McGlinn Island Causeway and Jetty Feasibility
Restoring Connectivity between the Skagit River and Swinomish Slough
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.
The McGlinn Island Jetty and Causeway block physical and physiological access for salmon from the North Fork Skagit River into the Swinomish Channel. Photo: SITC & Triathlon 2004.
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.
Panoramic photograph of the Jetty near La Conner, WA. In the foreground is Swinomish Channel (salt water). In the background is the North Fork of the Skagit River (freshwater) with Ika and Goat Islands. Photo credit: Eric Mickelson.
Project Status/Timeline
The McGlinn Island Causeway & Jetty Habitat Restoration Phase 1 Feasibility was completed in 2008. Further hydraulic modeling and design has been funded and has been underway since 2010. Beginning in spring/summer of 2011 SRSC will be holding public forums to discuss restoration options and scenarios in an effort to scope and select a preferred implementation strategy. Once a preferred alternative can be chosen, funds will be sought for construction of that alternative.
Primary Project Contact
Steve Hinton, Restoration Director
Funding Sources
Washington State Salmon Recovery Funding Board
Project Partners
Battelle Pacific Northwest National Laboratories
United States Geologic Survey (USGS)