Evaluating the Effects of Water Withdrawal on Juvenile Chinook Salmon Survival in the Roza Reach of the Yakima River, Washington

The Roza Reach of the Yakima River provides ideal conditions for examining the effects of water withdrawals on juvenile Chinook salmon survival. Flows in the Roza Reach are controlled by Roza Dam, a primary diversion dam on the Yakima River. Downstream migration of juvenile Chinook salmon in the Yakima River occurs during March–May each year when water withdrawal rates are high.  Roza Reach flows during this period can be less than 600 ft³/sec, which is concerning to fishery managers. We conducted an evaluation to examine the flow-survival relationship in the Roza Reach during 2012–2014 and evaluated survival during periods when Roza Reach flows were in the 600-5,000 ft³/sec range. We found that river flow and route-of-passage at Roza Dam were important predictors of juvenile Chinook salmon survival. Our analyses were able to partition mortality that occurred at the dam from mortality that occurred in the reach. Our presentation will summarize results from the three-year study and demonstrate how adaptive research and analytical approaches were used to address important and potentially contentious questions related to water use and fishery management.