The redevelopment of Treasure Island has been designed to account for sea-level rise. Because estimates of sea-level rise vary, Treasure Island is designed to accommodate various levels over time.
Sea-Level Rise Strategy
Moffatt & Nichol, who are the shoreline engineers for the project, developed a comprehensive approach to address the future sea-level rise. The strategy recognizes guidance from the 2009 Draft Climate Adaptive Strategy report prepared by the California Natural Resources Agency, the 2009 Living with a Rising Bay report by BCDC, project-specific coastal studies, an extensive review of the literature, and discussions with other City agencies including SFPUC and DPW.
This adaptive management strategy for sea-level rise includes:
All streets and entrances to below-ground parking will be at least 36 inches higher than the Base Flood Elevation (BFE). All base floor elevations will be 42 inches higher than the BFE.
The crest elevation of shoreline structures will be 11 to 13 feet higher than current mean high tide level.
All development will be set back at least 350 feet so that the island perimeter can be improved if sea levels continue to rise beyond current projections.
The Treasure Island Development Authority has created a tax-financing district that will raise $1.2 billion over 40 years for improvements to mitigate against sea-level rise.
Treasure Island is a man-made island built on a shoal that extends north from Yerba Buena Island. Dredged sandy material was pumped from the bay floor in 1936-1938 to create the island in its present shape.
To accommodate development and in order to raise the elevation of the island to guard against sea level rise, we are undertaking a sophisticated soil improvement program, costing in excess of $200 million. The soil improvement program includes:
Rapid consolidation of soils so that settlement is complete prior to building new roads, utilities, and buildings.
Increase the soil capacity so that the lower-height buildings (up to 7-stories) can be supported on mat foundations. Taller buildings will require deep foundations.