USGS-led Study: Shoreline Seasonality of California’s Beaches

One common pattern of beach morphology is the seasonal cycle of the shoreline. Shorelines often show cycles of erosion and recovery year after year, which results in recurring widening and narrowing of the beach.

Scientists know that these cycles are related to ocean waves, and that larger waves cause movement of beach sand offshore whereas smaller waves move this sand back to the beach.

Knowledge of these seasonal cycles comes from a long history of scientific measurement of beaches, and a general consensus is that beaches erode during winter conditions and recover during the summer. These descriptions of winter and summer beach conditions are so well accepted that they can be found in most earth and ocean science textbooks.

However, new research by USGS and partners using large datasets of beaches from satellite imagery shows that this winter/summer framework doesn’t fit all beaches—including the majority of southern California’s beaches.

This research shows that there is a great diversity in the seasonal timing of beach erosion and recovery cycles, and that many beaches show regular erosion cycles in the spring or the summer, rather than the winter. This indicates that the ‘winter-narrow/summer-recovery’ conventions for beaches are not expressed universally and that shoreline seasonality is far more diverse than these simple canonical rules.

The research suggests that the wave conditions and physical setting of beaches are adequately diverse to cause these differences in the seasonal cycles of shoreline.