WDFW Tokul Creek Fish Passage and Weir Restoration

Washington Department of Fish and Wildlife’s Tokul Creek Fish Hatchery has been located on the banks of lower Tokul Creek since the early 1900’s. Hatchery facilities on the creek include the primary hatchery supply intake and diversion weir structure, and a fish ladder structure. A series of flooding events undermined the diversion weir and severely damaged the fish ladder structure causing it to be impassable by returning salmon and steelhead. KPFF was retained by WDFW to provide project management, civil, and structural engineering for design of a new fishway, intake structure, screen and screen cleaning system and weir structure in compliance with current WDFW and NOAA criteria. KPFF assessed the condition of the existing concrete and timber weir structure and developed alternatives for repair or replacement that could be accomplished during short in-water work windows and while maintaining the functionality of the primary hatchery supply intake and ongoing operation of the hatchery. Multiple designs for the new fishway were considered and advanced to 60% design completion including a roughened channel fishway with sediment retention baffles, and a vertical slot fishway. WDFW selected the vertical slot design as their preferred configuration for the project. The fishway rises approximately 13 feet between the fishway entrance and exit. Seasonal flows in Tokul Creek vary widely, from approximately 22 cfs (95% exceedence) in late summer to 780 cfs (5% exceedence) in the winter months. An auxiliary water supply was incorporated in the design of the fishway to improve attractive flows at the entrance during high winter flows. A segment of the weir also incorporated an adjustable height weir that can be used to concentrate flows and improve sediment transport over the weir during low summer flows. The new intake structure removed a flat screen and replaced it with a vertical perforated steel plate screen, with a brush cleaning system. The replacement weir structure was designed for a 500-year flood event and consists of a combination of precast and cast-in-place concrete components to facilitate a very limited construction window for in-stream work on Tokul Creek. Constructibility planning for the project was complicated by the need to maintain hatchery operations (including water supply) throughout the duration of construction and the construction of footings, walls and piping below the grade of the natural stream bed and water table. A multi-stage construction sequencing plan was developed and incorporated in the Contract Documents to define the requirements for diversion of the stream in multiple phases to allow for weir replacement and substantial dewatering of fishway foundation excavations while sustaining the hatchery water supply and hatchery operations.