We carried out the field observation and numerical simulation to grasp the water environment and topographic change at river mouth by the flood. Study site is Akashi River mouth, Hyogo Prefecture in Japan. From field observation, it is clarified the river mouth bar and terrace tend to be formed in the winter and be washed away by the flood in rainy season. On the other hand, from the results of numerical simulation, it is clarified that the water level at peak discharge under 300 m3/s effects on the river bed variation.
