Understanding of dynamics of coastal morphology and sedimentary environment is critical topics for sustainable use and management of coastal and estuarine area. The target area of the present study, the Ariake Bay and the Tokyo Bay, are typical embayment in Japan, where mud or fraction of silt and clay is dominant in the bottom sediments, and the process of fine sediment transport is an important factor for their water environment in the area. Several field monitoring were carried out in the present study for capturing characteristics of spatial distribution of muddy sediment and near-bottom processes including transport process of mud and water quality changes under the forces of waves and currents. Furthermore, the knowledge obtained through the field monitoring were applied for modelling of fluid mud transport processes.
For the capturing sediment characteristics, besides the acquisition of key parameters of sediment strength such as bulk density and water content from sediment cores, an in-situ device was also newly introduced for direct measure of bulk density of bottom mud. In the Tokyo Bay site, thickness of fluid mud layer is relatively higher in the offshore from the river mouth area with the thickness of over 20 cm. Through the deployments of long-term monitoring in the fields, where several acoustic velocimeters and synchronized measurements of water qualities including turbidity, dissolved oxygen and so on, the present study examines sediment dynamics and water quality change due to waves and currents. Considering dominant forces in the study sites, suspended sediment transport processes due to tidal current is examined and modeled with the data from the Ariake Bay. On the other hand, sediment transport and water quality changes near the bed due to wind waves are focused on for the study of the Tokyo Bay.
Dynamical processes during an extreme storm events due to a passage of typhoon were
successfully captured in the monitoring campaign of the Tokyo Bay and the data analyses revealed the importance of fluid mud transport in the near surface mud layer. Model for the fluid mud transport is newly derived and applied for numerical simulations of mud transport process under the storm condition. Through the validation process of the model, it appears that stochastic approach is effective for the evaluation of wave forces on the fluid mud transport simulation.