Federal Agency Urges Bolstering of Casitas Dam

A $20-million reinforcement of Casitas Dam is the most cost-effective and reliable way to reduce the risk of dam failure during a large earthquake and protect human life, according to a new federal study.

More than 400 people could die if the 39-year-old earthen dam fails, states the environmental report released to the public Tuesday by the Bureau of Reclamation.

“The seismic modification of Casitas Dam should proceed as soon as possible to reduce public risk,” the 97-page report concludes.

The bureau’s construction plans for the 335-foot-high dam include excavating 1.2 million cubic yards of earth from a nearby 60-acre site to widen the structure’s base.

The material would be used to replace earth in the dam that experts fear would liquefy in a major earthquake and to build a 130-foot high berm around the dam to fortify it.

“There’s anywhere from a 1 in 100 to a 1 in 300 chance in any given year that an earthquake large enough to damage the dam will occur,” said Bill Pennington, dam safety project manager with the bureau’s Fresno office. “The kind of damage we’re expecting is not a sudden catastrophic failure, but you don’t expose people to that--you fix it.”

The bureau considers odds of about 1 in 10,000 an acceptable level of risk, Pennington said, noting that no dam is risk-free.

Casitas is considered a high-risk dam, not because of the work the agency has determined needs to be performed, but because of the number of people in the Ojai Valley and west Ventura who live in the potential flood path.

The bureau believes a flood stemming from damage to the dam could threaten the lives of 14,000 people in Casitas Springs, Oak View and west Ventura. As few as six to more than 400 could die depending on the type of dam failure and time it occurs, according to the report.

As far as nine miles downstream in west Ventura, water depths could reach 34 feet within one hour and 40 minutes after a dam break, the bureau said.

“If water starts leaking out, it won’t go boom,” Pennington said. “It will take time.”

The agency has known since 1989 that a degree of liquefaction could occur in the dam’s foundation. But it wasn’t until 1996 that the severity of the problem was found to be greater than originally believed, Pennington said.

The construction work would enable the dam to withstand a magnitude 7 earthquake, the size of a tremor that could damage the dam, Pennington said. An earthquake fault lies directly beneath the dam at a depth of about four miles, he said.

The bureau report also proposes installing reinforcement strips in the crest of the dam. The 18-month project could begin as soon as April.

“It’s our intent to try and design the project to minimize the [environmental] consequences,” said bureau spokesman Chris Eacock, adding that the project isn’t expected to have a “significant impact” on the environment.

The public has until July 23 to comment on the report, which will be available later this week at libraries in Ventura and Oak View.

Environmental activist Russ Baggerly welcomed the bureau’s report, but said such work is overdue.

“As soon as they knew about it, they should have been working on it,” he said. “History has shown us that Ventura County faults usually have a major quake every 200 years. The last major quake was in 1812, it was just offshore . . . The geologic time bomb is ticking.”

Pennington agrees, which is why the bureau wants the work to begin quickly. Indeed, temporary wells installed last November to keep water away from the dam’s foundation and reduce the likelihood of significant liquefaction have reduced the danger and made the dam safe for operation, he said.

The risk of a dam failure in an earthquake would increase again once work begins, he said.

“Whenever the foundation is open, it isn’t as stable as it is with the dam fully intact,” Pennington acknowledged, but added the bureau would not jeopardize the public’s safety.

“The dam is safe for continued operation until we get the project done,” he said.

It’s unknown yet whether water will be drained from Lake Casitas during construction to minimize the risk of flooding. The lake is the primary source of drinking water for more than 50,000 people from Ojai to Ventura.

The Casitas Municipal Water District, which operates the bureau-owned dam, is expected to pick up about 15% of the project’s cost.

A warning system ranging from sirens to an automatic telephone dialing system could be installed before the work begins, Pennington said.

Pat Baggerly, a member of the Environmental Coalition of Ventura County, believes some kind of warning system is essential regardless of the construction.

“How can they warn over 10,000 people in a period of two hours to evacuate?” she said. “We hope they will leave the system in permanently.”