Once completed in 2018, the replaced Elliott Bay Seawall will be a triumph of engineering and design. It will also place Seattle as a leader when it comes to implementing major infrastructure that actively benefits habitats and ecology.
That’s not to say the old seawall was sub-par. Far from it. Constructed in 1934, the original seawall utilized some 20,000 old growth timber piles to create a sturdy foundation for the Seattle waterfront. But while that seawall served the city well for decades, the years of residing in salt water and other environmental wear and tear had deteriorated the seawall to the point where it needed to be rebuilt.
The new Elliott Bay Seawall is designed to last at least another 75 years, and it brings with it some innovative changes. Chief among these changes is a focus on habitat — salmon migration in particular — which had been disrupted by the original seawall. Achieving this goal was a challenge, however. As research scientist Jeff Cordell, one of the minds behind the new seawall design, stated during our recent event on the seawall and ecology, “how do you make a vertical, concrete seawall fish friendly?”
The answer, as it turned it, came down to four things: light, depth, texture, and vegetation.
Salmon in particular don’t like dark places. It can take up to 30 minutes for their eyes to adjust, and predators like to hide in the dark. To help provide a more natural, comforting habitat, the replaced seawall features a sidewalk that is cantilevered (i.e., hanging over) the water, and the surface of this sidewalk is penetrable by light to illuminate the water below.
Marine “mattresses” and habitat “benches” create a shallower area next to the shoreline featuring gravel surfaces to provide hiding and foraging places for sea life. This shallower depth also more closely resembles a natural shoreline ecology.
In order to support growth of vegetation and marine invertebrates, the seawall is cobbled and features shelves. This surface provides pockets where life can thrive.
Native vegetation will be planted all along the base of the seawall, and an intertidal beach will be created to further bolster the ecosystem.
All of these additions to the seawall were made so that the actual wall itself is much less intrusive to the environment. Even if that environment changes drastically in the coming years.
The new seawall design also took into account rising sea levels due to climate change. The challenge was to build a seawall high enough without knowing exactly how high water could get.
To solve this problem, the Seattle Department of Transportation (SDOT) turned to the Climate Impacts Group at the University of Washington, who provided estimates ranging from six inches to 50 inches. SDOT then used the highest estimate when designing the new seawall.
Another benefit of the rebuilt seawall is an opportunity for Seattle to revitalize the waterfront with the seawall as its foundation. Among the features of this transformation:
- 26 blocks of park spaces, a pedestrian promenade, and a bike path
- An expansion of the Seattle Aquarium and a new central public space
- An overlook walk connecting Pike Place Market and the water
- Redesigned public piers for hosting events, concerts, water access, and public art
With the rebuilding of the seawall and revitalization of the waterfront, Seattle is creating both a better environment for sea life and for all the city’s citizens. And the city is excited, as evidenced by public input over the past six years, input that included over 10,000 comments influencing the design of the waterfront.
To learn more about the Elliott Bay Seawall project, visit our partners at Waterfront Seattle.