The Change Of Scouring And Filling Environment After The Construction Of Zhangjiabu New Port And The Study Of Limit Depth Of Scouring

In normal conditions the seabed sediments are in a relatively balanced status of erosion and deposition on a relatively stable coast. But in strong wind case, synthesis effects both of wind-induced wave and tide destructed the state of equilibrium, sediments were set off as suspended load. When wind stopped, the water turbulent intensity gradually weakened , as a result, the capacity of current to carry sand reduced, so that supersaturated suspended sediment deposited, resulting in decreased sediment concentration until a new relatively balanced status of erosion and deposition of the seabed sediment formed. The combined effects of wave and current cause different degrees of erosion and siltation of the original beach structure. The depth of erosion is closely related to the stability of sediment. If the scour depth reaches a certain extent, not only the building may tilt and collapse, causing significant losses, but also the surrounding seabed topography will change, forming dynamic linkage coupling effect with structure and complex marine water power .. This paper studies the impacts of the construction of Zhangjiabu new port on the marine environment and indicates that the new port has destroyed the original state of the natural shoreline and waters,causing current to change in direction and size. The construction of pier, embankment, cofferdam and dredging works of sea-route has changed the flow field locally, in which the direction of flood-tide and ebb-tide near the project changed in a small angle after the formation of a new shoreline, consequently, the environment of erosion and deposition changed, and so did the topography accordingly. In this paper, three-dimensional model ECOMSED was used to simulate the evolution of the seabed terrain under the condition of tide and wave (imposed by the wind), and the variation of scouring and filling after the completion of the project. Both the current and wave fileds were established and then coupled to get the shear stress to the seabed. This calculated stress was compared with the critical stress of threshold motion of sediment so that the variation of scouring and filling can be analyzed. For the scouring area, the scouring depth limit was predicted by changing the depth and iterative calculation of table deck shearing stress induced by wave and current, which,consequently, provides a scientific basis for engineering design and protection.