Urban Runoff Simulation And Sponge City Construction Scheme Based On SWMM Model

In recent years,high-speed economization and urbanization led to a rapid increase in the impervious area of urban underlying surface,and the natural hydrologic cycle changed a lot.With frequent heavy rains and poor gray infrastructure,urban flooding is becoming the serious urban disease in China.How to accurately simulate the process of urban surface runoff and mitigate urban flooding is an urgent problem to be solved.In this paper,the simulated rainfall-runoff process and hydrological effect of the study area were assessed based on SWMM(Storm Water Management Model)model,and the traditional drainage pipe network was optimized.With the construction of sponge city in flood control areas based on LID(Low Impact Development)measures,an optimized combination scheme and LID proportion scheme have been proposed.It aims to provide theoretical basis and technical supports for the sponge city construction in the study area.The main research contents and results include:(1)The hydrologic effects of low,medium and high frequency design rainfall in the study area of 2225 ha based on SWMM model are analyzed,and the optimization scheme of drainage network is proposed.Results present that the main problem of traditional drainage pipe network in waterlogging area is that the diameter of the pipeline is small and the node depth is low;The improvement of a few local pipe networks alleviates the waterlogging in the nearby areas but has little effect on the overall runoff process;The optimization of traditional pipe network is limited by topographic factors.The simulation results can provide reference for the improvement of traditional drainage system.(2)Taking flood control area of Sucheng District--270 hectares around the government as an example,hydrologic effects of two SWMM models under different generalization principles were compared,and the influence of different generalization methods on rainfall runoff process was further discussed.Research shows that generalizing a river as an outfall is better for runoff to drain out quickly compared with generalizing a river as a pipeline.The simulated peak flow becomes larger as the number of subcatchments and nodes become smaller.The research work can provide theoretical basis for the establishment of stormwater model.(3)Four LID scenarios(no LID technique,LID technique based on infiltration,LID technique based on water storage,combined LID technique)are set up to analyze hydrological effects under various rainfall conditions,then the optimal scheme is selected,meanwhile,the effect of various LID scenarios on local flooding regions is discussed.It was found that combined LID facilities had the best effect on reducing runoff,LID techniques based on infiltration had better performance in runoff reduction of the overall system than LID techniques based on water storage,but performed worse in local flooding regions.(4)A comprehensive evaluation system based on analytic hierarchy process(AHP)was established to quantify the performance of LID facilities.Economic benefits of LID facilities are taken into account while exerting the hydrological benefits of water infiltration,detention,storage and purification.Research found that increased proportion of the green roof,permeable pavement,and concave greenbelt,with smaller rain gardens can obtain maximum comprehensive benefits.And then optimal proportion of LID facilities was proposed.The results can provide technical support for the selection of LID facility proportion for sponge city construction in Sucheng District.