| In recent years,with the acceleration of urbanization and the frequent occurrence of global extreme climate,the frequency and intensity of urban rainstorms are increasing.At the same time,with the improvement of urban surface hardening,the lack of drainage infrastructure or poor planning,the increasing extreme precipitation far exceeds the flood control capacity of urban drainage system,which not only causes losses to people’s lives and economy,but also disturbs the normal operation of the city and seriously affects the development of the national economy.Therefore,it is necessary to deeply simulate the disaster process of urban rainstorm,study the drainability of urban drainage network and its influence on rainstorm waterlogging,discuss the existing problems of drainage system and optimize the design.This paper systematically reviews the research progress of Storm Water Management Model(SWMM)at home and abroad,comprehensively expounds the principle and modeling steps of SWMM,and takes the northern part of Huangpu District in Shanghai-Nanjing East Road Central Business District as the empirical area.Simulate the surface runoff,manhole flooding,conduit surcharge and waterlog in different rainstorm return periods,accurately analyze the law of urban waterlogging,and fully consider the actual drainage capacity of pipe network.It is convenient to identify the weak links of pipe network operation and optimize of pipe network by increasing pipe diameter and adding low impact development measures.The main conclusions are as follows:(1)The SWMM parameters were validated by selecting a short-duration rainstorm with 100 year recurrences(August 25,2008).After adjusting the parameters such as roughness coefficient,the maximum infiltration rate,the minimum infiltration rate and the attenuation rate manually for many times,the relative errors of measured and simulated values of monitoring points were controlled within 10%.The simulation results are satisfactory and meet the requirements of calculation precision,which indicates the reliability of the model.(2)The surface runoff simulated by SWMM with different recurrence periods(once every 3,5,10,20,50 and 100 years)was analyzed,including total runoff,infiltration and runoff coefficient.With the increase of rainstorm recurrence period,the surface runoff,infiltration and runoff coefficient continue to increase,but the proportion of infiltration to rainfall decreases gradually.It shows that the sensitivity of infiltration to rainfall intensity decreases with the increase of rainfall intensity.In high recurrence period,infiltration is far less than the total rainfall.A large amount of rainwater enters the urban drainage system,and the burden of pipeline network becomes heavier and heavier,which is prone to rainstorm waterlogging.(3)In this paper,the manholes flooding in the verified area simulated by SWMM during different recurrence periods were studied,including the total number of node flooding,total flood volume and the maximum flood time.The proportion of node flooding has increased by nearly 12 times from 5 years to 100 years.More than 75% of manholes flood volume in each recurrence period is within 100m3.However,with the increase of recurrence period,the proportion of manholes flood volume over 100m3 gradually increases,and the total manholes flood volume has increased by nearly 60 times.The maximum flood time increased from 1.04 h to 2.94 h with the increase of recurrence period,far exceeding the design time of rainstorm for nearly one hour.As the return period increases,the total number of node flooding,total flood volume and the maximum flood time increase significantly,resulting in greater risk of rainstorm waterlogging.(4)The conduit surcharge in the study area in different recurrence periods was discussed,including the number of conduit surcharge and hours capacity limited.Under the 3-year recurrence period,the proportion of conduit surcharge accounts has reached more than 80%.With the increase of recurrence period,the proportion within 60 min of conduit surcharge time decreases gradually,hours capacity limited between 60-120 min increases first and then decreases,and the proportion of load time over 120 min increases gradually,and the maximum surcharge time is controlled at 3.7h to 3.85 h.During the 100-year recurrence period,except for 5% of pipelines not overloaded,94% of the conduit surcharge time exceeds 1h,and the drainage capacity of the pipelines has reached its limit.(5)Coupled SWMM with Arc GIS software,the flooded depth of the study area during different recurrence periods(once every 3,5,10,20,50 and 100 years)was calculated,and the risk level of waterlogging were analyzad.The results show that the flooded depth is less than 0.15 m in three-year and five-year recurrence period,which does not affect the passage of pedestrians and vehicles,and there is no risk of waterlogging.In 10-year return period,the flooded depth begins to reach 0.15-0.3m area,which will not cause vehicle losses and casualties,and it can be considered that there are low-risk areas of waterlogging disasters.Under the recurrence period of 20 years,the flooded depth begins to reach 0.3-0.5m,the smooth passage of vehicles and personal safety is threatened,and there are medium risk areas.During the 50-year and 100-year recurrence period,the flooded depth is greater than 0.5m,traffic congestion and even paralysis,serious threats to personal safety,and high-risk areas of waterlogging,mainly located on Xiamen Road(Guizhou Road-Middle Tibet Road),Yunnan Central Road(Hankou-Fuzhou Road),Yunnan South Road and Ninghai East Road intersection and the northernmost end of the Zhongshan East Road.(6)The effects of increasing pipe diameter and adding low impact development measures on pipe network optimization were investigated.According to the relationship between the slope of the conduit and the slope of the water surface,some conduits are properly adjusted to increase their diameter,so that the piping system can meet the drainage requirements with 5-year return period.With the increase of the recurrence period,the number of node flooding and total flood volume are decreasing,and the proportion of both is decreasing.In addition,the total runoff,runoff coefficient,peak flow,the number of node flooding and total flood volume is reduced by adding LID measures to SWMM.However,as the return period increases,the reduction of these factors is weakening.The results show that the optimization effect of increasing pipe diameter and adding LID measures is better in the low recurrence period,but worse in the high recurrence period.Especially,LID measure has more obvious mitigation effect on rainstorm waterlogging in low recurrence period.When the increasing rate of rainfall is lower than the change rate of surface runoff,the "seepage","backwater","storage" and "water absorption" of LID begin to weaken,and the optimization effect decreases. |
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