The river mouth closure of the Okukubi River in Okinawa Prefecture, flowing into the coral reef, was studied. In this area, the shoreline material was extensively excavated after World War II, resulting in the disappearance of sand beach. Since then, coral sand was naturally supplied from the reef edge, resulting in recovering sandy beach. Sand reached the shoreline was then transported by longshore sand transport due to waves, and the river mouth bar was formed. The river mouth closure associated with this sand accumulation was predicted by the BG model proposed by Serizawa et al. (2006). The predicted beach changes are in good agreement with the measured.
