Numerical Simulation of Beach Changes on Seisho Coast by Typhoon Jongdari

Abstract

The Seisho coastline, in Kanagawa Prefecture, Japan, has historically suffered the consequences of the many typhoons that traverse the area. In 2018, this part of the country was damaged by Typhoon Jongdari, which was a very rare typhoon that moved from the east to the west of the Japanese main island of Honshu. The goal of this study is to attempt to reproduce the beach changes that took place along the Seisho coast during the passage of this typhoon by means of a numerical simulation. First, the authors simulated the wavefield by using the SWAN model, with the maximum simulated significant wave height (5.25 m at 21:10 on 28^th July) being in good agreement with observed values (5.14 m). Mean wave period and wave direction also showed close agreement with observed records. The XBeach model was then used to simulate the hydrodynamic and morphodynamic processes on Seisho coast, which indicated significant cross-shore sediment transport near the shoreline, resulting in shoreline erosion. This matched bathymetric surveys that were carried out by the government some months after the event.