Assessment Of Urban Drainage Capacity And Analysis Of LID Reconstruction Based On SWMM

The increasingly serious and unpredictable urban flooding problem has become one of the major "urban diseases" in the whole society.The traditional idea of grey management has gradually lost its desired effects due to the accelerating process of times,and the concept of low-impact development is undoubtedlya prescription for this headache "urban disease".Numerous successful practices at home and abroad have also demonstrated the unique advantages of low-impact development technologies.`In my paper,the flooding-prone area in Changsha city is taken as the study case.SWMM model was used to model the study area,the sensitivity of the uncertainty parameters in the SWMM model was then ananlyzed the parameters N-imperv,Max.infil.Rate Min.infil.Rate and Decay constant with high sensitivity were taken as reference values according to the typical values in the relevant literatures.Liu xingbo's comprehensive runoff coefficient method was used to verify the study area.Short-term rainfall with a return period of 1 to 5 years and long-term rainfall with a return period of 10 to 50 years were input into the model respectively,then we will evaluate the drainage capacity and flood control and drainage capacity of the research drainage network.According to the results of the model,the changes of runoff amount,discharge amount,runoff coefficient,infiltration amount,pipeline overload and node overflow are obtained,We can evaluate the current drainage and flooding capacity of the study area,then find out the reason of flooding and draw out the necessity of development and reconstruction with low impact in the research area.The common LID measures are selected based on the underlying surface,space and site requirements and other special requirements.Finally,six LID facilities including green garden will be taken as the construction objects of this research area.The underlying surface of the sub-catchment zone is relatively complex,in this study,five LID schemes are proposed for the criteria that multiple LID measures work together in the study area.The flood control and drainage effects of the scheme are evaluated with the following two control objectives guaranteed:(1.Flood control and drainage standards in the study area will be raised to a level of 50 years;2.Runoff coefficient of rainwater discharge in the study area should not be greater than 0.5).According to the simulation results,all the five proposed LID schemes meet the control objectives,The sensitivity parameters including N-imperv,Max.Infil.Rate,Min.Infil.Rate and Decay constant were perturbed with the error range of 5%,the flood control and drainage effects of each scheme are investigated in the worst case in order to further verify the rationality of LID scheme design.The results show that when the above sensitive parameters are disturbed within a reasonable error range,the model runoff amount and the runoff peak have obvious numerical fluctuation.However,each scheme can still meet the flood control and drainage requirements of the study areaThese five LID schemes are comprehensively compared from three aspects of drainage efficiency,cost efficiency and social efficiency,The judgment matrix is established by AHP,Finally,the effect analysis is carried out to optimize the evaluation of each program.