Cusps and mega cusps on a mixed sediment beach

Improved understanding of beach morphology is needed for coastal planning and hazard mitigation. Using a ground-based mobile LiDAR system, this study describes about one year of weekly observations of cusps, semi-circular alongshore rhythmic patterns, along a ~2 km mixed sediment beach consisting of sands and gravels/cobbles. Cusp shape (e.g. horizontal and vertical undulations), alongshore rhythmic spacing, and surface sediment types varied in space and time. The observation revealed previously unreported, composite mega cusps with rhythmic 200-400 m spacing and surface sediment zonations (sand versus gravel/cobble). The results highlight the potential of new survey technology (e.g. repeated ground-based mobile LiDAR) to explore the highly dynamic and complex behavior of mixed sediment beach morphology. This research was supported by the U.S. Army Corps of Engineers, and California Department of Parks and Recreation.