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Investigation of the River Mouth Topography Change by the Response Characteristics of River Discharge and Ocean Waves at Yoneshiro River

ABSTRACT Watanabe K. and Kumagai K., 2018. Investigation of the River Mouth Topography Change by the Response Characteristics of River Discharge and Ocean Waves at Yoneshiro River. In: Shim, J.-S.; Chun, I., and Lim, H.S. (eds.), Proceedings from the International Coastal Symposium (ICS) 2018 (Busan, Republic of Korea). Journal of Coastal Research, Special Issue No. 85, pp. 61–65. Coconut Creek (Florida), ISSN 0749-0208. Frequent occurrence of water level rise caused with increase in abnormal weather such as the local torrential rain by the influence of the global warming. Therefore, apprehensive the saline water intrusion was generated at the tidal area due to water level rising and the River mouth topography change in recent years. Saline water intrusion was generated to go up upstream by the ocean waves during winter at the river mouth especially. Hence, riverine environment was affected from saline water intrusion. It was in particular thought river mouth shape have a high impact on tidal discharge and saline water intrusion. However, it was not understood in sufficient elucidation of the mechanism of the increase of tidal discharge saline water intrusion. For this reason, it was very important to examine the long-run effect of river shape on tidal discharge and saline water intrusion. In this study, it was investigated about the hydraulic characteristics by the field observation and data analysis target at Yoneshiro river where the extension of the sandbar was remarkable. As a result, the amount of change of the river mouth width ΔB grows large more than up to approximately 20m from a previous week. It was revealed that river-mouth closure up to approximately around 10m occurred by the reverse case. Saline water intrusion was not confirmed in Yoneshiro River which was developed of the sandbar. It was thought to cause the river-mouth closure by the development of the sandbar. Furthermore, discharge of wave set-up was about 70m3/s from calculation of the tidal discharge. In addition, it became clear from river mouth width rate of change α that there were many changes of the river mouth width in 500m3/s or less river discharge in Yoneshiro River