Replacement of Seattle’s seawall along the waterfront is underway, not only to protect public safety and create the foundation for the future waterfront, but also to improve aquatic habitat, and ultimately the overall health of Elliott Bay.
Before the seawall was built, Seattle’s shoreline included forested bluffs, beaches and marshes – like many of the natural shorelines seen throughout Puget Sound today. When the natural shoreline was filled in to create the active waterfront we know today, some of the natural ecosystem functions were adversely impacted, most critically was a key portion of a larger salmon migration corridor.
The seawall replacement presents a unique opportunity to enhance Elliott Bay’s habitat – through light, surface textures, and creation of a shallow fish-friendly migration corridor.
We have worked closely with the University of Washington and other experts to better understand the ecosystem of Elliott Bay. We know that four different species of salmon migrate along the seawall – but this journey isn’t easy. When salmon exit the Duwamish River, half of them turn right, swimming along the Seattle waterfront. With 90 pecent of the central waterfront shaded by piers and overwater structures, salmon hesitate when they reach these dark areas, and swim into deeper and more dangerous water to stay in the light.
Given that the dark and deep areas along the waterfront impact habitat diversity and fish migration, the project looked at innovative ways to create a more natural migration corridor through light and improved natural habitat. Ultimately, the project will include a variety of habitat enhancements including glass blocks in the cantilevered sidewalks, to filter light to the water below, a textured wall face, habitat shelves, substrate enhancements to the existing sea floor, and riparian plantings – all contributing to an improved migration corridor.
Plants and sea life, which are important food sources for fish, have difficultly attaching to the flat surface of the existing seawall. Several textured wall sections and surface treatments were installed on the current wall and monitored for four years. Studies showed that the textured surfaces promoted additional habitat growth, and we have incorporated these treatments into the wall design.
Finally, we’ll also install intertidal habitat benches along the seawall to create a continuous shallow water corridor, allowing migrating juvenile salmon to avoid deeper water and potential predators. This corridor, and the salmon it will serve, will also benefit from natural light filtering through the light penetrating sidewalks.
As we continue our work to replace our city’s aging Seawall, we are taking full advantage of a once in a lifetime opportunity to improve the nearshore ecosystem and create a salmon migration corridor through these unique habitat enhancements.
For more information on the Seawall project’s habitat improvements, please visit waterfrontseattle.org/seawall.