Residents say the shoreline has visibly receded over the years.
"Thirty years ago, I remember when they had the volleyball courts and it was beautiful," said Mark Turzynski of San Juan Capistrano.
Those courts, he noted, have since vanished.
Researchers at UC Irvine attribute the erosion to human development and rising sea levels, and officials say Capistrano Beach is among the hardest hit stretches of coastline in Southern California.
"It seems like it just keeps eroding every year, and it's just getting worse and worse," Turzynski said.
To counter the loss, trucks are unloading 13,500 cubic yards of sand hauled from a quarry in San Juan Capistrano. The goal is to rebuild portions of the beach that have washed away.
The California Coastal Commission approved the sand replenishment as an interim measure before construction of the Capistrano-Doheny Beach Nature-Based Shoreline Adaptation project, a long-term project that will consist of a 1,150-foot system of sand dunes over a cobble berm at the north end of Capistrano Beach and the south end of Doheny State Beach.
"The more sand we add to the beaches, the more the sand will stick," said Orange County Supervisor Katrina Foley.
Foley, Orange County's District Five Supervisor, said the project's $440,000 cost is justified by the long-term benefits.
"We're getting $3,000 on every dollar returned on our investment," she said. "It's kind of the same as we repair potholes. We repair infrastructure all across the county. The beaches are part of our county infrastructure. We need to start treating them like that."
OC Parks staff told Eyewitness News they previously placed 20,000 cubic yards of sand at Capistrano Beach in 2024, but by fall 2025 the sand had disappeared, leaving nearby rail lines and homes increasingly vulnerable. Foley warned that inaction would worsen the threat.
"If we do nothing, we are sure to see erosion all the way up to the rail corridor and maybe even onto the street. So it's important that we keep our beaches protected," she said.
Work in Capistrano Beach will be from 7 a.m. to 4 p.m. and is expected to last through June 16.