| In recent years,with the rapid development of climate change and urbanization,urban flooding has been frequent in China.Extreme rainfall events and massive hardening of urban ground have brought serious challenges to urban drainage engineering,and the optimal layout of urban drainage engineering must be carried out to ensure urban safety.In this paper,Langfang Economic and Technological Development Zone is selected as the study area,and the relationship between municipal rainfall type and hydraulic rainfall type is coordinated.The LHydrwork model is used to build a comprehensive urban watershed drainage model for Langfang Economic and Technological Development Zone to simulate,analyze and study the drainage capacity of the pipe network and the flooding capacity of the river in the development zone.In view of the existing drainage problems in the development zone,we optimize the layout of rainwater pipe network,rainwater pumping stations,river channels,sluice gates and other drainage projects in the study area,compare the inundation depth and inundation ephemeris before and after the optimized layout of drainage projects,and analyze the rationality of drainage projects after the optimized layout.The main research contents are as follows:(1)Effectively linking municipal rainfall patterns and hydraulic rainfall patterns,and calculating the drainage flow of rivers and drains in the study area.In this paper,the Chicago storm water process line method is chosen to calculate the municipal rainfall pattern in the study area,and the contour map method recommended by the relevant design storm water atlas of the development zone is used to calculate the hydraulic rainfall pattern in the study area.Based on the analysis of comparing municipal rainfall pattern and hydraulic rainfall pattern,the method of "large package for small" and "long package for short" is adopted to realize the effective connection between municipal rainfall pattern and hydraulic rainfall pattern.Three methods,namely frequency analysis,empirical formula and other reported reference values,are used to calculate the drainage flow of rivers and drains in the study area and provide data support for the later model construction.(2)Construction and validation of an integrated urban watershed drainage model for Langfang Economic and Technological Development Zone.By comparing flood modeling software,LHydrwork model was selected to model the study area.Based on the design rainfall pattern results,flood flow calculation results,pipe network data,channel cross-sections and DEM data,a 1D pipe network catchment model,a 1D river catchment model and a 2D surface diffuse flow model for the study area were constructed,and the three models were coupled to build a comprehensive urban watershed drainage model for Langfang Economic and Technological Development Zone.The accuracy of the model parameters was proved by comparing the historical record water depth and the simulated water depth.The model was validated by simulating and analyzing the distribution of ponding points under the 2-year rainfall intensity and the 5-year rainfall intensity,which proved that the model could be used for the analysis of the current drainage capacity of Langfang Economic and Technological Development Zone.(3)To simulate and evaluate the drainage capacity of the current pipe network and flooding capacity of the river in Langfang Economic and Technological Development Zone,so as to optimize the layout of drainage projects in Langfang Economic and Technological Development Zone.The water accumulation points with water accumulation time greater than1 h under different recurrence periods from 1 to 5 years are counted separately,and the drainage capacity of each pipe section under the current pipe network and pumping station conditions is analyzed,and the runoff coefficient of the study area is analyzed.Simulation analysis of the river under the 20-year flooding standard was conducted,and three river sections were flooded separately.The main problems that exist in the study area drainage status quo after the study and analysis are: the drainage capacity of the study area stormwater pipe network is low;the imperviousness rate of the study area is high,and the downstream main pipe network is operating under high load;the bank protection capacity of the study area river is insufficient;and the layout of the study area stormwater pumping station is not reasonable.(4)To address the problems of flood control and drainage in the development zone,the layout of drainage projects in Langfang Economic and Technological Development Zone is optimized and the rationality of the optimized layout is analyzed.The model simulates the flooding depth and duration of flooding after the optimization of the layout.8 monitoring points are taken to compare the waterlogging situation before and after the optimization of the layout.By simulating the changes of water depth with time at the eight monitoring points,the changes of water depth with time at each monitoring point before and after the optimized layout are basically the same,which indicates that the optimized layout of the flooding project in the development zone is reasonable and can provide reference for the layout of flooding project in the future. |
