Los Angeles County seeks to improve flood control in the face of climate change

Los Angeles County seeks to improve flood control in the face of climate change

Catastrophic flooding prompted city leaders and engineers a century ago to begin taming the Los Angeles Basin’s stormy rivers with dams, storm drains and concrete.

Now scientists are warning that, in a warming world, the region can expect an increase in epic downpours that could quickly overwhelm its aging flood control system, releasing floodwaters into low-lying working-class communities. .

On Tuesday, the Los Angeles County Board of Supervisors approved a motion calling on the Department of Public Works to prepare a report on the viability of existing flood control infrastructure, as well as plans to reduce flood risk and make disadvantaged communities more resilient.

The motion authored by supervisor Janice Hahn was spurred by a recent study by researchers at UC Irvine. The report aims to provide county officials with the data needed to determine how hard and where the floods will hit hardest, and to deploy tools and apps that would help speed recovery.

“The latest available science warns that the potential for catastrophic flooding is real,” Hahn said, “and would be most devastating to communities of color in low-rise neighborhoods.”

“Now the county needs to take a hard look at our infrastructure and see what we can do to protect these communities if and when the storm we’re all worried about arrives,” she added. “I’m sure some of the challenges this report will expose will be daunting, but we’re not going to abandon these communities.”

The study, which was published in the journal Nature Sustainability, is among the first to examine how extreme weather conditions due to climate change can affect the region, whose development has been guided by social and racial divisions that have favored white residents.

The unprecedented combination of the study’s high-resolution flood modeling and socio-economic data indicates that major flooding would occur between the Dominguez Canal to the west and the Los Angeles River to the east.

Communities most at risk include Carson, Paramount, Compton, Bell Gardens, South Gate, North Long Beach and parts of downtown Long Beach, including the south end of Pine Street near the Long Beach Convention Center.

Analysis of data from 1,767,588 parcels of land across approximately 2,700 square miles indicates that approximately 874,000 people and up to $108 billion in properties stretching from the Santa Monica Mountains south to Long Beach are at risk of flooding.

That’s about 30 times more people at risk than the Federal Emergency Management Agency suggests, according to Brett Sanders, professor of civil and environmental engineering at UC Irvine.

Until recently, it was thought that a flood of this magnitude was likely to occur every 1,000 to 10,000 years. However, new research suggests that the odds of seeing another of this scale in the next 40 years are around 50/50.

“Severe weather and increased flood risk are inevitable impacts of climate change,” said Mark Pestrella, director and chief engineer of the Los Angeles County Flood Control District. “Council’s action today aligns with the county’s sustainable plan to make infrastructure improvements that reduce flood risk, increase local water supplies through stormwater capture and groundwater recharge, and improve water quality throughout the county.”

Today, one of the top priorities for the US Army Corps of Engineers in Southern California is to spend an estimated $600 million to upgrade the 63-year-old Whittier Narrows Dam, built in a natural ditch in the hills about 11 miles east of downtown Los Angeles. .

The earth dam was placed in the agency’s highest risk category when it determined that three potential failure modes threatened more than one million people downstream from Pico Rivera in Long Beach.

They include premature opening of the San Gabriel River spillway gates, erosion resulting from channeling water through the dam foundation, and overtopping during extreme flooding.

“Our infrastructure was built at a time when the county only cared about two things: economic development and security from destructive storms,” Sanders said. “Now we have the opportunity to rebuild it with a new set of goals.”

“Today we care about drought, heat waves and water conservation,” he said. “We want rivers with trees and ecological connections to the land around them.

“We also want to make sure that all communities are equally served by infrastructure,” he said.

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