The Seattle Seawall Project: Transforming Salmon Habitat
Salmon are keystone species that deliver vital nutrients to the soil and support the local economy. These fish have been a cultural icon since the earliest days of human settlement in the Pacific Northwest. But the salmon’s preservation has not always been a priority.
In the early 1900s, 68 percent of Seattle’s shoreline habitat was destroyed by the construction of the Elliott Bay Seawall. It was intended to prevent shore erosion and enable waterfront development, but the seawall also decimated salmon populations, reducing them by 90 percent.
Now, a major urban reconstruction project, including the replacement of the seawall, offers hope for the salmon by creating a more hospitable migratory corridor.
“We needed to replace the seawall. It’s the face of our waterfront,” says Jessica Murphy, project manager of Waterfront Seattle. “This is a unique opportunity to replace habitat that was lost.”
Murphy coordinates a team of marine scientists and engineers in Seattle developing an innovative construction plan to address three main problems that the migrating salmon currently face.
Shaded Shoreline Habitat
Juvenile salmon can’t see well in the dark, and piers, sidewalks, and other structures shroud about 60 percent of the downtown shoreline in darkness. To avoid swimming blindly, juveniles swim around these structures into deeper waters where they face food competition from larger fish and predation from harbor seals.
Glass blocks inserted into the sidewalks offer a solution. The glass blocks will allow light to penetrate from the sidewalk into the water and create a safe, well-lit path for the salmon.
Juvenile salmon eat the zooplankton and other invertebrates that congregate near marine and shoreline plants. But few plants can grow in the shadow of waterfront structures, and there is little shoreline vegetation amid the bustling business landscape.
New light-penetrating sidewalks will help plants grow underwater. Plans to create riparian zones include planting trees and shrubs along the banks and planters along the walkway.
The greening of the waterfront will not only support salmon but also reduce shoreline erosion, improve water quality, and add to the beauty of Seattle’s shoreline.
Much of Elliott Bay is very deep to allow ships to dock, but juvenile salmon prefer shallow water where they can find food and shelter. Engineers will manufacture a “bench” around the edge of the seawall, approximately two and one-half feet below the surface, creating a shallow migration corridor for returning salmon.
These ambitious waterfront plans may take years to complete, but the design team is confident the changes will create a more prosperous future for the salmon that pass through Seattle’s Puget Sound. From the Duwamish River to the open ocean, salmon will have a safer and more suitable migration route, and the Elliot Bay Seawall Project could become a model for urban waterfronts around the world.