Contribution of Infragravity Waves to Storm Water Level Along a Large Inlet: Implications for Flooding and Overtopping Hazards

Abstract

Tidal inlets are transitional area between the ocean and an estuary or a lagoon. They are characterised by very complex hydro-morphodynamics processes, resulting from the interaction between tidal currents and waves with large and rapid water level changes. The coastline around the inner part of the inlet and more generally the entire lagoon often host important economic and touristic activities. In these environments, the studies of hazards associated with energetic events are mainly based on modelling approaches. However, the phase-averaged numerical models typically used for large-scale coastal applications exclude infragravity waves (long waves ranging from several tens of seconds to several minutes, noted hereinafter IG) and phase-resolving model are too computationally expensive for such large domains. Therefore, the propagation of waves from the open sea to the lagoon and in particular the characterisation of IG waves are still poorly understood (Bertin et al., 2018). To study the amplitude and spatial variability of IG waves in the Arcachon lagoon during storms, the Xbeach model (Roelvink et al., 2009) was implemented in surfbeat mode (SB mode).