The City Council will introduce legislation Monday, with a decision expected in July on whether to submit a sea-wall bond proposition to voters.

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In 2002, then-Mayor Greg Nickels pronounced the Elliott Bay sea wall so damaged that “immediate action” was required to prevent the wall from failing and the waters from threatening life and property.

In 2010, after just a few weeks in office, Mayor Mike McGinn displayed a crumbling block of wood — from a sea-wall support post — and again declared the sea wall in need of immediate replacement.

The City Council at the time said design work for the project was just beginning and that reliable cost estimates couldn’t be made. And there was another critical piece of damaged infrastructure — the Alaskan Way Viaduct — sucking up all the city’s political oxygen.

With voters finally deciding to tear down the viaduct and build a replacement tunnel, the City Council is now poised to consider putting a 30-year bond measure on the November ballot to replace the 70-plus-year-old sea wall.

Council members will introduce legislation Monday that begins the process. The council will get up-to-date cost estimates later this month, determine the size of the bond measure, hold a public hearing in June, and decide in July whether or not to submit the measure to voters.

Current estimates to replace the sea wall are between $310 million and $390 million.

The sea wall was damaged in the 2001 Nisqually earthquake, but the full extent of its deterioration wasn’t discovered until the following year, when inspectors found infestations of gribbles — tiny marine crustaceans — in the sea wall’s untreated posts.

Engineers estimate that between 50 and 60 percent of the sea wall is weakened and could fail in another earthquake.

The sea wall, which runs along the downtown waterfront from South Washington Street to Broad Street, was built between 1916 and 1936 and wasn’t designed to modern seismic standards. City consultants have put the risk at 1 in 10 that an earthquake in the next decade could cause the sea wall to fail and low-lying property along the waterfront to flood or liquefy.

In a letter Thursday to the council, McGinn said, “By replacing the sea wall we protect public safety, preserve transportation access to the core of our city, and support the businesses and workers who depend on the waterfront for their livelihood.”

The council last week approved another property-tax measure — a $123 million levy to restore and enhance library services — for the Aug. 7 primary ballot. And King County leaders are planning to place a $200 million measure on the same ballot to build a new juvenile court and detention facility.

Despite competing capital needs, city leaders say they’re convinced the sea-wall measure no longer can be delayed. The sea wall holds up the fill where the new Alaskan Way will be rebuilt once the viaduct comes down in 2016.

Working backward from that date, city planners say construction of the sea wall has to start in September 2013. And before it can be built, the design work and financing must be in place.

“We really have a timing crunch in front of us,” said Councilmember Tom Rasmussen, chair of the Transportation Committee. “The sea wall has to be in place before Alaskan Way can be rebuilt.”

In addition to replacing the existing sea wall, the bond measure could include some improvements to shoreline and habitat, such as creating a pocket beach at Washington Street.

It could also include rebuilding Waterfront Park, just south of the Seattle Aquarium, and Piers 62 and 63, just north of the aquarium. All are owned by the city and are also badly deteriorated, city officials say. Summer concerts used to be staged at the piers, but were discontinued in part because of concerns they could no longer safely support large crowds.

Council members hope some of the funding for the sea wall comes from other government sources, including the King County Flood District and the Army Corps of Engineers.

Council President Sally Clark said that in addition to the engineering challenges of working under water and holding out the bay during construction, the permitting for the sea-wall project is complicated by the number of jurisdictions that must sign off.

She said it will require approval from the state Department of Natural Resources, the region’s Indian tribes and the Corp of Engineers, which authorizes all work on rivers and harbors.

The dangerous condition of the sea wall as well as the need to coordinate its construction with the viaduct replacement project leave the council with few options, Clark said.

“Fundamentally, this is a public-safety issue. The thing is crumbling.”

Lynn Thompson: 206-909-7580 or On Twitter @lthompsontimes.