Hydrodynamics and Morphology on Composite Beaches
Chris Blenkinsopp (University of Bath)
Alex Minnigin (University of Bath)
Ollie Foss (University of Aberdeen)
Paul Bayle (TU Delft - Environmental Fluid Mechanics)
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Abstract
Composite beaches, characterised by a dissipative sand beach backed by a steep cobble berm, exhibit unique hydro and morphodynamic behaviors due to their bimodal sediment size distribution. This study analyzes morphological variability and wave runup on a composite beach in Borth, Wales, using continuous Lidar data collected from July 2021 to October 2024. Results indicate that the lower berm face is dynamic due to regular swash inundation, while the primary berm crest remains stable with minimal changes. Secondary berms located seaward of the primary berm can be formed and removed within a single tide. This is in contrast to sand beaches where they tend to translate landward, controlled by the neap-spring tidal cycle. Existing wave runup equations provide reasonable estimates of total water level, but perform worse than previously observed at other composite beach locations due to a higher dependence of wave runup on offshore wave height.
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