Storm Tide Level And Wave Due To A Super Typhoon And Its Action On Seawall In Coastal Region Of Zhejiang Province

Based on summary of the former research work and the need of research task, systemic review is made of pure storm surge, coupling storm surge, influence of typhoon to storm surge, patterns of wave propagation and typhoon wave, wave runup, wave overtopping discharge and stability of layer covering. The study aims to analyze storm tide water level and typhoon wave due to typical super typhoon, destroying pattern and characters of defending wave of seawalls, in coastal region of Zhejiang province, so as to provide the base of designof coastal engineering and minimization of damage preventing super typhoons.Based on Mike21 and globe astronomical forecasting software (TPXO6), combined withparametric wind and pressure models, the high-resolution numerical model of the coupling between astronomical tide and storm surge is applied in the coastal region of Zhejiang province. The most intense typhoon to land in China since 1949, is taken as the typical super typhoon for studying the storm tide level and storm surge, each landing at a different location along the coast during spring tide. The result shows that the high storm tide level will be 100～300cm under the conditions of typical super typhoons coinciding with the astronomical high tidal level of spring tide when they lands, if the super typhoon lands at low tide,the high storm tide level will generally be lower than historical highest tide level. Influence of tidal type and strength of super typhoon to high tidal level are discussed in detail. The type of storm surge and distribution caused by typical super typhoon landing along different route are analyzed in this study. The difference between storm surge caused by super typhoon and historical highest surge and difference between storm surge caused by super typhoon landing at high tidal level and low tidal level are provided.The constructed numerical model is applied to calculate storm tide current and storm current. On the basis, action of wind on astronomical current, the type of coupling storm current and its difference with pure storm current is analyzed. the result shows that storm-tide current is less than linear imposition of astronomical current with storm current, storm-tide current field has much character of storm current field, storm-tide current flows along coastal line in open sea, which is more important for the study of material transport and abrupt sedimentation of navigation channel.On the base of numerical model of coupling astronomical tide and storm surge, the wave propagation model suitable for nearshore(SWAN) is built to applied in the coastal region of Zhejiang province. The typhoon wave is attained, which caused by typical super typhoon landing on the moment of high tidal level of astronomical tide when it goes along 5 routes. The distribution of wave height and its distribution for typhoon wave are analyzed. Compared with storm tide process, the highest wave occurs on high storm tide level in coastal region at open sea, there is different phase in Hangzhou bay, return period of high storm tidal level is much greater than return period of typhoon wave height.Damage characters of clay-stone seawalls previously built in the coast is analyzed, main reasons of damage is that the determination of crown elevation is irrational and the covering layer is weak. Tank experiments of seawall show that permitted wave overtopping discharge is less than 0.05 m~3/m·s while the leeside slope remains stable on the condition that leeside slope is protected by dry stone and crown is constructed by concrete plate. The design method according to permitted wave overtopping discharge can reduce the crown elevation, which has been adoped in some related regulation. The seawall designed by this method has suffered several strong typhoons and a super typhoon, cover layer remain no damage. Comparison of designed high water level with high storm tidal level, and designed wave element with wave height of typhoon wave which caused by typical super typhoon landing on the moment of high tidal level of astronomical tide while goes along 5 different routes. The status of loss stability of seawalls is analyzed when the seawalls are attacked by tidal level and wave over designed standard. Vertical seawall and slope seawall in the north bank of Hangzhou bay are selected as typical seawalls, the experiments in multi-function sluice reveal that the damage occurs at leeside at first, and then the section is destroyed under the action of storm tide level and typhoon wave, the seawall cannot defend the tidal level.