COLUMBIA RIVER FISH MITIGATION
Gas Abatement
Spilling water and juvenile fish over the dam spillways is considered one safe way to get fish past the dams. However, spill has associated risks because spilling water entrains air when the water plunges into the spillway basins, causing raised levels of gas supersaturation that, if high enough, can be harmful to fish. Spillway flow deflectors produce a more horizontal spill flow and limit the plunge depth of water over the dam spillway, reducing the amount of entrained nitrogen.
Spillway flow deflectors (also called flip lips) are now in place at seven of the eight Corps dams on the lower Columbia and Snake rivers. (The Dalles Dam is not targeted for flow deflectors because it has a shallower stilling basin which allows higher spill levels with lower gas production.)
Spill pattern and stilling basin modifications are being evaluated for potential ways to further reduce gas supersaturation from spill.