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Cramer Fish Sciences: Lower Yakima River Flow Alterations   Innovative Scientific Solutions for Fisheries and Environmental Challenges  
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Port of Portland



Lower Yakima River Flow Alterations

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The Kennewick Irrigation District (KID) and United States Bureau of Reclamation (USBR) are considering a range of alternatives to reduce diversions of water at Prosser Dam and thereby increase flows in the lower Yakima River. The key motivation for this work is the assumption that higher flows will increase survival of emigrating juvenile salmonids and ultimately increase returns of adult salmon to the Yakima River.


Cramer Fish Sciences was retained to estimate the effects of flow on emigrating salmonids and to quantify the potential benefits to salmon of the various flow alternatives being considered. Using passive integrated transponder (PIT) tag data from 1998-2004 for spring Chinook, fall Chinook and coho salmon juveniles emigrating between Prosser Dam and McNary Dam, we developed relationships between daily survival estimates and flow, temperature, travel time, etc. These relationships were then combined with historic smolt passage estimates and results of hydrological modeling to predict the potential increases in smolt and adult abundances associated with each flow alternative.Figure 1


Our results showed that flow had a strong effect on Prosser-to-McNary survival rates for fall Chinook, an intermediate effect for coho, and a minimal effect for spring Chinook. Commensurate with flow-survival relationships, estimated increases in smolts surviving to McNary were relatively high for fall Chinook, intermediate for coho, and minimal for spring Chinook. Although estimates were uncertain, they provide valuable information for decision makers who must weigh the costs and benefits of numerous flow alternatives.Figure 2


  • Flow has a strong effect on salmonid survival rates
  • Survival rates vary for different salmonid species
  • Prediction of increases in fish abundances with each flow scenario

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