Two Decades of Downstream Fish Passage Research: How Can We Apply What We Have Learned to Optimize Fish Passage at High Head Dams

Since the 1990s the strategy of retrofitting dams with low-volume surface flow outlets to pass juvenile salmon during their seaward migration has been met with mixed success.  While the effectiveness ratio (percentage of fish passed to percentage of water passed) of these outlets can be relatively high (17:1) the actual number of fish passing the dam via these routes can vary from 5% to 95%.  We took a retrospective look at what has been learned in the last two decades and how it could be applied to optimize the success of implementing downstream passage alternatives at high head dams.  For example, many evaluations have focused solely on quantifying the percent of fish collected and often failed to gather data needed to identify where breakdowns in performance occurred when initial expectations were not met.  Expanding the application of available research tools could accelerate our understanding of the factors that contribute to a successful passage alternative.  Similarly, while efforts have been made to standardized the metrics used to quantify the performance of bypass alternatives, these metrics are not consistently applied.  Application of expanded analytical methods and standardized metrics could help resource managers make science-based decisions to improve passage at high head dams.