On the Equilibrium State of the Beach Profile Based on the Concept of Wave Phase Potential and Its Changes due to Sea Level Rise

Despite much academic progress and groundbreaking changes in thinking, research results on how sandy terrain forms its current profile shape and how it evolves in the short term based on the equilibrium profile state are minimal. In this study, based on the concept of wave phase potential, which was devised based on the equation of equilibrium beach profile in the surf zone, it is shown which type of beach profile is in equilibrium in the inflow of flat waves. In order to interpret the erosion problem caused by sea level rise on the basis of this concept, we will show how the beach profile responds to sea level rise. As a representative result, the beach retreat width due to sea level rise is given as a function of the dominant wave period and the beach scale factor (a factor obtainable from the sand grain size) as well as the sea level rise. This equation is compared to Bruun's proposal and also discusses the constraints in applying Bruun formula. The results of this study can provide a scientific basis for predicting how a seabed topography composed of sand can be formed or to reverse estimate the wave incident condition from the current landform and seabed conditions, as long as the inflow wave data and the sampled sand grain size data are available. Moreover, it shows how devastating the inundation erosion caused by sea level rise can be. It is time to judge how urgent it is to secure a coastal buffer zone behind this, and to hasten technical and policy responses to mitigate the damage caused by it. As an example of application, the sea level rise trend for the coast of the Korean Peninsula and the inundation erosion predicted for 2050, 2070 and 2100 for 350 beaches of the Korean Peninsula will be presented.