Process Research on Estuarine Turbidity Maximum and Mouth Bar of Yangtze Estuary after the Improvement Works

摘要

In Yangtze Estuary, the ETM is always accompanied by a board shallow area (basically around 6 m water depth) in the mouth zone, called mouth bars. After more than 40 years study, North Passage was selected as the deep-draft navigation channel and the regulation works started in 1998. Extensive engineering works, consisting two long training dikes and 19 groins, are implemented to achieve deeper water depth with the help of dredging activities in the North Passage of the Yangtze Estuary. After Yangtze Estuary deepwater channel improvement project in 1998, in north passage mouth bar terrain disappear, but turbidity maximum zone is still persisting. At the same time, since the completion of the engineering works, high siltation appears in the middle segment of the North Passage. To fulfil the needs of navigation, the maintenance dredging amount is unexpectedly large which is inefficient economically. Studies through field data analysis before and after the project reveal the evolution models of North Passage on the Yangtze Estuary, as well as the impact to the deep water channel siltation. Three-dimensional models using Delft3D are developed and validated including density gradients and fine sediment transport to investigate the respective role of several processes on the turbidity maximum behavior in the Yangtze estuary. The main goal of this work is to reproduce the turbidity maximum in the model and to compare sensitivity of the turbidity maximum to different model parameters. The stydy also aim to explore consequences for morphodynamic development and to reveal the reasons of high siltation in the North Passage by the simulation of ETM of numerical modeling.