Gilbert Cosio's truck rolled to a stop on a Delta levee recently fortified with $4 million worth of rock and engineering.
On one side is a large lake formed when a different levee broke and flooded the area known as Franks Tract in the 1930s. On the other, grazing land and a much smaller lake formed when the fragile levee here failed and was quickly repaired in 1980.
Since then, hundreds of millions of dollars in voter-approved bond funds have been spent to reinforce levees that corral and shape today's Delta. For the first time, the state is on the verge of meeting a federal mandate to protect an area that is a key source of water for 23 million Californians and about 2 million acres of farmland.
But is it enough?
No expert considers California completely safe from the failure of century-old levees that protect a statewide water system, highways, a major railroad line and energy transmission routes, not to mention an aqueduct that serves the East Bay's largest water district.
Cosio, an engineer who has worked on Delta levees for decades, is among those who contend the threat is more or less manageable and that much of the pessimism is based on outdated information.
"We've been waiting around for levee money for 50 years," Cosio said. "We never had the luxury to build them as big as they needed to be. Now we do."
Others, however, shudder at the vulnerabilities that remain. They note that even though investments
"I think the Delta is the single most serious seismic vulnerability in the state," said Jonathan P. Stewart, an earthquake expert and engineering professor at UCLA.
Once a great marsh, the Delta today is a vast network of channels and sunken "islands" that begins where the Sacramento and San Joaquin rivers meet upstream of San Francisco Bay. The Delta and its 1,100 miles of levees -- many of which were first built in the years after the Gold Rush -- cover about 740,000 acres, nearly the size of Yosemite National Park or more than 1½ times the area of Contra Costa County. In addition to being a critical thoroughfare for migrating salmon and stopping point for birds on the Pacific Flyway, it is also perhaps California's most important water source.
Many of the engineering experts and scientists who have looked at the Delta's levees have come away alarmed about the possibility that a large earthquake could lead to multiple levee failures.
In one nightmare scenario, an earthquake during a dry season collapses several levees. The ensuing flooding draws saltwater into the area of huge pumps that serve water users across California. If that happened, little could be done but to turn off the pumps and wait for enough runoff from mountain rivers to drive the saltwater out.
"Once it happens, we're in deep trouble," Stewart said.
That is why a levee failure on a parcel east of Discovery Bay known as Jones Tract on a clear summer day in 2004 sent shivers throughout the state's water management community.
With that disaster still fresh in their minds, California voters the following year approved two multibillion dollar bonds known as Proposition 84 and Proposition 1E, each containing money to fix levees.
So far, about $615 million from those bonds has been awarded to the state Department of Water Resources to fund Delta levee improvements, and about one-third of that work has been completed, said Mike Mirmazaheri, the department's program manager for Delta levees. There might be some money available for additional Delta work, but it is unclear exactly how much, Mirmazaheri said.
The work has gone slower than anticipated because of the state's budget problems, he added. But the most recent round of bids should result in nearly all of the levees in the Delta reaching the standard developed in 1983, known as the Hazard Mitigation Plan, Mirmazaheri said.
Some levee improvements have gone further. Among the recent projects is a significant enlargement of the levees around Jones Tract, the site of the 2004 flood, in an area that contains a railroad track and the East Bay Municipal Utility District's aqueduct.
Though mass levee collapse like what happened in New Orleans has never hit the Delta, many experts say it is likely to occur eventually, despite recent improvements.
"The levee agencies in the Delta have done a good job on a shoestring, really," said Jay Lund, an engineering professor at UC Davis who is also a member of a team organized by the Public Policy Institute of California that concluded the Delta's stability in the long term is doubtful. "I think they've done a valuable job for 150 years, but time and tide is going to work against them in the long haul."
Lund and others contend the Delta's levees and their foundations are too unreliable to securely convey water across California and should be replaced with an engineered aqueduct. Despite sharp disagreements on the reliability of the levees, experts do seem to agree that the bond funding has significantly improved the structures, although more needs to be done.
Stewart was recently in western Japan, near Niigata, to inspect earthquake damage to levees there.
What was striking, he said, was that levees located where the water table was high were much more likely to fail than those in areas where the groundwater is deeper.
In the Delta, the water table is always high. Not only that, the Delta's waters are constantly in contact with the levees -- making them more like earthen dams than levees that sit dry on a floodplain until there is a flood.
In other words, they would appear to be even more vulnerable than the Japanese levees Stewart saw.
"The evidence from around the world, where conditions are not as bad, is not encouraging," he said.
Last year, Stewart and his team conducted an earthquake simulation in the western Delta. Their equipment rocked a model levee with increasing intensity but failed to damage it as the peat foundation rolled like the skin of a waterbed.
Although the results of that initial test appeared reassuring, many Delta levees have sandy foundations, which are subject to liquefaction, instead of peat. Those levees might not fare so well, Stewart and other engineers say.
Still, Cosio expressed confidence the risk can be managed. The most vulnerable levees have been upgraded, and so the remaining structures are both less risky and in need of less work -- meaning they would be cheaper to fix, he said.
"We know what to do to reduce the flood risk, and we just got the money to do it," said Cosio.
"The earthquake risk is less clear," he acknowledged.