Analysis On Waterlogging Hazards Assessment And Countermeasures In A Coastal City Based On Joint Impact Of Rainstorm And Tide Level

Over the past decade, the increase in frequency and intensity of extreme weather as well as the city urbanization, the "magnifying effect" caused by them in waterlogging disasters is very significant. For coastal cities, its flooding hazards are complex and multidimensional, while as the two major hazards, the joint impact of rainstorm and high tide has a direct influence on the extent of disaster loss in waterlogging disasters. Combined with the location and climate characteristics of coastal cities, this paper analysis the joint impact of rainstorm and tide level and propose the method of flooding hazards assessment coupled with the hazard zonation and probability of the encounter of rainstorm and tide level, the waterlogging disaster countermeasures based on which is also analyzed. The main innovations and specific contents are as follows:First, the method of hazards zonation in waterlogging disasters combined with the joint impact of rainstorm and tide level is put forward. The main city of Haikou is chosen as the research area, characteristic values of rainstorm and tide level are selected to set various combined conditions and the drainage network generalized model and numerical simulation model are used to calculate the submerged areas in different combined conditions. The identified and quantified methods of the degree of hazard are proposed, while, by analyzing the trends of the submerged area, the impact of rainstorm and tide level to different regions are identified and quantified, and thus the risk of hazard are zoned. The result shows that: to the main city of Haikou, the rainstorm is the main hazard of inland areas and high tide level is the main hazard of island regions, while they are both the hazard of other areas.Second, the encounter probability and waterlog prevention risk rate of rainstorm and tide level are analyzed and the standard of waterlog prevention based on two hazards is given. By using the Copula function theory, the joint distribution of rainstorm and tide level in Haikou is constructed, while the co-occurrence rate and the waterlog prevention risk rate based on two hazard are calculated, as well as combination of rainstorm and tide level in the isoline of the same standard of waterlog prevention. The result shows that the encounter probability of heavy rainstorm and high tide level in the main area of Haikou is no more than 0.05%, and 15 year-frequency is the standard of waterlog prevention based on two hazards.Last, based on waterlogging risk assessment of hazard zonation and waterlog prevention standard, waterlogging countermeasures in different areas are proposed: in the area which main hazard is rainstorm, increase the drainage capacity of the pipe network can effectively reduce the degree of waterlogging; while in areas which main hazard is high tide level, the construction of new pumping station in downstream is the effective countermeasure. Based on the standard waterlog prevention of 15-year-frequency, which is the combination of 50-year-frequency rainstorm 382.1mm and 2.46m(8.5-year-frequency) climax design tide level, the scale of the prevention project in main area of Haikou are calculated. The result shows that the countermeasures based on waterlogging risk assessment can cause the decline of submerged area to more than 50%, which proved to effectively deal with waterlogging disasters.