Ice Harbor Dam spill efficiency determined by radio telemetry, 1997

The spill program prescribed by the National Marine Fisheries Service (NMFS) in its Biological Opinion was designed to alleviate migrational delays associated with passage at hydroelectric dams. However, high spill volumes increase total dissolved gas (TDG), often above State and Federal water quality standards deemed "safe" for aquatic organisms. The potential survival benefits for juvenile salmonids from increased spill volumes can be offset by mortality caused by elevated TDG levels. During summer 1997, radio-telemetry receivers were deployed to monitor the forebay, juvenile bypass system, spillway, fish ladders, navigation lock, and the tailrace of Ice Harbor Dam. Hatchery-reared subyearling fall chinook salmon were collected and radio tagged at Lower Granite Dam, released into the tailrace ofLower Monumental Dam and monitored as they passed Ice Harbor Dam. Radio-tagged fish that entered the study area but were not recorded in the monitored routes of passage and subsequently exited the study area were assumed to have passed the dam through a turbine unit. Contract no. E86970079