Study on the calamity and counter-measure of the super typhoon storm surge along the Zhejiang coastal area

Due to the global warming and variation of atmospheric circulation,the number of typhoon landing or affecting the Zhejiang coast has increased in recent years.The intensity,air pressure,wind velocity and local storm rainfall of the typhoon continually shatter the historic records.The typhoon 9711# and 9417# came up against astronomical spring tide,which resulted in significant disaster to Zhejiang coastal area in 1990s.After entering 21st century,four strong typhoons of 0414#,0509#,0515# and 0608# attacked the area,which brought about fateful disaster and fearful losses.The analysis of the historic data of typhoon in Zhejiang coastal area shows that the number of typhoon landing or affecting Zhejiang has a trend to increase.The historic maximum tidal levels at all the tidal stations of the province were caused by storm surge and most of them by the storm surge of typhoon 9711# and 9417#.During storm surge the tidal levels observed at coastal area consists of astronomic tide and water piling up by the typhoon.A nonlinear numeric model coupling tide and surge was used to study the phenomena.Base on the calibration of six storm surges of typhoon 5612#,9417#,9711#,0414#,0509# and 0608#,the parameters of typhoon 5612#,the strongest one that attacked our country since 1949,were taken as the base and five typhoon paths,that is,the north(Chuanshan),the mid north(Shipu),the mid(Jiaojiang),the mid south(Kanmen) and the south(Pipamen) of Zhejiang were selected to calculate the potential high water level when typhoon landed at different site in Zhejiang coastal area.Possibilities of overtopping or even levee break are analyzed by comparison of the high water levels calculated with the model and the elevation of the sea wall.And the inundation risk level is also studied for super typhoon landing at different sites of the Zhejiang coastal area during astronomical spring tide through seawall destruction mechanism analysis.Base on the above analyses and the actual conditions of Zhejiang coast area,engineering and non-engineering measures are proposed for protection against super typhoon storm surge.