Yuto KOIKE

Study on the generation condition of beach cusp topography on the coast where waves go beyond sand beach

Naoyuki INUKAI

Although many of the water accidents in the sea occurred during swimming, accidents occurred that they were kidnapped by waves on the sand beach. In Niigata Prefecture, there were also 5 people suffering from water accident at Zyougehama Beach in Joetsu city in Heisei 20 years. It is clear that the cause is the upstream wave and the return flow, and the return flow is the flow that the upward wave reverts to the offshore, and it is generated by the interaction between the backward wave and the topography.
In this research, in order to prevent water accidents, we analyzed the characteristics of beach cusp which is the cause of return flow, grasp of wave characteristics, and identify coast where return flow occurs. In the grasp of the characteristics of the beach cusp, a field survey was conducted on the coast of the coast where the accident caused by the return flow occurred, and the production conditions and characteristics of the beach cusp were clarified. The characteristics of the wave that induces the return flow were estimated from the characteristics of the beach cusp using the waves observed in the past. We have grasped by estimating the generation situation of the beach cusp. It was revealed that the characteristics of the waves that should watch for the return flow from the estimation occur when the wave height exceeds 1.0 m cycle 5.2 s. And the new method of specifying the coast where the return flow occurs is to extract and identify the coast where the beach cusp is generated from the topographical elevation data of 5 m mesh provided by the Geographical Survey Institute. As a result, we extracted beach cusp terrain by 5 m mesh topographical elevation data in Niigata prefecture and confirmed that 5 coasts are swimming baths.