O.C. flooding – What could happen here – Could the District at Tustin Legacy be Under Water – Literally and Financially –
Scenes of wrecked and submerged neighborhoods in the aftermath of Sandy, the East Coast superstorm, are unlikely to be repeated in Orange County anytime soon.
But something very like it happened in 1938. Days of rain dropped more than 9 inches over Orange County, more farther inland, turning much of northern Orange County into a lake as the Santa Ana River overflowed its banks.
The flood claimed at least 19 lives, left 2,000 homeless and yielded memorable black-and-white photos of drowning cars and buildings in Anaheim.
Something very like it also happened in December 2010. More than 9 inches of rain fell over 12 days in Orange County – enough for a 1938-style catastrophe. But the widespread devastation didn’t happen this time.
The difference comes down to human engineering. The 1938 flood prompted construction of Prado Dam above Orange County on the Santa Ana River, and the concrete channelization of riverbeds across Southern California.
Sealing riverbanks in concrete speeds storm flow on its way to the ocean, depriving us of the chance to capture some water, perhaps, but preventing catastrophic flooding.
“As much as everybody complains about concreting rivers, if we hadn’t done that, we would have had 1938 déja vu all over again,” said Bill Patzert, an ocean and climate researcher at the Jet Propulsion Laboratory in Pasadena. “We’re somewhat immunized against floods.”
Somewhat, however, does not mean completely. More localized flooding remains a genuine threat in Orange County.
And while the chances of a city-swallowing deluge are far lower because of flood control, they aren’t completely out of the question.
A 190-year storm – one that would be expected statistically once every 190 years – could wreak similar havoc even with present flood control measures, said Tom Bucklew of the U.S. Army Corps of Engineers, project manager for the Santa Ana Mainstem Project.
With a total estimated pricetag of $2.1 billion, the project so far has included a variety of improvements along the Santa Ana River, the raising of Prado Dam and the building of the Seven Oaks Dam near the river’s headwaters in San Bernardino County.
The goal is to provide Orange County with 190-year flood protection. At the moment, we have 70-year flood protection.
“There are still hundreds of millions of dollars needed to complete the project,” said Kevin Onuma, manager of Orange County’s OC Flood section.
The remaining work includes improvements around Prado Dam.
“It wouldn’t be something we have to do tomorrow,” Bucklew said. “But within the next few years, we want to make sure we finish the project.”
In our case, the culprit behind a massive downpour is unlikely to be a hurricane. While we sometimes experience the backwash from weakened remnants of Pacific hurricanes, in the form of heavy rains, the chance of the hurricanes themselves reaching this far north are close to zero.
A churning hurricane must be powered by warm water.
“We have a very cold California current, called a hurricane vaccine,” Patzert said.
Instead, the big threat to Southern California would come in the form of an “atmospheric river,” sometimes called the Pineapple Express.
That is when a chain of storms, one behind another, flow over the region from the Pacific.
The 1938 deluge might have been one such atmospheric river; the downpour in 2010 definitely fit the bill.
“Two things allowed us to have 20 million people – headed for 30 million, by the way – in Southern California,” Patzert said. “One was water infrastructure, the other was flood control infrastructure. Without all that concrete and all those pumping stations, most of us wouldn’t be here.”
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