Study Of Storm Surge And Waves In Zhoushan Sea Area Under The Influence Of Sea Level Rise And Typhoon

Sea level rise will have an impact on the hydrodynami.Under the influence of typhoons with different moving speeds,the process of surge and wave change will have different degrees of change.Measured tide levels from January 1978 to December 2021 at Daishan tidal level observation station are used to calculate the annual mean sea level rise rate.The sea level rise(444 mm rise)calculated in 100 years under this upward trend is used to analyze the impact of sea level rise on storm surge and significant wave height.A nested tidal model for the East China Sea-Zhejiang coastal waters is built by use of MIKE21,to simulate the storm surge and significant wave height generated by typhoon Chan-hom based on Holland wind field model.The comparison of the numerical results and the field measurements shows that the simulated values are reasonable and reliable.Previous studies mainly focused on the storm surge as the basis to analyze the influence of factors such as intensity,path,maximum travel radius,pressure and moving speed.In the analysis of moving speed,different fixed moving speeds are often set for comparative analysis.However,in the actual situation,typhoon moving speeds is not fixed,and it has been changing from the generation to the extinction of typhoon.Therefore,it is very necessary to study the influence of the change of typhoon moving speeds on the surge under the actual situation.Therefore,the historical typhoon velocity affecting the Zhejiang sea area is firstly analyzed.Based on the verified model,two extreme moving speed typhoons(low moving speed Typhoon 7413 Mary and high moving speed Typhoon0004Kai-tak)from 1949 to 2020 were simulated and analyzed.The coastal storm surge model of Zhejiang Province is used to simulate the process of water accumulation under extreme moving speed typhoons and analyze the characteristics of coastal storm surge under different moving speed.On this basis,in order to compare the influence of a single variable,velocity,on water increase and significant wave height,Typhoon Chan-hom was selected to study the three typhoon moving speeds(double moving speed,actual moving speed and half moving speed).The effects of 444 mm sea level rise on storm surge and significant wave height are discussed.The results show that:With the case of sea level rise,the surge of low moving speed typhoons to the coastal areas,especially the the wind direction points to the shore,is further increased compared with high moving speed.The significant wave height of wind wave increases more greatly under the condition of high moving speed.Although the significant wave height of Zhoushan offshore observation point located in the deep water area on the right side of the typhoon route is large under the three moving speeds,the variation of sea level rise on mixed waves,wind waves and swell waves is not obvious.According to the significant wave height change of wind wave and swell before and after sea level rise,although the maximum significant wave height of mixed waves at landing time before and after sea level rise has little change,but the impact of waves on Zhoushan Islands,especially the coastline of the eastern islands,is significantly increased.Under the comparison of typhoon conditions with different moving speeds,The high moving speed typhoon will further increase the threat of waves to the east coast of Zhoushan Islands.