海洋环流与波动重点实验室知识库

 东南沿海地区是我国遭受风暴潮灾害和台风浪灾害最严重的地区之一，风暴潮灾害和台风浪灾害对人民的生命和财产安全构成了极大的威胁，几乎每年都会给我国造成巨大的经济损失和人员伤亡，所以对于风暴潮和台风浪的研究具有重要的现实意义和理论意义，研究风暴潮和台风浪的致灾机理及其对承灾物的作用是防灾减灾工作的必然要求。风暴潮过程存在着多种影响因素，各个因素并不是孤立存在的，它们之间有着非常复杂的相互作用关系，因此对于风暴潮的研究需要将天文潮、风暴潮和台风浪之间错综复杂的相互作用也考虑进来。为了研究台风影响下中国东南沿海的天文潮，风暴潮与台风浪相互作用机理以及其引起的漫堤和漫滩的发展演变过程，本文基于目前国际上广泛使用的ADCIRC （Advanced Circulation Model for Oceanic，Coasts，and Estuaries Waters）有限元二维水动力模式和SWAN （Simulating Waves Near-shore）海浪模式，构建了高分辨率的适用于东南沿海地区的二维数值模式，这个模式综合考虑了风暴潮、天文潮和台风浪三者的实时相互作用。选取“桑美”（0608），“天兔”（1319）和“灿鸿”（1509）三场典型的台风为研究对象，模拟结果与实测数据符合得很好，为本文的数值模拟研究工作打下了良好的基础。

首先研究了东南沿海地区两次不同路径的强台风过程：台风“桑美”（直接登陆）和台风“灿鸿”（转向路径）影响下的风暴潮增水和波浪增水的时空特征。模拟结果表明，不同台风路径下风暴潮增水的空间分布有明显的差异。最大风暴潮增水出现在台风“桑美”路径的右侧和台风“灿鸿”路径的左侧，这种差异主要是向岸风将海水向岸堆积以及岸线约束作用的结果。在这两种路径下，台风路径左侧近岸海域都观测到了显著的风暴潮增水，这主要是因为风暴潮增水以陆架波的形式沿着大陆架传播造成的。由于较强的向岸风强迫的堆积效应，台风“桑美”类型的路径更有可能引起沿海地区极端的风暴潮增水。最大波浪增水受破波带内涌浪的传播方向和海底坡度的控制。台风“桑美”期间，最大风暴潮增水的位置和最大波浪增水的位置在空间上接近，但在台风“灿鸿”期间，两者位置却相距甚远。

其次研究了台风“灿鸿”期间波流相互作用对台风浪的影响，风暴潮对于台风浪的作用主要通过水位和风暴潮流场两种方式，在不同的条件下有效波高存在显著的差异。模拟结果表明水位导致有效波高的变化最大可达1.45m，近岸浅水区（水深小于40m）的有效波高主要受水位变化的影响。风暴潮流导致的有效波高变化最大可达1.17m，波流相互作用主要在在远海区域。有效波高的减小主要是由于波流相互作用引起的相速度变化。波流相互作用的强弱与台风移动速度和台风浪群速度的相对大小密切相关。

然后又基于高分辨率地理数据(海堤位置和高程、岸线和水深等)构建了福建沿海精细化漫堤风险等级评估系统，这个系统在近岸的计算网格分辨率最高能够达到100m，可以实现精确描述福建沿海地区复杂岸线和地形的效果。利用模拟的水位与海浪参数，采用波浪爬高公式计算得到各海堤堤前波浪爬高。按照总水位与波浪爬高之和与海堤高程的对比，将漫堤风险分为五个等级。对2013年的超强台风“天兔”过程引起的风暴潮漫堤过程进行后报验证，结果表明，该系统计算的漫堤情况与灾后调查的漫堤实况基本一致，结果准确，说明本研究中采用的漫堤风险评估标准和方法是可行的。在此基础上，设计了4种不同的台风强度等级，对福建沿海206条海堤进行了漫堤风险等级评估，探究台风强度对漫堤风险的影响。结果表明：波浪爬高对漫堤风险的影响高于单纯的风暴潮增水；台风强度增强时，所产生的风暴潮增量较小，因此可以认为风暴潮增水对于漫堤的风险影响较小；福建沿海波浪爬高普遍较高，随着台风强度的增强，波浪爬高会显著增加漫堤的风险等级，且应重视台风浪对海堤造成的冲击所导致的溃堤灾害。

最后针对杭州湾南部地区进行了风暴潮漫滩发展和演变过程的数值模拟研究。通过几组理想化的实验对沿海地区的风暴潮漫滩进行了模拟，包括不同物理机制的波浪作用（波致风应力、波致底应力和波致辐射应力）。模拟中考虑了不同海堤高度和在溃堤时不同溃口长度的溢流情况。结果表明，在精确模拟风暴潮漫滩中很有必要充分考虑波浪的作用，海堤高度对漫堤溢流导致的最大淹没面积的范围和发生的时间都有显著影响，溃口长度是影响漫滩最大淹没面积的重要因素。本文的研究成果对实际的防灾减灾工作具有重要的参考价值。 

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 50m 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.