| The storm surges in the coastal areas of China occur frequently.Unfortunately,these areas are of advanced economic development and great population density.Therefore,the storm surge will cause huge economic losses and casualties.This thesis conducts investigations on the development trend of typhoon landing in China,simulation of storm surge and analysis of seawall overtopping risk under super typhoon,and simulation of storm surge-sediment transport under mobile bed.The result of this thesis is of import theoretical and pratical value for riching coastal dynamics theory and improving the capability of coastal disaster prevention and mitigation,which includes the following aspects:(1)Based on the CMA tropical cyclone path set during 1950?2015,this study calculates the landfall probability of tropical cyclone landing in China.The landfall probability of tropical cyclone among Zhoushan and Sanya and the 'intensity probability' following the normal distribution are proposed.Therefore,the distribution law of tropical cyclones and the growth trend of typhoon landing in China coast are revealed.Afterwards,four common wind-pressure numerical models are established to simulate the wind-pressure field in Zhejiang coastal waters under typhoon 9711.It can be found that the Fujita-Takahashi model appears to be the most suitable model for simulating the wind-pressure field of typical typhoon landing in Zhejiang.(2)A storm surge numerical model according to 70%probability circle is established,and then a set of 112 cases are desinged to simulate storm surge in Zhejiang coastal waters during super typhoons similar to typhoon 5612,which includes typhoon tracks for different landfall positions,centeral pressures and wind moving speeds.Then,the influence under above three factors on the maximum storm surge along Zhejiang coast is investigated.A nonlinear relationship between storm surge and central pressure is proposed,which gives an improvement to the previous result and meets the simulated results.Afterwards,risk assessment of seawall is conducted using the overtopping probability.It can be found that under the influence of super typhoons like typhoon 5612 make landfall in Zhejiang,part of seawalls will occur overtopping event,of which Diaolang seawall of Zhoushan are the most serious with overtopping probability of 1;when the central pressures decrease,the number of seawall suffering overtopping risk changes little;however,when the moving wind speeds increase,the number of seawall suffering overtopping risk increases,especially when the moving wind speed increases by 30%,all the seawalls along Zhejiang coast could suffer overtopping risk.(3)Considering the influence of reclamation projects,a storm surge model is established during typhoon 9711 and typhoon 5612.The influences of coastline variation on storm surge in the Jiaojiang Estuary are analysed.The results show that under effect of onshore wind by typhoon 9711,the esturine hydrodynamics will be enhanced by reclamation project;the maximum increase in storm surge can reach up to 49 cm inside the estuary mouth after reclamation project.Affected by the offshore wind of typhoon 5612,the esturine hydrodynamics also will be stronger due to reclamation project but change little;the variations in storm surge are less than 5 cm inside the estuary mouth after reclamation project.Afterwards,based on the ideal estuary model,the influences of flood runoff,bed slope and channel constriction on storm surge are investigated.It can be found that increase of runoff will decrease the storm surge,while increase of the bed slope and decrease of the channel constriction give rise to increase of storm surge inside the entrance.(4)A nested three-dimensional and mobile bed model is established for investigation on storm surge and sediment transport in the Jiaojiang Estuary.Results show that the mobile bed model appears to be better than the fixed model.Then,an analysis on sediment transport is conducted under influence of typhoon and no wind,respectively.It can be found that suspended sediment concentrations during typhoon period can be 4?6 times than that with no wind;the suspended sediment transport capacity can reach up to 17 times than that under the windless condition.Additionally,the shift range of the turbidity maximum zone increases to 43.5 km.Under effect of storm surge,it can be concluded that the reach outside Haimen is eroded,while the reach inside Haimen is of deposition.The bed is about to be eroded by 0.15 m in Baisha-Haimen reach,which is about 3 times than that without wind.It occurs the maximum deposition about 0.3 m along Haimen-Matoushan reach,which is about 12 times than that without wind.The reason is that the water depth is small and the tide current is strong in Baisha-Haimen reach.The influence of reclamation project on sediment transport during typhoon period is also analysed.It can be found that the bed of Baisha-Haimen reach will be eroded up to 0.24 m.In addition,the shift range of the turbidity maximum zone further increases due to the reclamation project. |
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