Modeling hurricane wave propagation and attenuation after overtopping sand dunes during storm surge

Sand dunes are natural features providing protection to coastal communities against waves from extreme events such as hurricanes. In this study, the non-hydrostatic XBeach model (XBNH) was validated and applied to investigate wave propagation, breaking, and overtopping sand dunes in the coastal zone during various stages of the storm surge in Mexico Beach, Florida during Hurricane Michael (a Category 5 hurricane). Results indicate that, as storm surge rises and stronger waves propagate towards inland, waves break near the foot of the sand dunes, overtop the dunes, and then substantially attenuate toward the communities established behind the dunes. Sand dunes effectively reduce wave heights with a minimum reduction rate of 35% at peak storm surge and 91% reduction at upper rising surge stage. Maximum wave height and dune erosion rate occur around the peak storm surge stage. Model validations show that the non-hydrostatic model is more accurate than the hydrostatic model (XBSB). For significant wave height, the average error is 2.44% from XBNH in comparison with the 16.92% error from XBSB. The maximum error for the peak water surface elevation is 3.48% for XBNH verse the 5.39% for XBSB.