Risk Assessment Of Storm Surge Disaster

In recent years,the coastal areas of China have been gradually seriously affected by storm surge disasters,resulting in an upward trend in economic losses.Qidong City is located on the north side of the Yangtze River estuary,adjacent to the Yellow Sea on both northeast sides,separated by the Yangtze River on the south,and bordered by Chongming Island,surrounded by water on three sides.Relying on marine development,the city is more vulnerable to storm surge disasters.Therefore,carrying out risk assessment zoning with Qidong City as the research object can continuously improve the accuracy of storm surge warning in Qidong City,improve the ability to prevent storm surge disasters,prevent and reduce economic losses and human casualties caused by storm surge disasters,and also can better develop the marine economy and optimize the marine industrial structure.In this paper,the numerical model of storm surge and wave coupling based on ADCIRC+SWAN is adopted.The grid covers the entire East China Sea,and the blocking effect of coastal protection projects on the sea water is considered.The sea wall elevation is added to the grid,and the grid near Qidong City is locally encrypted.The grid resolution in the coastal area reaches up to 30 m.When simulating the inundation range and depth of storm surge,some areas on the land of Qidong City and adjacent counties and cities in Qidong were expanded to reflect the inundation process of storm surge floodplain.The verification of astronomical tides at Lusi Station and Yangkou Port for 30 days without significant weather processes was conducted.The average errors of the two stations were 0.16 m and 0.14 m,respectively,and the simulation errors were within a reasonable range.Five historical typhoon cases,such as Typhoon 7708,8211,8406,1109,and 1818,were selected to verify the accuracy of the maximum tide level and maximum water increase of the storm surge model.The statistical results of the errors between the simulated and measured values showed that the average relative errors were7.22% and 7.47%,respectively.The model had good accuracy and could better reflect the changes in the tide level and water increase in the sea area near Qidong City during the typhoon process,It is possible to better conduct inundation risk analysis and risk zoning analysis.Select the 7708 typhoon path that has the most severe impact on Qidong as the basic typhoon path that is most conducive to water increase simulation in Qidong City,and determine the maximum wind speed and center maximum wind speed radius of the typhoon;Translate the path of Typhoon 7708 to the sea area near Qidong City,and translate it to both sides with a radius of 0.25 times the maximum wind speed,forming15 translation paths,with two of the most unfavorable paths selected;Using the Gumbel function to construct different return periods,five strong typhoons,including 965 h Pa,955 h Pa,945 h Pa,935 h Pa,and 925 h Pa,were constructed;At the same time,915 h Pa probable maximum typhoons with 112.5 ° and 157.5 ° angles are also constructed as a hazard assessment typhoon dataset.During the simulation process,it is necessary to consider the impact of astronomical high tide levels,superpose the maximum water increase on the astronomical high tide level as much as possible,and simulate historical processes of different paths and intensities to obtain the maximum possible submergence range and submergence depth in different cases.According to the classification of the submergence depth from high to low,it is classified into Level I to Level IV hazard levels,and the hazard assessment is conducted for the submergence caused by Qidong City.The results show that when the typhoon level reaches 16 or above,it will cause flooding in Qidong,and the area of flooding caused by T15 path is significantly larger than that caused by T1 path.Under T1 path,the area of 16 level typhoon with flooding depth exceeding 1.2 meters is about 1.4 square kilometers,and the area of 18 level typhoon with flooding depth exceeding 1.2 meters is about 19 square kilometers.The area with the highest risk level is mainly distributed in Haifu Town;Under the T15 route,the area with a submerged depth of more than 1.2m for a level 16 typhoon is approximately 21 square kilometers,and the area with a submerged depth of more than1.2m for a level 18 typhoon is approximately 24 square kilometers.The area with the highest risk level is mainly concentrated in Donghai Town.The risk analysis results for two possible maximum typhoons with different incident angles indicate that typhoon landing paths with an angle of 157.5 ° are more likely to cause flooding and have a higher risk level.The vulnerability assessment was conducted based on the secondary classification of land use types and the distribution of important disaster bearing bodies in Qidong City.The research results show that the area of Class I area is 241.99 square kilometers,mainly distributed in various towns and villages under their jurisdiction,as well as port and wharf land,airport land,and mining land;The area of Class II area is 43.55 square kilometers,mainly for some scenic spots and special land in Qidong,as well as road land including railways,highways,rural roads at all levels,etc;Class III area covers an area of 14.62 square kilometers,which is used for hydraulic construction;Level IV area covers an area of 1397.06 square kilometers,mainly distributed in agricultural land,forest land,farmland,saline alkali land,grassland,coastal mudflat and other areas of towns under the jurisdiction of Qidong.Among the various vulnerability levels,the area of Level IV area is the largest,followed by Level I area,and Level III area is the smallest.Taking the village(community)as the basic assessment unit,select the highest risk level within the assessment unit as the risk level of the assessment unit;The vulnerability assessment needs to be determined based on the area ratio of the secondary land use type patches within the assessment unit.The level with the largest area within the assessment unit is determined as the vulnerability level of the assessment unit,and the risk calculation of the assessment unit is performed based on the risk and vulnerability of the assessment unit.The results show that the area of Level II risk area is 60.14 square kilometers,mainly distributed in the center of Qidong urban area.This area is a population gathering area such as schools and hospitals,with a high vulnerability level;The area of Level III risk area is 141.54 square kilometers,mainly distributed on both banks of the Yangtze River and the southeast coastal area of Qidong City.These two areas have a high risk level due to the large submergence depth;The area of Level IV risk area is 642.55 square kilometers;The area of Level V risk area is272.97 square kilometers.