Floods are a serious threat to Southern California, say CSUF geologists – Orange County Register

Seeing the devastation that Hurricanes Harvey and Irma inflicted, it’s tempting to take solace that Southern California escapes anything but the rare remnant of a tropical storm.

But that doesn’t mean we’re spared flooding, reminded two Cal State Fullerton geologists in the wake of Harvey and Irma.

Our water events might not have names, but they can wreak havoc on our beaches, canyons and low-lying communities. Just ask anyone who lived here in 1938.

The 1938 storm dropped 8 inches of rain in the days leading up to March 3, when the Santa Ana River overflowed its banks. The storm affected the entire region, including Fullerton, Placentia and Los Angeles, but Anaheim was particularly hard hit. (Register file photo)

“Floods are a serious threat to our region,” said Matthew E. Kirby, professor of geological sciences, after Hurricane Harvey left vast swaths of Texas underwater. “Land-falling hurricanes are highly unlikely in Southern California, but they are not out of the realm of possibility.”

A bigger threat comes from large atmospheric rivers connected to Pacific Ocean-sourced winter cyclones, Kirby said. These rivers of water in the sky contain huge amounts of vapor and usually bring heavy precipitation to the West Coast.

Several such events occurred earlier this year, ending the state’s five-year drought while dropping massive quantities of water that often had nowhere to go.

In 1938, five days of rain bloated the Santa Ana River, sending it spilling over its banks, killing about 100 people in the region, sending cows paddling down streets and wiping out entire neighborhoods. The Prado Dam is one legacy of the disaster.

Southern California’s low-lying areas adjacent to river channels, creeks and flood-control basins or downstream from dams, as well as coastal areas, are most vulnerable to flooding, noted Joe Carlin, assistant professor of geological sciences. Carlin, a Dallas native, in 2015 investigated flood deposits in the Gulf of Mexico…

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