sediment from the river’s navigation channel, potentially constructing large underwater containment structures in the estuary to store millions of cubic yards of material.
The proposal reflects the reality that the Columbia must now be dredged every year to keep a shipping channel open. The need for constant dredging is largely the result of more than a century of engineering that fundamentally changed how the river works.
It is essential to understand that sediment is vital to rivers and estuaries as communities in Washington and Oregon consider the ecological risks of new dredge-spoil storage projects in the estuary.
Sediment is the lifeblood of an estuary
Sediment is not pollution. In a natural river system, it is the raw material that builds landscapes.
Rivers carry sand, silt, and organic matter from mountains downstream. When the current slows near the ocean, that material settles out, forming marshes, mudflats, islands, and tidal channels. These constantly shifting features are what make estuaries among the most biologically productive ecosystems on Earth.
Historically, the Columbia River delivered enormous quantities of sediment to its estuary and the nearby Pacific coast. That sediment helped create tidal wetlands and shallow-water habitats that are critical nursery areas for juvenile salmon, as well as feeding grounds for birds, fish, and marine life.
In other words, the river was constantly building her own estuary.
Why dredging now happens every year
Industrial development started reshaping the Columbia River estuary in the late nineteenth century when the federal government began transforming the river into a major shipping corridor.
To allow ocean-going vessels to travel more than 100 miles inland to ports like Portland, Vancouver, Longview, and Kalama, engineers undertook massive modifications to the river:
- Deepening the navigation channel, which today is maintained at roughly 43 feet
- Building hundreds of pile dikes that funnel water into a single channel
- Constructing long jetties at the mouth of the river to stabilize the entrance
- Building dams throughout the Columbia basin
These projects succeeded in creating a reliable shipping lane, but they also forced the river into a shape she would not naturally maintain.
Rivers naturally deposit sediment in deeper, slower-moving areas. Once engineers created a deep navigation channel, sediment began filling it in. The result is that the Corps must now remove roughly nine million cubic yards of sediment every year just to keep the shipping lane open.
Without dredging, large cargo ships could not reach many of the river’s inland ports.
The river is also sediment-starved
At first glance, the dredging problem suggests there is too much sediment in the river. But the opposite is true.
The Columbia River basin now contains more than 400 dams, and reservoirs behind those dams act like giant settling basins. As water slows in the reservoirs, sand and silt drop to the bottom instead of continuing downstream.
Much of the sediment that once flowed freely to the estuary is now trapped upstream.
Scientists have documented that the Columbia estuary receives far less sediment today than it did historically. This reduced supply has consequences. Sediment is necessary to maintain tidal wetlands and marshes, which gradually erode or sink if they are not replenished.
As sea level rises due to climate change, wetlands need sediment even more urgently. Without it, marshes may drown and important fish and wildlife habitats could disappear.
The modern Columbia River faces a paradox: Too little sediment for wetlands, and too much sediment in the navigation channel.
How engineering changed the river’s sediment patterns
Human engineering reshaped how sediment moves through the river. Pile dikes and other training structures concentrate the river’s flow into a narrow channel. Instead of spreading sediment across a broad estuary with multiple channels and floodplains, the modern river funnels water and sediment into a single path designed for ships.
Sediment that might once have nourished marshes and tidal flats is instead swept toward the navigation channel, where it accumulates and must be dredged.
Meanwhile, upstream dams reduce the total amount of sediment reaching the estuary at all.
The result is an artificial distribution of sediment throughout the entire river basin.
Our concerns about dredging and disposal
Dredging has severe ecological impacts. Removing sediment disturbs the riverbed, where many organisms live, and increases turbidity in the water, potentially affecting fish and aquatic plants.
Another concern involves what happens to the dredged material afterward.
Sediments in large industrialized rivers like the lower Columbia contain decades of contaminants such as heavy metals, PCBs, and pesticides.
The Corps’ proposed plan for the lower Columbia would create underwater containment areas designed to store dredged sediment within the river system. These structures could occupy hundreds of acres of the estuary.
We know that concentrating large volumes of dredged material in confined areas could, and likely will, alter water flow, bury habitat, and potentially release contaminants from the sediment material.
The Columbia River estuary is a globally significant ecosystem and a vital migration corridor for salmon. Changes to sediment flows and habitats in this region can have cascading effects throughout the food web.
The river’s needs must come first
The most important question should always be: what does the river herself need in order to remain healthy?
For thousands of years, the Columbia shaped her own estuary. Seasonal floods spread sediment across wetlands and tidal flats. Channels shifted and migrated. Marshes rose gradually as new sediment arrived from upstream. These processes created one of the most productive estuarine ecosystems on the Pacific coast, one that supported immense runs of salmon, birds, and marine life.
Today, that natural community has been dramatically constrained. Dams trap sediment that once nourished the estuary. Pile dikes and jetties force the river into a narrow shipping lane. Millions of cubic yards of sediment must be dredged every year simply to maintain the artificial channel we have created.
In this engineered system, sediment has come to be treated as a problem: something to remove, contain, or dispose of. For the river, sediment is not waste. It is the material that builds habitat, sustains wetlands, and allows the estuary to adapt to rising seas.
The Columbia River estuary is already under enormous pressure from climate change, habitat loss, and declining salmon populations. Decisions about dredging and dredge-spoil disposal should not simply be driven by the needs of shipping infrastructure. The primary goal should be to understand the river’s natural processes that sustain the estuary will be further compromised as dredging continues and sediments are dumped.
Rather than asking only where to store dredged sediment, we should be asking larger questions: how can sediment once again support marshes and tidal habitats? How can we free the river’s sediments and help the estuary keep pace with sea-level rise? And how can the river regain some of the resilience she once had?
The Columbia River built her estuary over millennia. The choices we make today will determine whether that living community can continue to sustain the wildlife, fisheries, and coastal communities that depend on her.
If we want a healthy Columbia River in the future, the needs of the river must be primary in every decision we make.
References
Northwest Public Broadcasting. (2026). Corps of Engineers’ plan to address Columbia River dredge spoils could cost Southwest Washington ports millions.
U.S. Army Corps of Engineers (Portland District). Lower Columbia River Dredged Material Management Plan. Official project page explaining the 20-year dredged material management plan for the lower Columbia River.
U.S. Army Corps of Engineers. (2024). Public Notice: Lower Columbia River Channel Maintenance Plan and Dredged Material Management Plan. Notice describing the proposal to discharge dredged material while maintaining the federal navigation channel.
NOAA Fisheries. (2025). Incidental Take Authorization: Lower Columbia River Dredged Material Management Plan. Federal documentation on potential impacts of dredging activities on marine mammals such as harbor seals and sea lions.
NOAA (2021). Revision of the Critical Habitat Designation for Southern Resident Killer Whales Final Biological Report. See pages ii and 81 for impacts.
The Salish Current (2026). Dredging up risk: what’s at stake in Burrard Inlet. An article about similar dredging at the Burrard Inlet in Vancouver, BC, and the environmental risks the dredging poses.