Study On The Character Of Flow And Sediment Exchange And Transport Between Changjiang Estuary And Hangzhou Bay

This paper takes Nanhui nearshore which is an intersectant area of Changjiang Estuary and Hangzhou Bay as a study object. On the basic of former people's research, this paper studied systematically of the dynamical mechanism and the transport character of the water and sediment between Changjiang Estuary and Hangzhou Bay, especially the hydrodynamic character and sediment transportation of Nanhui nearshore.Firstly, the dynamical mechanism of water and sediment exchange and transport between Changjiang Estuary and Hangzhou Bay has been discussed in this paper. This dynamical mechanism includes: the water level change of Nanhui nearshore in one tidal cycle, the schlep of the flood tide, the effect of the wind and flow, the effect of the fronts. On the side of the sediment transport, It is considered that there is a straightly transport and an indirectly transport in this paper.Based on the analysis of the data collected in the flood season in 2005, the study of hydrodynamic character in Nanhui nearshore has been done. The results show: the landscape orientation characteristic of current velocity is smaller near shore and larger far away from shore. The direction of the residual flow is toward to the east, and the suspended sediment is transporting toward to the sea. The dominant flow is greater than 50% in spring tide, and the dominant flow of most station is less than 50% in neap tide. The landscape orientation characteristic of Euler residue is smaller near shore and larger far away from shore. The direction of Stokes residue is toward to the land, and the current velocity is almost the same.The character of the suspended sediment of Nanhui nearshore is that: the landscape orientation characteristic of suspended sediment concentration is higher near shore and lower far away from shore. In order to describe the vertical distribution, the coefficient "P" had been used. The results show: The curves of P1 and P2 are commonly above zero, and the effect of sediment suspending is weak. The suspended sediment stays in the near bottom water layer mostly. The computing result of calm flow shows: Sediment transports toward to the land in spring tide, otherwise to the sea in neap tide. The tidal pumping effect is larger in spring tide and slower in neap tide in the near shore area. The situation is opposite in the deep water area.The character of the bottom sediment has been analyzed in this paper. Furthermore, a triangular diagram advanced by Pejrup has been used to subdivide the sedimentary environment, the result shows that the hydrodynamic on this area is relatively strong and the grain size is generally coarser, and this area belongs to estuarine sedimentary environment influenced by both flow current and tide current. According to Cao-Collins grain size trends model (GSTA model), the sediment transport direction has been figured out. Above the Dazhihe estuary, the sediment transports parallel with the fathom line. Near the Dazhihe river mouth, the sediment transports eastwardly or southeastwardly in the area shallower than 2 meter. And the sediment between 2 meter and 5 meter transports westward or southwestward. The transport direction of the sediment between the Dazhihe river mouth and Nanhuizui is westward. The source of the sediment of Nanhui nearshore includes three sections: sediment from Changjing, sediment exchanged between nearshore and channel, sediment schlepped by the flood tide.