An "extreme" flooding event at the Mojave River Dam could put hundreds of thousands of Southern California residents nearby at risk, according to officials.
The U.S. Army Corps of Engineers announced Friday that it has changed the risk characterization of the dam, located in San Bernardino County, from low to high urgency of action after assessing that water during an extreme flood event could exceed the design capacity of the dam and overtop it.
The dam failure that could possibly result would flood the communities adjacent to the Mojave River, such as Hesperia, Apple Valley, Victorville and Barstow, according to the news release.
The dam, located on the northern side of the San Bernardino Mountains downstream of the confluence of the West Fork Mojave River and Deep Creek, was built in 1971 and designed and constructed with the "standards of the day," according to the Army. It reduces risk for more than 16,000 people and $1.5 billion in property and "continues to operate as designed."
It has never experienced a spillway flow or flood event that could load it "significantly," and a weather event powerful enough to do so is "unlikely."
However, officials want to be prepared in the event that it does, according to the Army.
"This is a storm that is unlikely to occur, but it is nonetheless a real possibility and one we must be prepared for," Col. Aaron Barta, commander of the Corps’ Los Angeles District, said in a statement.
The U.S. Army Corps of Engineers Los Angeles District owns and operates 17 dams across California, Arizona and Nevada, which collectively reduce flooding for about 7 million people and $200 billion in property, according to the release. The agency is currently evaluating interim risk-reduction measures associated with potential overtopping at the Mojave River Dam.
The agency recommends that residents prepare an emergency kit, register their mobile phones with San Bernardino County's telephone emergency notification system for alerts and create an evacuation plan in case of a flood event.
In 2017, nearly 200,000 people in Southern California were evacuated after the spillways at the Oroville Dam in Butte County were damaged.