Simulation Study On The Division Of Urban Complex Subsurface Catchment Area And Its Influence On Runoff Process

Under the current rapid urbanization process,the scale of cities continues to expand,and the rapid growth of population leads to changes in the underlying surface of the city,the increase of impervious surface,the rapid shrinkage of urban green spaces and river networks,and the lag of drainage pipe network construction,resulting in frequent urban waterlogging disasters.Therefore,it is of great significance to grasp the influence of the complex underlying surface of the city on the surface runoff path,accurately divide the sub-catchment area,and accurately simulate the urban rainfall runoff process on this basis to evaluate the risk of waterlogging disaster.Taking Haining City,where urban waterlogging problems are prominent,as an example,this study uses refined land use classification datasets,pipe network data and topographic data to improve the watershed division method suitable for complex underlying surfaces of the city by constructing a high-precision land surface elevation model,and improve the rationality of the catchment area division method.On the basis of analyzing and calculating the parameters of the catchment area,the local pipe network,hydrology and other parameters,the SWMM(Storm Water Management Model)model is established,and through the parameter rate determination and optimization,the model has good applicability to the research area of Haining City.Finally,the results of the division of different catchment areas are verified and evaluated through the measured rainfall data,and the urban runoff process is simulated and analyzed by the surface runoff,pipe network load and nodal overflow change law in the study area by using the rainfall in different recurrence periods,and the formation mechanism and temporal and spatial evolution characteristics of waterlogging are analyzed on this basis,and the waterlogging risk in the study area is comprehensively evaluated.The results of the study showed that:(1)The sub-catchment area division method considering the complex underlying surface of the city reflects the urban surface elevation more accurately,fully considers the influence of pipe network and feature type on surface runoff,and improves the accuracy of catchment area division.As an important input parameter of the SWMM model,the catchment area division method considering the complex underlying surface of the city is 21.7% and 16.1% higher than the catchment area division method based on drainage pipe network,which improves the accuracy of the model results.(2)By using the calibration method of rainfall runoff model based on runoff coefficient for eight parameters such as manning coefficient and maximum permeability in the impervious area in the SWMM model,the coefficients of variation of the simulation results obtained by calibrating the parameters under rainfall in different recurrence periods were 0.88%,2.20% and 6.99%,respectively,all less than10%,indicating that the calibration parameter set better reflected the actual situation of the study area and had high stability,which was suitable for subsequent SWMM model simulation research.(3)The load and nodal overflow of the pipe network in the study area were simulated by the rainfall of the 1a,5a,10 a and 30 a design return periods,and the overload ratio of the pipe section increased from 21.7% to 43.7%,and the proportion of nodal overflow increased from 4.9% to 21.4% under the rainfall of the four recurrence periods.1a During the reproduction period,the main road pipe sections in the central urban area were overloaded to varying degrees.(4)The regional waterlogging risk assessment was carried out in the study area based on the overflow duration and water depth,and under the design rainfall of P=30a,the area of low-risk,medium-risk and high-risk areas in the study area accounted for13.6%,63.7% and 22.7%,respectively,and the high-risk areas were mainly distributed at the intersection of Haining Avenue and Xishan Road,the old town near Longxing Port and part of the southern Luotang River.In this study,according to the runoff characteristics of the complex underlying surface of the city,the existing waterfall area division method is improved,and on this basis,the simulation analysis of surface runoff reveals the law of urban runoff process under rainfall in different return periods,which provides a basis for urban flood-prone area prediction,pipe network design and renovation,and waterlogging emergency plan.