Some OC Beaches Are Disappearing. New Data Gives Clues On How To Help

As the south Orange County coast continues to crumble into the sea, new research on sand movement could help officials figure out better strategies to save beaches from natural erosion and rising sea levels.

For the new study, a team at the University of California, Irvine pored over satellite imagery of the Southern California coast. They matched it with swell data to measure how much beaches are growing or shrinking between from Seal Beach in northern Orange County to La Jolla in San Diego County.

Satellite imagery allowed UC Irvine researchers to calculate beach loss and gain within what are known as "littoral cells," geographic compartments within which sand circulates.

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Courtesy Daniel Kahl, UC Irvine

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The findings uncovered new information about the way waves move sand along the Southern California coast, which researchers hope will help communities and policymakers decide where to carry out costly sand replenishment projects, and whether they're worth the money.

Key findings from the study

Researchers found:

• Despite periodic deliveries of sand to Oceanside beaches, they have continued to shrink. Wave patterns in the area pull the sand up the coast toward Oceanside Harbor.
• Meanwhile, despite the overall trend of rising seas as the climate warms, some sandy stretches of the coast are growing, like Huntington Beach, where the beach has been growing by about 3 feet per year.
• South Orange County beaches have shrunk in recent decades without new influxes of sand. But if new sand is brought in — which it has been recently in Dana Point and San Clemente — models show that sand is likely to stick around and widen beaches.

"If we're going to put investments into our beach, we want it to be as successful as possible and ultimately help sustain our beaches for the future," said Daniel Kahl, a UC Irvine graduate student and the lead author of the study.

UC Irvine professor Brett Sanders co-authored the study, which is set to be published in the April edition of the journal Coastal Engineering. Sanders said the use of satellite data to monitor changes in local beaches could also help with early detection of potential coastal disasters.

"Some of these problems can be managed more cost-effectively by taking early action and not waiting for railroads to shut down and for other types of major impacts to happen," he said, referring to frequent landslides that led to track closures near San Clemente over the past year.

Why sand matters

Sand is the coast's natural line of defense against the force of pounding waves. And some parts of Orange County have lost most of their sand in recent decades because of inland coastal development, rising seas and more powerful storms.

The Mariposa pedestrian bridge damaged by a landslide in San Clemente.

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Orange County Transportation Authority

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The late January landslide in San Clemente that destroyed part of the Mariposa pedestrian bridge marks the fourth time since 2022 that authorities have had to shut down coastal rail travel through the area. Last week, Caltrans issued an emergency declaration that provides up to $10 million in funding intended to get the tracks repaired quickly.

But many local authorities have come to recognize the limitations of such short-term solutions. "It really is whack-a-mole," said Congressman Mike Levin, whose coastal district stretches from Dana Point to Del Mar.

"One area of the corridor is seemingly always in need of some help," he said in an interview with LAist.

Erosion has also shut down train traffic through San Clemente State Beach.

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Jill Replogle

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LAist

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Still, SoCal's economy depends heavily on protecting the rail corridor and the beaches, Levin said. Tourism and recreation along California's coast generate more than 480,000 jobs and contribute more than $38 billion to the state's economy, according to a 2022 study from the Los Angeles Economic Development Corporation.

Plus, state and local authorities are planning on increased use of the rail line that runs through Orange and San Diego counties as an alternative to I-5 and a way to help meet the state's climate goals.

Levin, who has seen the new UC Irvine research, said he hoped the more nuanced understanding of coastal sand and wave dynamics will influence future investments in coastal protection programs. "Having this level of granular detail is really helpful for me, helpful to our team, and helpful for those who are going to determine how we invest in these projects moving forward," he said.

'We can't save every beach'

As sea level rises, many SoCal beaches will face ever greater "coastal squeeze," caught between the waves and human development.

Beach replenishment projects are generally seen as more environmentally friendly — and less likely to exacerbate erosion — than building seawalls or lining the coast with riprap. But they're expensive — at least $340 million has been spent on replenishing California beaches over the last century, according to the National Beach Nourishment Database.

The most recent project to bring sand to San Clemente — which has faced setbacks because of poor sand quality — is expected to cost $14 million over the next 50 years.

"We can't save every beach," said Sanders, the UC Irvine professor. "But with this type of data, which systematically maps beach width change and suitability over large spatial extents, it can help federal and state officials see the value of projects that make sense, and also see the projects … where something else really should be considered," he said.

Oceanside officials recently greenlit a pilot project that takes a hybrid approach to try and keep sand on the beach. It includes building two small headlands — strips of land that extend from the coast — and an artificial reef to blunt the power of incoming waves.

Kiki Patsch, who studies coastal management and erosion at Cal State University Channel Islands, said she hopes the new research from UC Irvine can combine with work by entities like the California Ocean Protection Council to ensure that plans for weathering climate change along the coast include a focus on public access to beaches, not just protecting infrastructure and private homes.

"If you make choices to protect houses in some areas [for example, with a sea wall], then you need to have a strategy in place where you're going to focus on widening the beach in other areas, because you're essentially taking away a public beach space," she said.

"These choices are going to get harder and harder. And if we're not careful and we continue to do it on an emergency basis, we're going to end up protecting infrastructure at the cost of all the beaches," Patsch said.