| Changj iang Estuary is the largest estuary in China, with the abundant fresh water and sediment discharge. It has three bifurcations and four outlets into the ocean shelf. In order to deepen the seaward channel of Changj iang Estuary, the Deep Waterway Project was constructed around the North Passage of the Yangtze Delta since 1997 and has been formally handed over in 2010. The construction consists of two dikes and groups of groynes. Due to the project, the hydrodynamics conditions, bed topography and sediment transport around the North Passage has been significantly changing. For instance, critical sediment siltation was founded around the North Passage. And quite a lot of scholars pay attention to the possible source of the silting sediment from various angles, using a variety of techniques. However, limited to the lack of observation conditions, the study of lateral exchange between the North and South passage, meaning the flux overtopping the South Leading Jetty, is far from comprehensive. Thus the research is a meaningful job for measuring the influence of the Deep Waterway Project, moreover the study is a useful supplement in some sense.A numerical simulation was implemented, based on the in-situ measured topographic data, using the unstructured-grid, three-dimensional primitive equation, finite-volume coastal ocean model (FVCOM) including a dike-groyne module, for the study of temporal and spatial variations of overtopping flow at the south leading jetty constructed around the Deep Waterway channel. Based on the above work, we calculated how the South Leading Jetty affects the flow diversion ratio and sediment transport of the North Passage.In addition, we had a preliminary discussion about the factors concerned the overtopping flux in view of sea level and mean velocity crossing the sections. The main conclusions in thesis are listed as follows:1. The net exchange water flux between the North and South Passage leads to the north at the upper and middle part and points to the south downstream before the project constructed. However, after that the net flux points to the North Passage all over the dike.As estimated, spatially varying unit width net overtopping water flux has a significant feature, which is bounded at the corner, shows that the flux increases gradually at the upper half and decreases at the latter with a larger value.On a time scale the amplitude appears no remarkable changes seasonally but on the other hand paces periodically in a tidal cycle. Specifically, the flux of flooding season is a little higher than the dry season and the amplitude of flux is much larger in the spring than in the neap. The maximum unit net flux during the spring is about twice during the neap.In a view of the total amount, the flux decreased by 21.7% after phase I and increased by 43.3% after phase II instead. Phase â…¢ has no remarkable effect on the flux.2. In a case of adding 5 m on the South Leading Jetty, we founded that it will weaken the sediment transport capacity in the North Passage and enhanced the capacity in the South Passage. Through the accurate calculation we found that if the depth of the dike increases by 5 m, the sediment crossing the sections around the North Passage will decrease by 4% and increase by 5% around the South Passage. In addition, t if the depth of the dike increases by 5 m, the flow diversion ratio will decrease by 0.76% at the entrance of the North Passage and increase by 0.47% at the exit.3. The results show a strong linear correlation between net water flux and sea level. In the research the correlation coefficients of the two points are 0.87 and 0.94. The effect of the velocity crossing the sections is much larger in the upper half than in the later half. |
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