Engineers raise risk level for Corona's Prado Dam to 'high urgency'; 1.4 million people live downstream

CORONA, Calif. (KABC) -- The U.S. Army Corps of Engineers says a recent assessment has raised concern about the potential for failure of the spillway of a flood control dam on the Santa Ana River where 1.4 million people live downstream.

The Corps said Thursday it has changed the risk characterization of Corona's Prado Dam from moderate urgency to high urgency.

The 96-mile Santa Ana River typically has little water flow except during winter storms and the dam is typically dry.

The Riverside County dam was built in 1941. Engineers say an assessment this month indicates potential for poor performance of the spillway during a "significant flood event."

Officials say nearly 1.5 million people living downstream in Riverside and Orange counties could be impacted if a major storm resulted in catastrophic flooding.

Over the last several years the Prado Dam has been extended and raised to increase its capacity to store floodwaters.

The final portion of the improvement project involves construction of the spillway.

"We continue to evaluate the risk associated with the dam. It does not mean that we believe the infrastructure is crumbling or it's going to fail tomorrow," Lillian Doherty of the U.S. Army Corps of Engineers said. "What we have identified is there are risks and uncertainties that we need to address immediately because of the communities downstream, and that's exactly what we're doing."

Work on the spillway will begin in 2021.

The Associated Press contributed to this report.