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Work to replace Seattle’s waterfront seawall starts this week with construction of a temporary road that will displace several blocks of parking spaces beneath the Highway 99 viaduct between Madison and Pike streets.

In January, traffic on Alaskan Way will be redirected to the new roadway. About 175 angled parking spaces will be removed to make way for the temporary north-south route. Alaskan Way will be closed until completion of the seawall project, expected in spring 2016.

“We’re really excited to get started on this project. The seawall has needed to be replaced for a long time,” said Jessica Murphy, project manager for the Seattle Department of Transportation (SDOT).

Access to all businesses along the waterfront will remain open, and the city has arranged for some spaces in several parking garages in the vicinity to have short-term rates comparable to the city’s charge for on-street parking, said Richard Sheridan, spokesman for SDOT.

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Eventually, angled parking beneath the viaduct will be removed all the way to Virginia Street as the seawall work progresses. To date, about 226 parking spaces from King Street to Madison Street have been eliminated to create staging areas for the deep-bore tunnel project, which is following a similar route underground.

Seawall construction is expected to take place Mondays through Saturdays both day and night, with the noisiest work stopping by 10 p.m.

“We’re nervous about construction over the next three seasons,” said Bob Donegan, president of Ivar’s, which is located on historic Pier 54. “We’re doing everything we can to protect the 1,500 jobs and 4.5 million visitors along the waterfront in 2013.”

The city is on a tight timeline to complete the seawall work so the seismically vulnerable viaduct can be removed when the Highway 99 tunnel is scheduled to be completed in 2016. Alaskan Way can’t be rebuilt until the new seawall is in place.

Seattle voters in November 2012 approved a $290 million bond measure to replace the seawall, badly eroded over the years by marine borers and tidal action. The seawall was built between 1915 and 1936 out of fill material and about 20,000 old-growth timbers.

In some places the seawall and fill material extend all the way under Alaskan Way, part of the reason the arterial must be cleared for the construction project, Murphy said.

The bond measure funds the first phase of the seawall project, from South Washington Street to Virginia Street, the oldest and most vulnerable portion, according to city engineers. An additional $30 million for the project will come from the city general fund and $30 million from the King County Flood Control District.

City engineers had warned that the wall was deteriorating, but the extent wasn’t known until after the 2001 Nisqually earthquake. Structural assessments found large chunks of decaying timbers, many destroyed by gribbles — tiny, shrimplike crustaceans.

The city estimates that about half of the seawall is deteriorated and has a 1-in-10 chance of failing in another major earthquake.

Material from Seattle Times archives was included in this report.

Lynn Thompson: or 206-464-8305. On Twitter @lthompsontimes

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