Study On System Resilience Assessment Method Based On A ’Do-nothing’ Benchmark Under Different Layout Scenarios Of Stormwater Storage Tanks

With the aggravation of climate change and the rapid expansion of cities,extreme rainfall occurs frequently around the world.Urban flooding has become a common issue faced by many countries,which restricts the economic and social development of cities to a large extent.Resilience refers to the ability of a system to withstand,absorb,adapt and recover from disasters in a timely and effective manner.Taking resilience into account in the design of urban drainage system is a relatively new design concept and also a future direction.In order to deal with the threat of flooding,it is of great significance to evaluate the resilience of urban drainage system in the planning and design stage.Stormwater storage tank is an important intervention measure for urban flooding control,which can improve regional drainage standards and flooding mitigation capacity.However,different spatial layout of stormwater storage tanks will have different effects on the resilience of a drainage system.In some cases,setting storage tanks in the drainage system reduce the resilience of the system.Aiming at this phenomenon,on the basis of the research literature review,this study carried out the research on resilience assessment methodology and changes in system resilience under different layout scenarios of storage tanks,and explore the reasons for the decrease in system resilience,based on stormwater management model(SWMM)and MATLAB,using model simulation,case analysis and other research methods.The main results and conclusions are as follows:(1)A new system resilience assessment methodology based on a ‘do-nothing’benchmark is proposed,which is also called the baseline method.The baseline method selects the number of flooded nodes in the system without any intervention as a benchmark to calculate the average flood duration and resilience,eliminating the impact of the different number of flooded nodes on the system’s resilience assessment due to the lack of comparison benchmarks under different layout scenarios of storage tanks.(2)Compared with the traditional method,the baseline method is more reasonable.Using the traditional method and baseline method to simulate and analyze the system resilience of a drainage area in Chizhou City(i.e.Chizhou case),the results show that,in most cases,the resilience of the system will be reduced by adding storage tanks in the system using the traditional method,while the system resilience will be increased by using the baseline method.Assuming that the acceptable level of system resilience is 0.7,the layout schemes higher than this level in the traditional method only account for 41.4%,and all the layout schemes in the baseline method are higher than this level.(3)In order to verify the reliability of the baseline method,the baseline method and the traditional method were used to study the resilience of a drainage system in Beijing(i.e.Beijing case).The results show that with the increase in the number of storage tanks,system resilience under the two methods is on the rise,and the resilience obtained by the baseline method may be lower than the resilience under the traditional method.This is because the number of flooded nodes in the system may be increased when storage tanks are not set up properly.At this time,the system resilience calculated by the traditional method will be larger.Although the resilience obtained by the baseline method is smaller,it is closer to the real resilience of the system.(4)Under the baseline method,the overall trend of system resilience affected by the layout of stormwater storage tanks is that,the flooding is somewhat alleviated and system resilience increases as the number of storage tanks increases.This method can be used to determine the optimal layout of rainwater storage tanks for a given system resilience level.(5)The optimal layout of stormwater storage tanks varies with assessment methods of system resilience,cases and the number of storage tanks.In the Chizhou case,when the number of storage tanks is less than or equal to 3,the optimal layout schemes under the given resilience conditions obtained by the baseline method and the traditional method are consistent;when the number of storage tanks is more than 3,the optimal layout schemes are different.In the Beijing case,when the number of storage tanks is more than 10,the optimal layout schemes under the resilience conditions obtained by the baseline method and the traditional method are consistent;when the number of stormwater storage tanks is less than or equal to 10,the optimal layout schemes are different.Therefore,the optimal layout of storage tanks and the system resilience enhancing strategies need to be analyzed in specific situations,one system one analysis,and one system one countermeasure.