# Net widening of Southern California beaches

## TL;DR

Southern California beaches unexpectedly grew despite human impacts, showing sand movement and management can help sustain coasts.

## Contribution

New satellite techniques reveal net beach growth in a heavily modified region, challenging global erosion trends.

## Key findings

- Southern California beaches gained over 2 million m2 from 1984-2024 despite urbanization and dams.
- Sediment supply and longshore transport explain beach widening at coastal structures and convergence zones.
- Adequate sediment exists but is not effectively distributed to vulnerable beaches, highlighting transport's role.

## Abstract

Human impacts from dams reduce river sediment fluxes and are primary causes of coastal erosion worldwide. Here we provide new satellite-derived shoreline observation techniques to examine beach area trends across the diverse coastal settings of California. Contrary to global trends, these data reveal that the most heavily urbanized and dammed region of southern California experienced net beach growth of over 2 million m2 during 1984-2024. While several beaches experienced severe erosion, overall widening is explained by sufficient sediment supply and concentrated widening from longshore transport captured at coastal structures and in littoral convergence zones. These results indicate that adequate sediment sources exist in this human-modified landscape to mitigate coastal erosion, but that this sediment is not effectively distributed to vulnerable beaches. This highlights the critical role that longshore sediment transport plays in long-term beach trends and illuminates management opportunities for coastal sustainability at the regional scale.

This work highlights how changes to beaches are related to sand movement and human impacts to the coast and illuminates opportunities for sand management to resolve shoreline erosion and enhance beach sustainability.