Of all the chaos a massive Southern California earthquake could cause, the most challenging may be losing all four aqueducts supplying the vast majority the region's water, causing a year or more of extreme rationing.
"It's something I, and others here, think about often," said Craig Davis, a manager and engineer with the Los Angeles Department of Water and Power who is looking for solutions.
This issue was highlighted in a recent report issued by the Los Angeles Mayor’s office titled Resilience By Design. By some estimates, Southern California could lose $53 billion in economic activity due to water shortages from a major quake.
Together, the Los Angeles, Colorado and East and West branches of the California aqueducts supply more than 70% of the total amount of water sustaining Southern California.
(A graphic showing where the aqueducts cross the San Andreas Fault. Image: Metropolitan Water District)
Modern seismologists estimate the San Andreas Fault could shift more than 20 feet in a quake, tearing apart any waterways crossing it. No pipe in the world could survive that amount of movement.
The potential crippling of Southern California's water lifelines by a magnitude 7.8 quake was spelled out in the 2008 ShakeOut Scenario. Officials with the Los Angleles Department of Water and Power, which manage the L.A. Aqueduct, said William Mulholland, the father of the aqueduct system, was aware of this danger more than 100 years ago.
But here's the rub: there’s no way to bring water from the north without crossing this fault.
Since the L.A. Aqueduct crosses the San Andreas Fault in large underground tunnel, Davis, of LADWP, said one answer is to add a secondary pipe that can survive some ground movement. High-density polyethylene pipes have survived significant quakes in Turkey, Chile and New Zealand.
"You can almost collapse this pipe in its entirety and still get water through this," Davis explained.
Under such a plan, several miles of this pipe would be slipped into the Elizabeth Tunnel portion of the aqueduct. Davis said the secondary pipe would supply about 20 to 30% of the normal volume of water coming through the aqueduct and could survive about 9 feet of movement at the fault before becoming too pinched to carry water.
(The left side diagram shows roughly how much space the HDPE pipe would occupy in the Elizabeth Tunnel portion of the L.A. Aqueduct. The right side shows where the tunnel is located relative to the San Andreas Fault (in black). The coloring represents the strength of shaking predicted from a quake on that fault. Image: LADWP).
Still, even this relatively straightforward solution could take years to complete and will cost roughly $10 million.
While Los Angeles Mayor Eric Garcetti has recently called for action on this issue, the city has yet to pony up the money for this project.
Other quake prone regions of the state have retrofit their systems using customer surcharges.
"We’ve done it, we’ve done the major improvements that needed to be done," noted Abby Figueroa with the East Bay Municipal Utility District.
After the 1989 Loma Prieta quake rattled much of that district's infrastructure, the agency started major improvements to prepare for the next big one.
Still, Figueroa says it took several years before the utility had enough internal support to begin the massive retrofitting effort. Work began in 1994.
The water district raised $189 million through a customer surcharge for the 11-year project that included things like strengthening pipelines, retrofitting important buildings and upgrading dams and reservoirs.
It also added a special elevated pipeline to a crucial tunnel that crossed the Hayward Fault.
"We made it so the pipeline could shift with the movement of the earth that way it would minimize any damage."
(An image showing the Claremont Tunnel retrofit. The left side shows the tunnel before a quake. The red line represents the Hayward Fault and the blue represents a special pipe added during a recent upgrade. The right side shows how that pipe would survive moderate fault movement. Image: EBMUD).
LADWP has studied this plan and other for ideas on how best to shore up its own water system.
But no pipe in the world could survive the worst scenario; the San Andreas Fault could move more than 20 feet.
The Metropolitan Water District, which manages the Colorado Aqueduct, is looking at other ways of preparing for a major quake, like storing water.
The man-made Diamond Valley Lake Reservoir near Hemet holds 800,000 acre-feet of water, enough to keep Southern California hydrated for 6 months with some rationing. It cost $2 billion to build.
"This is water from Northern California, it comes from the Sierras and it is very pure water," Johnson explained during a recent boat ride on the reservoir.
(MWD chief engineer Gordon Johnson on a boat floating on the Diamond Valley Lake Reservoir near Hemet, California. Image: KPCC)
MWD would use this water after a major quake while it repaired its aqueduct.
The agency wants to stockpile supplies to allow crews to quickly build a secondary aqueduct in the event its primary one is destroyed - but they haven’t done that yet.
The State Water Project, which manages the California Aqueduct, is also constantly monitoring its waterways for seismic vulnerabilities.
They - and the LADWP - have a long way to go before they are fully prepared for a major earthquake on the San Andreas. And that worries some engineers.
"We are effectively sitting on a time bomb," said Davis, of the LADWP. "We need to keep that in mind and get this done as soon as possible," he said.