We propose to investigate a major problem occurring in the mouth-bar area of the Yangtze Estuary and in the Ems Estuary (Wadden Sea), viz. the increased sediment concentrations and enhanced deposition of this material in waterways after engineering works. Specific objectives are 1. to identify sources, physical-chemical attributes and flocculation characteristics of fine sediment and to assess their influence on estuarine turbidity dynamics; 2. to quantify similarities and differences, regarding along-channel flow and sediment patterns, in a turbidity zone that is characterised by either multiple channels or by a single channel; 3. to investigate the role of time-varying mixing conditions, wind and channel-flat feedbacks on along-channel and across-channel trapping of sediment, evolution of the mouth-bar area and sediment accumulation in the waterways; 4. to propose methods to reduce deposition of sediment in navigation channels. An integrated approach will be adopted of analysing field data, and developing and analysing process-based models. Available data of the Ems Estuary will be used, whilst also new data will be collected in the Yangtze Estuary. Two closely linked subprojects are proposed. The first project (PhD at UU) focuses on modelling along-channel distributions of fine sediment in a tidal network, and comparing results with field data. Both a semi-analytical and numerical model will be used to perform a sensitivity study to changes in depth and mixing conditions resulting from interventions. Results will be unravelled in terms of physical mechanisms. The second project (PhD at ECNU) focuses on the collection and analysis of available and new field data, and investigates the physical-chemical properties of fine sediments in water and bed load samples. The results will be incorporated in a model to examine the effect of floc size and its rapid settling on both across-channel and along-channel patterns of sediment transport and accumulation under varying external conditions.