In August 2016, four swimmers carried away offshore and died at Ishikari-hama beach in Hokkaido, while, in recent years, several other similar accidents occurred around the Ishikari coast. In the past, analysis of the Ishikari Bay due to the seasonal wind has been conducted. However, the dynamics due to wind direction change in short time have not yet studied. Therefore, in this paper, we tried to comprehend the features of the current dynamics in Ishikari Bay, and, more specifically, around Ishikari-hama beach.As research contents, we grasped the accident that occurred in the past around the Ishikari coast. In this case, we used the on-line database of the newspaper article about the accident at Ishikari coast. As the result, we comprehended the feature of the accident in Ishikari Bay. Secondary, we made a field survey at Ishikari-hama beach in July 2017. This beach has cusp topography. The interval spacing of cusp topography was about 100 m, and the slope of the bottom was about 1/80. In the field, we pigmented the rip current by the sea water colorant, and the pigmented current was recorded as an aerial photography by the UAV. Thirdly, we confirmed the fluctuation of the current in Ishikari Bay due to short time fluctuation of the wind direction. As a result, we concluded that the current direction changed in several hours after the wind direction changed. Finally, we simulated the rip current and the wind driven current in Ishikari Bay.
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