When the next large quake strikes Santa Rosa, fires could break out across the city, potentially wreaking as much devastation as the quake itself.
But the water to extinguish those fires might be in short supply. That's because a quake of 7.0 magnitude or higher likely would rupture the vital but aging water transmission line that crosses the Rodgers Creek fault at Sonoma Avenue.
Not only would most of eastern Santa Rosa soon be without water, but the Sonoma Valley, too, would quickly run dry, causing untold additional headaches for residents coping with a major disaster.
But a project getting underway soon aims to strengthen a key portion of the line, known as the Santa Rosa Aqueduct, by installing a thicker gauge pipe specially designed to flex in the event of an earthquake.
"This project will help secure the future of our water supply when the Rodgers Creek fault decides to stir," Steve Koldis, project manager for the Sonoma County Water Agency, told the Santa Rosa City Council.
Construction is set to begin in early February and last until August. Heavy machinery will dig a big trench in the westbound lane of Sonoma Avenue between Doyle Park Drive and Doctor's Park Drive. One lane of traffic will remain open in each direction, but delays of five to 30 minutes are expected. The work will be limited from 8:30 a.m. to 4:30 p.m., but still has the potential to affect nearby schools, hospitals, offices and homes.
The project is the first of four major earthquake-related upgrades to the agency's sprawling collection and distribution system, which provides water to agencies servicing 600,000 people in Sonoma and Marin counties.
The other projects involve upgrades of transmission lines that cross the Russian River and Mark West Creek, as well as the installation of 20 isolation valves designed to help reroute water around quake damage.
All told, the projects are estimated to cost $18 million, about half of which will be borne by the Federal Emergency Management Agency and the balance by ratepayers.
The Santa Rosa aqueduct project is the first because it is considered one the most vulnerable points in the agency's system.
It pipe runs from the agency's water collectors on the Russian River near Forestville, across Santa Rosa to four storage tanks in Spring Lake Regional Park. From there it continues into the Sonoma Valley, delivering 800 million gallons of water a year to the Valley of the Moon Water District.
An agency analysis showed that the three-foot wide pipe, which was installed in 1959, has a high likelihood of rupturing in the event of a 7.0 earthquake. There is a 31 percent probability of a magnitude 6.7 or greater quake occurring on the fault in the next 30 years. It is the highest-risk fault in the Bay Area, according to the agency.
The aqueduct is 12 feet beneath Sonoma Avenue. It is made of an eighth-inch thick steel that is coated on the inside with mortar to protects the pipe against corrosion. The pipe crosses the fault in a three-block wide area of Sonoma Avenue near the Santa Rosa French-American Charter School.
The Rodgers Creek fault is what is known as a lateral strike-slip fault. That means that when a quake hits, the ground is likely to shear north to south.