| In recent years, with the increase of the port constructions on the silty coast, the problems of the sediment transport, especially the channel siltation become more and more prominent. Therefore, the sediment transport on the silty coast was studied in the present dissertation. On the one hand, the mechanism of sediment suspension under different conditions was analyzed with the fininte mixing length theory and a theoretical model was developed to describle the suspended sediment concentration profile with the high-concentrated near-bottom suspension under combined waves and current. Based on the new theoretical model a three-dimensional sediment mathematical model was improved to simulate the phenomenon of channel siltation on the silty coast. On the other hand, the cross-shore sediment concentration distribution and channel siltation on a generalized silty coast were also investigated.The main results are summarized as follows:1. According to the finite mixing length theory, the characteristics of the suspended sediment in current were investigated. The relation between the turbulent vortex and mixing length was analyzed and a new sediment mixing length equation was derived based on the mixing length theory and Karman's turbulence hypothesis.2. The mechanism of sediment suspension under waves was discussed. A theoretical model for the sediment concentration distribution under wave was developed. Using the experimental results by Lamb et al, the characteristics of turbulence intensity and mixing length in the water with the high concentrated sediment suspension were analyzed. Based on the conclusions in pure current and pure wave conditions, the vertical distribution model of the suspended sediment for the combined waves and current was devepoled. In this model, the damping of turbulence due to the presence of high sediment concentrations is taken into account. The comparison of the calculated results and measurements shows that the present model is reasonable.3. The three-dimensional mathematical model for the sediment transport by Wai and Jiang was improved through using the present suspended sediment model with hight concentration influence for combined waves and current. The improved mathematical model is verified through comparison between simulated and experimental results of channel siltation.4. The process of channel siltation was simulated by the improved three-dimensional sediment mathematical model to illuminate the effect of suspended sediment on channel siltation. The simulated results show that the strong wave is the source of the high concentrated near-bottom suspensions. The thickness of high concentration suspensions (where concentration >20kg/m3) can be in the range of 0.8m-1.25m due to the shorewards wind of force 8. From the particle trajections of the suspended sediment particle, it is the deposition of high concentration near-bottom suspensions that results in the channel siltation. The bed-load sediment transport also plays a subtle role for channel siltation.5. The sediment carrying capacity formula for waves was improved according to the variation of the wave energy dissipation inside and outside the surf zone. The new formula predicts that the sediment suspension increases with the wave period. Measured data were collected to determine the coefficients.6. The carrying capacity model was used to investigate the effects of wave on the cross-shore sediment suspension on a generalized silty coast. The results show that the main factor for the sediment suspension on silty coast is the bed shear stress of wave instead of the wave breaking except in the surf zone very near the coastline.7. Finally, a simplified formula for channel siltation was developed based on the vertical distribution model of the high concentrated sediment suspension, which was used to calculate the thickness of the channel siltation.
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