Passage behavior and survival for hatchery yearling chinook salmon at Ice Harbor Dam, 2004

The voluntary spill program at Ice Harbor Dam has been very effective at guiding fish to the spillway. However, recent studies to evaluate spillway passage survival have resulted in lower-than-expected survival estimates. Based on results from research in 2003, it was hypothesized that increasing the volume of water spilled through individual bays would increase spillway passage survival. To achieve this condition without additional volumes of water, fewer bays would be opened during periods of spill. This "bulk" spill operation would comply with spill volumes mandated by the 2000 National Marine Fisheries Service biological opinion; that is, daytime spill of 45,000 ft3/s and nighttime spill up to 100% of total river flow, or to the total dissolved gas limit. Contract no. W68SBV92844866