California's sinking delta
Efforts are under way to reverse the deterioration of a major water source, the Sacramento-San Joaquin Delta in California, which is sinking.
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Hundreds of pumps toil to remove water that seeps through the levees, a Sisyphean task. No one knows the exact amount, but on an average day, they probably push more than 300 million gallons of water uphill over the levees, consuming fossil fuels and emitting carbon dioxide as they do.Skip to next paragraph
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As islands sink, the pumping costs rise. “Eventually this just gets nonsustainable,” says Jeffrey Mount, a geomorphologist at the University of California in nearby Davis. The hydraulic force pressing against levees rises twice as fast as the height of the water behind them, increasing the risk of floods.
The roads that run atop the delta’s 1,100 miles of levees often bump and sag unevenly – a sign of levee instability. The levee break that destroyed Baldocchi’s grandmother’s house in 1969 was no fluke. Delta maps show two blank spots in the jigsaw puzzle pattern of islands that were formerly occupied by islands permanently lost to levee breaks in 1938 and 1984. In the past 150 years, 144 levee breaks have occurred.
The most recent – Jones Tract, in 2004 – illustrates a danger that worries people throughout California. The delta supplies much of the state’s fresh water. But when Jones Tract flooded, it “swallowed” enough water to reverse the flow of the delta, sucking in salt water from San Francisco Bay and tainting the delta’s fresh water. The harvesting of fresh water was halted for 10 days.
In a worst-case scenario, levee failures during a storm could cause many islands to collapse at once, and the delta could “gulp” in enough salt water to shut down freshwater supplies to 20 million Californians for months.
Ongoing subsidence worsens the risk. “The more volume you have below sea level, the more [saline] water can flow onto those islands,” says Dr. Deverell. “That’s one of the driving concerns.”
Subsidence is not just a California problem. Wetland drainage has caused some parts of Florida to deflate by three feet or more. And New Orleans could not have been devastated to the same degree by hurricane Katrina in 2005 were it not for 150 years of drainage that caused parts of it to sink as much as 20 feet.
In many instances, the problem has been papered over by a montage of historic myopia, denial, and mythology, say some experts. Consider the granddaddy of cases, the Netherlands.
“God made the world, but the Dutch made the Netherlands” is a saying that evokes images of Dutch farmers heroically reclaiming land from the sea. But the commonly accepted account contains as much fable as fact, says Robert Hoeksema, a professor of engineering at Calvin College in Grand Rapids, Mich.
A thousand years ago, the Netherlands stood above sea level. It was the Dutch themselves who lowered their country into the ocean. “There is this sense that they won land from the sea,” says Dr. Hoeksema, “whereas, in fact, they’re just reclaiming land that they had first lost to the sea.”