Engineers raise risk level for Coronas Prado Dam to high urgency; 1.4 million people live downstream – KABC-TV

Engineers raise risk level for Corona\s Prado Dam to \high urgency\; 1.4 million people live downstream - KABC-TV

Engineers up failure risk for dam protecting Disneyland, dozens of Orange County cities

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The Prado Dam, as seen in February 2017, was designed in the 1930s and built in 1941. Situated near the 71 and 91 freeways in the Corona area, the flood-control dam is designed to protect 1.4 million people downstream in Orange County. The U.S. Army Corps of Engineers has changed its risk rating for the dam to “high urgency.”(File photo by Will Lester-SCNG/Inland Valley Daily Bulletin)

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. (File photo)

Federal officials are working urgently to strengthen the spillway at Prado Dam near Corona to prevent it from failing in a major flood, which could imperil hundreds of thousands of people living downstream in Orange County.

According to the Los Angeles Times, “dozens of Orange County communities from Disneyland to Newport Beach” could be inundated if the dam fails.

After a May inspection determined the dams spillway could perform poorly in a major flood, the dams risk rating was changed from moderate urgency to high urgency.

Dena ODell, a U.S. Army Corps of Engineers spokeswoman, said Thursday that the agency is taking immediate measures to reduce the risk that the spillway will fail.

And she said the agency was preparing to launch a project in 2021 to bolster the spillway and raise it 20 feet.

ODell said the corps notified area congressional representatives, Orange County officials and flood-control agencies in Orange, Riverside and San Bernardino counties about the heightened risk.

Built in 1941, Prado is a flood-control dam on the Santa Ana River near the 71 and 91 freeways in western Riverside County. Its primary purpose is to shield 1.4 million people and $61 billion in property downstream in Orange County from flooding.

Dams are assigned risk ratings of 1 to 5, ODell said, with 1 being very high urgency, 2 being high urgency, 3 being moderate urgency, 4 being low urgency and 5 being normal.

The corps dam safety system defines high urgency as dams where failure could begin during normal operations or be initiated as the consequence of an event. The likelihood of failure from one of these occurrences, prior to remediation, is too high to assure public safety.

Lillian Doherty, chief of operations for the corps Los Angeles District, said the risk is the spillway might not safely pass water if the dam reaches capacity.

We have identified a risk, Doherty said. I dont think anyone can say definitively whether or not the spillway will or will not perform. No one has a crystal ball.

In any event, she said, the corps expects to reduce the risk by the time the next rainy season arrives.

We are definitely aware of the population that is relying on us, Doherty said. And we are really committed to finding a solution in the short and the long term.

Doherty said the dam functioned properly this winter and spring, when we saw a lot more water than we have seen in a long, long time.

Prado benefits from a huge basin to the east. ODell said the dam is capable of holding back 217,000 acre-feet of water and ongoing improvements will boost capacity to 362,000 acre-feet. One acre-foot, about 326,000 gallons, is what two typical Southern California families use in a year.

Rep. Ken Calvert, R-Corona, said via email he would work to ensure the corps has money to cover short-term-fix costs.

We also need to fully fund the planned modification of the Prado spillway sooner rather than later, Calvert said.

Rep. Gil Cisneros, D-Yorba Linda, whose north Orange County district is bisected by the Santa Ana River, said he will continue to push for adequate funding.

With this recent assessment, I stand ready to support the needs of the Army Corps of Engineers and will ensure that high priority projects like the Prado Dam are funded in order to protect our residents, Cisneros said.

Herb Nakasone, executive director of the Santa Ana River Flood Protection Agency in Orange County, said the rating change may accelerate repairs.

Related Articles Oroville Dam spillway concerns? DWR say no Four years after California’s largest dam removal project, how are the fish doing? Since 2002, ODell said, the corps has been working to raise Prado Dam, extend its reach, enlarge its reservoir and improve the outlet works and downstream channel. Early on, a dike was added along the 71 Freeway.

Doherty, the operations chief, said experts are investigating to determine whether that plan needs to be enhanced.

Public safety is our number one priority, said Col. Aaron Barta, commander of the Los Angeles District, in a statement. The primary objective of the Corps Dam Safety Program is to review our dams and ensure resources are prioritized to address the highest risks.

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