Study On Safety Measures Of Northern Seawalls In Qiantang River Under The Storm Surges Over Design

The seawall in north bank of Qiantang River is an important protective shield to defense the attacks of storm surges due to typhoons in Hangjiahu Plain, southern Jiang Su and Shang Hai. With the frequently happening of extreme climates, it can not eliminate the possibility of super typhoon hitting the Zhe Jing coastal area. For this reason, it is very important and urgent that researching and coming up with the reasonable engineering measures and non-engineering measures to cope with the disaster induced by storm surges especially the ones over designed standard.This paper takes the typical macro-tidal estuary in China-Qiantang River estuary as an example. First, the front seawall structure is calculated under the condition of existing tide levels and waves results according to the former study. Then the evaluation standard and parameters to analysis the ability of seawalls are put forward and the extreme defense ability has been evaluated systematically. These works are under the basis of the investigation of historical dangerous cases, wave model experiment of seawalls, results of structural calculation. In this paper, submerged losses are worked out, the risk of storm surge disasters are analyzed, different risk areas are graded and the inundated risk map is finished under different grades of storm surges.Contraposing the situations of damages caused by the different grades of typhoon storm surges and engineering technical feasibilities, three projects are chosen to present the studies of engineering strengthening measures according to the proper strengthening principle. These three projects respectively are critical super typhoon, typhoon NO.9711 for north route and the planning standard which is the combination of the high tide level 300a and wave 100a. A more reasonable engineering measure to cope with storm surges over design is confirmed according to the above works. Considering the long implementation cycle and high inputs of engineering measures, the non-engineering measures in risk areas are studied, storm surge manager defense plan, information system of early-warning and decision, system of disaster insurance are raised. From these works a relatively integrated defense and response system of storm surges over design is formed.