Hydroacoustic Evaluation of Deep and Shallow Spill as a Bypass Mechanism for Downstream Migrating Salmon at Rock Island Dam on the Columbia River

by Tracey W. Steig, Hydroacoustic Technology Inc, Seattle, United States,
Bruce H. Ransom, Hydroacoustic Technology Inc, Seattle, United States,

Document Type: Proceeding Paper

Part of: Waterpower '91: A New View of Hydro Resources


Hydroacoustic data were collected on downstream migrating juvenile salmon (Oncorhynchus spp.) during the springs of 1983 and 1984, and summer 1990 at Rock Island Dam on the Columbia River in Washington State, USA. The objective of the studies was to estimate the effectiveness of spill in passing downstream migrants. Water was spilled from the surface, but three spill bays nearest the powerhouse opened deeper than the others. Both deep and shallow spill bays were used in 1983, and only shallow bays were used in 1984 and 1990. During 1983, the relationship between the proportion of flow spilled and the proportion of fish passed through spill was curvilinear, with increasing spill levels passing proportionately more downstream migrants. Shallow spill bays alone appeared to be nearly as effective (on a number of fish/spill bay basis) at passing downstream migrants as did a combination of deep and shallow bays. During 1984, the use of shallow spill bays for the lower spill levels significantly increased the effectiveness of spill in passing fish. The best fit regression between percentage of fish passing in spill and the percentage of flow spilled was linear. Under the resulting relationship, a 20% spill level predicted passage of 30% of the fish, and a 40% level predicted passage of 49% of the fish. During 1990, the effectiveness of passing summer migrants was similar to the results found during the 1984 spring study. There was no significant difference between the 1984 and 1990 best fit regression lines. Downstream migrants were found to be surface-oriented. Studies at other Columbia and Snake river dams have found downstream migrants to be more effectively passed in surface flow.

Subject Headings: Bays | Rivers and streams | Rocks | Islands | Earthfill dams | Regression analysis | Linear flow | Hydro power | United States | Washington

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