An Investigation on Excessive Storm Surge Impacts on Typical Seawall in Shanghai

摘要

Shanghai is the most important coastal city in eastern China, the mainrnarea that will be influenced by the north pacific tropical cyclones. Tornprotect the city from direct invasion of storm surge, 532 km seawallsrnhave been built along the Changjiang Estuary and Hangzhou Bay area.rnThey are the first promising barrier to Shanghai’s safety from tidalrnflood. Currently, the standard for the dike design in Shanghai is mainlyrnof 200 years return period in tide level combined with force 12 wind,rnwith the world climate change and frequent severe weather, the safetyrnof dike structure under the excessive storm surge, if happens, is thernmost concern by city managers. A 7.0km long dike at the junction ofrnChangjiang Esutary and Hangzhou Bay is chosen to be studied here. Arntyphoon route which may have negative effect on the dike is given afterrnsome numerical simulation. By using storm surge model and typhoongeneraternwave model, tide level before dike, wave force and windrnspeed are calculated under the conditions of severe typhoon (40 m/s atrncenter) and super typhoon (60 m/s at center) with the selected route.rnAccording to the tide level and wave conditions of these excessivernstorm surge in the seawall of Lingang, the feature of armored structure,rnseawall stability and anti-scouring ability of back-slope fromrnovertopping are studied.rnThe result shows, the No. 9711 typhoon route with a 1.5 degree latituderntranslation to the north will be the most harmful to the research arearnand two different typhoon intensities are set on this rout, separately thernintensity equal to No. 9711 as severe typhoon and No. 5612 as superrntyphoon. Under the condition of severe typhoon, the highest tidal levelrncan be 6.74 m (Shanghai Wusong Datum) and the average wave heightrnbe 2.99 m, with the condition of super typhoon separately be 7.68m andrn3.50 m.rnUnder the severe typhoon, the fence board thickness on current seawall,rnsingle wing shape block weight and the overall anti-slipping are allrnsatisfy the stability condition, but the anti overturning stability isrndissatisfy, and wave overtopping exceed to the normal extent, as arnresult the back-slope can easily be scoured.rnUnder the super typhoon, fence board thickness approaches to criticalrnnumber, other indicator such as single block weight, anti-slipping, antioverturningrnare all dissatisfy the stability condition. Also, thernovertopping extremely beyond the normal extent and the back-sloperncan be easily scoured.rnIn this paper, we also present some advanced advice to deal withrnexcessive typhoon.