A COMBINED COLOR AND WAVE-BASED APPROACH TO SATELLITE DERIVED BATHYMETRY USING DEEP LEARNING

We studied how sandy beaches evolve by tracking the shoreline and offshore sandbars from satellites over many years. By rebuilding beach behavior directly from observations, we show that beaches follow organized but chaotic motion shaped by internal feedbacks. Beyond the seasonal rhythm imposed by waves, shorelines and sandbars exchange energy through the surf zone, producing repeated erosion and recovery cycles with limited predictability, explaining why beaches remain difficult to forecast.

Shorelines often change in rhythmic ways that cannot be explained by storms or climate cycles alone. Using global satellite observations, we show that a repeating two-year shoreline pattern emerges from interactions between seasonal wave activity and delayed shoreline adjustment. This hidden interaction transfers energy across timescales, creating previously overlooked variability, which matters for understanding and anticipating future coastal change.

The erosion of sandy beaches affects human activities and ecosystems. Research has mainly focused on sea level and wave changes, and while localized sediment research is abundant, the global effect of reduced fluvial sediment supply remains unexplored. This study presents a global sediment model that demonstrates the significant impact of river dams on beach erosion worldwide. Sediment can travel long distances via wave-induced transport, often away from river outlets.