Simulating Of The Effect Of Urban Deep Tunnel Drainage System In Waterlogging And Pollution Control

Climate change,population growth and urbanization have significantly impacted the processes of urban hydrology.Recently,urban waterlogging occurs frequently and the problem of initial runoff pollution gets worse,which has seriously affected the sustainable development of cities and the health of ecological environment.The deep tunnel drainage system is one of the important engineering measures for urban waterlogging and pollution control.The advantages of it are low-impact construction and effective regulation of urban runoff,which could assist to overcome the difficulties of the transformation of shallow pipe-network in high density built-up areas and play an active role in relieving urban waterlogging and controlling initial runoff pollution.Therefore,this study takes Y-shape deep tunnel drainage system in Chengdu as an example.Based on the SWMM model,it proposes a set of simulation methods of urban deep tunnel drainage system.Besides,a method for determining the parameters of the sub-catchments is drawn as well.Moreover,it also constructs a hydro-hydrodynamic model and simulates various scenarios including the control of waterlogging and initial runoff pollution.The main contents and innovation point of this study are shown as follows:(1)A method for determining the parameters of the sub-catchment area in the complex urban underlying surface is proposed to accurately obtain the impermeability rate of underlying surface and the proportion of different types of land use in the modeling of urban stormwater system.(2)A set of effect evaluation methods for the urban deep tunnel drainage system based on the hydro-hydrodynamic model is proposed to provide key support for quantitative evaluation of the role of deep tunnel drainage system.(3)Based on the SWM M model,the coupling simulation between the shallow pipe network and the deep tunnel drainage system is approached,and the control rules are applied to generalize the shaft gate to simulate different working conditions of the deep tunnel drainage system.In the aspect of application research,it simulates the effect of the urban deep tunnel drainage system in preventing waterlogging and controlling initial runoff pollution:(1)It analyzes the effect of the Y-shape deep tunnel drainage system during the process of flood control and drainage.The results show that the reduction rate of overflow points and overflow rate decreased by approximately 17%with increasing rainfall return period.Also,with the postponement of peak occurrence,the reduction rate of overflow point and overflow rate decreased by about 6%and 4%,respectively.It shows that the effect of eliminating urban waterlogging by the deep tunnel drainage system is weakened with the increase of rainfall return period and the delay of peak occurrence,and it is more sensitive to the changes of rainfall intensity.(2)It analyzes the effect of the Y-shape deep tunnel drainage system during the process of controlling the initial runoff pollution.It shows that the system can effectively cut down the pollutants in the river from the source and mitigate the pollution caused by the direct discharge of surface runoff.Taking the rainfall event with a return period of 2 years as an example,the reduction rate of TSS,COD,TN and TP were about 70%,51%,37%and 46%This study improves the simulation-evaluation method of deep tunnel drainage system,and promotes the method of extracting the parameters from urban stormwater modeling.The results of this study could provide theoretical and technical support for the planning and construction effect evaluation of deep tunnel drainage system.