Numerical Perspective on Tsunami Hazards and Their Mitigation by Coastal Vegetation

Abstract

Tsunamis are among the most threatening natural hazards that can affect coastal communities and infrastructures. In order to provide useful information for coastal protection, one of my aims in this dissertation is to identify the physical metrics that better represent the damage cause by tsunamis. I approach this problem by carrying out three-dimensional-SPH numerical simulations of solitary waves which allow to track spatial-temporal evolution of physical variables during their breaking. By comparing these evolutions it is possible to visualize the complex hydrodynamic process that occurs during breaking. Results show that the highest danger lies in the environment of the shoreline. However the highest vulnerability of coastal communities and infrastructures lies onshore where they find themselves more exposed to the destructive capacity of extreme tsunami waves. In this regard, the second main goal in this dissertation is to understand how coastal vegetation reduces and modifies the onshore wave inundation. I address this problem by using shallow water equations and Serre-Green-Naghdi equations employed in a set of two-dimensional depth-integrated simulations. Analysis of results indicate the existence of a transition zone located between where runup is not affected at all and where runup suffers the maximum reduction by the vegetation. This infers the requirement of a minimum length of the vegetated barrier in order to achieve the maximum runup reduction under a specific set properties such as barrier location, barrier width, beach slope and/or wave amplitude. Overall we conclude, after intense validation work, that numerical approaches are very convenient tools to analyze difficult wave processes. However it is necessary to be aware of the limitation of each numerical approach.