In constructing the Irabu bridge connecting Miyako to Irabu islands, a causeway was exended as part of the bridge on the reef flat, resulting in the formation of a wave-shelter zone on both sides of the causeway. After the construction, marked beach changes occured on the carbonate surrounded by a coral reef, and the nesting sites of the sea turtles were extensively lost. The BG model (a three-dimensional model for predicting beach changes based on Bagnold's concept) was applied to predict these beach changes. Then, the stabilization method of the beach was considered. A suitable measure was to install groins as well as beach nourishment
