Study On The Spatial-temporal Features Of Disastrous Marine Dynamic Process And Its Effects On Hazard-bearing Body Under The Influence Of Typhoon

Storm surges and typhoon waves are marine disasters that pose a grave threat to people’s lives and property.The southeast coastal area is one of the major hard-hit areas of storm surges and typhoon waves in China.These disasters result in huge economic losses and casualties every year.Meanwhile,the premise for disaster mitigation and prevention is to totally understand storm surges,typhoon waves and the dynamic mechanism of these disasters.Overall,the research on storm surges and typhoon waves have important value on related theory as well as its practice.Previous studies have shown that there are many factors influencing the formation of storm surges and the interactions among these factors are complicated.So it is necessary to take account of the complex interactions among astronomical tides,storm surges and typhoon waves.In order to figure out the astronomical tides,storm surges,typhoon waves and the interaction mechanism among them in the East China Sea under the influence of typhoon,as well as the development and evolution process of overtopping and inundation caused by these disasters.A two-dimensional numerical model with high-resolution based on ADCIRC(Advanced Circulation Model for Oceanic,Coasts,and Estuaries Waters)two-dimensional finite element hydrodynamic model and SWAN(Simulating Waves Near-Shore)wave model was adapted to the East China Sea area.The real-time interaction among storm surges,astronomical tides and typhoon waves was considered.Three typical typhoons "Saomai"(0608),"Usagi"(1319)and "Chan-hom"(1509)are selected as the research objects.The simulation results are in good agreement with the measured data,which lays a good foundation for the numerical simulation.Firstly,the spatial and temporal characteristics of storm surges and wave setup heights in the southeastern coastal area of China are studied during two severe weather events with different tracks,those are,Typhoon Saomai making direct landfall and Typhoon Chan-hom bypassing.The simulation results showed clearly different spatial patterns depending on the track type.The maximum storm surge resulted from the cumulative effect of the local onshore wind forcing,occurring on the right side of track of Typhoon Saomai and left side of track of Typhoon Chan-hom.Significant surge levels along the coast on the left side of typhoon track were well observed in both cases,resulting from the coastal-trapped shelf waves.The track type of Saomai is more likely to cause extremely high storm surges along the coast due to the stronger cumulative effect of the onshore wind forcing.The maximum wave setup was governed by the swell and slope of sea floor.The locations of maximum wave setup and surge level were close in space during Typhoon Saomai,but they were separated far away during Typhoon Chan-hom.Then the effect of wave-current-surge interactions on waves during the Typhoon Chan-hom is studied.The modeling results reveal the effect of storm surge on typhoon waves is mainly through storm current and water level.The results show distinguishable differences in significant wave height under different experiments.The water level causes the maximum differences of up to a 1.45 m significant wave height,the significant wave height of wind-wave is mainly influenced by the water level change in nearshore shallow water regions(depth smaller than 40 m).The storm current causes the maximum differences of up to a 1.17 m significant wave height,and the wave-current interaction dominate in far offshore deep seas.The decrease of SWH mainly attributed to the phase speed changes by the significant wave height.The significant wave height strongly depends on the relative speed of the typhoon translation speed and the group speed of dominant waves.Then a fine risk level assessment system of overtopping seawall in Fujian coast,South China,is established,based on unstructured triangular meshes and high-resolution geographic data(location and elevation of seawall,shoreline and water depth).The system can accurately depicts the complex terrain along Fujian coast in resolution of up to 50 m in the nearshore grid.Using the simulated water level and wave parameters,a formula of wave runup is used to calculate the wave runup in front of each seawall.According to the comparison of the sum of total water level and wave runup and seawall elevation,the risk level of overtopping seawall is divided into five levels.We made a hindcast on the process of super Typhoon Usagi in 2013,the risk level of overtopping seawall is basically the same as that of post-disaster investigation.The results are accurate and shows that the risk assessment criteria and methods for overtopping seawall adopted in this study are feasible.On this basis,four different typhoon intensity scales were designed,206 seawalls along Fujian coast have been assessed for overtopping seawall risk to investigate the impact of typhoon intensity on the risk of overtopping seawall.The results show that the impact of wave runup on the risk of overtopping seawall is higher than that of pure storm surge.The increase of storm surge is small with the enhance of typhoon intensity,and has small impact on the risk of overtopping seawall.The wave runup is generally high along the coast of Fujian Province,with the enhance of typhoon intensity,the wave runup will significantly increase the risk level of overtopping seawall,and attention should be paid to the disaster of seawall breaking caused by the shock of typhoon waves on the seawall.Finally,the numerical simulation study of the development and evolution of storm surge inundation in the southwestern Hangzhou Bay region is carried out.The storm surge inundation in the coastal area was simulated for several idealized control experiments,including different wave effects(wave-enhanced wind stress,wave-enhanced bottom stress,and wave radiation stress).Dike overflowing cases with different dike heights and dike breaking cases with different dike breach lengths were considered in the simulation.The results highlight the necessity of incorporating wave effects in the accurate simulation of storm surge inundation.Dike height significantly influences the magnitude and phase of the maximum inundation area in the dike overflowing cases,and dike breach length is an important factor impacting the magnitude of the maximum inundation area in the dike breaking cases.This study may serve as a useful reference for accurate coastal inundation simulation and risk assessment.