Shaken and stirred in California's recent earthquake

How seismic events can make drought impacts worse.

 

At first glance, the 6.0-magnitude earthquake that struck near Napa, California last Sunday seems to have little connection to the state’s “other” major unfolding disaster — the drought. But, in fact, the two are closely linked and illustrate California’s precarious reliance on a complex network of water infrastructure stretching across the state.

The day after the quake, inspectors from the Army Corps of Engineers and Bureau of Reclamation and local reclamation districts examined dams, canals and levees scattered across the area that experienced the heaviest shaking. They found no structural damage in the agency’s facilities near the quake’s epicenter, including the Coyote Valley Dam at Lake Mendocino and the Warm Springs Dam at Lake Sonoma. Inspections of a flood wall in Napa, which hems in the Napa River as it snakes through downtown, however, have revealed signs of cracking.

In spite of the dozens of injuries and extensive damage to homes, historic buildings and roadways – estimated to exceed $1 billion –  things could have been much worse. Consider a scenario that has been imagined by experts for years: If Sunday’s earthquake had occurred further to the east – nearer the tangled tidal channels in the heart of the Sacramento-San Joaquin Bay Delta – the resulting damage could compound tremendously the severity of the drought's effects.

That’s because engineers and geologists say the more than 1,000 miles of earthen levees that interlace the Sacramento-San Joaquin Delta – source of irrigation water for millions of acres of Central Valley farmland and drinking water for more than 24 million Californians – are highly vulnerable to an earthquake.

The Sacramento-San Joaquin Bay Delta. Photo by Flickr user Daniel Parks.

In a 2006 report, University of California Davis geology professor Jeff Mount put the probability of massive levee failure from an earthquake within the next 50 years at 64 percent. The next year, a report from the now defunct state-federal water management partnership CALFED, predicted that a 6.5 magnitude earthquake in the region could result in $40 billion in damage. A 2012 report from the National Academy of Sciences stated that a breach in the levees could result in massive flooding and saltwater intrusion from the bay to the Delta’s water infrastructure, tainting the state's most important source of freshwater with salt. “Depending on the severity of the damage and other factors, water deliveries could be disrupted for months, or even years,” according to one particularly nightmarish scenario, meaning that farmers, ranchers and municipalities already facing major water cuts would see even greater curtailments.

But this is California, and where water is involved, politics inevitably rush in. For several years, Gov. Jerry Brown and the Department of Water Resources have used the specter of a massive earthquake to support a highly controversial re-engineering of the state’s plumbing. The project, known as the Bay Delta Conservation Plan, or BDCP, would include two 35-mile long tunnels that would shunt water from the Sacramento River, fast-tracking it under the Delta to pumping plants many miles south.

Boosters of the estimated $25 billion tunnel project say it would make the system more earthquake-resistant by moving the intake point for water upstream and away from the Delta’s levee-laden heart. Ted Thomas, a Department of Water Resources spokesman, points to a report his agency published in 2009 that says there’s a one percent annual probability that ground shaking capable of damaging levees will occur along the western edge of the Delta. “This level of ground motion could induce liquefaction in Delta levees, thereby causing a breach,” wrote Thomas in an email. “Not knowing when or where an earthquake will strike does not justify inaction.” 

Yet tunnel critics, including Restore the Delta, a Stockton, California-based group opposed to the project, say the seismic threat to the Delta levees has been hyped by powerful agricultural and municipal interests in Southern California in order to secure more northern water – and that excavation of the giant boreholes would result in the ruination of the Delta itself. 

Barbara Barrigan-Parrilla, Restore the Delta’s executive director, says the Delta and, by extension, the state’s water resources, would be far better protected by bolstering the levees. "Fat, robust levees protect the delta," she said in 2012. “Large engineered projects are more vulnerable to earthquakes than the levees."

It’s not just an earthquake that has the potential to exacerbate the drought's impact, however. A recent report from researchers at the University of Nevada, Reno in the journal Nature suggests that the drought could, in turn, be enhancing quake activity.

As farmers continue to rapidly draw down Central Valley aquifers, soils in the valley floor have subsided, in some places as much as 30 feet. But the Nevada researchers have found that the reduction in water weight from aquifers – estimated at around 176 billion tons – may be causing deeper crustal layers to “rebound” upward, thereby increasing seismic activity along the San Andreas Fault.

Of course, no one knows when the next earthquake will strike. Could last weekend’s event have relieved tectonic stresses building up in the region, thus reducing the likelihood of a major earthquake in the near future? Or was it a mere prelude to an even larger tremor – perhaps along the Hayward Fault, which runs beneath several East Bay communities, and is projected to be due for an even larger quake?

For now, we Californians are left merely to hope that the drought and a major future earthquake don’t come into a doubly disastrous alignment.

Jeremy Miller is a contributing editor for High Country News. He tweets @JeremyJ_Miller and writes from Northern California.