IT COULD happen tomorrow. As California is sweltering through another hot, dry summer, the ground in the Sacramento-San Joaquin delta begins to shake as a large earthquake strikes. Here, a network of river channels wend their way around dozens of “islands” as they flow down to San Francisco Bay. The locals call them islands but that’s not quite right, for the land in between the rivers has sunk well below the water level – in places by as much as 8 metres. In reality, they are immense pits, protected only by often-fragile earthen levees.
Geologists had warned that a big earthquake nearby might liquefy the levees and cause them to fail. Within minutes of the quake, they are proved right. The levees give way in dozens of places, and the fresh water in the river channels begins to pour down onto 40 of the region’s 60 or so islands. With little fresh water flowing through the delta after years of drought, saltwater from the tidal zone starts to flow upstream towards the breaches in the levees, deep into the heart of the delta. Within hours, brackish water is flooding across vast areas of farmland and thousands of delta residents and farmworkers are forced to flee. Almost all survive, but many lose their homes and livelihoods.
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It’s a major disaster, and it has only just begun. On the seaward side of the delta are massive pumps that usually work ceaselessly every day, transferring vast quantities of fresh water from the delta into canals and aqueducts heading for the farms and cities of southern California. A significant proportion of the water for the 19 million people living in California’s Metropolitan Water District comes from the delta, but as saltwater rushes in, the pumps have to be shut off. It will be a year or more before the levees can be repaired and the saltwater flushed from the channels. Only then can pumping resume.
This would be a serious problem at the best of times. The green of Southern California is only sustained by extraordinary feats of water engineering – no wonder some have called the state a “magnificent illusion”. But California is already suffering its worst drought in history. The loss of the delta water could not have come at a worse time and threatens to destroy the illusion completely.
Even before the quake, farmers had begun abandoning their crops and laying off workers. More are soon forced to follow suit. The US relies on the state for much of its fresh produce, so fruit and vegetable prices soar across the country and beyond. As the drought continues and the pumps remain silent, reserves dwindle, and water supplies to homes and factories have to be rationed. The economy shrinks even further and unemployment rises as the world’s 8th largest economy runs dry. The effects are felt across the nation and the rest of the world…
California’s Katrina
This is the worst case scenario. Let’s hope it doesn’t come to pass but as we saw with hurricane Katrina in 2005 and Sandy two years ago, the worst can happen. If California’s Department of Water Resources (DWR) is to be believed, it is only a matter of time before an earthquake or large flood causes multiple breaches in the 1800 kilometres of levees. If it happens at a bad time, this really could be California’s Katrina.
Much depends on the precise circumstances. “There is no simple answer to how water supply disruption in the delta would affect the state,” says Nancy Vogel of the DWR. If the levees fail when water reservoirs are full and plenty of fresh water is flowing through the delta, much less seawater will penetrate inwards and the pumps will not have to be turned off for long, if at all. But the risk of disruption to the supply of water from the delta is one of the reasons why the DWR says California needs to spend $25 billion on an immense tunnel project to bypass the fragile levees and guarantee the supply of fresh water to southern California, come earthquake, flood or storm. Many delta residents are fiercely opposed to the idea. They see the project as an attempt to steal their water, and dismiss talk of catastrophe as scaremongering. So who is right? It really is a billion-dollar question.
Strictly speaking, the Sacramento-San Joaquin delta is but a tidal estuary formed where the Sacramento and San Joaquin rivers meet. Much of it once flooded with every high tide. Starting around 160 years ago, gold rush pioneers and farmers began to build levees to hold back the water. Without fresh deposits of mud, the land has been sinking as the organic matter within it rots away – as is happening in many other places around the world. Were it not for the levees most of the delta would be covered by several metres of water.
From the mid-20th century, huge quantities of water began to be taken from the southern side of the delta for cities and farms. “The water pumped down from the delta is the backbone of the California water system,” says Vogel. Yet .
The system may have served the state well for decades, but the one thing almost everyone agrees on is that things can’t go on as they are. Sea level is slowly rising and is set to rise much more over the coming century. One consequence is higher pressure on the levees, which means a greater risk of breaches if they are not raised.
Another is an increasing problem with saltwater incursions: not only is the sea rising, but less fresh water is flowing into the delta, due to increasing extraction upstream and climate change. When the rivers are low, seawater is pulled upstream from the bay by the huge pumps that supply the south.
These incursions are bad both for native wildlife and for people. They cause pollutants to accumulate as well as adding salts such as bromides, making the delta water costly to purify for drinking. “Over time, the cost of treating the water for urban purposes is only going to increase,” says Jay Lund, a civil engineer at the University of California, Davis. The current drought is causing such severe incursions that to hold the saltwater back.
Meanwhile, what little native wildlife remains in the region is struggling to cope. Extinction is a real possibility for the salinity-sensitive delta smelt, for example, a tiny fish that was once a linchpin of the region’s ecosystem. “This is the canary in the coal mine,” says local resident Robert Pyke.
Also in trouble are the Chinook salmon that migrate through the delta. The reversals of river flow caused by the pumps can confuse them. And although the pumping stations are equipped with screens that are meant to prevent large fish such as salmon from being sucked in, they don’t work well when little water is entering the delta and river flows are slow. Fish can get trapped and killed in the intakes, or become sitting ducks for predators. Not all wildlife is suffering, though. Many invasive species, from quagga mussels to water hyacinths, are thriving.
Multiple levees could fail in the event of a quake (Image: DWR Public Affairs Office/State of California)
Then there is the issue of the levees failing. One or two breaches happen most decades. The , when a levee failed on a fine day, flooding Jones island (pictured above). There have been some close calls since, like when waves overtopped some levees during winter storms in 2005 and 2006. Such storms are expected to become more intense as a result of global warming. And in 2009, .
Occasional breaches are costly but manageable. The big question is whether a major flood or earthquake could breach many levees simultaneously. Flooding increases the pressure on the earthen structures, and can rapidly erode them if water starts flowing over them. Could the levees withstand a megaflood like the one that hit California in 1861, when it rained every day for more than six weeks? They might fail in part, but not wholly, reckons Pyke, who is a geotechnical engineer with experience of levee construction and repair in Europe and in post-Katrina New Orleans.
Raising the levees
For one thing, he points out, every island that floods reduces the pressure. What’s more, for the last three decades, state and local engineers have been working to bring the levees up to a standard known as PL 84-99 – making them 15 centimetres higher and reducing the slope of the inside wall to increase stability. Levees built to this standard are resistant to the kind of flooding event that happens once a century. Roughly half of the network is now at that standard, Pyke says. “Within a couple of years it will all be there.”
The upgraded levees will still be vulnerable to a large earthquake, though. “A magnitude 6 or 7 quake would probably do for all of them,” says Lund. Their resilience has yet to be tested, perhaps because . But . A concluded that “there is a 40 per cent probability of a major earthquake causing 27 or more islands to flood at the same time in the 25-year period from 2005 to 2030”. This is the basis for the “doomsday” scenario used to help justify the twin tunnel project.
“A magnitude 6 or 7 quake would probably do for all the levees”
It’s not quite that simple, however. The delta is 50 kilometres from the nearest fault, the Hayward fault, and the risk of a major earthquake here is thought to be low. Even if it happened, Pyke thinks the effects will die off significantly 50 km away, so the threat is overblown. Is he right?
The 2009 report made certain assumptions about how seismic tremors would travel to the delta and what effect they would have on the levees. Though it took the composition of local soils into account, the report used what Joe Fletcher of the USGS calls “a fairly standard attenuation model”. This is not the best way to do it, Fletcher says, and he and his colleagues are trying to do better. “We are making progress but are a ways from actually producing a model.”
So the odds of an earthquake bringing down dozens of levees at once could be lower than the 40 per cent figure suggests. But it could also be higher: there is a chance that the local topography could amplify some seismic wave frequencies, says Fletcher. Even if it does turn out to be lower, what level of risk is acceptable, given the importance of the delta water to millions in southern California? Even Pyke thinks something must be done. He helped write recommending that half of the system be built up to the “fat levee” standard, which means making levees so wide that they cannot fall over when shaken by a quake. “That would effectively flood and earthquake-proof all the islands that are below sea level,” he says.
At a cost of between $1 and 2 billion, this would be relatively cheap. But fat levees would not solve the problems of saltwater incursions and the resulting interruptions to the water supply. “The water deliveries continue to get more erratic,” says Vogel. “We have tens of millions of people who depend upon them.” That’s where the twin tunnels come in. The idea is to build two earthquake-proof tunnels that would run side by side and carry water from supplies further upstream on the Sacramento river down to where the pumping stations are now. This would provide purer, fresher water for southern Californian even when river levels fall in the delta or levees fail. But at $25 billion it will not come cheap.
The tunnels are the central plank of a package of measures being put forward as the . The plan is supposed to benefit wildlife as well securing the water supply, but an independent scientific review found that the DWR “tends to overreach conclusions of positive benefits” and “needs to be reconsidered and revamped”. Hardly a ringing endorsement.
With growing and conflicting demands for a shrinking supply of water, no scheme can satisfy everyone. Delta residents, however, see themselves as the big losers. “If they build the tunnel they will suck this region dry,” says Jeff Hart, who used to conduct eco-tours of the delta and now runs a farm there. “We’re being treated like we’re a colony.”
“If they build the tunnels they will suck the delta region dry”
That’s not the only worry for residents. Once the tunnels are complete, there will be less reason to protect the “islands”, or restore them after floods. Several have already been abandoned after levee failures, from Frank’s Tract in 1938 to Liberty Island in 1998. Those parts of the delta that are home to important infrastructure such as state highways as well as farms, though, are unlikely to be abandoned. So California may well decide both to build the tunnels and continue to strengthen most of the levees.
When that will happen is another matter. Even if the plan’s proponents get their way, the tunnels would not be completed until 2027 at the earliest. And political wrangling over the plan and its funding could cause endless delays. “We have been debating, arguing and litigating over the delta for the last 40 years,” Vogel says. What happens here, though, could ripple across the rest of the world. The rest of us can only hope that the “magnificent illusion” does not crumble to dust.
Leader: “A six-state California faces a water war”
This article appeared in print under the headline “Water, water, everywhere…”
