Washington Dam Fish Passage Construction Advances

Abstract

A long-planned project to build a fish passage facility on the Howard A. Hanson Dam is advancing with new funding. The Corps' preferred plan, outlined in an April 2022 report, calls for construction of a fixed multiport collector with steep slope bypass that would allow juvenile fish to move downstream-the least-cost design option with the highest likelihood of meeting survival criteria, according to the Corps. Once collected at the intake ports, fish would travel downstream through steep slope bypass pipes and a deceleration tunnel, then be released into the lower river, most likely through the dam's left abutment, though the Corps report notes the final design could run the pipe further downstream. Fish access to the upper watershed has been blocked since construction of a diversion dam that was built in 1913 downstream from the later Hanson Dam, which was built without a fish passage as a result. The fish passage facility was first planned in the 1990s. Once the fish passage is built, adult salmon would be trucked from the diversion dam to someplace upstream from the Hanson Dam. For the fish passage, a cofferdam was installed and a 60-ft-wide, 180-ft-long, 100-ft-deep area was excavated, but Corps officials realized they likely faced insufficient funding and suspended construction of the fish passage in 2011.