A giant submerged curtain anchored under the Golden Gate Bridge that rises in storms to hold back big waves. Huge levees with pumps run by tidal power. Vast networks of new wetlands from Silicon Valley to San Francisco, some created on old parking lots and bayfront warehouse sites.

Science fiction? Maybe. Or perhaps San Francisco Bay in 100 years.

On Tuesday, the ideas were among six winners in the Rising Tides contest, a design competition to engineer possible solutions for San Francisco Bay in the next century as its waters are predicted to rise as much as 4½ feet because of global warming.

The winners included some of the Bay Area's most prestigious architectural firms, chosen from 130 entries from 18 countries.

"We are going to have to deal with the issue of protecting the airports, Silicon Valley, and downtown San Francisco much sooner than we thought," said Will Travis, executive director of the San Francisco Bay Conservation and Development Commission.

Since 1965, the commission, a state agency, has regulated development around the Bay shoreline. It sponsored the contest, along with the National Oceanic and Atmospheric Administration, or NOAA, which put up $25,000 in federal funding for prize money that was split six ways.

San Francisco Bay already is rising.

Since 1900, its waters have risen 8 inches, according to a gauge at Fort Point, beneath the Golden Gate Bridge, the longest continually monitored tidal gauge in the United States.


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According to a study last year by the U.S. Geological Survey, based on current warming trends, it will rise 16 more inches by 2050 and as much as 55 inches by 2100 as ice caps around the world continue to melt.

That much rise would put major sections of the Bay's shoreline underwater in future storms when tides are high, according to scientists at USGS and NOAA who have studied the data with computerized maps.

Among the places most at risk: the runways at San Francisco and Oakland airports; Alviso, which already sits 7 feet below sea level because land subsidence; major portions of the Dumbarton Bridge; Foster City, and much of San Francisco's waterfront, including the Embarcadero, Mission Bay near AT&T Park and parts of Treasure Island.

Almost any comprehensive solution could cost billions — from restoring huge amounts of wetlands to buffer the flooding to building higher levees and sea walls.

Travis said his agency held the contest to get the public to start thinking about the issue.

While 2100 is a long way off, 2050 is just "one refi(nancing) of your current mortgage away," he said.

"We are going to have to be thinking about this and preparing for it much sooner than we thought. We don't want to be in the Hurricane Katrina situation, where you deal with fixing the levees after the city has flooded."

Chosen by a jury of architects and scholars that was chaired by Marcel Stive, scientific director for the Water Research Centre in Delft, Holland, the winning entries can be viewed at www.risingtidescompetition.com.

Among the winners is "BAYArc," designed by a team led by Craig Hartman, a partner at Skidmore, Skidmore, Owings and Merrill in San Francisco, along with engineers at Moffatt & Nichol Engineers in Oakland.

Their idea is to stretch a carbon-fiber membrane under the Golden Gate Bridge. It would be anchored to concrete pylons and would rise via an inflatable top in storms, limiting the amount of water and tidal energy that could come into the Bay.

The goal would be to negate the need for billions of dollars in permanent sea walls, since the main flood risk would only occur a few hours a year during big storms, said Hartman, who also designed the international terminal at San Francisco International Airport.

"This is the biggest challenge of the 21st century," Hartman said. "For the Bay Area, it occurred to us that there must be some way to deal with the problem at its most minimal point, and obviously that's where the water passes through the Golden Gate."

Other winners included Elizabeth Ranieri and Byron Kuth, both of San Francisco, who designed a series of massive ventilated levees that would allow water to flow at times while protecting shorelines at other times; and Thom Faulders, of Berkeley, who proposed a series of 30-foot high towers shining laser beams to show the public how high water could rise.

Another winning entry, by Lee Stickles and Huaiche Yang, both of San Francisco, calls for restoring massive amounts of wetlands, similar to other entries, to buffer floodwaters. Their entry, however, proposed reconfiguring waterfront areas, including parking lots and warehouses, while building more densely on higher ground, even constructing floating parks.

David Lewis, executive director of Save the Bay in Oakland, said the solution will involve higher sea walls around key areas such as airports, restoring wetlands, and discouraging development in risky areas.

"In some places, the region will have to decide which developed areas are worth the cost of protection," Lewis said. "SFO, yes. Google server farms, yes. But a strip mall somewhere, probably not."

Reach Paul Rogers at 408-920-5045.