2019-11-04 19:58:39

Californians have recently endured the dual hardships of wildfires and mass power outages meant to prevent them, not always effectively.

Now comes word that desert communities in the Golden State could be at risk of flooding.

What’s next, locusts and pestilence?

Well, it’s not quite that dire, but a recent decision by the U.S. Army Corps of Engineers serves as a reminder that everyone is at the mercy of Mother Nature, and preventive measures can go a long way toward sparing life and property.

Here are five questions addressing a new risk that most Californians didn’t even know existed:

What did the U.S. Army Corps do?

It switched the Dam Safety Action Classification of the Mojave River Dam from low to high urgency of action, meaning steps must be taken to safeguard communities close to the river – such as Hesperia, Apple Valley, Victorville and Barstow – from flood hazards.

A recent risk assessment determined that, in an extreme weather event, water could flow over the nearly 50-year-old dam and it could breach, endangering 16,000 residents downstream and property valued at $1.5 billion. Flood waters could reach as far as Baker, more than 140 miles away.

What measures must be taken?

The most immediate is raising awareness about the importance of preparation among residents, who are encouraged to assemble an emergency kit, sign up for phone alerts and formulate evacuation plans.

“We’re going to be enacting a lot of emergency-preparedness activities,’’ said Kristen Bedolla, dam safety program manager for the Corps’ Los Angeles District. “As we turn the corner toward winter, we’re definitely going to be more proactive in working with our downstream partners.’’

Bonanza Spring emerges from the Clipper Mountains in the southeastern Mojave, the driest desert in North America with an average precipitation of less than 5 inches per year.
Bonanza Spring emerges from the Clipper Mountains in the southeastern Mojave, the driest desert in North America with an average precipitation of less than 5 inches per year.

The agency will also conduct further studies to assess whether the dam – which goes through regular maintenance and upgrades – needs further hardening. Some interim measures are also being considered before the rainy season arrives in the coming weeks.

How big is the risk for Californians?

It’s minimal, but it does exist. The dam is about 200 feet high and its highest watermark ever, 72 feet in 2005, did not reach the halfway point. The emergency spillway has never been used.

Lillian Doherty, chief of the operations division for the L.A. District, said the chances of water flowing over the dam are about .01% percent on any given year.

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Why bother, then? Perhaps the names Katrina and Harvey will answer that question. Those hurricanes brought on unthinkable damage, and the Corps wants to take any steps necessary to avoid a future disaster. In February 2017, both spillways for the Oroville Dam in Northern California were damaged by floodwaters, resulting in a crisis that forced nearly 190,000 to flee their homes.

Is climate change a factor?

Of course. Although the Mojave River Dam, built in 1971, has been performing as designed, old weather models no longer accurately predict what conditions to expect. Evidence of climate change has been a motivator in the decision to further assess the dam’s ability to withstand extreme floods.

“That is our mission, to reduce the risk for the communities we serve,’’ Doherty said. “With climate change, we are seeing more severe events on a more regular basis, so being prepared, ensuring that our communities are aware of these risks and preparing themselves is critical.’’

Floods in the Mojave Desert, really?

The Mojave – primarily located in southeastern California and southern Nevada – is regarded as the driest desert in North America, with an average yearly precipitation of less than 5 inches.

The western part is not quite as parched, averaging 6.7 inches, mostly stemming from winter storms rolling east from the Pacific. When that happens, the water can accumulate quickly in areas not used to it.

“We have a very reactive system,’’ Doherty said. “Just a little bit of rain can cause huge flash floods in any area, including the desert. We’ve seen events like that happen, and it’s one of the reasons we’re most concerned. Because we are dry year-round, there’s a lack of sensitivity to the fact that flooding is a true risk that we need to prepare for.’’

This article originally appeared on USA TODAY: In California, wildfires and power outages might not be only threat



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