Research On Calculation Method And Optimization Design Of Urban Storm Sewer System

Urban flooding disasters have occurred in China frequently in recent years.Improper design scale of stormwater pipelines is an important reason for the occurrence of urban flooding.In the meantime,the construction of a certain scale of stormwater storage tank to reduce stormwater peak intensity is also conducive to improving the drainage capacity of urban storm sewer system.Therefore,this paper studies the methods of design flow calculation in stormwater pipeline and effective volume calculation in stormwater storage tank,and optimization design of urban storm sewer system.Firstly,current methods of design flow calculation in stormwater pipeline and effective volume calculation in stormwater storage tank are expounded comprehensively in this paper.Based on calculation formulas of rainfall and runoff,the assumptions and procedures of rational formula method are analyzed.The theoretical method and simplified formulas of effective volume calculation in stormwater storage tank for reducing stormwater peak intensity are introduced.These provide theoretical basis and guidance for the follow-up studies.Secondly,problems existing in area superposition method and flow superposition method are put forward.Flow superposition method is modified.Four kinds of new calculation methods of stormwater design flow with high accuracy and relatively simple process are proposed,which are maximum flow method based on rainfall intensity formula,maximum flow method based on rainfall hydrograph and runoff coefficient method,maximum flow method based on rainfall hydrograph and deduction method,and difference method.A new method of effective volume calculation in stormwater storage tank is proposed.The difference of economic benefit among different setting positions and storage capacity of stormwater storage tank is analyzed.Finally,new calculation methods of stormwater design flow proposed in this paper are programmed by MATLAB.Traditional and new methods are applied in a project example.Results are analyzed and conclusions are drawn as follows: The design flow of each pipe is less than that of area superposition method except for the initial pipe with modified flow superposition method,the average reduction is 18.2% and the maximum reduction ups to 25.4%,so it still needs to be improved.Compared with calculation results of area superposition method,average design flow with maximum flow method based on rainfall intensity formula is increased by 7.9% and the maximum rate of increase is 12.9%,those with maximum flow method based on the rainfall hydrograph and runoff coefficient method 19.2% and 28.6%,those with difference method 22.6% and 33.9%.All the new methods have improved the safety and rationality of design flow calculation in stormwater pipelines,which is of great significance for relieving urban flooding.Calculation results of maximum flow method based on rainfall hydrograph and deduction method can be greatly influenced by the values of model parameters,so it is not recommended in cases when there’s no measured data.Stormwater storage tanks for reducing stormwater peak intensity are set up in different positions in the stormwater pipeline.Calculated effective volume with trial method can reach 1.5 ~ 2 times of that with the recommendation method in the design code.So it can be concluded that the calculation result of trial method is safer and more comprehensive.In the meantime,the total cost of stormwater pipes and storage tank is the lowest when the storage tank is set up in the middle of the stormwater pipeline and has higher peak flow throughput efficiency.It can be used as a reference in engineering practice to improve economic efficiency.