Assessment of empirical relationship among cross-shore beach profile morphotypes, sediment characteristics, and wave signature in beaches in estuaries and bays (BEBs)

Beaches in estuaries and bays (BEBs) are usually distinct from open coast beaches in terms of environment, process, and morphology, and their morphodynamics remain unresolved. The present study aims to establish a relationship between profile morphology, sediment characteristics, and hydrodynamic forces. We investigated four beaches of Gamay (Botany Bay) located in the south of Sydney, SE Australia. Profiles of these beaches were measured regularly from 2016 to 2022 and sediment samples were collected from each beach. Wave data were recorded from the Sydney Waverider buoy. We used principal component analysis (PCA) to ascertain the temporal and spatial scales of the data variability, and spectral analyses to investigate the waves. Sediment samples were analyzed by Laser Diffraction Particle Size Analyzer (Mastersizer 3000).

Our preliminary results indicate that different profile morphotypes are associated with different sediment characteristics and wave climates on BEBs.  BEBs with the least exposure to ocean swell waves have the narrowest and steepest profiles, with BEBs more exposed to ocean swells having moderately steep profiles. BEBs containing coarser sediments show steep profiles compared to beaches with fine to very fine-grained sediments. In general, the shape of profiles changes in order from straight-through concave to convex-concave with increasing wave energy. Current research aims to parameterize these relationships with offshore and locally generated wave parameters. The insights obtained from this study will assist to understand fundamental mechanisms governing the morphological evolution of BEBs.