Loading…
Every few years the Chehalis climbs out of its banks and spreads across the valley — sometimes deep enough to close Interstate 5, the main highway of the entire West Coast. It’s one of Washington’s hardest flood problems, and it’s ours.
The Chehalis gathers water from one of the largest river basins in the state, then runs through a wide, flat valley on its slow way to the sea. When a warm, wet “atmospheric river” parks over us — sometimes melting snow in the hills at the same time — rain pours in far faster than the flat, lazy river can carry it out.
Near the coast it gets harder still: a high tide can push back against the river like a hand on a hose, so the water has nowhere to go but up and out. The flat land that floods is called a floodplain — and flooding is exactly the job it has always done. The trouble is that the floodplain is also where our towns, farms, railroad, and freeway all sit.
Try it: raise the river and watch the water climb past the fields, the town, and finally the freeway.
Normal flow — the Chehalis runs quietly in its channel.
One of the modern benchmark floods — Centralia and Chehalis under water, I-5 and rail lines cut.
The big one. Interstate 5 sat under about 14 feet of water near Exit 77 and closed for four days. Damage topped half a billion dollars — a flood so large it's rated a roughly 1-in-500-year event.
Two years later, the same stretch of I-5 flooded and closed again — proof this isn't a once-in-a-lifetime problem.
There’s no easy answer, which is what makes it a great real-world problem. In 2016 the state created the Office of the Chehalis Basin to tackle it with a twin goal: cut flood damage and bring back salmon habitat at the same time — because the healthy side-channels and log-jams that help fish also slow water down.
The ideas on the table include a large water-retention damon the upper Chehalis to hold back the worst floods, raising and flood-proofing buildings, better early warning, and restoring wetlands. Each choice has trade-offs — a dam that protects towns can also block fish — so people are still debating it. That’s not a failure; that’s civics, happening in our own valley.
The same floods shape the rivers salmon depend on — see the salmon’s journey →
Follow a salmon from a gravel nest in the Satsop or Wynoochee all the way to the ocean and back.
Every spring, hundreds of thousands of shorebirds refuel on our mudflats on their way to the Arctic.
A fault offshore, a giant wave in the year 1700, and why we practice for the next one.
The Satsop cooling towers on the skyline — a true story of energy, engineering, and economics.
A logging mill pond right above town became one of Washington’s early state parks.
How a temperate rainforest works — and how it feeds the cold, clean streams salmon need.
North America’s largest elk, in herds around our valley and the Olympic Mountains.
Satsop, Wynoochee, Chehalis — our rivers carry Indigenous names and a deep salmon culture.
Real Montesano numbers to play with — salmon returns, rainfall, elk, floods, and towers.