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May 21, 2021
Stillaguamish Weir Permanent Fishway
Location: Silvana, Snohomish County
General contractor: Northbank Civil and Marine
All in-water work on this project was completed within a strict 60-day window. Due to the critical nature of the schedule, Northbank worked seven days a week for most of the project. Northbank successfully completed all in-water work seven days early, helping to avoid potential winter storm delays. The design and construction schedule was additionally complicated by the volatility in the construction materials market caused by the pandemic. Northbank implemented creative design solutions to minimize construction days to the minimum required due to the critical in-water work window. Fish passage was provided without interruption for the duration of construction. Several days of fish handling were provided to remove endangered species prior to dewatering the work areas. Northbank satisfied the compliance with multiple permits from various agencies including NFMS, USFWS and the state Department of Ecology. A challenging construction aspect was maintaining a dewatered work area with a depth of over-excavation required within the fish ladder of approximately 13 feet below the existing water level. The existing river soil and gravel was extremely porous, making a fully sealed cofferdam nearly impossible. A 5,000 GPM pump system was maintained within the dewatered work area. The project was completed safely and without incident with over 5,000 worker hours.