The Mayor's office is holding a Seawall Open House event Wednesday, February 3rd to share information about the need for a replacement.
Scheduled to last just an hour, Deputy Mayor Darryl Smith will guide the discussion.

The Seattle Department of Finance will present information on the plan for funding the project and department staff will be on hand to answer questions and address concerns.
The open house will be from 5:00 to 6:00 PM in the Bertha Knight Landes Room, City Hall, 600 4th Avenue
Refreshments will be served.

The Seawall Today

The existing seawall is an aging structure constructed out of wooden platforms, steel sheet piling, concrete and fill. The design of the seawall changes over its length depending on the period in which each section was constructed.

The southern end of the wall (S. Washington St. to Madison St.) consists of a mixture of concrete wall sections that were built along the central waterfront area along with timber-supported concrete sidewalk sections between each wall. Some of these sections were rebuilt in 1964 and 1987.

The remaining portion of the seawall consists of a bulkhead system: approximately 5,000 feet of steel and concrete anchored by timber relieving platforms. Construction is either Type A or B; Type B is larger and is used in sections of deeper water.
Behind type A and B seawall sections are liquefiable soils that are flooded daily with tides. The street in these areas is supported by a timber platform.

The Significance of the Seawall

Downtown Seattle was developed with the seawall in place and relies on its continued existence. The seawall holds the soil in place along Seattle’s waterfront that supports vital infrastructure and services:

The seawall supports and protects major utilities, including power for downtown and the region, sewer water, storm water, combined sewer overflow (CSO), natural gas and telecommunications.
The seawall supports the Alaskan Way Viaduct that carries State Route 99 and approximately 110,000 vehicles a day and the Colman Dock ferry terminal, with over 8,800,000 annual riders.
The seawall supports and protects the Burlington Northern Santa Fe rail lines in the region, which serve both north/south and east/west freight movement for the nation and passenger rail service for the region.
The seawall also protects Seattle’s downtown waterfront from wind driven storm waves and the erosive tidal forces of Puget Sound and Elliott Bay.

What's at Risk?

The seawall has served its purpose well but is showing the effects of its age and the corrosive marine environment. As a result of continual deterioration, the seawall has sustained damage to the timber platform from a variety of marine borers called Gribbles and ship worms. While the City continues to maintain the seawall, damage to the timber platform found along its length makes the seawall vulnerable to failure. In addition, the original seawall design did not account for earthquakes. Even undamaged, the seawall would not be able to resist loads associated with liquefaction of the loose soils behind the wall. The damage to the timber platform means that the seawall's vulnerability to an earthquake is greater than previously thought.

It is predicted that the current seawall has a 1 in 10 chance of failure from an earthquake in the next 10 years. Even without an earthquake, the seawall could fail in places as a result of continued deterioration. If the seawall were to fail, sections of the viaduct, the Alaskan Way surface street, and adjacent structures and utilities could collapse or become unsafe. Because of these risks, the seawall needs to be replaced.

For more information, please contact: Seawall Project Manager Stephanie Brown at 206-386-4635 or via e-mail at stephanie.brown@seattle.gov.