Astoria, OR · $140B (proposal)
AST-21 · Columbia River Deepwater Tidal Gate
Massive mechanical lift gates across the mouth of the Columbia River at Astoria, holding back Pacific storm surges and saltwater intrusion to protect the agricultural heartland of the Pacific Northwest — with a temporary bypass channel to keep the river flowing during construction.
Pros
- Protects billions in irrigated agriculture from saltwater intrusion, not just cities.
- The temporary bypass channel is a genuinely clever construction solution for a working river.
- Lift-gate mechanics are proven; this is a scaling challenge, not an invention challenge.
Cons
- The Columbia is one of North America's great salmon rivers — a gate at its mouth threatens already-endangered runs.
- Halting even part of the river's outflow risks upstream flooding across a huge watershed.
- 1.8 million tons of steel in a cold, corrosive Pacific estuary means brutal maintenance.
Feasibility: Buildable but ecologically fraught. The engineering is a scaled-up version of existing river barriers. The salmon question is the real veto — the Columbia's runs are protected by treaty and law, and no gate design has proven fish-safe at this scale. Solve the fish passage or don't build it.
Aerial mock-up: A massive mechanical barricade spanning the wide river mouth, regulating the Columbia's immense outflow while blocking Pacific saltwater from pushing inland.
