Record Rainfall Allows Dam Testing

The recent record rainfall that created misery for some Southern California homeowners and commuters was a blessing for engineers who, for the first time, had enough storm water to begin testing a dam designed to protect residents from Highland to Huntington Beach from flooding.

The test was meant to ensure the safety of the Seven Oaks Dam, at the foot of the San Bernardino Mountains, which holds back the flood-prone Santa Ana River and, at 550 feet, is one of the nation’s tallest dams. The earthen structure is a crucial part of a mammoth flood-control project that protects more than 3 million people in San Bernardino, Riverside and Orange counties.

Crews from the Army Corps of Engineers cranked open one of the dam’s release valves Wednesday, allowing a torrent of water to shoot into a giant concrete- and gravel-lined pool on the riverbed.

Based on this early test, the dam’s pressure release mechanisms worked properly, although federal engineers said they noticed some unusual vibrations during the release that indicated the dam needed minor modifications.

Generally, though, “things are behaving according to design,” said Robert Kwan, a project engineer for the corps.

Because of a four-year state drought, the dam, built in 1999 at a cost of nearly $500 million, had never been tested.

“This is the first time we’ve had this much water behind the dam,” project manager Girish Desai said as he looked down on the huge spray of water dumping into the Santa Ana River.

The dam is the sixth-tallest in the nation. The reservoir behind the dam has a capacity of 145,000 acre-feet of water, or more than 47 billion gallons.

The rains dumped about 43,000 acre-feet of water into the reservoir, or about 14 billion gallons, according to federal engineers.

The Seven Oaks structure works in tandem with Prado Dam in Corona, also on the Santa Ana River, which winds from the mountains to the ocean near Newport Beach and Huntington Beach. It’s part of a $1.3-billion flood-control improvement project that includes an ongoing plan to raise the height of Prado Dam.

To test Seven Oaks Dam’s pressure-releasing gates, the engineers opened one of six gates Wednesday. The 5-foot-wide gate was raised about 2 1/2 feet, releasing about 1,400 cubic feet of water per second, the equivalent of about 10,500 gallons per second.

“No one has seen this much water in nearly 30 years or so,” David Cozakos, a senior hydraulic engineer for the Army Corps of Engineers, said of the recent rains.

The engineers plan to gradually release more water today until two gates are completely open, unleashing about 6,600 cubic feet per second, or nearly 50,000 gallons per second.

The water released from the dam will engorge the Santa Ana River.

The San Bernardino County Sheriff’s Department has assigned swift-water-rescue teams to keep an eye on the river and be ready to save onlookers who become victims of the strong current.

Most of the water released during the test will run along the Santa Ana River to Prado Dam before being diverted underground for storage. The water can later be treated and used as residential drinking water, mostly for Orange County residents.

“Very little water will be wasted into the ocean,” Cozakos said.