Cross-scale modelling of coastal-ocean dynamics: integrating benthic boundary layer interaction, wave-current coupling, and sediment-driven morphodynamics

Accurate prediction of coastal–ocean hydrodynamics and associated hazards is constrained by the intrinsic complexity of multiscale, strongly coupled physical processes governing these nonlinear systems. This work formulates, develops, and validates an integrated numerical framework to resolve emergent dynamics arising from such interactions. Conventional single-process models often neglect critical cross-scale feedbacks among waves, currents, sediments, and benthic layer, leading to oversimplified hydrodynamic and morphodynamic responses. To address these limitations, a modular multi-model framework was developed through progressive coupling of complementary numerical cores within a shared unstructured-grid architecture, enabling seamless cross-scale modelling from open-ocean circulation to nearshore morphodynamics and benthic interactions. This configuration enables consistent transfer of momentum, mass, and energy across dynamic interfaces, capturing feedbacks that govern coastal-ocean evolution and enhancing predictive skill. The framework was integrated through successive coupling stages. First, a dynamically consistent two-way wave–circulation coupling was established, exchanging sea-state-dependent momentum fluxes, radiation stresses, Doppler shift, dynamic water depth, and effective wind speed. This was validated in idealized domains and applied to an extreme Mediterranean tropical-like cyclone, quantifying wave-induced surge contributions and impacts on upper-ocean thermal structure. The framework was then extended to include biomechanical effects of the benthic boundary layer through an improved bottom-dissipation parameterization. Applications in the Balearic Islands and along the Civitavecchia coastline quantified wave attenuation and spectral changes induced by aquatic meadows. Finally, a sediment transport and morphodynamics module was implemented, introducing Exner-based bed evolution feedback in the circulation model. Benchmarking against state-of-the-art models demonstrated robust performance, while application to the Tiber River delta reproduced observed sediment dispersal patterns consistent with satellite and in-situ data. This integrated system provides a transferable framework for compound coastal hazard assessment and advances the representation of complex coastal–ocean dynamics. Future work and existing limitations are outlined to inform subsequent model refinement and applications.