Numerical Simulation Of Sediment Transport In The Changjiang Estuary And Siltation In The Deepwater Channel

The Deepwater Navigation Channel in the Changjiang Estuary has brought tremendous economic and social benefits, but the problem due to large siltation quantity with strong siltation at specific channel position is also serious. In this thesis, a hydrodynamics-salinity-sediment numerical model was established in the region of Changjiang Estuary based on the FVCOM model with three-dimensional hydrodynamics, salinity, sediment model and two-dimensional vertically-averaged fluid mud movement model. The sediment transport in the Deepwater Channel and mechanism of channel siltation are investigated through the developed model. The contents and main conclusions are as follows.(1)A settling velocity formula of cohesive sediment, considering the effects of temperature, particle size, sediment concentration, salinity, turbulence intensity, was proposed. The parameters of the formula were determined by field observations and experimental data, and this formula can be applicable in the Changjiang Estuary. The range of the settling velocity calculated from the formula is in good agreement with previous studies.(2) Based on the simulated results of the three dimensional, hydrodynamics, salinity and sediment transport in the Changjiang Estuary, The effects of salinity stratification on the hydrodynamics and vertical distribution of suspended sediment were investigated. The results show that, the turbulence suppression by salinity stratification decreases the vertical eddy viscosity and affects the velocity distribution obviously. It is known that the depth-averaged velocity increases, the surface velocity becomes larger, the bottom velocity becomes smaller. Furthermore, the suspended sediment becomes more stratified, the suspended sediment concentration in the surface becomes smaller, while that in the bottom becomes larger The velocity and sediment concentration with salinity effects are in better agreement with the measured data. Stratification effect has important influence on hydrodynamics and sediment transport in the Changjiang Estuary.(3) The three-dimensional numerical model was verified and the results show that the suspended sediment concentration, water and sediment flux and deposition results are in satisfactory agreement with the measured data. It is indicated that the three-dimensional model we developed can reflect the water and sediment movement properly in the Changjiang Estuary. And the results show that the fluid mud comes from the two side shoal of the channel is the most important source of the siltation in the channel.