Impacts of sediment transport due to the kumamoto earthquakes on an intertidal flat at the mouth of the Shirakawa river, Japan

Landslides frequently occurred in the Shirakawa basin due to the Kumamoto earthquakes occurred in 2016, a large amount of sediment flowed into the river channel of Shirakawa River. They were deposited on an intertidal flat at the mouth of the Shirakawa River. That is concerned about the influence on the water environment and the fishery industry. Therefore, in this study, in order to examine the influence of the sediment on the intertidal flat at the mouth of the Shirakawa River, we conducted a field survey and estimated the state of the river sediment budget. Regarding the field survey, we conducted grain size analysis and bed elevation survey on the intertidal flat at the mouth of the Shirakawa River. As for the estimation of the state of the river sediment budget, we estimated the amount of bedload using turbidity data. The results showed that the sediment deposited was fine. As for the ground height on the intertidal flat at the mouth of the Shirakawa River, the period from May to July was rising, however, the period from July to January was declining. Regarding the estimation of the state of the river sediment budget, the amount of sediment that flowed into the intertidal flat due to the flood of last year contains a large suspended load and it was about 10 times compared with the whole year of it.