Urban Hydrological And Hydrodynamics-Topology Structure Coupling Simulation And Its Application In Flood Disaster Prevention

Flood has become one of the frequently occurring disasters in cities around the world.The high-density built environment and changing natural environment exacerbate the negative impact of flood disasters on cities,making the inundation issue the focus of current research.Many countries have taken engineering and non-engineering measures to deal with flood disasters,but this problem is still aggravating.The development of numerical simulation provides important technical and theoretical support for the related research.However,the existing simulation methods mainly focus on the hydrodynamic process and do not consider an urban drainage system’s topological characteristics and failure mechanism.In urban areas,there is a significant correlation between different infrastructures.As a critical part of urban infrastructure,drainage and road network systems serve different functions,but they are highly related to geographical spatial distribution and system functions.The flow exchange between the two systems during rainfall makes the drainage and road network system form a new coupling network.This coupling network system has the hydraulic and topological characteristics of the two systems.The function failure of the pipe section in the drainage system propagates in the coupling network,resulting in the cascade failure of the coupling system.Therefore,creating a new simulation method to explore the failure mechanism of the drainage system in the coupled network system,analyze the formation and development of floods,and design inundation control measures have greater significance in improving the reliability and resilience of urban infrastructure and the prevention of urban flood disasters.Based on the urban hydrology-hydrodynamic simulation method and the theory of complex networks,this paper constructs the urban hydrological and hydrodynamic-topological structure model,simulates and analyzes the dynamic operating characteristics of sewer networks and the formation of floods under different rainfall patterns,and reveals the failure law of sewer network system.The relationship between the performance of the local pipe and the system is studied,and the critical pipe sections that lead to the drainage network performance significant decline are identified.At the same time,combined with the distribution of critical pipe sections,the upgrading schemes based on Green Infrastructure and Gray Infrastructure are designed,and the effects of different schemes are quantitatively evaluated.The main conclusions are as follows:(1)Combined with SWMM model and complex network theory,the coupling model of drainage network and road network is constructed.The coupling model considers the topology and hydraulic properties of the two systems,and forms a complex network with a new topology.In the process of modeling,an improved sub-catchment division method is proposed.The improved method can improve the accuracy of pipe inflow calculation and reduce the error in the traditional method.By comparing with the actual monitoring data and overflow records,the parameters of the coupling model are calibrated,and the accuracy of the model is verified to ensure the model reliability.Also,combined with the calculation method of the Giant Connected Component in the complex network,the coupling model can identify not only the hydraulic failure of the pipe network system,but also the topological failure of the system.(2)By analyzing the hydraulic and topological failure of components and system in the drainage network,the failure law of the drainage network is revealed.The results show that the hydraulic failure of local pipe sections has a significant and complex impact on the whole performance of the drainage network,and the performance of the whole drainage network depends on some critical pipe sections that are easy to be ignored.When most pipe sections are not overloaded,the overload of the critical pipe sections will lead to the significant decline of system connectivity,resulting in the sudden decline of the performance of the whole drainage network,and this topological failure occurs much earlier than the hydraulic failure of the sewer system.Although the failure of critical pipe sections can significantly reduce the drainage system’s performance,the system’s failure will not continue to deteriorate with the increase of the overloaded pipes.When the connectivity of the whole pipe network is destroyed,the pipe network system collapses into several sub-networks.With the increase of overloaded pipes,the sub-networks will be decomposed into several smaller networks.However,when the number of sub-networks reaches a certain threshold,even if the overloaded pipe increases,the number of sub-networks will not increase.(3)From simulating the response of drainage networks under different rainfall patterns,the results show that different rainfall have different effects on the operation of the sewer network.Short duration and high-intensity rainfall has a great impact on the pipe network system,mainly due to the serious damage to the connectivity of the sewer network.Short-duration rainfall causes a large number of pipes to be overloaded rapidly in a short time,resulting in the whole sewer network being directly decomposed into a series of unconnected single pipe sections.In the long-term rainfall,although the functional connectivity of the whole pipe network will also be damaged,the drainage system is divided into several sub-networks,which can ensure the drainage system will not be directly reduced to the minimum,which also explains the main reason why the short-term rainfall has a great impact on the sewer network.Through statistical analysis of the numerical relationship between the number of overloaded pipes,the number of Giant Connected Component,the number of sub-networks,and the inundation ratio,it is shown that for the topology,there is a threshold indicating the limitation of connectivity that can be destroyed.When the number of sub-networks reaches the threshold,it indicates that the pipe network’s connectivity has been reduced to the lowest,and the drainage capacity has also been reduced to the lowest.(4)Based on the coupling model,the identification method of critical components and risk areas is proposed.The critical components play an important role in the topological structure and hydraulic characteristics of the sewer system.Since the physical properties of the critical pipes are similar to the adjacent pipes,it is difficult to be identified.Although the critical pipe segments do not dominate in quantity,they have a significant impact on the system’s function.In addition,the coupling model can identify the microstructure of the Giant Connected Component.From the different microstructures,it can locate the abnormal component in the sewer system and road network system,respectively,to serve different flood control objectives.Different microstructures show that the development and inundation degree of the flood are closely related to the local performance of the drainage system during rainfall.The performance of these different components leads to the difference in ponding degree and distribution.(5)The coupling model provides a new method for the implementing Green Infrastructure and the updating the drainage network system.It is feasible to set flood mitigation measures based on the distribution of critical pipes.By designing and simulating a variety of different integration schemes,the synergy between mitigation measures and the dynamic operation of the drainage network is studied.The results show that the dynamic operation of the drainage network has a significant impact on the flood mitigation measures.The unreasonable layout can not reduce the impact of flood disasters but also cause a waste of resources,increase the burden for the network,and lead to more serious disaster risks.The Green and Gray Infrastructure implemented with the critical pipes can reduce the adverse effects such as runoff and ponding,ensure the reliability and topological stability of the sewer network system,and improve the drainage capacity of the sewer system,so as to realize the comprehensive control of flood disaster risk.Figures,80;Tables,18;References,204.