Modeling wave-surge effects on barrier-island breaching in St. Joseph Peninsula during Hurricane Michael

Better understanding the effects of hurricane waves and storm surges on barrier-island breaching is important for both scientific research and coastal hazard mitigations. In this study, the 2D non-hydrostatic Xbeach model has been applied to investigate interactions of hurricane wave, storm surge, and morphological processes in the case study of St. Joseph Peninsula during Category 5 Hurricane Michael. Model validations show a 2.45% average error and the 0.88 skill score between modeled and observed high water marks and bed elevations, respectively. Analysis of spatial distributions of currents and water levels indicates that a narrow area was overtopped at peak storm surge and wave. The gap was then quickly enlarged as the breaching area by wave-surge actions. By investigating foredune and peak dune along the central axis of breaching area, it shows that the foredune erosion on the ocean-side by wave-surge-current directly lead to the breach of the peak dune area in the barrier island. The Froude number shows a strong correlation with quick erosion of the barrier, indicating wave-surge supercritical flow is one of the major factors causing the barrier breaching. Results of cross sections of bed elevations and instantaneous surge-wave profiles at different storm surge stages reveal the evolution of the barrier-island breach. Results from this study provide valuable references for coastal hazard mitigation and resilience communities. Application of non-hydrostatic Xbeach model reveals barrier-island breaching process and wave-surge-barrier interactions.Model validations show a 2.45% average error and the 0.88 skill score for high water marks and bed elevations, respectively.The breach started with a narrow gap overtopped in the peak of storm surge and was then quickly enlarged by wave-surge actions.Wave-surge induced supercritical flow is one of the major factors accelerating the barrier breaching.Foredune erosion by wave-surge-current is another factor that accelerates the breach of the barrier island.