HyWaThy: hybrid modeling of nearshore waves with different baThymetric states

Abstract

Coastal areas such as sandy beaches are highly pressured environments by humans worldwide, as they provide a wide range of ecosystem services that directly benefit societies. The growing concentration of human settlements along these coasts arise the need for improved coastal management strategies, where a robust knowledge of nearshore processes is fundamental. Given the inherently dynamic nature of sandy beaches, advancing our knowledge of nearshore hydrodynamics requires accurate modeling of the complex interaction between bathymetry and waves: bathymetric features affect wave propagation towards the coast, while waves, in turn, reshape the seabed through longshore and cross-shore sediment transport. This study presents a methodological advancement beyond the dynamic downscaling of wave conditions over a static bathymetry by introducing a coupled hybrid metamodel that simulates nearshore waves while accounting for the different bathymetric states of the beach. For doing so, statistical methods and numerical models are combined in La Salvé beach (Spain) to capture the bathymetric configurations using Principal Component Analysis applied to field-surveyed data, as well as to propagate waves from a single offshore point to a two-dimensional nearshore domain. The phase-resolving, non-hydrostatic XBeach model is employed to simulate key physical processes in the surf zone, including refraction, shoaling, diffraction, reflection and breaking. Once trained, the coupled hybrid metamodel can reconstruct nearshore hydrodynamics ?represented by spatial fields of significant wave height and mean wave direction? in a matter of seconds. The model performance is numerically validated, showing satisfactory accuracy for the study site.