Recommendation for Stable Flows in the Hanford Reach During the Time When Juvenile Fall Chinook are Present Each Spring
The Northwest Power Planning Council in its Fish and Wildlife Program (FWP) specifies a Council policy "The program preference is to support and rebuild native species in native habitats, where feasible." (NPPC, 1994, Section 2.2A). The Council, through its FWP, has expressed an interest in evaluation of the effects of improved flows on production of fall chinook in the Hanford Reach (NPPC, 1994, Section 6.1C.2).The Independent Scientific Advisory Board (ISAB) initiated this report because of our special interest in the stock of fall chinook that spawns in the Hanford Reach. Our interest has its origins in the Independent Scientific Group of the Northwest Power Planning Council and Bonneville Power Administration (ISG) and is now shared by all members of the ISAB. That interest developed during preparation of Return to the River (ISG, 1996), in which we identified the Hanford Reach as the only remaining significant mainstem spawning area for fall chinook in the Columbia River (Geist, 1995; ISG, 1996; NRC, 1996; Huntington et al., 1996; Whidden, 1996). It contains the largest natural spawning population of chinook above Bonneville Dam (Dauble and Watson, 1997).Over the last two decades, Hanford Reach fall chinook have continued to be productive, while other stocks have declined. Our continuing interest and concern for that particular stock of fish arises precisely because it is a relatively healthy stock. It deserves our attention as we attempt to identify and measure the factors that are responsible for its continuing productivity, so that these favorable elements might be extended to other stocks. Furthermore, we believe the productivity of the Hanford stock can be improved.As our interest in this stock developed, we persuaded the Council, in the summer of 1995, and again in May, 1996, to visit the Hanford Reach. During their 1996 site visit, Council members observed numerous juvenile fall chinook that had become stranded on the bank as river flow had been suddenly reduced, exposing the near shore areas where these fish had concentrated. Following that visit, the ISG recommended that there be a study to identify the magnitude of the stranding and to suggest appropriate minimum flows or ramping rates that would provide protection for these fish.Such a study was funded by BPA in 1997. Further information from that study is provided below.