Seattle Seeks Designs for $225M Waterfront Seawall

Wed December 16, 2009 - West Edition
Marc Stiles -Seattle Daily Journal of Commerce



SEATTLE (AP) Designers have been dreaming about what the shoreline on Seattle’s central waterfront could look like if the Alaskan Way Viaduct and seawall were replaced.

In November, the city council appropriated $225 million to make one of those projects a reality: replacement of the approximately 3,750-ft. seawall between Washington and Pine streets.

Teams of consultants are forming in hopes of winning the contract for a project that will help shape the waterfront’s character for the next century and beyond.

Replacement of the seawall is one part of $4.24 billion project to replace the earthquake-damaged viaduct.

Bob Powers, deputy director of the Seattle Department of Transportation, had some advice for the more than 100 consultants and contractors who have sought information on the project from the city: “be cutting edge.” He said to reconnect downtown with the waterfront, the new wall must be very different than the vertical one that exists today.

SDOT put out a request for qualifications from seawall design teams in November. The deadline to submit has been extended three weeks to Jan. 8, according to Powers, because there have been a lot of questions from consultants. He said the extension allows city officials to respond to those inquiries and say more about the qualities the city is seeking in a team.

Powers and Bob Chandler, SDOT’s program manager for the Alaskan Way Viaduct and seawall replacement program, said different teams may be hired for different stretches of the seawall. Teams likely will include waterfront planners, marine biologists, architects, urban planners, engineers and community outreach specialists.

“We really want to come at this a little differently than just an engineering job,” Chandler said.

Construction bids will be sought when design is complete. Test construction could begin in 2012, but the bulk of the work is expected to start in 2013 and last three years, with substantial completion in 2015, according to Chandler. In late 2015 or 2016, the city will begin a projected $123 million project to create public space along the waterfront.

The seawall was built between 1916 and 1936. Some areas along the wall are shallow while others are deep. Powers said the new seawall must respond to different conditions along the shoreline.

The winning team will come up with science-based plans that create new habitat while allowing the public “to really experience the waters of Puget Sound,” Powers said.

These kinds of ideas were floated six years ago when Allied Arts, a Seattle group focused in part on urban design, hosted some charettes in anticipation of the viaduct and seawall being replaced. More than 100 designers and planners came up with myriad ideas, including “habitat islands,” that would bring pedestrians to Elliott Bay.

“There’s a huge amount of excitement in the design community about the possibilities for the waterfront,” an Allied Arts representative said at the time. “People see this as a way of reconnecting us to a part of our history and future. We have this opportunity to create a new space for people and to create a front porch for the city.”

The seawall is a vital piece of Seattle’s infrastructure and replacing it is complicated. It was built to support rail and road access to shipping piers. Downtown developed with the wall in place and still relies on it. The wall supports and protects the Union Pacific and BNSF rail lines, as well as major utilities and the viaduct.

The wall consists of un-reinforced concrete sections along the central waterfront. Between each section are timber-supported concrete sidewalks. Despite its importance, the wall was built on loose soils and the design did not account for earthquakes. And there’s another problem: marine organisms called gribbles and toredos are eating away at the timber platform, increasing the wall’s vulnerability to an earthquake.

In addition to keeping the supports in place during construction, crews must be aware of some timing issues. Due to environmental constraints, in-water work can’t be done during the February-to-June fish window. And, due to commercial concerns, work along the promenade needs to be limited during the summer tourist season.

“It doesn’t make it easy, but we think we can work through this,” Chandler said.

Another issue is what materials to use for the new wall. SDOT and the University of Washington are conducting research. Habitat test panels were installed in 2008 to determine what shapes and textures best serve the marine habitat. In addition to the panel installation, “troughs” that extend out from the face of the seawall were created. The intent is to mimic shallow water habitats that have largely been lost along the Seattle shoreline. The UW is sampling marine life to measure the effectiveness of the panels and troughs.

“Each section [of the new seawall] is likely to be different,” said Powers. “It’s much more than just concrete and steel that we’re going to be looking at.”

The Washington-to-Pine seawall is one portion of the work. Other parts of the seawall also will need to be replaced, and Chandler thinks that could cost $200 million. It’s unclear when that work will occur.

Powers said the city needs to get the seawall along the waterfront done first because it is vulnerable in an earthquake.

“We need to move forward with that to provide for the safety of the citizens of Seattle.”