In the Ushizu river, high suspended sediment concentrations can be often realized under normal conditions because of a strong tidal difference. Such a high concentration sediment transport causes a large mud accumulation in the riverbank. It will make a big problem of a river cross-section closure and prevention of river flowing. Also, the mud sedimentation may be accelerating the growth of a wide spreading of Phragmites australis in the river bank.
The purpose of this study is to survey suspended sediment transport, the behaviors of fluid mud, sediment flux and try to control the growth of Phragmites australis in the Ushizu river. As a result of field surveys, mud sedimentation rate was about 1mm/day during non-flooding term. In addition, sedimentation near the waterline is strongly related to acceleration to waterside intrusion of Phragmites australis and the average rate of intrusion progress was about 2.6cm/day though it depends on the step of the growth of Phragmites australis. Finally, the effectiveness of a new vegetation control system for the spreading of Phragmites australis was shown.
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