As you may or may not be aware, the Sacramento-San Joaquin River Delta is made up of a series of levees, all of which protect a freshwater source that supplies water to two-thirds of the state of California, or some 25 million people, as well as farmland. And on this tenth anniversary week of Hurricane Katrina, Wired sounds the alarm bells of how these levees could be vulnerable to breaching — if not by a hurricane, which would be rare, then by an earthquake or other disaster — potentially impacting the water resources of a huge number of people for years to come.

They explain that since the 1960s, a couple of large pumps have been responsible for dispensing water for the State Water Project, which feeds into the municipal water systems of towns from San Jose to San Diego.

Every drop of water that passes through those those pumps first passes between many miles of levees. If a levee breaches, water rushes in. If enough levees breach on enough islands — or on a large enough island — the volume of fresh water in the Delta is insufficient to fill the void that was once an island. That brings in water from the Bay. Salty, Pacific Ocean water. “If you have ten or 15 levee failures and a big slug of salt water comes in, the salinity goes way up and you have to shut down the pumps,” says Mraz. Engineers call this scenario the Big Gulp.

The levees, also, are just piles of silt and dirt, almost none of which are built to Army Corps of Engineers standards using concrete foundations.

Thankfully, the chances of an earthquake on the nearby Concord Fault are relatively low, with the USGS putting it 3 to 4 percent for a 6.7 or higher earthquake in the next 30 years. But add to that the possibility of a storm-borne levee breach, especially one during a drought, and the state could be equally screwed, and not just temporarily.

The worst case scenario would happen during a drought, when freshwater pressure is lowest. Fifty breaches across many islands would flood the Delta with about 1.2 million acre-feet of Pacific Ocean water. Getting the salinity levels back to drinking quality could take years. First, engineers would have to rebuild the levees and pump out the submerged islands. Then, they’d have to wait for enough fresh water to flow through the Delta to flush out the salt.

So, just add this to your list of impending disaster scenarios about which you can do little or nothing.