REDWOOD CITY, Calif.—A 1,400-acre swath of salt flats along the western edge of San Francisco Bay has become the latest site for a development dispute that promises to become increasingly common in coastal U.S. cities: Whether new waterside growth makes sense when sea levels are rising.

Agribusiness giant Cargill, which owns the Redwood City site, has made salt in San Francisco Bay for decades. Cargill has downsized in recent years, selling 16,500 acres of salt ponds in the area–60 percent of its local operations–to the state and federal government in 2002 for $243 million in cash and tax credits. But it held on to the 1,400-acre site near Redwood City that the company believes is suitable for building.

Several years ago Cargill hired Arizona development company DMB to identify future uses for the site, which is separated from downtown Redwood City by busy Highway 101. DMB has proposed Redwood City Saltworks, a planned community with 8,000 to 12,000 low-rise housing units. It includes new schools and retail stores, sports parks and open space along the bay and mass transit links connecting the development with regional bus, train and ferry lines. "This project is the poster child for an integrated, walkable community" said DMB vice president David Smith.

Opponents have other priorities. A long list of conservation groups, neighboring cities, and local government agencies has endorsed restoring the salt flats to their original state: tidal marshes, which filter bay water, provide habitat for fish and birds, and buffer shoreline communities against flooding by soaking up storm surges.

Redwood City is proceeding with a state-mandated environmental impact review, which could produce a decision sometime in 2011. The study will tackle issues including impacts on traffic, air quality, and water supplies. But a longer-term question that will be unavoidable in the official review is whether building the project would reduce climate change impacts or make them worse.

These choices aren't unique to San Francisco. Officials in New York, Boston, Seattle, and other coastal cities are brainstorming ideas for flood-proofing urban areas, from raising roads to building giant sea gates. So far, however, Orrin Pilkey, professor emeritus of geology at Duke University, sees little action to limit new waterside growth.

"Historically coastal states haven't been serious about limiting shoreline development," said Pilkey, a longtime critic of building in flood-prone areas. Given current projections for sea-level rise, he supports barring construction of high-rise buildings and major infrastructure in vulnerable areas.

"Why increase the cost of preserving cities in the future when we know what's going to happen in less than a century? Our barrier islands [in North Carolina] are going to be un-developable within 40 to 60 years, dikes or no dikes," Pilkey argued.

Timothy Beatley, a professor at the University of Virginia's School of Architecture and author of Planning for Coastal Resilience (Island Press, 2009), has identified a few small cities and counties across the country that are actively steering growth out of flood plains, but says that larger cities are just starting to consider that idea.

In San Francisco the Bay Conservation and Development Commission, known as BCDC, regulates dredging and filling in the Bay and all development within 100 feet of the shoreline; BCDC has proposed identifying low-lying areas where abandoning new development may be more cost-effective than protecting it, but doesn't have jurisdiction to enforce such a policy now.

"Building in vulnerable locations will involve significant public costs in the not-too distant future," Beatley said. "It may make sense to protect some places, but we're going to have to gracefully retreat from others."

Making salt is a simple process: Water flows through a series of shallow ponds, thickening into increasingly saline brine, until salt solidifies and falls out of solution. Fully-saturated brine moves from "pickle ponds" to crystallizer beds, where it dries and is scraped up by giant harvesting machines. Other ponds hold bittern, a highly saline waste solution colored red by salt-loving bacteria. Cargill's Redwood City tract includes crystallizer beds, pickle ponds, and bittern storage ponds.

"Salt ponds are not land to be paved – they are part of San Francisco Bay to be restored to tidal marsh for wildlife habitat, natural flood protection for our communities, cleaner water, and recreation areas for everyone to enjoy," argued 92 current and former elected officials in a February letter to the Redwood City council. The San Francisco Chronicle and San Jose Mercury News have also opposed the project.

Climate change will affect California's Bay Area in many ways, but sea-level rise is an urgent concern: Many homes and businesses in the region sit at or below sea level. The BCDC projects that climate change will raise water levels in the bay 16 inches by 2050 and 55 inches through 2100.
That will put some 270,000 people and $62 billion in economic assets at risk from flooding, including the San Francisco and Oakland airports and major Silicon Valley companies like Google and Intel. Commission maps show that a 16-inch sea-level rise will make all of Redwood City east of Highway 101 vulnerable to flooding.

DMB officials tout the Saltworks as a climate-friendly smart growth project that will provide homes for Silicon Valley workers, thus cutting greenhouse gas emissions from transportation, which generates about half of the Bay area's total emissions. "Right now there's no affordable housing nearby, so everybody moves out to the hinterlands and commutes," says Smith. The region's median home price is $746,800; fewer than 15 percent of homes are affordable for families earning the median income, according to the Silicon Valley Leadership Group, a business coalition.

But building thousands of houses at the water's edge contradicts California's climate change adaptation strategy, published in 2009. It urges agencies to "consider prohibiting projects that would place development in undeveloped areas already containing critical habitat, and those containing opportunities for tidal wetland restoration, habitat mitigation, or buffer zones." The plan supports "activities that can increase natural resiliency, such as restoring tidal wetlands, living shoreline, and related habitats."

"California aspires to be a national leader on adapting to climate change, and this approach could be a model for other coastal areas," said David Lewis, executive director of Save San Francisco Bay, which opposes the Saltworks. "But it's still just a strategy–it hasn't been written into regulations yet, so we don't know whether agencies will honor it."

DMB's "50/50 Balanced Plan" for the Saltworks preserves half the site as open space, including 430 acres of restored wetlands. These marshes and a massive bayside levee are designed to protect houses from flooding. The levee would be wider than a football field in some places, with trails and parklands along its top and more plantings along its sloping sides. Because it's so wide, says Smith, the levee could be raised if necessary without building out into the bay. "It's not a mystery—it's a matter of engineering, cost, and land," he contended.

To convert the entire 1,400 acres to salt marsh, Cargill would have to agree to sell its land and someone other than DMB would have to pay for restoring it. (For comparison, a 1,400-acre parcel of former Cargill crystallizer ponds in Napa, north of San Francisco, is being restored now at a projected cost of $16 million.) Save the Bay's Lewis thinks that can happen.

"We've always found public or private funds to buy restorable Bay parcels, and we've proven time and time again that it isn't necessary to destroy part of the Bay to save another part," he said.

This article originally appeared at The Daily Climate, the climate change news source published by Environmental Health Sciences, a nonprofit media company.