SHORELINE CHANGES OWING TO SEASONAL CHANGES IN WAVE DIRECTION ON KOMAKA ISLAND OFFSHORE OF CHINEN PENINSULA IN OKINAWA

Abstract

 Selecting Komaka Island 3 km offshore of Chinen Peninsula in Okinawa and surrounded by coral reef was selected as a study site, field observation on the shoreline changes of a cay was carried out on July 13, 2019, and the shoreline changes were investigated using satellite images. The shape of cuspate foreland behind the island was classified into three types (circular, slender oval, and elongated oval). Then, numerical simulation on change in cuspate foreland was carried out using the modified BG model. In this model, wave height distribution changes in response to the wave-sheltering effect by the island is assumed, although waves are incident from the direction normal to the circular shoreline. Longshore sand transport is assumed to be induced owing to the spatial distribution of the wave height. The results of numerical simulation explains well the deformation of Komaka Island given a K_d value.