Lidar-informed spectral wave transformation in the surf zone – IMPASTO

As ocean waves break in the nearshore, they generate intense currents, contribute to storm surges by elevating mean water levels (the wave « setup ») and eventually run up beaches, playing a key role in erosion and inundation hazards. Although it is critical for coastal hazard predictions, the spectral transformation of surf zone waves is still poorly understood, and no theoretical framework currently exists for predicting energy dissipation by breaking and how this dissipation spreads across frequencies. This partly explains why the runup contribution to extreme water levels at the coast is currently neglected in large-scale models for coastal hazards prediction. The IMPASTO project aims to address this research gap by improving our understanding of the wave-breaking physical processes and unravelling the spectral connections between inner surf zone waves and runup dynamics. Starting from a comprehensive lab and field database of surf and swash zone hydrodynamics obtained with infrared lidar scanners, we will study the applicability the new theoretical framework for inner surf zone waves spectra developed by Bonneton [Journal of Fluid Mechanics, 977, A48 (2023)]. We will exploit lidars' unique capacity to directly measure the free surface elevation for characterizing the diffusive regime at high frequencies, which is associated with breaking processes. We will then perform a thorough assessment of phase-resolving models for accurately reproducing surf zone wave energy dissipation and their spectral transformation of surf zone waves. Aided by the most high-fidelity model obtained, we will analyse the spectral response of runup under varying surf zone forcing and beach morphologies and (re-)explore the existence of universal laws for the spectral characteristics of runup. Combined with a deeper understanding of the spectral wave transformation of surf zone waves, this will open new avenues for seamless and robust parametrisations of wave runup that are adapted to spectral wave models used for coastal hazard prediction.