Research On Calculation Method Of Urban Storm Sewer Design Flow

In recent years,storm sewers in many cities can not deal with waterlogging disasters caused by rainfall,because the former design standards and methods of storm sewer are unable to adapt for urban development.The designs of storm sewer needs to keep pace with the times and constantly improve on the basis of traditional methods.The calculation of design flow is an important process of storm sewer design,and the accuracy of calculation is a guarantee for reasonable construct of storm sewer.Practical engineering is complex and variable,when there are different return periods in the same drainage system,or when inflow mode of storm sewers are different,the traditional storm sewer design flow calculation method has its limitation,the calculation results have deviations with reality.In order to solve these problems,the design flow calculation method of storm sewer is studied deeply in this paper.Firstly,this paper totally expounds traditional design flow calculation methods of storm sewer,and explains various assumptions and design principles in the process of calculation,also analyses the problems of current calculation methods in different return period storm sewer.To obtain the calculation results of main pipe with high design return period,maximum flow method is applied,to obtain the practical flow of branch pipe with low design return period under high return period heavy storm,a trial method is proposed.Secondly,based on practical rainwater collect process,this paper summarizes inflow distribution situation of storm sewer and extends distributed inflow mode,through comparing the characteristics of two inflow modes,a series of methods about distributed inflow are proposed.Finally,this paper uses new methods to check the calculation results with a practical case.Calculation contents include traditional methods and new methods.According to the results,design flow of storm sewer which contains different return period in main pipe in maximum flow method is overall lager than that in pressure coefficient method and in concentrate flow method.The difference between the two types of methods is increased while calculating downstream sewer.Because of considering all examples for flowing states,the results are more accurate and safer.The use of trial method gives the practical outflow of branch pipe,through removing excess rainwater,it also gives the calculated discharge capacity of storm sewer in pressure flow.The design flow calculation result in dispersed inflow method is usually larger than that in traditional area superposition method and smaller than that in traditional flow superposition method.It is closer to flow superposition method and changes by specific engineering conditions.Dispersed inflow method improves the rationality of calculation and makes a supplement in former single method.