Chapter 9: Dams and mitigation of their effects

Nat'l Acad. Press, Washington, DC

This paper examines the effects of dam construction and operation in the Columbia River Basin on salmon populations. While the hydrograph of the Columbia River has been significantly impacted by dams, the seasonality of regulated flow on the Snake River has been less affected. The Snake River storage has been used for agricultural diversion while the Columbia has been for electrical generation. The reservoir system has effects on flow velocities, water chemistry (nitrogen supersaturation), habitat availability and reliability, and stream temperatures. Dams block about one third of the Columbia River watershed to access by anadromous fish.
Effects of Dams on Salmon;
Fish kills occur as a result of several characteristics of dams. Bruising, descailing, and stress caused by by-pass facilities; susceptibility to prey following delivery from by-pass to outfall; estuary damage; effects on the homing ability of fish; limited success in fish use of by-pass facilities. The effect of migration speed on smolt survival is uncertain but assumed to have an impact. More research is necessary.
Mitigation of Dam's Effects on Salmon:
Seven measures for mitigation of dams' effects on salmon are discussed
1. Fish passage facilities 2. Predator control 3. Transportation 4. Spill 5. Flow augmentation 6. Reservoir drawdown 7. Dam removal.


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