Pacoima Dam Not Up to Standards, Study Says : Flood control: The structure could not handle the worst possible storm, according to report. But engineers say there is no immediate hazard.

The Pacoima Dam does not meet state requirements intended to protect downstream residents during the largest possible storm, according to a report released Tuesday to the Los Angeles County Board of Supervisors.

At the request of the county Department of Public Works, the board approved spending $235,000 to study ways to improve the 370-foot concrete dam, which was constructed in 1929 and reinforced after the 1971 Sylmar earthquake.

The dam is in the San Gabriel Mountains, about five miles above the city of San Fernando. During wet years, its runoff flows through the Pacoima Wash and into the Los Angeles River.

After the vote, county and state engineers said in interviews that the dam’s shortcomings present no immediate hazard. The dam is equipped to handle larger storms than any experienced since it was built, but it is not strong enough for the maximum possible amount of rain.

“We’re talking about the worst storm you could expect,” said Robert Kroll, county hydraulic engineer. “That would occur something like once every 10,000 years.”

Kroll said the county realized the dam was inadequate during analyses after the Sylmar quake but worked first to build seismic reinforcements. In 1976, the county developed a plan to divert water exceeding the dam’s capacity through a tunnel into the Pacoima Wash. But Kroll said that proved to be too costly, about $6 million.

“We never went ahead with that because of the cost,” he said.

In the ensuing years, the science of predicting maximum potential rainfall and evaluating dams’ safety advanced dramatically, leading to the conclusion that the Pacoima Dam needs work, he said.

The dam is built to handle a water flow of 10,800 cubic feet per second, Kroll said, and it must be able to withstand the force of 24,700 cubic feet per second.

The private consultants--Dames & Moore--hired Tuesday by the county are to evaluate other options including the possibility of building a larger spillway at the top of the dam to allow excess water to spill over.