Tsunami risks covered in proposal for Treasure Island redevelopment 

San Francisco officials re-examining the proposed Treasure Island redevelopment project in the wake of the recent tsunami in Japan say the threat of inundation has already been addressed in design plans.

The multibillion-dollar redevelopment project was questioned at last week’s Board of Supervisors Land Use and Economic Development Committee meeting by Supervisor Eric Mar, who wanted more information about a tsunami’s potential impact.

On Friday, Deputy Director Rich Hillis of the Mayor’s Office of Economic and Workforce Development said no major changes are in store because the disaster potential has already been addressed.

According to developers, Treasure Island is prepared to endure a nightmare 10-foot wave as long as the ground is elevated and compacted, as the plan already calls for, with structures set back at least 300 feet from the coastline.

San Francisco Bay provides a natural barrier for protection from the deadly earthquake-triggered waves. But in the off chance a tsunami came directly into the Bay, Treasure Island, its people and the development would be in the wave’s direct path.

Only a freak disaster could send the low-lying island more than the 10-foot wave envisioned by the current worst-case scenario, devised by tsunami inundation maps recently released by the California Emergency Management Agency.

Steven Ward, a UC Santa Cruz research geophysicist, said any disaster of that scale would likely be caused by a 9.0-magnitude earthquake originating off the coast of Alaska, giving the Bay Area about five hours to prepare.

San Francisco’s local earthquake triggers, such as the San Andreas and Hayward faults, are vertical tectonic plates, which means they pose less tsunami danger than the horizontal plates that caused the Japanese tragedy.

But just the right movement in the San Andreas Fault has the potential to trigger wave action. Ward said the 1989 Loma Prieta temblor sent a 25-centimeter wave into the Bay.

Redevelopment of the island will serve to update protections against rising sea levels, whether they rise gradually from climate change or more suddenly from a quake-related tsunami, according to Chris Meany, a manager with master developer Treasure Island Community Development. A wall of rocks lines the perimeter of the island, and the setback area leaves room for earthen levees in the future, Meany said.

The entirety of Treasure Island is marked clearly on the state’s tsunami inundation maps, but the recent caution warnings in San Francisco didn’t include the island. Some prepared for the worst nonetheless.

“I thought it was a little strange, but since nothing happened it was fine,” said Lacey Todd, the operations manager of the Treasure Island Sailing Center. “We canceled classes that day just to be safe. We would rather be safe than sorry.”


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Dan Schreiber

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Friday, Oct 21, 2016


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