Study On Urban Waterlogging Disaster Risk Assessment And Multi-Objective Optimal Allocation Of Sponge Facilities

Under the dual influence of frequent extreme weather and rapid urbanization,the problem of urban waterlogging disasters has become increasingly prominent.It is a serious threat to people’s life and property safety and socioeconomic development.Waterlogging disaster risk assessment is an important non-en gineering measure for disaster prevention and mitigation,and sponge city construction is an important engineering measure for flood control.It is of great significance to scientifically carry out the risk assessment of waterlogging disasters and conduct in-depth research on the optimization of sponge facilities layout in urban flood control and drainage.This paper takes the Xiaozhai area of Xi’an as the research object.Starting from the formation of waterlogging problem,multi-factor disaster risk assessment is studied;Starting from the governance of waterlogging problem,the problem of multi-objective optimal layout of sponge facilities is studied.The main results and conclusions are as follows:(1)The drainage pipe network and overland flow model in the study area are constructed,and the two are coupled through MIKE FLOOD to complete the construction of the waterloggi ng coupling model.Based on the measured soil data in the study area,the hydrological parameters of the model catchment area were set.Calibration and verification of model parameters were carried out using typical maximum water depth survey method.The relative errors of simulated and measured water depth are all less than 10%.It shows that the model can accurately simulate the urban stormwater process in Xiaozhai region.(2)The risk assessment index system of urban waterlogging disaster based on " HazardVulnerability" is constructed.The scenario simulation method,index system method and GIS method are combined to realize the risk assessment of urban waterlogging disaster considering multiple factors.According to the analysis of the risk zoning map,the overall risk of waterlogging increase significantly with the increase of rainfall return period,and the risk is higher in the northwest than in the southeast of the study area;According to the analysis of vulnerability zoning map,vulnerability risk is higher in areas near the subway entrance and with high economic value of land use.Based on the analysis of comprehensive risk zoning map,it can be concluded that the overall risk of waterlogging disaster is small and mainly low in the low rainfall recurrence period.With the increase of return period,the area of medium-risk area increase most obviously.When the rainfall return period increase from 5a to 50a,the area of low,medium,and high risk areas increased by 2.0 times,15.9 times and 6.2 times,respectively.It can be seen that the medium-risk area is the key prevention area of flood control and drainage.(3)A method of constructing sponge facility layout-effect objective function based on polynomial fitting is proposed.122 kinds of grey facility simulation conditions and 40 kinds of green facility simulation conditions are designed to study the effects of different layout of grey and green facilities on waterlogging reduction and runoff control.The polynomial curve fitting method is used to construct the grey-green facility layout-effect function.It can be seen from the analysis that grey and green facilities have a good regulation effect on waterlogging water reduction and runoff control,but there is a great difference in the effect reflected by different types of facilities and different locations.Among them,the effect of green facilities on waterlogging reduction is inferior to that of grey measures,and the control effect of grey measures is different with different layout positions.As for the constructed gray-green facility layout-effect function,different gray-green facilities all showed a good response relationship between the layout scale and the effect,and the polynomial fitting effect is good,with R2 greater than 0.99.(4)The layout effect function of grey-green facilities constructed by polynomial curve fitting method is taken as the objective function of multi-objective optimization model,and considering the construction cost of different sponge facilities,NSGA-Ⅲ algorithm is used to solve the optimal layout of grey-green combined sponge facilities.Based on the specification standard of sponge construction in the research area,the Pareto frontier solution set is analyzed to explore the optimal sponge layout scheme suitable for the research area.It has been proved that the optimal schemes meet the requirements of waterlogging reduction and runoff control.Compared with the situation without sponge facilities,the runoff control increased from 54%to 85%,and the waterlogging basically subsided.Compared with the unoptimized preliminary design,the cost is saved by 127 million yuan.The risk assessment of the modified scheme shows that the optimized gray-green sponge layout scheme can reduce the waterlogging disaster caused by rainstorm events to a certain extent.