Laura Bliss is CityLab’s West Coast bureau chief. She also writes MapLab, a biweekly newsletter about maps (subscribe here). Her work has appeared in The New York Times, The Atlantic, Los Angeles magazine, and beyond.
You don’t need a hurricane to have a catastrophic flood.
“California’s Katrina Is Coming,” proclaimed an article on WIRED yesterday. And you know what? It could be true.
Though the West Coast almost never gets hurricanes, an earthquake- or storm-induced flood could still do serious damage one of the state’s populated regions.
Only problem is, WIRED got the wrong one. Nick Stockton trumpeted the impending doom of Northern California’s Sacramento/San Joaquin River Delta. But, measured in terms of possible loss of life and property, the risks surrounding the city of Sacramento are what are most alarming.
Much of Sacramento sits on a massive, deep floodplain where the American and Sacramento Rivers meet. South of there, the SSJR Delta is the confluence of Sacramento and San Joaquin Rivers, plus their countless offshoots and channels around islands of land. The largest estuary on the U.S. West Coast, the SSJR Delta feeds into Suisun Bay, which is connected by a strait to the San Francisco Bay.
Over the past century, people have radically transformed the SSJR Delta. Once a vast freshwater marsh, pocked with peaty, tule-covered islands, the Delta is now largely used for agriculture. Farms cover the majority of its 57 islands and tracts, whose delicate edges have been leveed with little more than rammed earth.
Meanwhile, those levees also allow the state to divert and pump freshwater to other parts of California, via the State Water Project. The SSJR Delta now supplies more than 25 million people and 3 million acres of irrigated farmland—it’s truly the heart of the state’s water system. But farming and water development have both led to the land’s oxidation and subsidence; the islands are sinking below sea level.
That’s a perfect recipe for flooding if a severe El Nino storm raised sea levels, or if a close enough, strong enough earthquake caused the levees to break. “When you’re on a subsided island, ringed by a levee all the way around, one break fills the entire island,” says Jeffrey Mount, a senior fellow at the Public Policy Institute of California’s Water Policy Center, and the founding director of UC Davis’ Center for Watershed Sciences.
However, the population on these islands is small and spread out. Nearly three-quarters of the Delta is used as farmland. Mount says the probability of a serious levee collapse occurring on any given year varies significantly from island to island, from 1 percent, which is relatively low, to about 7 percent, which is quite high. But in terms of economic damage and loss of life, the risks are fairly minimal—especially compared to what could happen if the right kind of earthquake broke the fragile, aging levees around the city of Sacramento.
“The loss of lives and economic damages would be in the ballpark of Katrina,” says Mount. “Up until recently, New Orleans had better flood protections than Sacramento did.”
The Sacramento metropolitan area contains nearly two and a half million people, at the intersection of two huge rivers. Interstates 5 and 80, and US 50*, all run through its heart. It’s the capital of the world’s eighth-largest economy.
Yet according to the U.S. Army Corps of Engineers’ National Levee Database—which inventories the condition of all federally maintained levees, as well as some local and state ones—the majority of levee systems within the Sacramento region were deemed unacceptable in their most recent inspections. Like the islands in the SSJR Delta, parts of the city are bowl-like—deep below sea level. According to the L.A. Times:
A recent state report predicts that if certain weather conditions occur, Sacramento could be buried under more than 20 feet of water. The worst-case scenario projects 500 dead, 102 square miles flooded, 300,000 residents displaced and a cost of $25 billion.
Sacramento lawmakers have been “busting their asses” (according to Mount) to get the city’s levees in better condition—particularly since Katrina. Progressive flood-management laws are in effect at the local and state level. Funding from all levels of governance is going towards bolstering the levees. Residents have been able to buy federally subsidized flood insurance. Because of these efforts, Mount says that the chance of catastrophic levee failure in any given year is down to about 1 percent, and possibly lower.
But given how much is at stake, Sacramento’s risk is still tremendous. “Nature has a way of finding the weak spots,” Mount says. “You can’t rule out a Katrina-style disaster.” One study has pointed to how the city’s low-income neighborhoods may be particular vulnerable.
This is not to diminish the scary, likely outcomes associated with the fragile state of the SSJR Delta. For example, the environmental costs of levee failures are likely to be significant. “Out of five islands where levees have failed and are already underwater, four have been terrible for native fish and wildlife,” says Doug Obegi, a staff attorney with the National Resources Defense Council who focuses on Delta water policy. “Invasive species have come to thrive while native species have died.”
The state’s water supply, of which the SSJR Delta is the hub, could also be threatened in a “perfect storm” of conditions, especially under the unusually dry conditions California is experiencing right now. “The volume of area below sea level would be so large that a multi-island levee failure would draw water from the Bay into the Delta,” Mount says. High salinity levels “would shut down the State Water Project.”
That means the state’s overall water supplies would be thrown for a loop for months, at least.
State water officials are working to protect these supplies, as well as contingency plans in the event that it gets too salty to drink. That’s fortunate. In this time of drought, floods are likely the last thing on most Californians’ minds, despite the fact that, according to Mount, “there are only two kinds of levees: those that have failed and those that will.”
*A previous version of this post incorrectly referred to US 50 as an Interstate.