Research On Urban Storm Flood Management Based On SWMM Model

With the expansion of urbanization in China,the ground gradually covered by impervious materials resulted in increasing runoff on earth surface.Influenced by global warming as well as frequent extreme rainfall,water logging disasters happened a lot due to the limited capacity of aging urban drainage network.At the same time,pollutants on earth surface,after being washed by rains and accumulated were discharged into natural water causing water pollution problems such as deterioration of water quality and river ecosystems.Flood disasters,water pollution and shortage have severely impeded the social and economic sustainable development further.Hence,the practical research on urban storm flood is very important in combining five rainwater processing methods--infiltration,retention,savings,purification and recycling with storm-water drainage,by way of which the water resources in cities can be used properly.In this research,SWMM model was used to simulate the rainwater pipe network system in Luoxi,Quanzhou.First,during the recurrence interval of little rain,the location of the flooding area of the pipeline network system was analyzed,and the overloaded section of pipe as well as overflowing node were also modified to improve the drainage capacity of rainwater system.Secondly,in different recurrence intervals,the influences of the four-type LID facilities on runoff volume and peak,flood volume,overloaded section of pipe,overflowing node and pollutants in rainwater were studies.Finally,effects of the actual construction scheme of sponge cities in these four types were designed and evaluated.The main conclusions of this paper are as follows:(1)The model parameter was adjusted in the method of using model parameter of runoff coefficient and constructing SWMM model based on water pipe network system.This method can reduce the difficulties of model construction and data requirements under certain precision condition.(2)During recurrence interval of small rainfall,the flood and overload problems existing in parts of rainwater pipe network were studies.When P=5a,the segment overload and node overflowing were obvious with flood volume reaching to 7079m3 lasting for 0.33h limited within 0-0.3h.The SWMM model was used to determine the overload pipelines,which were L3,L11,L13,L31,L34,and L37.After adjusting the pipe diameter,the flood discharge decreased by 59%,the duration was shortened by O.lh,the number of overloaded pipes and overflowing nodes decreased,the limited time was controlled within 0.25h,and the drainage capacity of the pipe network was thus improved.(3)The structure,function and range of application of the four LID measures were summarized.During the recurrence period of 8 kinds of rainfall,the permeation pavement,green roof,sunken green land,and rainwater garden were analyzed and compared for the hydrological,water quality(concentrations and total amounts of SS,TP,TN,and COD pollutants),and pipe network torrent optimization effects of the pipe network system.Permeation pavements and rain gardens had significant effects on reducing surface runoff and purifying water.(4)For study,the four-group designing schemes had different functions in cutting down runoff volume and peak,flood volume,and pullutants of pipe network in certain areas.The result of annual controlling rate of runoff volume showed that the fourth group(permeation pavement+green roof+concave green space+rain garden)and third group(permeation pavement+concave green+rainwater garden)had good effects on optimization of hydrology and water quality of the rainwater pipe network system in Luoxi.In the four standard rainfall conditions,the runoff controlling capabilities of the third and fourth groups were basically in line with the requirements of Sponge City Construction Guideline.