The aim of the research is to elucidate suspended sediment transport and their deposition processes especially at river mouth or estuarine area. Field measurements were carried out in the port of Niigata to clarify characteristics on spatial and temporal variations of bottom sediment properties around navigation channel and turning basin in the river mouth port. The measurements includes acoustic sounding, in-situ mud density measurement with a tuning folk type densimeter and taking sediment core samples by Scuba-divers. The data shows that diversity of sediment properties such as mud content and water content according to river flood condition. The survey successfully captured also the formation of three layer structure during a river flood condition with the higher turbid fresh water in the upper layer and the lower turbid sea water in the middle layer. Further high concentrated mud or fluid mud layer was found in the lowest layer at the deeper dredged channel area. The hydraulic model experiments were also carried out with a circulating flume to elucidate the fluid mud transport on the steep slope modeling the edge of navigation channel. The experiments clarified the influence of the hydrodynamics conditions on fluid mud behavior and suspended sediment transport process at river mouth area.

Key Words: River mouth port, sediment discharge, fluid mud, dredging, pycnocline