Evaluations of Adult Fish Passage at Ice Harbor and Lower Monumental Dams, 1982.

Evaluations of adult fish passage at Ice Harbor and Lower Monumental Dams were conducted from 12 April to 16 June 1982. Each fishway entrance was monitored with electronic fish detectors and chinook salmon (Oncorhynchus tshawytscha) were radio tracked in the projects\u27 tailraces and fish collection systems. An additional study with electronic detectors was conducted from 23 August though 10 October 1982 at Lower Monumental Dam. The study was conducted during a year of unusually high spring river flows. High spill levels and reductions in powerhouse discharge were characteristic during the spring study at both projects; therefore, results may not fully describe fish behavior during all conditions of project operation. Spill did not occur during the fall study at Lower Monumental. Radio tagged fish characteristically held in areas several hundred feet downstream of the powerhouse at both projects. The behavior was related to high spill and low powerhouse discharge conditions and may have been a response to tailrace eddies that developed during these conditions. The most frequently used entrance into the Ice Harbor fishway under all conditions except low powerhouse discharge was located at the north end of the powerhouse next to the spillway. The next most frequently used entrance, and the most frequently used entrance during low powerhouse discharge, was on the shore at the south end of the powerhouse. The most commonly used entrance to the Lower Monumental fishway was on the shore at the north end of the powerhouse. The entrances at the south end of the Lower Monumental powerhouse, next to the spillway, had either net fallout or low net entry. The use of submerged orifice entrances along the powerhouse generally decreased with increased distance from the shore at both projects. Radio tagged fish moved both up and down the collection channels and held at the ends of the channels, particularly at the north end of the Ice Harbor fishway and near the base of the Lower Monumental powerhouse fish ladder. Also, tagged fish sometimes backed down the fish ladders, especially at the Ice Harbor powerhouse ladder. Several operational conditions were assessed at both projects. The operation of the ice and trash sluiceway at Ice Harbor was associated with decreased entry at the south end of the powerhouse and increased entry along the submerged orifice entrances. The entrances at the south end of the Lower Monumental powerhouse were opened in several combinations during the spring and fall research seasons to study the net fallout phenomenon at the entrances. Net fallout or very low net entry continued at the two entrances facing downstream into the tailrace during all conditions in the spring and fall. Net entry occurred at the entrance facing the spill basin during all conditions in the fall. Radio tagged fish were delayed a median of 118.6 hours at Ice Harbor and 44.8 hours at Lower Monumental. Probable causes of delay included holding downstream of the dams, fallout at the south end of the Lower Monumental fishway, fish backing down fish ladders and falling back over dams, holding at extensive movement in the collection channels, and recovery from handling and tagging stress