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Dam failure could flood Disneyland and dozens of cities, says U.S. Army Corps of Engineers

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Christian Fernsby |
Prado Dam
America   Prado Dam

The U.S. Army Corps of Engineers has changed Prado Dam’s risk characterization from moderate urgency to high urgency, based on a recent assessment.


In May 2019, a site specific evaluation was conducted to assess conditions associated with the dam as part of a periodic review of its performance.

Risk factors identified indicate the potential for poor spillway performance, which could have adverse impacts to the downstream population, if a significant flood event occurs.

The dam, which is typically dry, has historically operated without incident.

It has not experienced a large enough storm to cause water to flow over the spillway.

“Public safety is our number one priority,” said Col. Aaron Barta, commander of the U.S. Army Corps of Engineers Los Angeles District.

“The primary objective of the Corps’ Dam Safety Program is to review our dams and ensure resources are prioritized to address the highest risks.”

The Corps is working with a national team of experts to reduce the risks associated with the spillway.

The agency is implementing interim risk-reduction measures.

Modification of the existing spillway is expected to begin in 2021.

The agency also is actively coordinating with its partners and conducting public outreach as interim risk-management strategies.

“We value transparency and our relationships with our local, state and federal partners,” Barta said.

“We will continue to work together to keep the public informed about Prado Dam.”

Prado Dam is a flood-risk management project and a major feature of the ongoing Santa Ana River Mainstem project.

It was designed in the 1930s, constructed in 1941 and is located on the Santa Ana River in the city of Corona in Riverside County.

It is operated and maintained by the Corps’ Los Angeles District and is in the process of being modified as part of the larger Santa Ana River Mainstem project.

More than 1.4 million people live and work in 29 cities downstream of Prado Dam, with more than $61 billion in property.

Modification of the dam began in 2002 to provide additional capacity for storage of floodwaters and sediment by enlarging the existing Prado Dam and reservoir.

This includes raising the main dam embankment, replacing the outlet works, constructing other embankments, also known as dikes, and improving the downstream channel.

Modification of the spillway is the last feature of the project to be constructed.

Although the dam is undergoing improvements, it continues to be fully functional and operable during storm events.

Corps’ staff are routinely on site at Prado Dam to operate and monitor the dam during rain events.

The Corps’ assessment of the dam doesn’t mean that failure is taking place; it means the agency has identified performance concerns that require attention to meet the Corps’ rigorous Dam Safety standards.


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