Study on deformation Process of a Tombolo throughout a whole year at Chiringa-shima Island ,Ibusuki City

Abstract

A long-tied tombolo with the length of 800m at Chiringa-shima island emerges only during ebb-tide in spring tide condition from March to October. In this study, the physical processes of the emerging are investigated. The field surveys have revealed that the base underneath the surface sands consists of rocks, and a shallow area with huge amount of sand extends around the tombolo, and beyond the area, the sea bottom suddenly deepens. A series of numerical simulations for the wave fields, current fields, sediment motion and bathymetric changes were conducted. The result suggests that the emerging process of the tombolo can be explained by the seasonal change of thewind direction and the resultant changes in the wave fields.