Delta Blues

(Page 4 of 5)

There is still a chance that the delta will dodge the bigger crisis -- a sudden, widespread levee failure. But a single natural disaster could alter the delta's landscape as thoroughly as Hurricane Katrina changed the Gulf Coast.

Most delta levees were not designed by engineers, and over the past century they have failed 166 times, usually affecting one island at a time. On a sunny day in 2004, the earthen levee protecting Jones Tract, west of Stockton, collapsed without warning, burying the island's asparagus and tomato farms under 12 feet of water. The force of the Middle River, as it poured across the breach, scooped out automobile-size chunks of peat. It took more than six months to pump out the water, which caused $90 million worth of damage and forced a three-day shutdown of both the state and federal export pumps.

A levee breach may cost California taxpayers from $20 million to $40 million to repair, says Jeffrey Mount, the geologist. And the Jones Tract incident was a single breach on one agricultural island. What would happen if multiple levees failed at once? And what if they failed on islands with larger populations?

According to geologists, northern California is ripe for an earthquake. The shock waves from the 1906 San Francisco earthquake -- with an estimated magnitude between 7.7 and 8.3 on the Richter scale -- reached the delta in less than half a minute. Back then, though, the delta was not as vulnerable as it is today. "In the 1906 quake, you could rest your arm on the levees because the islands hadn't subsided yet," Mount says. "Now the levees are 30 feet tall, on unstable foundations, and poorly constructed." The U.S. Geological Survey says there is a 62 percent chance that a tremor of at least 6.7 in magnitude will hit the Bay Area by 2032.

A strong earthquake could damage many levees at once, liquefying the sand beneath them by reducing the cohesion of the grains, and causing those levees to sag and fail. "Once water starts pouring over the top, that's an unstoppable force," Mount says. Because the islands are deep bowls, they would suck in a huge amount of water, much of it salty water from San Francisco Bay. Until that water could be flushed out -- no easy task -- the export pumps would have to be shut down, and farmers on the intact delta islands would not have freshwater for irrigation.

It wouldn't even take a trauma like an earthquake to destroy the levees. They could buckle under the incremental pressure caused by rising sea levels, which the Intergovernmental Panel on Climate Change predicts could reach 23 inches by 2100 (and more if the ice  melt from Greenland and Antarctica accelerates). The delta could also be besieged by flooding as global warming melts California's mountain snowpack more rapidly and causes more precipitation to fall as rain rather than snow. A study published in the Proceedings of the National Academy of Sciences in 2004 predicted a reduction of up to 90 percent in the Sierra Nevada snowpack by century's end.

One California state government study estimated in 2007 that multiple levee failures could cost tens of billions of dollars and displace up to 35,000 of the delta's 400,000 residents. What makes this scenario all the more frightening is that parts of the delta no longer look like the sparsely populated Jones Tract, where the levee failed in 2004.

A 1992 California law divided the Sacramento-San Joaquin Delta into two zones with very different approaches to land use. In its rural center, known as the Primary Zone, new construction is sharply limited. Last March state regulators quashed plans for a 123-home neighborhood centered on an abandoned sugar-beet processing plant in the farm community of Clarksburg. This would have been the Primary Zone's first "urban" development, and opponents argued that it would harm the ecosystem and put new home owners at high risk for flooding.

Tracts closer to the periphery, in the so-called Secondary Zone, have few protections, though, as becomes clear on a drive through the small city of Oakley. Along Highway 4, billboards lined up like the old Burma-Shave signs beckon home buyers to brand-new subdivisions. In one of them, Summer Lake, residents are moving into two-story houses painted taupe and dark goldenrod as bulldozers clear the land around them for expansion. When finished, Summer Lake will include 1,330 new homes, a fire station, two public schools, and a 25-acre man-made lake. It's an attractive location for people who are priced out of the Bay Area and don't mind an hour's commute.

Hotchkiss Tract, where Summer Lake is being built, has the Anyplace, U.S.A. look of a rural patch primed for suburban development. Less apparent to the untrained eye is that Hotchkiss Tract sits below sea level. To protect the development, city officials authorized a ring of wide levees designed to withstand the type of flooding that comes once every 300 years. (This is tougher than federal requirements but pales next to the 10,000-year standard for cities in the Netherlands, which lies mostly below sea level.) "We have homes behind levees throughout the country," says city manager Bryan Montgomery. "We have homes in Tornado Alley, in Hurricane Row" -- in the Midwest and on Gulf Coast, respectively. "All those occurrences are far more likely than any kind of flooding in this area."

When Greenbelt Alliance, a Bay Area anti-sprawl group, challenged Oakley's flood protection plans, a state judge ruled with the city, clearing one of several obstacles to construction. But experts warn against too much confidence -- especially when extreme weather events are rendering terms like "100-year flood" virtually meaningless.

"If you ever hear anyone say they have designed something breach-proof, run," says Robert Bea, the Berkeley engineer. "Nature can always come up with a card that trumps your card." And John Cain, director of restoration programs for the San  Francisco-based Natural Heritage Institute, warns, "When your house is below sea level and that levee breaks, it's the Ninth Ward."

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