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Engineers up failure risk for dam protecting Disneyland, dozens of Orange County cities
Federal engineers are raising alarms that a “significant flood event” could compromise the spillway of Southern California’s aging Prado Dam and potentially inundate dozens of Orange County communities from Disneyland to Newport Beach.
After conducting an assessment of the 78-year-old structure earlier this month, the U.S. Army Corps of Engineers announced that it was raising the dam’s risk category from “moderate” to “high urgency.”
“Our concern right now is about the concrete slab of the spillway and how well it will perform if water were to spill over the top of the dam,” said Lillian Doherty, the Army Corps’ division chief. “We will determine whether or not it is as reliable as it should be.”
Located beside the 91 Freeway on the border of Riverside and Orange counties, the dam impounds little to no water for much of the year. During periods of heavy rain, however, the structure is intended to collect water and prevent flooding along the Santa Ana River.
An $880-million effort to increase storage capacity for floodwaters and sediment at Prado Dam has been underway since 2002. It includes raising the spillway crest by 20 feet to an elevation of 563 feet, replacing outlet systems, increasing the reservoir area, building new dikes and improving the wetlands behind the dam and the downstream channel for flood control purposes, as well as for habitat and possible recreational opportunities.
Despite a development boom in neighboring Chino, Corona, Norco and Eastvale, the 2,150 acres of wetlands behind the dam comprise a labyrinth of channels, ponds and forests that are havens for threatened and federally endangered species including red-sided garter snakes and least Bell’s vireos.
In the meantime, the Prado and Whittier Narrows dams continue to be fully functional and operable during storm events, said Dena O’Dell, a spokeswoman for the agency.
“Corps staff is routinely on site at Prado Dam to operate and monitor the dam during rain events,” she said. “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.”
But some researchers doubt the overall safety of aging federal flood control systems that were not designed with climate change in mind.
They argue that in a warming world, regions such as California will experience more whiplashing shifts between extremely dry and wet periods. These cycles, they say, will seriously challenge California’s ability to control flooding, as well as store and transport water.
“A troubling theme is emerging as the Corps reviews its portfolio of large flood control systems that were built a long time ago and are now showing signs of severe stress,” said Daniel Swain, a UCLA climate scientist. “Federal engineers are finding that these systems are not as resilient as they thought they were, and that the frequency of what were regarded as once-in-a-lifetime storms is increasing significantly.”
https://www.latimes.com/local/lanow/la-me-ln-prado-dam-flood-risk-failure-20190516-story.html
Federal engineers are raising alarms that a “significant flood event” could compromise the spillway of Southern California’s aging Prado Dam and potentially inundate dozens of Orange County communities from Disneyland to Newport Beach.
After conducting an assessment of the 78-year-old structure earlier this month, the U.S. Army Corps of Engineers announced that it was raising the dam’s risk category from “moderate” to “high urgency.”
“Our concern right now is about the concrete slab of the spillway and how well it will perform if water were to spill over the top of the dam,” said Lillian Doherty, the Army Corps’ division chief. “We will determine whether or not it is as reliable as it should be.”
Located beside the 91 Freeway on the border of Riverside and Orange counties, the dam impounds little to no water for much of the year. During periods of heavy rain, however, the structure is intended to collect water and prevent flooding along the Santa Ana River.
An $880-million effort to increase storage capacity for floodwaters and sediment at Prado Dam has been underway since 2002. It includes raising the spillway crest by 20 feet to an elevation of 563 feet, replacing outlet systems, increasing the reservoir area, building new dikes and improving the wetlands behind the dam and the downstream channel for flood control purposes, as well as for habitat and possible recreational opportunities.
Despite a development boom in neighboring Chino, Corona, Norco and Eastvale, the 2,150 acres of wetlands behind the dam comprise a labyrinth of channels, ponds and forests that are havens for threatened and federally endangered species including red-sided garter snakes and least Bell’s vireos.
In the meantime, the Prado and Whittier Narrows dams continue to be fully functional and operable during storm events, said Dena O’Dell, a spokeswoman for the agency.
“Corps staff is routinely on site at Prado Dam to operate and monitor the dam during rain events,” she said. “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.”
But some researchers doubt the overall safety of aging federal flood control systems that were not designed with climate change in mind.
They argue that in a warming world, regions such as California will experience more whiplashing shifts between extremely dry and wet periods. These cycles, they say, will seriously challenge California’s ability to control flooding, as well as store and transport water.
“A troubling theme is emerging as the Corps reviews its portfolio of large flood control systems that were built a long time ago and are now showing signs of severe stress,” said Daniel Swain, a UCLA climate scientist. “Federal engineers are finding that these systems are not as resilient as they thought they were, and that the frequency of what were regarded as once-in-a-lifetime storms is increasing significantly.”
https://www.latimes.com/local/lanow/la-me-ln-prado-dam-flood-risk-failure-20190516-story.html
