流量折减系数对雨水系统设计标准的影响

Impact of Attenuation Coefficient on Urban Storm Sewer System Desining

我国室外排水设计规范规定采用折减系数计算雨水排水设计流量,造成了设计标准和抗灾能力与国外的类似工程相比偏低.在适当假设的基础上,推求出折减系数为1和2时重现期关系的数学表达式,根据实例分析,当折减系数为1时设计重现期为1年不同时刻的设计流量相当于折减系数为2时重现期1.531～4.028年的标准;当折减系数为2时设计重现期为1年的设计流量仅相当于折减系数为1时的重现期0.690～0.393年标准.由于引入折减系数已经造成雨水排水系统设计标准实质性降低,使城市区域形成洪涝灾害的设计风险增加.

Based on the Code for Design of Outdoor Wastewater Engineering,calculating storm sewer design flow（Q） with an attenuation coefficient（m） leads to a lower design flow than that of projects abroad,and reduces the capacity for disaster resistance of urban storm sewer system for the same design standard.This manuscript focuses on discussing the impacts of flow attenuation coefficient（m） on storm sewer system design.Based on appropriate assumptions,the mathematical expressions of the relationship between return periods with m=1 and m=2 were deduced,which lays the theoretical foundation for the analysis of the relationship among return periods.According to several examples,it is confirmed that the design flow rates defined by m=1,design return period at one year（P=1） and with same time intervals,could reach the same level as in the case with P=1.531 ～4.028 years when m=2 is taken.Reversely,when m=2 and P=1 year,the design flows are approximately equivalent to the values in situations with m=1 and P=0.69 ～0.393 years.In conclusion,the research suggests that the use of an attenuation coefficient would result in substantial reduction in storm sewer system design criteria and consequently increase the risk of waterlogging in urban regions in China.