Fault Check : Calleguas Water Board Considers New Seismic Study of Dam to Allay Public Fears

Sometimes new residents in Wood Ranch get a little nervous.

They look up above their luxury homes and cast a suspicious eye at the earthen dam that forms Calleguas Municipal Water District’s Bard Reservoir.

It’s usually dry as a bone in Simi Valley, but with an enormous artificial lake hanging over their heads, a fault zone under their feet and property values to protect, it’s hard for residents to resist imagining a catastrophe.

The next step in the fretting process is usually a trip to visit Don Kendall, Calleguas’ general manager.

“They come by or call me about once a week,” Kendall said. “Usually right after they’ve bought homes in Wood Ranch.”

The burning question they have is simple: Is that dam safe?

The water district wants to put those fears to rest once and for all.

Studies have so far shown them to be ungrounded, but next month the Calleguas board of directors is considering ordering up a new engineering study to reassess the seismic safety of the dam. The board has already spent $10,000 on preliminary work and could spend at least $25,000 on more detailed studies.

“Is the dam safe?” Kendall said. “I think it’s safe. But we probably want to do some more studies, just to be sure. Hopefully we’ll put people’s minds at ease.”

The study proposed by Calleguas is hardly the first in-depth look at the dam’s seismic safety; as recently as 1994, the city examined the issue before approving an expansion at Wood Ranch.

“I know people look at it and say, goodness, gracious, what would happen if that broke?” Mayor Greg Stratton said. “Well, if you were on the golf course, you would get pretty wet. But otherwise all that would happen is you would have riverfront property temporarily.”

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Stratton said early development plans at Wood Ranch called for houses to be built in the flat area just below the dam, where the golf course is now. But the city vetoed that idea, concerned that residents would be put in harm’s way, and asked that the golf course be built there instead.

Rex Gowdy lives on Fresh Meadows Road in Wood Ranch. Because he is on relatively high ground, he said he feels safe in his home. But he does worry about his neighbors.

“I think any person who lives in the path of the dam has got to be concerned about it,” Gowdy said. “It’s a natural thing with an earthquake situation. It’s an earthen dam. I don’t think there is any earthen dam that is earthquake proof.”

But on the other hand, Gowdy said any quake big enough to break open the dam is going to damage more than just Bard Reservoir and Wood Ranch.

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“I don’t think I’d be around to worry about it,” Gowdy said.

When Doug Wieben moved into Wood Ranch eight years ago, he checked with two knowledgeable friends--the chief of the Fire Department and the city’s engineer--to make sure it was safe to live under the dam. He said he isn’t overly concerned about the dam breaking. But the Northridge quake did remind him of the danger.

“I have to say, the morning of the quake I thought about it,” Wieben said.

Bard Reservoir was built in 1965 on 860 acres above the water district’s headquarters in Simi Valley. It was originally the main water source for eastern Ventura County. Now its 10,000-acre-foot capacity represents just a tiny fraction of the water sold by Calleguas.

Initial work on the seismic study, done by Harza Engineering of Los Angeles, has concluded that the Simi-Springville fault--a mere 3 1/2 kilometers from the reservoir--could produce an earthquake of magnitude 7.0. But Harza project geologist Scott Lindvall said scientists don’t have any idea when, or if, the Simi-Springville fault will move.

“You can only do those conditional probabilities on faults that you have lots of information on,” Lindvall said.

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There are no modern records of movement along the fault, which runs along the northwest margin of the city. But Lindvall said advances in research on ground motion over the last 10 years mean geologists can produce computer models showing what might happen to the dam.

Using sample materials from the dam and lab tests on their strength and composition, geologists will feed the data into the model and see what results.

Lindvall said he thinks the study will show that there is no danger of the dam breaking in an earthquake. But he commended Calleguas for taking the precaution.

“Calleguas is just doing some due diligence,” he said.

“It’s the way things ought to be done. You go to a doctor for a checkup, you don’t wait until something is wrong.”