County supervisors received a troubling update on the Lake Isabella Dam Tuesday. Emergency response personnel met later in the day to plan for a full-scale evacuation in Bakersfield in the event an earthquake were to cause the dam to fail.
A 600-foot-long trench, full of monitoring devices, snakes along the western-side of Lake Isabella's auxiliary dam. Geologists and engineers hope to gain crucial data from those devices, about seismic activity in and around the Kern Canyon fault, which runs underneath the lake and its two dams.
"We are trying to get an idea of how big this fault is, the magnitude of this fault and what kinds of materials have been moving over the last, say, thousands of years,'' said Tony Kittner, a geologist with the Army Corps of Engineers.
That fault line is thought to be capable of producing an earthquake strong enough to rupture the auxiliary dam, plunging thousands of people downstream into massive flooding.
"The auxiliary dam has a liquefaction potential in the soils,'' Kittner said. ''There are sands that can move."
County supervisors learned Tuesday that multiple scenarios have been identified which could cause problems at the dam, everything from seepage and erosion, to a full-blown rupture.
"We've identified a total of 46 potential failure modes at the dam,'' said Ronn Rose of the Army Corps of Engineers. ''That is a huge number. Eighteen of those PFM's are judged as being significant."
Meanwhile, work continues on a comprehensive evacuation plan.
In a worst case scenario, more than 250,000 people in Bakersfield would have to seek shelter and higher ground, less than eight hours after dam failure, said Georgianna Armstrong, manager of Kern County Emergency Services.
"Our plan assumptions build on an earthquake being the triggering event,'' Armstrong said. ''We assume a maximum pool of water behind the dam, which is a worst case scenario. There are several pieces missing to the evacuation puzzle."
Officials stress, the likelihood of a dam failure at Lake Isabella is remote. But if it happens, everyone needs to be ready.
Experts say the biggest hurdle in all of this is to figure out the best way to repair the dam, perhaps even build a new dam.
The Corp of Enginners says it will be extremely expensive and in the best case scenario, we wouldn't see construction start until 2014.
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