The explosive waves of Ocean Beach, a 3.5-mile stretch separating San Francisco from the grey edge of the Pacific Ocean; have long been a draw for tourists, local families and an international tribe of surfers.

But every few years, stormy surf driven by the weather pattern known as “El Nino” grinds away at a thinning section of the beach, pulling the sand out to sea. Some comes back, but two years ago, bluffs collapsed and massive amounts of sand disappeared for good.

Holding back the sea here seems as impossible as holding back the fog. But planners see Ocean Beach as a top priority in a long roster of Bay Area sites threatened by inundation because of what lies on its landward side: the Great Highway, a $220-million wastewater treatment plant and a 14-foot-wide underground pipe that keeps sewage-tainted storm water away from the ocean.

Action plan

The question facing at least eight local, state and federal agencies boils down to this: With California officials expecting climate change to raise sea levels here by 14 inches by 2050, should herculean efforts be made to preserve the beach, the pipe and the plant, or should the community simply bow to nature?

“We are in some ways the tip of the spear for this issue,” said Benjamin Grant, a city planner who is leading a study of the problem for the non-profit San Francisco Planning and Urban Research Association, or SPUR. Grant describes the beach’s south end as “an erosion hot spot.” But, he said, all coastal communities will have to grapple with rising seas.

A disruptive rate of sea-level rise is one of the most daunting potential consequences of climate change. Recently, researchers warned in two new studies that severe coastal flooding could occur regularly in the United States by the middle of the century and that California would be among the states most affected. Previous studies have suggested that the rise in sea levels is poised to accelerate globally, although the evidence that this is happening is not yet definitive.

Erosion, of course, is a perennial issue for beachfront communities, and Ocean Beach, artificially expanded more than a century ago, has always been vulnerable. But as the planet warms, the problem is expected to become far more severe all along the northern Pacific Coast. Sand bluffs in the Bay Area, which for decades have eroded by an average of more than a foot a year, are expected to collapse at an ever-faster clip. The options are to keep installing hard structures in front of vulnerable areas, replenish the sand or simply retreat and let the shoreline move where it will.

Each has a cost. Building walls or piling up riprap protects infrastructure. But it amplifies wave action as water ricochets off the hard surface with enough energy in its retreat to scour the sand. The scouring hastens the disappearance of bluffs and beach.

The armouring of the coastline interferes with beachgoers, infuriates environmentalists and surfers and disturbs vegetation and bird habitats. But after destructive storms, it has been San Francisco’s solution of choice in recent years, with city bulldozers dumping thousands of tons of rock and chunks of concrete, granite and brick sidewalks into new breaches.

Mark Massara, a local lawyer and an avid surfer who has spent two decades lobbying and litigating over coastal disputes, is fiercely critical of the piles of stone. “No one is willing to move or adapt – they think we can armour everything,” he said. “Guess what? Not everything can be defended.”

Prefer to replenish

Environmentalists tend to prefer the second solution: replenishing the shore with some of the tons of sand regularly dredged by the Army Corps of Engineers to ensure that the waters are deep enough for cargo ships rumbling away from the Golden Gate Bridge.

With enough sand, dunes could be rebuilt to mimic those that once covered the area, they say; areas on or near the beach are critical to the survival of species like the bank swallow, which nests in burrows inside sandy bluffs on the beach’s southern edge and is listed as threatened in California.

The corps is considering an infusion of sand that could cost $10 million. It would last perhaps three or four years, Dingler estimated. “Our economists said, given the value of the infrastructure, it’s a worthwhile endeavour to try it once and see what really happens,” he said. Still, one bad El Nino storm could undo everything, he added.