INVESTIGATING DISTRIBUTION CHARACTERISTIC OF STORM BOULDERS AT OKINOSHIMA ISLAND, JAPAN BASED ON NUMERICAL MODELING

Abstract

 Coastal boulders formed by past tsunami or storm waves have been reported around the world. The relationship between size of tsunami or storm wave and boulder weight is nesssary to be investigated in more cases for contributing the research of coastal boulders to future disaster prevention at coastal area. At Okinoshima, Chiba prefecture, several tones of coastal boulders were transported by storm waves during the 2019 Typhoon No. 15 (Faxai). In this study, we conduected numerical simulation of storm waves during this event in order to estimate ths size of storm wave which emplaced these boulders onto the land. As a result, we estimated that the maximum size of boulder was transported from areas that water depth is less than 9.1 m. The computed maximum wave height and velocity over the shoreline was respectively 4.7 m and 14.5 m/s. Hereinafter, by accumulating the data of boulder distribution and size of tsunami or storm wave, the estimation of past tsunami or storm wave that transported coastal boulder can be conducted in many places.