Study On Construction Of Low Impact Development Rainwater System For Campus Based On SWMM Model

In order to deal with the increasingly serious problem of urban rainwater,the research and application of Low-Impact Development Rainwater System are deepening.The use of storm runoff model to assist the scientific construction of rainwater system has gradually become an important means.SWMM model,as an open source model with simple operation and wide application range,has attracted extensive attention from scholars and technicians at home and abroad.The study found that the runoff control effect of LID combination was better than that of single facility,but it lacked systematic differentiation method of combination scheme.The scheme optimization is realized by analyzing the characteristics of individual facilities and taking the characteristics of facilities as the target in equal proportion,providing engineering reference for the construction of campus low-impact rainwater system.Taking a university campus as the research area,the research area consists of 134 nodes,18 water outlets and 134 pipe segments.The rainwater system model of low impact development on campus was constructed by using two levels of division,with17 rainwater districts in the first level and 126 sub-catchment areas in the second level.Four typical LID single facilities,vegetative swale,bio-retention cell,green roof and permeable pavement,were selected to compare and analyze the runoff control effects of the four single facilities under different rainfall return periods.In terms of total runoff control,the effect of LID single facilities from high to low is permeable pavement,bio-retention cell,green roof and vegetative swale,and the reduction rate of total runoff is 31.50% ～ 35.60%,28.92% ～ 31.21%,11.23% ～ 15.52% and 7.36% ～ 10.13%,respectively.In terms of runoff peak control,the effects of LID single facilities from high to low are vegetative swale,permeable pavement,bio-retention cell and green roof,and the reduction rates of runoff peak are 31.64% ～ 43.67%,31.14% ～ 31.75%,29.49%～30.28% and 10.24%～10.98%,respectively.In terms of rainwater storage,the effects of LID single facilities from high to low are bio-retention cell,green roof,vegetative swale and permeable pavement,with water storage capacity of 10.30 ～15.07 mm,5.49～5.95 mm,4.17～6.25 mm and 0.81～3.51 mm,respectively.In terms of infiltration performance,the effect of LID single facilities from high to low is permeable pavement,bio-retention cell,green roof and vegetative swale,and the infiltration volume is 39.29 ～ 56.64 mm,28.08 ～ 43.04 mm,26.04 ～ 37.46 mm and25.63～34.41 mm,respectively.The total runoff control effect,peak runoff control effect and regulated storage volume are divided into three schemes,and each scheme allocates LID facilities according to fixed area ratio.The comprehensive analysis shows that the scheme aiming at the effect of total runoff control is the best.Under different return periods,the total runoff reduction rate is 30.43%～38.75%,which is higher than other schemes 6.34%～11.71%;the reduction rate of peak runoff was 34.83%～39.49%,and the best effect was achieved in the return period of 20a;the storage capacity was 6.09mm～12.21 mm,and the effect was the best after a return period of 10a;the infiltration rate is 35.04mm～46.80 mm,which is higher than 2.62mm～4.88 mm of other schemes.Therefore,scheme1 is selected as the construction scheme of campus Low-Impact Development Rainwater System.Taking the 5a of the return period as an example,the stormwater storage of the Low-Impact Development Rainwater System was 9.40 mm higher than that of the single-peak rain type under the double-peak rain type,and the infiltration amount was 8.69 mm higher than that of the single-peak rain type.Taking the rainfall event of 2021.9.16 as an example,the runoff control effect of the existing 3waterlogging points under the Low-Impact Development Rainwater System was explored.The total runoff control rate of the sub-catchment area where the 3waterlogging points were located was increased by 13.26%,32.38% and 17.40%,respectively.The runoff control effect of low impact development rainwater system was obvious,and the rainwater waterlogging phenomenon in the campus could be effectively alleviated.