Study On The Response Of Shoreline Change And Sea Level Rise To The Tides Of Hangzhou Bay

Located on the eastern coast of China,the Hangzhou Bay area is a typical wide,shallow,funnel-shaped bay with complex tidal changes.The most significant features are strong tidal currents,large tidal differences,and high concentration of suspended sediment.Due to global sea level rise and high-intensity human activities in offshore areas,especially in estuarine coastal areas,tide changes have a significant impact on the estuarine coastal environment,water and sand transport characteristics,coastal floods and other extreme events.Therefore,this paper uses MIKE21 to numerically simulate the tidal characteristics of Hangzhou Bay to analyze the characteristics of Hangzhou Bay tides under the background of different shoreline changes and sea level rise,which provides a reference basis for the scientific utilization of space in Hangzhou Bay,and has certain scientific and engineering significance for resource protection and utilization,disaster prevention and mitigation in Hangzhou Bay.The tidal characteristics of Hangzhou Bay were studied in detail from the shoreline changes,and the response characteristics of Hangzhou Bay tides were compared and analyzed by the numerical experimental results of three sets of shorelines in different years（1997,2007,2020）without considering topographic deformation and other meteorological factors.On the one hand,the changes of tide level,flow field and tidal change under three shoreline scenarios were calculated and analyzed,and the tide level of the inner bay increased by 0.8～1.0 m from 1997 to 2020,while the tide level in the inner bay and outer bay area decreased by 0.4～1.0 m,and the tidal difference decreased from the inner bay to the outer bay with the overall decrease of the shoreline of Hangzhou Bay,and the tidal difference value gradually decreased from the inner bay to the outer bay,and the tidal difference in most sea areas increased between 25%～50%.On the other hand,the amplitude and delay angle changes of M₂ and M₄ tides under different shoreline changes were explored,and the amplitude was more than 1.6 m in the area east of the Luchaogang-Sizaopu section,and the propagation speed of the north bank of the M₂ tide was greater than that on the south bank.The amplitude of M₄ above the top of the bay is above 0.08,and the amplitude gradually increases from the outside of the bay to the top of the bay.The four measurement points analyzed that the M₂ tidal amplitude decreased,and the M₄ tidal amplitude decreased and then increased along the course.The tidal coastline of Hangzhou Bay is directly affected not only by mean sea level rise,but also by tidal dynamics.The computational domain of the MIKE21 hydrodynamic model covers the entire Hangzhou Bay and takes into account the feedback between tidal motion and the erodable bottom.The tidal characteristics under different sea level rise scenarios（0.44 m,0.56 m,0.68 m and 0.77 m）were simulated,and the interaction between tidal duration,skewness,maximum possible tidal change and astronomical tides was analyzed.The results of the tidal asymmetry of Hangzhou Bay include four aspects:first,the high tide advantage of Hangzhou Bay gradually weakens from west to east,and the deviation gradually increases from the outside of the bay to the top of the bay;Secondly,the tidal difference increase affected by sea level rise is between 25%～50%,and the sea level rise value is about twice the tidal range increase value,and the tidal range increases to the left side of the tidal wave propagation direction;Thirdly,sea level rise accelerates the speed of tidal wave propagation,which will cause the advance and amplitude increase of M₂ tide in the inner and outer bays,while the M₂ tide phase is the opposite,with a decrease of about 50%.Finally,the ratio above the top of the bay decreased by about 0.4,and the ratio of most of the sea areas between 0.01～0.02 increased by about 50%.The purpose of this study was to emphasize the importance of the predictions of the response area affected by tidal asymmetry based on the action of the sea level rise in Hangzhou Bay.In overall,this thesis shows that the changes in hydrodynamics and tidal processes in Hangzhou Bay caused by shoreline changes are of certain significance for the tidal characteristics and prediction of future projects in Hangzhou Bay,and based on the study of sea level rise on the tides of Hangzhou Bay,the influence of sea level rise on tidal asymmetry,tidal asymmetry and shallow water tides is explored,which has important theoretical and practical significance for in-depth understanding of the performance characteristics and dynamic mechanism of tidal asymmetry.