Study On Waterlogging Disaster Mechanism And Numerical Simulation Of Disaster Mitigation Measures In Coastal Cities

Influenced by increasing frequency of extreme rainfall,storm surge and accelerating urbanization process,waterlogging disasters in coastal cities show the characteristics of complexity,diversity,linkage and magnification.In order to deal with waterlogging disasters scientifically and effectively,it is necessary to identify the causes of waterlogging accurately and put forward reasonable and feasible waterlogging control schemes.Based on this,this paper constructs an integrated 1D-2D waterlogging simulation model of Haikou city by PCSWMM.The spatial and temporal distribution characteristics of waterlogging and the causes of waterlogging in typical areas are analyzed from multi-dimensional and process perspectives.According to the causes of waterlogging,the multi-type combined regulation measures are implemented in the water-logging area,and the scale effect and disaster reduction effect of the measures under the condition of separate treatment are studied.On this basis,the study of multi-regional cooperative governance with hydraulic and hydraulic linkages was carried out.The main research work and results of this paper are as follows:(1)A 1D-2D waterlogging simulation model for the main urban area of Haikou City is constructed.The model realizes the real-time dynamic simulation of the interaction of river channel,pipeline,ground water and groundwater,and takes into account the double disaster-causing factors of rainfall and tide level.The determinant coefficients,Nash efficiency coefficient NSE and relative error Re of measured and simulated water depth during Typhoon Wilmson are 0.80,0.796 and 0.9% respectively,which meet the accuracy requirements,indicating that the model has good reliability.(2)The characteristics and causes of regional waterlogging are analyzed.The spatio-temporal distribution characteristics of waterlogging in Longkun gutter drainage subsystem during the design recurrence period and the correlation between the degree of waterlogging and the regional characteristic parameters are analyzed.The causes of waterlogging in typical upstream and downstream waterlogging areas are analyzed from the aspects of pipeline network,river drainage and overflow process,the interaction process between underground and surface.The results show that the process of waterlogging is affected by rainfall,tide level and its process.There are mainly two serious waterlogging areas in the region.The degree of waterlogging is greatly affected by the average elevation and slope of the region.The causes of serious waterlogging areas in upstream and downstream include inadequate drainage capacity of rivers and pipelines,low-lying and flat terrain.Besides,causes in the downstream areas include excessive inflow from upstream,jacking effect of tide to river,jacking and backfilling effect of river to pipeline.(3)The framework of urban waterlogging control is put forward.According to the causes of regional waterlogging,multi-type combination measures are selected to treat the upstream and downstream areas separately,and the calculation method of the optimum opening and closing time of pumping stations in upstream areas is put forward.The scale effect and disaster reduction effect after the implementation of various measures are studied,and the optimum layout scheme under the condition of separate treatment of upstream and downstream areas is selected according to the cost comparison.Considering the close relationship between the upstream and downstream watershed,30 groups of upstream and downstream combined harnessing scenarios(5 upstream harnessing schemes and 6 downstream harnessing schemes)were set up to reflect the different upstream inflow processes and the different drainage capacity of the downstream area.In the case of fixed upstream inflow and fixed downstream drainage capacity,the scale and cost of drainage facilities vary with the regulation scheme,and the optimal layout scheme under the fixed scenario is determined.Finally,the optimal overall layout scheme is selected,which saves 153 million yuan compared with the single optimal combination scenario.Therefore,the overall layout strategy proposed in this paper has strong economic benefits and can provide ideas for the construction and transformation of other urban drainage systems.