Numerical Simulation of Rapid Erosion of Seisho Coast Triggered by Storm Waves during Typhoon 0709

On September 6, 2007, the Seisho Bypass extending along the Seisho coast was severely damaged over a length of 1.1 km owing to storm waves associated with Typhoon 0709, resulting in roads being closed to traffic for urgent repairs. During the typhoon, severe beach erosion occurred owing to both strong offshore sand transport and westward longshore sand transport by storm waves, and the foreshore was rapidly narrowed. However, the foreshore was recovered except the damaged area of the highway as a result of the effect of normal waves. These beach changes were predicted using the contour-line-change model incorporating Fukuhama et al.'s concept. The predicted results were in good agreement with the measured beach changes.