Waterlogging Early Warning Based On Simulation Of Coupled Drainage System Between Surface Runoff And Underground Network

Extreme rainfall events occur more frequently due to the impact of climate change..Urban waterlogging has become one of the critical factors affecting urban safety,livability and sustainable development,and has drawn more and more public attention.After a rainfall event,the surface runoff flows into rivers through the stormwater drainage network.It is of great significance to take surface runoff,underground pipe network,river system,drainage pumping station and sponge facilities as a whole,the systematic simulations and analyses of surface flooding levels and river levels under extreme rainfall events,especially for urban waterlogging early warning,disaster prevention and mitigation measures as well as drainage system planning and design in polder areas where stormwater outlets tend to be submerged.In this research,a two-dimensional urban surface hydrodynamic model,and a onedimensional unpressurized-pressurized alternating flow model of river-pipe network are developed.A coupled 2D-1D hydrodynamic model is then proposed on this basis.The corresponding algorithm is developed and verified through numerical simulations,and the coupling model is applied and evaluated in a real case study.The main work and results are as follows:A two-dimensional urban surface hydrodynamic model has been developed.Taking the2 D shallow water equations obtained by simplifying the Navier-Stocks equation in the water depth dimension as the governing equations,dividing the calculation unit/grid with unstructured arbitrary triangles method,a three-step calculation method is proposed: a)applying a Riemann solver in Roe format to get the numerical solution of the infinitesimal flux of water flow;b)reconstructing the space into a second-order-accurate scheme in MUSCLTVD format;c)applying Runge-Kutta for the second-order discretization on the time dimension.The proposed unsteady hydrodynamic model is programmed with Python and verified through classic numerical simulations(hydraulic jump,constant flow,symmetrical dam breach,Stocker dam breach,urban surface flow field with sponge facilities).Result shows that the proposed model can handle complex calculation boundaries well and avoid numerical oscillations effectively.A one-dimensional unpressurized-pressurized alternating flow model for river-pipe networks has been proposed.The model is developed based on solving the one-dimensional Saint-Venant equations under the Preissmann slit hypothesis,which is capable of simulating the dynamic status of: a)river network as open channel flow;b)underground pipe network as open channel flow,pressure flow or open full flow.A numerical solution framework is proposed by integrating four-point implicit discretization,three-gradation method,and simplified matrix identification.The model is programmed with Python,and verified through classic numerical simulations(constant pressure flow,tree pipe network,ring pipe network,mixed tree-ring river network with drainage pumping stations).Result shows that the proposed model consumes a small amount of storage space in simulating plain polder areas with large amount of nodes,while providing high accuracy and convergence speed.A coupled surface-network-river hydrodynamic model(with detention sponge systems)has been developed and a meshing method is proposed to support the coupling.The model programmed with Python and verified through classic numerical simulations(front coupling,side coupling and vertical coupling).Result shows that the proposed model could simulate the overall hydrodynamic process of the surface-network-river system,while the proposed meshing method as well as coupling method based on broad-crested weir equation are effective and feasible.Finally,the coupled 2D-1D model is applied to a case study in Jiangpu Polder,Kunshan for three historical extreme rainfall events.Result indicates accurate predictions of waterlogging location,area and depth,compared to observed data.The coupled model is also applied for identifying the vulnerable urban areas to waterlogging in the case study area under a 50-year designed storm.