Southern California’s beaches have grown more than 500 acres over the past four decades despite being one of the most heavily urbanized and dammed coastal regions in the world, according to a new study conducted by researchers at the University of California, Irvine, the U.S. Geological Survey and other institutions.
The conventional wisdom-challenging revelation about coastal erosion and replenishment is the subject of a study published recently in Nature Communications.
The research analyzed shoreline changes across California from 1984 to 2024 using newly developed satellite-derived measurement methods. It found that Southern California beaches expanded by approximately 10 percent during this period, even as dams and urban development were expected to starve coastlines of sediment and accelerate erosion.
“This is a counterintuitive finding considering previous reports of widespread beach erosion in Southern California,” said co-author Brett Sanders, UC Irvine professor of civil and environmental engineering. “While several individual beaches did experience severe erosion, there were also several that experienced dramatic widening, and the overall trend shows widening at an average rate of 7.2 meters across 320 kilometers of Southern California coastline.”
The researchers found that 49 percent of the shoreline showed significant widening, and 31 percent experienced narrowing. The Zuma littoral cell near Malibu and northern portions of the Oceanside littoral cell, which include the revered surfing and recreational beaches of Doheny, San Clemente and San Onofre, experienced some of the region’s most severe erosion, with beaches narrowing at rates exceeding 1 meter per year, causing damage to public and private property.
Beach growth has been concentrated at human-made coastal structures such as harbors, jetties and natural convergence zones that trap longshore sediment transport. Rapidly growing beaches include popular locations like Huntington Beach and Santa Monica, and less frequented stretches of coast, such as the beach between Ventura and Oxnard.
The study examined three California regions – northern, central and southern – with dramatically different results. Southern California showed a highly significant positive trend in beach area, while Northern California exhibited moderate growth, and Central California showed no significant trend.
“The primary challenge facing Southern California beaches is not sediment shortage, but sediment distribution,” said lead author Jonathan Warrick, research geologist at the U.S. Geological Survey’s Pacific Coastal and Marine Science Center in Santa Cruz, Calif. “Some of the most rapidly widening beaches – including McGrath State Beach, Huntington Beach, and Venice Beach – now measure approximately 200 meters, or over 600 feet, wide. These locations benefit from sediment trapped by coastal structures or accumulating in natural sand convergence zones.”
The findings were made possible by newly developed satellite-derived shoreline data and signal-processing techniques that provide unprecedented accuracy and temporal resolution compared to previous methods that relied on only 2-3 historical snapshots with large uncertainties.
“These new tools are revolutionizing how we assess beaches and their changes,” Sanders said. “Beaches were previously monitored by field crews using surveying equipment, or with aerial flights that scan the coast with laser surveys, but the costs of these approaches limited the frequency and spatial extent of available data. Satellite imagery now allows us to measure beach width everywhere, several times per month.”
The research highlights significant opportunities for improved coastal management and sustainability. Rather than sediment shortage being the fundamental problem, the study suggests that strategic redistribution of existing sediment could address localized erosion.
Several Southern California harbors – including Santa Barbara, Ventura and Channel Islands/Port Hueneme – already operate sediment bypass systems to move sand past barriers such as jetties and breakwater structures. The study suggests that expanding such efforts could provide “more equitable, widespread and natural use of littoral sediment resources.”
The San Pedro littoral cell, which includes the shoreline of the Sunset Beach, Huntington Beach and Newport Beach communities, provides a dramatic example, where beach engineering projects have resulted in massive beach expansion, according to the researchers. Centered near Huntington Beach, there was an average widening of 25 meters (over 80 feet) across the cell during the 40-year study period.
The findings challenge assumptions about the impacts of dams and land use on coastal change. While California’s large dams have indeed reduced sand flux to the coast to approximately half of historical levels, other sources, including bluff erosion, and especially beach artificial additions of sand through mechanical means, have sustained or expanded beaches in many locations.
Despite identifying clear management opportunities, the study acknowledges significant barriers to improved sediment redistribution, including financial costs, regulatory processes, institutional inertia, political boundaries and resistance to change.
The research emphasizes that continued use of satellite-derived shoreline data with advanced signal processing techniques will be essential for understanding and managing coastal systems, particularly as climate change and sea level rise add new pressures to coastal environments.
“These data give us a much-needed systems perspective of beach dynamics, making it easier to find the entry points required for effective management,” Sanders said.
Joining Warrick and Sanders on this project were Kilian Vos of OHB Digital Services in Bremen, Germany; Daniel Buscombe of the Washington Department of Ecology; Andrew Ritchie and Sean Vidousek of USGS; and Teresa Hachey of the UC Irvine Department of Civil and Environmental Engineering. Funding was provided by USGS and NASA.
