In 2008, SRSC assessed the feasibility (SRSC et al. 2008) of restoring the connectivity of natural processes between the North Fork of the Skagit River and the historic distributary of Swinomish Slough. Swinomish Slough, connecting Skagit Bay and Padilla Bay in the northern Puget Sound, was historically a significant migratory corridor for juvenile Skagit River Chinook salmon seeking rearing habitat in Padilla Bay. SRSC has worked in collaboration with the United States Geological Survey and Battelle Memorial Institute to conduct surveys of existing conditions, developed analytical models to explore hydraulic processes, looked to historical conditions for clues and strategies, and considered the chronology, construction, and management of the waterway developed by the US Army Corps of Engineers between the late 1800s and the mid-1900s. The researchers found sufficient evidence to merit further investigation of actions aimed at re-establishing connectivity through the causeway and/or the jetty.
Availability of low‐salinity water to juvenile Chinook salmon is critical to their physiological adaptation to marine conditions during the early phases of seaward migration. These conditions were formerly present in the channel but were eliminated by the construction of the jetty and the causeway. Thus, in addition to providing direct conveyance of fish from the North Fork Skagit River to the Swinomish Channel, restoring low‐salinity waters in the Swinomish Channel is also a project goal. Field data as well as modeled scenarios within Swinomish Channel show that salinity ranges in Swinomish Channel are generally much higher than the desired salinity for juvenile Chinook migration. The abrupt salinity gradient presents a physiological barrier within Swinomish Channel to juvenile salmon on their seaward migration. Freshwater discharged from the North Fork is currently restricted by the McGlinn Causeway and jetty, and is either transported to the south away from Skagit Bay during ebb tide or to the north end of the bay around the jetty during flood tide.
The McGlinn Island Causeway & Jetty Habitat Restoration Phase 1 Feasibility, completed in 2008, examined restoring historical connectivity between the North Fork Skagit River and the Swinomish Channel. The second phase of this analysis examined the predicted effects of breaching the Swinomish Jetty and McGlinn Causeway to facilitate Chinook salmon access to important rearing habitats in Padilla Bay. It responds to issues identified in the first phase and evaluates a particular restoration alternative. The second phase tasks included extending the modeled domain into Padilla Bay; developing a salinity probability histogram/rating curve for points along the Swinomish Channel; and producing substantial project designs. Outreach to stakeholders is ongoing.
Primary Project Contact
Steve Hinton – Director of Restoration
Washington State Salmon Recovery Funding Board
Battelle Pacific Northwest National Laboratories
United States Geologic Survey (USGS)