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Elliott Bay Seawall Project
| What’s happening now? (updated 9/2/10)
Join Us for a Design Walking Tour
Mark your calendars! You’re invited to attend a walking tour with the Elliott Bay Seawall Project Team along the waterfront on Saturday, September 11, starting at 8:30 a.m. The tour will be open until 1:00 p.m.
Participants can begin a self-guided tour at the south end of the project area near the Washington Street Boat Landing at Alaskan Way and Washington Street (Pier 48 ) or at the north end near the Seattle Aquarium at Alaskan Way and Pike Street (Pier 59)—tour locations will be marked with signs and balloons—and walk the waterfront at their own pace or join a guided tour leaving from Pier 48 at 9:15 a.m. or Pier 59 at 11:15 a.m. Informational packets and maps will be available at both piers. No RSVP is necessary.
Join us to:
- Learn about the seawall project—while you’re standing on the seawall.
- Understand types of habitat and recreational opportunities being considered for the seawall different areas.
- Provide your input on these potential seawall opportunities.
Seawall Stakeholder Subgroup Meetings
The Seattle Department of Transportation (SDOT) has formed a Seawall Stakeholder Subgroup as part of the larger Central Waterfront Stakeholder Group, which will begin meeting in October, for the Central Waterfront Project. The work of the Seawall Stakeholder Subgroup focuses on the Elliott Bay Seawall Project, and the subgroup is considering topics related to the design of the new seawall and potential construction impacts of the project. The group will provide perspectives and recommendations for the project team and will serve as a bridge between the Central Waterfront Project and the Seawall Project. The subgroup is comprised of waterfront business owners and tenants, professionals from the design and environmental fields, representatives from the Port of Seattle and Washington State Ferries, and downtown community members and residents.
Meeting #3 is coming up:
September 28, 2010
Seattle Municipal Tower, 700 Fifth Avenue, Floor 40
5:00 – 7:30 p.m.
We encourage alternate transportation to this meeting.
Previous Meetings:
The first meeting was held on July 20, 2010 and covered the Subgroup organization and operating guidelines, and an overview of the Elliott Bay Seawall Project.
The second meeting was held on August 24, 2010. The agenda covered project goals, as well as identification of opportunities and issues for each seawall zone. If you were unable to attend, the materials presented at the meeting are available in the project library, and comments are welcome.
We’re in the Field—Business Survey Underway
Throughout September, the Elliott Bay Seawall Project team will be administering a waterfront business and recreational survey. Interviewees include businesses that may be affected by construction in the project area between South King Street and Broad Street. In addition to verifying previously collected information, the team will be asking for contact and operational information that can be used for design and construction planning.
Public Scoping Comment Period
The official scoping comment period for the Elliott Bay Seawall Project ended July 19, 2010. Thank you to those who provided comments. |
Project Overview
The Elliott Bay Seawall Project runs along the waterfront in downtown Seattle from South Washington Street to Broad Street. The Seattle Department of Transportation (SDOT) and U.S. Army Corps of Engineers (Corps) are studying alternatives to provide continued protection to the Seattle waterfront from the erosive forces of Puget Sound and to ensure the waterfront is safe for public uses. SDOT and the Corps are beginning the environmental review process for the seawall project.
The existing seawall protects Seattle’s downtown waterfront from wind driven storm waves and the erosive tidal forces of Elliott Bay. Major utilities, Alaskan Way and SR 99, the ferry terminal, and rail lines are also supported by the seawall. The seawall was built between 1916 and 1934. It has deteriorated significantly over the last 90 years and does not meet current earthquake standards. An environmental analysis process is underway, and scoping is beginning in June 2010. The scoping period will run from June 1 through July 19, 2010.
The seawall project design will be coordinated with the Central Waterfront Planning process. It is not necessary to know the final plans for the waterfront redevelopment in order to move forward with the seawall project. The intent is to design a seawall that will accommodate and work with the range of Seattle waterfront design options.
Public and Agency Participation
The Elliott Bay Seawall Project is committed to including the public and local stakeholders in the planning process. Currently, the project is accepting comments as part of the NEPA/SEPA scoping period. You are invited to submit scoping comments by July 19, 2010.
Comment Form
All comments are welcome, but the project team is especially interested in hearing your thoughts on:
- Potential construction of the seawall
- Future seawall alignment
- Potential habitat/recreational opportunities
Timeline
| DATE |
EVENT |
| June 16, 2010 |
Scoping Meeting |
| June 1 – July 19, 2010 |
Public comment on scoping |
| Spring 2010 |
The City of Seattle selects the Tetra Tech consultant team to carry out the work to replace the Seawall. |
| Fall 2009 |
The City of Seattle releases a Statement of Qualifications seeking consultants with experience in innovative seawall design and construction, engineering, environmental analysis and documentation, economic analysis, and public involvement. |
| 2002 - 2007 |
Ekki wood facing removed, sheet pile wall patched, and a new cathodic protection system was installed at Clay Street. |
| 2001 |
Approximately 300 lineal feet of street adjacent to Waterfront Park settled due to a combination of liquefaction from the Nisqually earthquake and voids caused by deterioration of the Type A timber relieving platform. |
| 1999 |
Repairs made to Ekki wood facing. Pea gravel behind facing was eroded in some areas potentially exposing retained fill to further erosion. |
| 1987 |
Repairs on Type B seawall timber platform at Clay Street included adding Ekki wood facing to all Type B steel sheet piles to help retain bulkhead-supported soils where sheet piles were corroding. |
| 1956 - 1961 |
Cathodic protection installed on Type B wall at Clay street. Despite the cathodic protection measures, new holes continue to appear in sheet piling. |
| 1951 – 1955 |
Corrosion first noted in the steel sheet pile wall. Patch repairs were made in 1951. The later discovery of leaks and a large void under both the relieving platform and Alaskan Way led to the excavation and backfilling in August 1954. Further sheet pile patching and grouting below the platform occurred in 1954 & 1955. The seawall supported roadway near Clay Street sank 2 feet during this time. |
| 1947 |
First holes appear in Type B sheet pile wall due to corrosion. Fill begins to be washed out from behind the wall. |
Additional information
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.
View Seawall Types
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.
A History of the Seawall
The Alaskan Way Seawall runs along Elliott Bay in downtown Seattle from S. Washington Street to Broad Street. It was built between 1916 and 1934 to support rail and road access to the shipping piers.
Seawall Scientific Habitat Enhancement Study
In 2008, the City and the University of Washington began the field work phase of a collaborative scientific research project investigating opportunities to enhance the marine habitat surrounding the seawall. To accomplish this, test panels were designed to increase habitat complexity and installed at three locations on the seawall. Results from this study will help determine shapes and textures that may work to enhance the marine habitat function of the seawall face.
Eighteen (18) panels were installed along the seawall with six (6) different shapes and textures at each of the three locations – Clay Street, Vine Street, and between Pier 62 and the Seattle Aquarium. In addition to the panels, “troughs” were installed 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 has been sampling the test panels and troughs for a two year period. What they found so far is a succession of colonizing algae on the test panels, mobile invertebrates and barnacles. Monitoring will continue through 2011.
What Now?
Maintenance The City of Seattle has committed over $3 Million to temporary repairs of the seawall since the Nisqually Earthquake; which includes $1,940,581 in costs associated with the earthquake and $1,125,560 in Ekki Wood repairs. Failure of the seawall would have significant impacts to Washington State and its effects would have national and international impacts. The shoreline protection provided by the seawall is vital to preserving Seattle’s downtown, the State’s economic stability, and the region’s economy and quality of life.
Army Corps of Engineers Involvement
Seattle has requested that the U.S. Army Corps of Engineers help replace the seawall. The Corps provides assistance in solving water resource problems that are beyond the capabilities of local governments, due to financial constraints, lack of technical expertise or jurisdictional boundaries. The Corps is developing a General Investigation Feasibility Study to determine its involvement in the project
For more information:
Email: seawall@seattle.gov
Call: Stephanie Brown, Project Manager at 206-386-4635
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