Pacific Northwest Waterways Association 2008 MID-YEAR MEETING

1. Pacific Northwest Waterways Association2008 MID-YEAR MEETING Puget Sound Update:The Elliot Bay Seawall and Swinomish Channel Mona ThomasonChief of Planning, USACE, Seattle District Tom SzelestNavigation Business Line Manager, USACE, Seattle District

2. US Army Corps of EngineersElliott Bay Project The Alaskan Way Seawall

3. Seattle Waterfront 1931 Before the Seawall – Railroad Ave.

4. Seawall Construction In the mid-30’s, Seattle built a concrete wall, secured by a 60’ wide timber tie-back structure, and placed fill, to create Alaskan Way.

5. Seawall Construction The timber was untreated, but was expected to be protected from marine borers by the steel and concrete face wall. The risk and the solution were both noted at the time.

6. Seawall Construction The seawall supports the fill that the surface street and the Viaduct are built on. The strength of the seawall is in the timber tie-back. The concrete and steel that is visible would collapse without the tie-back.

7. February 28, 2001 Nisqually Earthquake • The Puget Sound area was shaken by a magnitude 6.8 earthquake at around 11:00 a.m. on February 28, 2001. The quake was located 32 miles below ground, about 35.7 miles south of Seattle, and lasted about 45 seconds. • The earthquake was felt as far away as Salt Lake City, and caused widespread damage to buildings, roads, and bridges, including the Alaskan Way viaduct in Seattle.

8. Urgent Need • Earthquakes • Current structures cannot withstand another earthquake • Gribbles and Teredos are eating the seawall • Safety • Weight restrictions and inspections are required Regardless of the alternative, the central seawall must be replaced.

9. City Response • The earthquake prompted the City to inspect the seawall for damage. The road had settled near the Aquarium due to liquefaction, a result of the earthquake. • Inspection of the seawall revealed extensive damage and deterioration that preceded the Nisqually earthquake.

10. Gribbles • Test pits revealed that gribbles have been consuming the timber tie-back structure. • Gribbles are marine borers, microscopic marine life that consumes wood. • The usual protection against borers was creosote.

11. The Risk to Seattle Failure of the seawall would cause extensive disruption to the economy. • 110,000 vehicles per day on Alaskan Way Viaduct • 12,000 vehicles per day on Alaskan Way surface street • 30,000 passengers per day use the Colman Ferry Terminal

12. The Risk to Seattle • The waterfront is a major utilities corridor serving downtown Seattle and the region. • 24 freight trains and 6 passenger trains per day travel the waterfront. • The waterfront is a major tourist destination.

13. Condition of the Seawall • The seawall was built prior to recognition of the Puget Sound as a seismic risk area. Even in new condition it would not meet modern seismic code. • If the Nisqually quake was longer, more liquefaction could have caused the wall to fail. • Deterioration due to gribbles continues. The seawall is not expected to last another 50 years, even without another quake. Eventually, enough of the timber will be lost and parts of the wall will begin to fail.

14. The Solution The City is pursuing complete replacement of the old seawall. Options include combinations of large concrete drilled shafts and injected grout. Costs may reach $1B. Engineering studies are currently in progress.

15. Study Overview • Atypical Corps Project • No past storm damage events • Seawall planning and design well advanced by local partner • WRDA 2007 added seismic damage prevention to authority, allows City to work ahead of Corps • Project Phases • Reconnaissance – Feasibility – PED – Construction • Feasibility study estimated at $9.5 million • $4.0 million in work accomplished so far • Federal appropriations = $2.074M 2004-2008

16. Study Accomplishments • Advancement of without project condition • EIS scoping meeting • Participated in AWVSR outreach events • Phase 1 environmental/HTRW site assessment completed • Sampling for cultural resources study • EIS baseline conditions reviewed, nearly complete

17. Way Forward – Best Case • Complete new no-action/without project condition analysis this winter • Feasibility Scoping Conference next spring • Alternatives Formulation Briefing, early 2010 • Final EIS/Feasibility report, early 2012 • PED phase, 2 years • Construction, 2014

18. Seawall - Habitat Test Panels

19. Background Information - Seawall Corrosion Led to Street Collapse in 1954 Gribble Attack on Timber Platform

20. Background Information - Seawall Proposed Repair – Option 1

21. Background Information - Seawall Proposed Repair - Option 2 20’ 10’ + 16 + 9 #18 Bar Anchor 1 Casing pipe @ 5.33’ o.c. 2 Similar to Type A wall Till @ Seneca St. Temporary Shoring Wall as Required

22. Before the Seawall The Seattle waterfront was occupied by Railroad Avenue, a dangerous, wooden planked street on piles over Elliott Bay, until construction of the seawall.

23. Pacific Northwest Waterways Association2008 MID-YEAR MEETING Puget Sound Update:The Elliot Bay Seawall and Swinomish Channel Mona ThomasonChief of Planning, USACE, Seattle District Tom SzelestNavigation Business Line Manager, USACE, Seattle District