COLUMBIA RIVER BASIN - DAMS AND SALMON
Spill for Fish
Another means of diverting fish from the turbines as they approach a dam is to spill water and juvenile fish over the dam spillways, rather than putting the water through the powerhouse to produce electricity. The Corps began spilling water for fish at several of its projects in 1977 as a way of improving juvenile fish passage survival. A more comprehensive spill program was initiated at the request of the region in 1989 when a long-term spill agreement was signed by Bonneville Power Administration, the fisheries agencies, tribes and others.
Under the National Marine Fisheries Service Biological Opinion, spill at the dams has been increased substantially during juvenile fish migrations. But spill has associated risks because spilling water entrains air when the water plunges into the spillway basins, causing raised levels of gas supersaturation that can be harmful to fish. Spillway deflectors have been installed at five of the eight lower Columbia and Snake dams to produce a more horizontal spill flow and limit the plunge depth of water over the dam spillway, reducing the amount of entrained nitrogen. Installation of spillway deflectors has begun at two more dams. The Corps is also evaluating other potential gas abatement measures.