Analysis On The Cumulative Effect Of Hydrodynamic Change Caused By Topographical Change In Ningbo Sea Area

Under the back ground of the high-speed economic development and the lack of lands in coastal areas, several times on Large-scale construction have been carried through in our country.At the beginning and later years of the foundation of our country, the impact on the environment by sea reclamation can’t be evaluated and predicted properly because that we didn’t pay enough attention to the environment and our technology on the measures of environmental impact assessment was immature. In these years, with the development of science, technology and our concern on marine environment, methods on engineering evaluation which may cause the change of coastline topography such as the reclamation have developed rapidly. When environmental impact evaluation was practiced in coastal and offshore areas, sediment transport and pollution indicators of water were all based on the accurate simulation of area hydrodynamic characteristic, hydrodynamic field can be the carrier of the evaluation. In this paper, hydrodynamic field in different years has been simulated and studied by means of a3-d hydrodynamic model, the results which were calculated by different combination of hydrodynamic.coast line and topography were analyzed and compared, so that a powerful reference can be ready for evaluation methodology research on the cumulative effect of hydrodynamic change in reclamation engineering.There has been an increasing active on reclamation engineering in recent years, especially in Hangzhou Bay and Xiangshan Harbor where our research lay emphasis on, these engineering has caused great change in coastline and topography which will certainly cause the change of hydrodynamic field. Also, the coast line and topography in Ningbo-Zhoushan area was quite complicate, there were many islands in this area and more sea reclamation constructions were carried out in tidal marshland on the south bank of Hangzhou Bay, hydrologic and the sediment data here is quite plentiful, so this area is a typical place to conduct a study on the influence of hydrodynamic field under the influence of natural and artificial factors.In this paper, a FVCOM model is used to construct two hydrodynamic models in the year2009and1983. By means of comparing the actual measured tidal level and flow rate to the results of this model, it is known that this model can properly simulate the hydrodynamic field of Ningbo-Zhoushan area. According to the results, this paper briefly analyzed the characteristics of flux and reflux. A stagger time method of which the simulation of shoreline and topography are in different times and the hydrodynamic is in the same time is used. By comparing the influence of the flow of cross sections and area flow velocity caused by the change of shoreline and topography in40years, it is known that flow in the three important cross sections on the south bank of Hangzhou Bay has a cumulative decrease trend and the flow also has a cumulative decrease trend, it is the same with area flow velocity. These results also occurred in Xiangshan Harbour.A new evaluation methodology which called same time method is raised based on the shortcomings of stagger time method in the evaluation of cumulative effect of hydrodynamic change caused by topographical change in many years. In this method, the shoreline, topography and hydrodynamic field are all in the same year. The comparison shows that there may be bias using stagger time method to simulate hydrodynamic field, and this method may influence the results of the research conclusion.