Rain Flood Simulation Of Sponge City And LID Disaster Reduction Benefit Assessment Based On IFMS

With the change of global climate and the influence of human activities,the frequency of extreme precipitation has increased greatly.Traditional drainage concepts and measures have resulted in the loss of a large amount of rain and flood resources and a certain degree of urban waterlogging.In this context,the national level put forward the construction slogan of "sponge city",to realize the purification,collection and reuse of rainwater,to achieve the purpose of reducing urban waterlogging disasters and rainwater resources.Therefore,the effective evaluation of LID facilities in sponge cities is of great guiding significance for the promotion and construction of sponge cities in the future.In this study,the downtown area of Guyuan was selected as the research object.Based on the collected basic data,the characteristics of precipitation change in Yuanzhou region in the past 60 years were analyzed to obtain the trend change and abrupt change time of precipitation in the interannual and each period of the year.Through the comparative study of a variety of rain and flood calculation models,IFMS Urban calculation platform was selected to construct the rain and flood model of the downtown area of Guyuan City,so as to obtain the water accumulation in the lower Urban area at different rainfall recurrence periods.On this basis,LID facility parameters were added to simulate the improvement of urban waterlogging after the construction of sponge city,and a reasonable disaster loss assessment method was selected to calculate the disaster reduction benefits brought by the construction of sponge city.The main results and conclusions of this study are as follows:(1)Collected precipitation data from 1957 to 2016 in Yuanzhou District,Guyuan City,and made trend analysis and mutation analysis on precipitation data of 60 years.The linear regression method and the m-k trend test method showed that the annual,flood season and summer precipitation all showed a downward trend,while the spring,autumn and winter precipitation showed an upward trend.Except for winter,the trend changes in other periods failed the significance test of 0.05.By using m-k mutation test,cumulative anomaly curve and sliding t test,the abrupt change year of rainfall in each period was comprehensively analyzed.The abrupt change point of annual precipitation was similar to that of flood season and autumn precipitation.The abrupt change occurred in spring,summer and flood season in 1991,and the significant abrupt change occurred in winter precipitation in 1979.(2)The two-dimensional surface and Urban pipe network model of the downtown area of guyuan was constructed based on the IFMS Urban platform,and its coupling was used for valuation calculation.Through two actual rainfall processes and flow processes in 2017 and 2018,the model simulates inundation areas,and compares them with the actual reconnaissance results,so that the model can be calibrated and verified.The results show that the model is reliable and accurate.(3)Through the combination simulation of 24-hour design rainstorm and corresponding flood flow process in 5a,10a,20a and 50a recurrence periods,urban waterlogging conditions in each recurrence period were obtained.Through the comparison of the inundation situation before and after LID facilities construetion,it can be concluded that the reduction effect of LID facilities on the overall inundation area of the city decreases with the increase of rainfall recurrence period,with the maximum reduction rate reaching 13.63%in the 5-year recurrence period and the minimum reduction rate of 11.06%in the 50-year recurrence period.(4)Based on the calculation results of the rain-flood model,the calculation method based on the relationship between flood depth and loss rate was adopted to calculate the economic losses of various major social assets in different rainfall periods before and after LID construction,and then the disaster reduction benefits brought by LID construction were compared.The results show that LID facilities have a better disaster reduction effect for rainfall events with a small recurrence period than for rainfall events with a large recurrence period.