High Conservation Hydro-hydrodynamic Coupling Simulation Method For Urban Stormwater Process

As the urbanization process continues to accelerate,it has an impact on the main areas and the surrounding natural and ecological systems.The changes in the urban hydrological process have gradually increased the threat of urban rainstorm disasters.As an important method for assessing and preventing urban rainstorm disasters,numerical models can provide important technical support for flood control and drainage.In this paper,based on the advantages and disadvantages of both hydrology method and hydrodynamic calculation,i.e.the hydrology method is computationally fast but the physical quantity is partly missing,and the hydrodynamic calculation is time-consuming but the physical process description is detailed,combining the advantages of the hydrological model and the hydrodynamic model.A new set of surface hydrology-hydrodynamic model is constructed,that is,a non-linear reservoir method is used to simulate the surface confluence process.When overflow of the rainwater from the rainwater node of the pipe network system occurs,two-dimensional shallow water will be used on the surface.The equation is a hydrodynamic simulation process in order to quantify the detailed description of the hydraulic parameters of each grid on the surface of the surface when the overflow flood occurs,the depth of the water,especially the velocity vector.It is helpful for the later flood risk management and the city disaster prevention and reduction.The confluence layer adopts hydrological method.Rainfall obtains net rain depth by deducting infiltration and water storage in depressions.Manning formula is used to calculate the confluence process.The goal of surface confluence is the rainwater well.When the rainfall is small or the rainfall time is short,the rainfall is continuous The confluence enters the pipe network system.When the pipe network system reaches saturation,backfilling occurs,and the water in the rainwater well overflows to the surface backfilling layer.The backfilling layer is calculated by the hydrodynamic method,and the terrain is divided into grids,which can accurately reflect the water depth and flow velocity of each grid.For the one-dimensional pipeline network hydrodynamic module,this paper mainly made two significant improvements,one is the updating calculation method of the pipe wetted-area,and the other is the method of solving the water depth by area.The former used in the previous method is to add the water increment into the water depth increment during the time step.The improved method is closer to the essence,and the total water volume of the pipe is calculated by directly accumulating the water volume during the time step.Then,the length of the pipeline is used to convert the water volume into the water depth of the pipe.This method effectively guarantees the conservation of water volume in the calculation process of the system and has a crucial impact on the improvement of simulation accuracy.The second improvement is based on the fact that the theoretical analytical solution of solving the water depth through the cross-sectional area contains the trigonometric function,so it is necessary to choose a suitable numerical solution to solve this problem.The commonly used method is to adopt the dichotomy in mathematics.The accuracy of the simulation can be controlled by setting the target value.The disadvantage of this method is that it requires multiple attempts to infinitely approximate the target error to obtain the result,which consumes computing power.This article innovatively proposes a method using the table method for calculation,which is to list the tables corresponding to the wetted-area and the depth relationship in advance,and directly look up the tables where needed in the simulation.For data outside the accuracy,linear and quadratic interpolation are used respectively.The improved method can ensure the accuracy of the calculation.Finally,the improved part above is integrated into the existing urban rain and flood model-GAST model,through a practical example and two ideal examples to verify the model's strict high conservation of water volume.It can be seen that the model in this paper has important application value for guiding flood control and sustainable urban rainwater management.