Multi-year morphological changes at two adjacent high-energy composite beaches: La Palue and Lostmarc’h in northwest France.

Composite beaches, defined by a steep gravel berm fronting a low-angle sandy foreshore, remain understudied despite their increasing relevance as models for nature-based coastal defenses called dynamic cobble berm revetments. To support development of effective designs in diverse coastal settings and improve understanding of coastal change and resilience across beach types, detailed field observations of composite beaches are required. Since September 2020, a regular monitoring program has been conducted on two adjacent high-energy composite beaches — La Palue and Lostmarc’h on the Crozon peninsula (northwest France). Using drone photogrammetry, this program investigates the morphodynamic response of gravel berms to varying wave energy and changes in sand level on the beach face. The results reveal consistent temporal patterns, including a pronounced seasonal signal: The gravel berm tends to widen over winter, when sand levels are lower, whereas gravel exposure decreases during calmer, low-energy periods. Berm and foreshore morphologies also exhibit large interannual variability driven by fluctuations in winter wave energy and storm characteristics. Integration of high-frequency satellite imagery further demonstrates that gravel exposure adjusts rapidly to shifts in wave forcing and sand levels. These findings highlight the dynamic and coupled nature of gravel-sand interactions on composite beaches and underscore the need for comparative investigations across sites with differing hydrodynamic and sedimentological settings. [ABSTRACT FROM AUTHOR]