Rare Mega-Storm Would Flood Long Beach

LONG BEACH, CA — Southern California may be due for a storm of biblical proportions, and the region is simply not ready for it, experts warned Tuesday.

A team of researchers and engineers warned that an ARkStorm or the "other big one" could cause triple the damage of a major quake along the the San Andreas Fault, the Los Angeles Times reported. Dams would likely give way, rivers would overflow and 1.5 million people would be forced to flee the devastation.

California has suffered such deadly mega-storms in the past, and another one is all the more inevitable due to climate change, according to the U.S. Geological Survey. Such a mega-storm would last for weeks, and floodwaters would inundate cities from the Mojave Desert to the coast, the USGS found. An ARkStorm, which stands for Atmospheric River 1,000, would cause more than $725 billion in damage statewide, the Times reported.

In Los Angeles Basin, residents would have to contend with the epic runoff from the San Gabriel Mountains, which could overwhelm flood control measures, overflowing the San Gabriel River from Pico Rivera to Long Beach and Seal Beach, according to analysis by the U.S. Army Corps of Engineers cited by The Times. Places like Downey could see 15 feet of floodwater.

A government study created computer models to estimate the effects of 900-year, 7,500-year and 18,000-year storm events. In each case, much of the region ended up under catastrophic flooding including cities such Artesia, Cerritos, Seal Beach, Long Beach,Rossmoor, Bell Gardens, Bellflower, Carson, Commerce, Compton, Cypress, Downey, Hawaiian Gardens, La Palma, Lakewood, Lynwood, Montebello, Norwalk, Paramount, Santa Fe Springs, and Whittier. Officials say as many as 1 million people could be affected. Among the communities hardest hit in a dam failure would be Pico Rivera, a city of about 63,000 people immediately below the dam.

In a series of recent public hearings, corps officials told residents that the 60-year-old Whittier Narrows Dam no longer met the agency's tolerable- risk guidelines and could fail in the event of a very large, very rare storm, such as the one that devastated California more than 150 years ago.

Specifically, federal engineers found that the Whittier Narrows structure could fail if water were to flow over its crest or if seepage eroded the sandy soil underneath. In addition, unusually heavy rains could trigger a premature opening of the dam's massive spillway on the San Gabriel River, releasing more than 20 times what the downstream channel could safely contain within its levees.

In the event of a rare storm, the Whittier Narrows Dam could overflow and erode. The U.S. Army Corps of Engineers has a proposal to protect it in such an event.

The corps is seeking up to $600 million in federal funding to upgrade the 3-mile-long dam and say the project has been classified as the agency's highest priority nationally, due to the risk of "very significant loss of life and economic impacts," The Times reported.

The funding will require congressional approval, Doug Chitwood, lead engineer on the project, told the newspaper.

Standing atop the 56-foot-tall dam recently, Chitwood surveyed the sprawl of working-class homes, schools and commercial centers about 13 miles south of Los Angeles and said, "All you see could be underwater."

The dam, which stretches from Montebello to Pico Rivera and crosses both the San Gabriel and Rio Hondo rivers, is one of a number of flood control facilities overseen by the corps. Throughout much of the year, it contains little water.

David Reid, a water historian and expert on the Whittier Narrows area, told the Times “the false sense of security included in the phrase ‘900-year flood’ combined with the promises of 20th century water infrastructure have put us in a bind.

“That’s because a mega-flood is impossible to predict,” he said. “And if the water infrastructure fails, we’re in big trouble.”

City News Service and Patch Staffer Paige Austin contributed to this report. Photo: Shutterstock