The Research Of Risk Assessment About Drainage System Of City Waterlogging Based On FTA

In recent years, with the city of excessive development, a large number of natural land and water lake is artificial development and landfill, city underlying surface properties is changed of resulting in increased the proportion of city impervious pavement, the permeable pavement is artificially with concrete, waterproof brick, asphalt paving, the city losts its original storage function. All sorts of problems results frequent waterlogging phenomenon in the city. City waterlogging risk assessment is carried out about this project, risk analysis of city waterlogging of the drainage system actson the system level and the level of local composition level, ability level and the safety performance of the drainage system from the whole understanding of the ability to resist the heavy rainfall drainage system have a full understanding of the city and environment has a clear understanding of knowledge. In order to provide scientific reference for mitigation measures such as city waterlogging, each part of the system states from the local level and identifies the weak links of the system. This paper focuses on the influence of network system of city waterlogging drainage capacity and finds out the corresponding risk factors, establishs a risk evaluation index system to solve the city waterlogging risk value.Taking the evaluation factor into the SWMM software to simulate the waterlogging may occur that checks if it is consistent with the actual verification of waterlogging phenomenon. Selecteing the northwest of Yunnan city as a case, using the SWMM software to simulate the existing drainage system with different rainfall conditions of city waterlogging situation.Selecting fault tree as rating model construction of waterlogging risk assessment framework, the establishment consists the top event, structural evaluation of intermediate events and bottom events from the design, management and maintenance that 12 indicators were selected, as the water rate, terrain slope, greening rate, discharge rate, drainage facilities, pipe diameter, pipe gradient, density pipe roughness coefficient and inspection wells rich space, pipeline section, reservoir, water outlet way. By using triangular fuzzy number method and expert scoring method, AHP two methods to determine the weight of indicators, the final selection of the analytic hierarchy process as the final method of city waterlogging risk evaluation index weight. In the literature under the premise of the index system of the evaluation grade is defined as grade 5 levels carring on the quantitative and qualitative analysis of each index. According to the weight accumulation solution, city waterlogging risk value is ranged from [0.6,1] that the concept of risk assessment is divided into 5 grades:low risk, medium risk, high risk, high risk, high risk. The lower the value, the higher the risk, the lower the security. The average water depth to determine the simulated Road Waterlogging degree in different areas flooded part index into SWMM software verifying the city waterlogging risk evaluation system.The city of Northwest Yunnan area is divided into six areas as a case to verify the evaluation system of city waterlogging risk and at the same time part index into SWMM software in different return periods under the scenario simulation to verify the possibility of waterlogging occurred. In waterlogging risk assessment, the catchment area four waterlogging risk value is 0.7493 of the best, the most serious waterlogging in the catchment area are catchment two, the risk value is 0.7099. Simulation of serious overflow point is as same as the status of the current situation.Selecteing such as diameter, greening rate, inspection wells rich space as a slow improvement measures to reduces city waterlogging degree, and calculating the corresponding waterlogging risk value with simulating by SWMM software. Effect comparison of three kinds of measures for improving the degree of waterlogging in different rainfall:increase diameter, greening rate of waterlogging control effect, reducing the overflow of 23.8% nodes,33.13% overflow.10A and more than the return period of rainfall, the effect is relatively weak. Check wells rich space leads to conventional rainfall waterlogging have a role in mitigation, but unconventional rainfall does not play a role. Overall, three improvements in conventional rainfall could effectively reduce the city waterlogging degree but is not obvious for non conventional rainfall.Through the pre drainage pipeline flow solution produces unconventional rainfall conditions. In the overflow of the inspection wells along the road to set the drainage pipeline, the size of the pipeline inspection wells in the flow and the width of the road width of the integrated setting, the cross-section of the use of DN600-DN1000. By increasing the drainage pipe, the catchment area of two waterlogging risk to enhance the value from the value to 0.8081. Useing of SWMM simulation:to design rainfall return P=10a rainfall control effect, rate of flow decreased from 4.769×103m3 to 1.253×103m3 fand that decrease the ratio of 73.72%, the overflow point decreased by 10, the road average water depth is 0.21m, waterlogging risk rating for stroke risk. Response to the design of rainfall to reproduce the P=20a of rainfall, the average water depth of the road is still more than 0.30m.