By Jessica Wertheim
The Public Press
According to the U.S. Geological Survey, "there is a 70 percent probability that one or more damaging earthquakes of magnitude 6.7 or larger will strike the San Francisco Bay area during the next 30 years."
And San Francisco is taking no chances. The city’s newest project, headed by the San Francisco Public Utilities Commission, is the construction of a five-mile long tunnel located under the San Francisco Bay.
The tunnel, which will lie 103 feet beneath the floor of the Bay, would provide protection to the Bay Area’s water supplies if a major earthquake were to compromise other sources.
"By building extra tunnels and strengthening our pipelines, it means we have much greater assurance that we’ll have water after the next earthquake," said Ed Harrington, general manager of the San Francisco Public Utilities Commission.
The tunnel also will be replacing "two large steel pipes built in 1925 and 1936 that sit on the floor of the bay." According to a recent article in the Oakland Tribune, these pipes could easily break in a major quake, which would effectively cut off water for weeks to many major cities.
By burying the tunnel deep into the earth, in "stronger, tighter materials, there is much smaller vulnerability to being pulled apart from shaking and liquefaction," said David Schwartz, a geologist with the U.S. Geological Survey in Menlo Park. "From an engineering point of view, it’s much stronger."
In addition to the construction of the tunnel, pipelines, water treatment plants and the Calaveras Dam also will be rebuilt over the projected timeline of five years. The retrofitting will result in the stabilization of the structures so each could "withstand a quake of up to magnitude 7.9 on the San Andreas fault and 6.9 on the Hayward fault."
The tunnel’s undertaking is scheduled to begin next spring with the projected completion date of 2015. In addition to the construction of the tunnel, “an additional 16 miles of pipe connecting to the tunnel on either side of the Bay also will be replaced.”
The estimated cost — $347 million. The funding is expected to come from revenue bonds and additionally financed by a 73.9 percent increase of the price of residential water in San Francisco ($23 each month to $40 in 2015).
For now, the construction work is racing against the clock, as it appears to be only a matter of time before the next earthquake. But not all of the preemptive engineering marvels are going on under the surface of the water.
Caltrans has retrofitted several freeway overpasses and is rebuilding the Bay Bridge; Pacific Gas & Electric has upgraded substations and gas lines; and Bay Area Rapid Transit has made improvement on the Transbay Tube.
News Notes are compiled from outside news reports and other online resources.
