• 2013 survival average, travel time faster with spill and structural improvements

    Jan 14, 2014: The Northwest Fisheries Science Center has completed its analysis of 2013 survival for juvenile Snake River chinook and steelhead through the eight dams and reservoirs on the lower Snake and Columbia rivers. See the report here. 

     

    The survival rate for spring chinook was 52.5 percent, equivalent to the long-term average survival for this species.

     

    Steelhead survival for the same reach was estimated at 50.1 percent, also similar to the long-term average, but relatively low compared to recent years. NWFSC noted that steelhead survival between Lower Granite and McNary Dams decreased through the last few weeks of the season, possibly due to increased predation and increasing temperatures during that period.

     

    Other facts that NWFSC noted: 

     

    Flows on the rivers were below average. Spring flow in the Snake River was the fifth lowest in the past 21 years.

    Water temperatures were higher than average.

    Surface passage and spill continue to promote faster fish travel times through the dams and reservoirs.

    q Spill percentage was higher than average.

    q Survival was unusually low in the pool behind Lower Granite Dam.

    q The estimated percentage of fish transported was among the lowest known estimates over the past 20 years.

     

     

     

     

     

    Improved fish passage installed at all lower Snake and Columbia federal dams

    Click here for larger image.

     

    Surface passage routes such as spillway weirs are yielding survival rates of 95 percent or better at every one of the eight federal dams on the lower Snake and Columbia Rivers.

     

     

  • Surface passage provides a route where the fish swim

    Surface passage structures such as spillway weirs and the Bonneville corner collector provide more natural river passage conditions.

     

    Most juvenile salmon tend to travel in the upper 10 to 20 feet of the water column as they migrate downstream to the ocean. When approaching the dams without surface passage structures, juvenile fish need to dive to depths of 50 to 60 feet to access passage routes such as a spillbay opening or a guidance screen that will guide them into a juvenile bypass channel.

     

    Surface passage structures allow downstream migrating fish to pass the dam at the surface. This reduces juvenile fish passage delay, improves water quality, makes more efficient use of spill and improves juvenile fish survival.

     

    Read more at the Corps of Engineers Walla Walla District web page.

    The Dalles Dam spill wall

    The Corps added a spill wall at The Dalles Dam (above, center) that steers juvenile fish out from the shallower parts of the river where they were more vulnerable to predators. Tests in 2010 showed a 4 to 7 percent survival improvement over 2004 and 2005 tests: 96 percent for juvenile spring chinook; 94 percent for fall chinook and 95 percent for steelhead. Read more here.