The Alaskan Way Seawall: The Facts

What’s New

Seawall Rehabilitation

SDOT will replace the deteriorated wood facing (Ekki wood) on the seawall between Piers 69 and 70. Specifically this work consists of removing the deteriorated timber, releasing clean pea gravel between the Ekki wood facing and the sheet pile, and patching the original sheet pile structure where holes are present. The rehabilitation work is scheduled to be complete, weather permitting, by March 2008.

Seawall Scientific Habitat Enhancement Study

Habitat Test Panels will be installed at three locations on the seawall. This work is part of the collaborative scientific research between SDOT and the University of Washington. This study will help to determine what shapes and textures will best serve the marine habitat of Puget Sound. The results will help inform the final design of the seawall face.

18 panels will be installed along the seawall with six at each of the three locations – at Clay Street, Vine Street, and between Pier 62 and the Seattle Aquarium. In addition to the panel installation, “troughs” will be created that extend out from the face of the seawall. The intent of the trough is to mimic shallow water sediment habitats that have largely been lost along the Seattle shoreline. The potential benefits could include higher production of marine life and trapping additional sediment and organic matter.

The University of Washington will sample for marine life in the area over a two year period to measure the effectiveness of the habitat panels and troughs. Once a long-term solution has been determined for the central waterfront of the Viaduct replacement, SDOT intends to use the findings of this study to build a seawall that will improve the ecological function of the seawall and sustain marine life.

Frequently Asked Questions

See the November Construction Notice

For information on the Seawall Rehabilitation and Habitat Research Project contact either of the following:

John Arnesen, Project Manager at 206-684-8921 or john.arnesen@seattle.gov

Katherine Bush, Communications Office at 206-233-1084 or katherine.bush@seattle.gov

Related Initiatives

Climate Action Now

Restore our Waterways

A History

The Alaskan Way Seawall was built between 1916 and 1936 to support rail and road access to shipping piers.

2,000 feet of un-reinforced concrete wall sections were built along the central waterfront area along with timber-supported concrete sidewalk sections between each wall.

5,000 feet consists of steel and concrete anchored by timber relieving platforms. Poor liquefiable soils that were used to fill in behind the wall sections are supported by a timber platform, which is buried 13 feet deep and is up to 60 feet wide.

View Seawall Types

What's at Risk?

The seawall has served its purpose well, but is showing the effects of its age and corrosive marine environment. The original design did not account for earthquakes. One of the two primary vulnerabilities of the seawall is its inability to resist loads associated with liquefaction of the loose soils on which it is constructed. In an earthquake similar to that of the Nisqually Earthquake in 2001, liquefaction of the fills is expected to occur. The likelihood of such a seismic event occurring in the next 10 years is one in 20.

The second vulnerability is significant damage to the timber platform from a variety of marine borers called Gribbles and Toredos. Found in multiple locations, the damage means that the seawall's vulnerability to an earthquake is greater than previously thought. Even without an earthquake, there will be serious consequences as a result of continued deterioration.

View Maintenance History

The Significance of the Seawall

Downtown Seattle was developed with the seawall in place and relies on its continued existence.

• The seawall supports and protects the Union Pacific and Burlington Northern Santa Fe rail lines in the region, which serve both north/south and east/west freight and passenger rail service.
  
• The seawall supports and protects major utilities, including power for downtown, sewer, storm water, natural gas and telecommunications.
  
• The seawall supports the Alaskan Way Viaduct that carries State Route 99 and approximately 110,000 vehicles a day.