from The San Francisco Chronicle

Is California overdue for biblical, catastrophic flooding? History says it could be

By Katie Dowd

Sacramento underwater due to floods in an 1862 rendering that ran in local papers.

Californians are always talking about the coming Big One, but what if the big one is a flood, not an earthquake?

With this recent cavalcade of rainstorms, there’s been renewed interest in a 2011 USGS study on the so-called “ARkStorm.” In it, the USGS lays out a case for a hypothetical “megastorm,” one that could cause up to $725 billion in damage and impact a quarter of California’s homes.

The ARkStorm would bring with it catastrophic rains, hurricane-force winds and hundreds of landslides. Central Valley flooding alone is projected to span 300 miles.

If that sounds far-fetched, there’s historic precedent: Geological evidence indicates that California endures massive flooding caused by atmospheric rivers every 100-200 years. And settlers who moved to California after the Gold Rush soon found what the native population had known for centuries: Northern California is prime flooding territory.

The most prominent example is the Great Flood of 1862, a natural disaster that still ranks as the largest flood in the history of the American West. Between Dec. 1861 and Jan. 1862, the West Coast received a near-constant deluge of rain. Sacramento received a stunning 23 inches in that period, turning the city into a watery ghost town.

“The people are leaving the city as rats would a sinking ship” the Red Bluff Independent wrote on Jan. 14.

[ click to continue reading at SFGate.com ]