Yoshiki TSUKADA

A Study of Beach Cusps Formation in Jogehama Beach, Nigata Coast

Naoyuki INUKAI(Tokuzo HOSOYAMA)

We need to think about prevention of water accident caused by swash running up the steeply sloping beach.
The big wave suddenly invaded to the beach, and three children were carried off to the sea by the wave although they played on the beach, and the accident of which 5 people die including 2 adults heading to rescue occurred in Jogehama Kakizaki Joetsu Niigata on May 4, 2014.
Because this water accident occurred by a strong swash, it is related to the form of the beach. Two step beach cusps are formed on Jogehama beach. So far, it has been found that after the swash hits the cusp, the water flowing down in the bay gathers and causes a dangerous return flow.
It is necessary to grasp the forming factors of the beach cusps of the Jogehama beaches where the accident occurred. We examined the relationship between the waves and the weather and beach cusps formed in Jogehama Beach.
There is a weather chart pattern in which the high pressure moves eastward in the Sea of Japan. This pattern has good weather and low waves, but it is easy to form a beach cusp, and there is a high possibility that a swash like an accident happens.
Surf waves on Jogehama Beach are estimated from the waves observed Naoetsu Port. The beach cusp on the land side is likely to be formed by the usual wave when the significant wave height is 1.2 m at Naoetsu Port. Waves forming the beach cusp on this land side are not observed frequently. However, it can not be formed with calm waves. And the shape of the beach will not change until high waves erode.
The first stage beach cusp would have been formed by the wave of the survey day. As a result of estimation, there is a possibility that the particle sizes of beach sand are not homogeneous.