Mike Koozmin/THe S.f. ExaminerTo rebuild the seawall along The Embarcadero would take an estimated $5 billion. Without some sort of a fix

San Francisco Bay waters are projected to rise as much as 6 feet by 2100, but long before then about 700 acres of land along The Embarcadero could be inundated.

As much as $5 billion may be needed within the next two decades to rebuild the wall that has been San Francisco's waterfront for 100 years, and now defends prime real estate from a rising Bay, according to a Port of San Francisco official.

Built over 30 years, the 4-mile-long rock-and-concrete seawall turned 700 acres of tidal marsh into developable land — most of it highly coveted real estate today — and allowed for the construction of the 40 piers that made San Francisco a shipping hub for most of the 20th century.

The Embarcadero — with Muni's F-Market and Wharves streetcar line and several light-rail lines, along with major sewer infrastructure — is all on backfilled land made usable by the seawall, which runs from Fisherman's Wharf to Pier 50 south of AT&T Park.

Most of the seawall has held up well during a centurylong pounding by saltwater waves and heavy maritime use, though the Port of San Francisco has had to replace crumbling piers and repair the outer wall at Brannan Street and at Pier 43 in recent years.

However, the seawall has never been tested by a major earthquake, and just how well it would perform during a temblor is currently anybody's guess.

The 1906 earthquake hit before much of the seawall was built, and the 1989 Loma Prieta earthquake, with its epicenter far away, was much weaker by comparison.

Parts of the seawall could move as far as 1 foot after a major earthquake, a 1992 study found.

A review of the seawall's ability to withstand an earthquake of up to magnitude-8.0 could begin this winter, pending Port Commission approval. Results from the $425,000 study could be released next summer.

Even if a big earthquake never hits, rising tides could overwhelm the current seawall within the next few decades, said Steven Reel, project manager at the Port's engineering division.

Already, the Bay encroaches over the seawall during winter high tides.

By midcentury, unless significant improvements are made to the seawall to keep the Bay away, flooding could reach as far as The Embarcadero BART and Muni tunnels, Reel said. And by 2100, sea levels could rise as high as to reclaim all of the 700 acres made developable by the seawall.

Within the next 50 years, a series of levees or other walls may be required to keep rising tides away from Mission Bay, where new hospitals and a new police headquarters are under construction.

The Warriors' new basketball arena is also planned to be built in this seawall-protected floodplain.

Building interim improvements to keep the current seawall functional could cost as much as $500 million, a cost that may be needed as early as 2025, Reel said.

Re-engineering the seawall to withstand climate change-caused rising tides or replacing it entirely could cost as much as $5 billion, Reel told The City's Capital Planning Committee recently.

Seattle is currently replacing its seawall, which is about 1.3 miles, at a cost of $500 million per mile, Reel said.

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