Fish Passage Tour
Salmon are the most well-known species that migrate up and down Northwest streams and rivers. When young salmon (smolts) migrating downstream encounter a hydroelectric project, they will either pass over a SPILLWAY, through the TURBINE area, are TRANSPORTED around a dam, or enter a BYPASS SYSTEM.
Adult salmon migrating upstream will most often use a FISH LADDER as they journey to their spawning grounds.
Graphic adapted from U.S. Army Corps of Engineers: Northwestern Division
1. Spillways
Migrating smolts can pass over a spillway, fall into the pool of water below, and then continue their journey downstream.
Spill deflectors are sometimes used to reduce the effect of total dissolved gas, or TDG. This happens when water plunging into the pool below collects air and becomes supersaturated with nitrogen. This can cause gas bubble disease in fish, which has the same effect as divers suffering from the bends.
2. Turbines
Migrating smolt can pass into the turbine area, and exit via the tail race. A new generation of turbines has greatly increased survival rates.
Minimum gap runners increase turbine efficiency while decreasing fish being trapped, bruised, stressed or disoriented. Simply put, this technology eliminates gaps on the turbine hub and tips of the blades.
3. Juvenile Fish Transportation
Along the main stem of the Columbia and Snake rivers, some migrating smolts are collected in barges and then transported several miles downstream. They are released below the Bonneville project, where they migrate through the estuary and into the ocean.
4. Bypass Systems
Surface collectors are a common means of guiding juvenile salmon around a project.
One method is to use fish screens to guide fish into a bypass system. Another method is to use a surface collector to channel fish into a bypass system. Each surface collector must optimize water flows for fish passage while also working within the structural design unique to each project.
5. Fish Ladder
Adult salmon migrating upstream will most often use a fish ladder as they journey to their spawning grounds.
