北运河上游降雨演变特征对合流制溢流的影响

Effect of Rainfall Evolution Characteristics on Combined Sewer Overflows in the Upstream of North Canal

为明确气候变化背景下降雨特征对合流制管网溢流的影响,分析了1975年—2018年北京市北运河上游降雨演变特征,并考察了2018年8月两次典型降雨对合流制管网溢流的影响。结果表明,北运河上游80%的降雨量集中在汛期6月—9月,降雨事件主要分布在21:00左右,大部分降雨间隔小于10~15 d;近年来年降雨量呈下降趋势,平均降雨强度降低,这表明合流制溢流污染主要发生在夏季夜晚,主汛期“七下八上”极端降雨峰值强度增大;年均1.7次的双峰型强降雨冲刷了管道底泥,使合流制管网溢流成为北运河上游突出的瞬时污染源。冗余分析结果表明,合流制管网溢流量主要受累积降雨量和降雨历时的影响。综上,降雨特征对北运河上游的合流制溢流污染控制尤为重要,应重点关注主汛期管道底泥控制、汛期溢流总量控制,因此天气预报对合流制溢流污染管控具有特别重要的指导意义。

This paper analyzed the evolution characteristics of rainfall in the upstream of North Canal in Beijing from 1975 to 2018,and investigated the effect of two typical rainfall on the combined sewer overflows in August 2018,so as to clarify the influence of rainfall characteristics on combined sewer overflows under the background of climate change.80%of the rainfall in the upstream of North Canal was in the flood season from June to September.The rainfall events mainly distributed around 21:00,and most of the rainfall intervals were less than 10 days to 15 days.In recent years,the annual rainfall showed a downward trend,and the average rainfall intensity decreased,indicating that the combined sewer overflows mainly occurred in summer nights.The peak intensity of extreme rainfall from July 16 to August 15 in the main flood season increased,and the double peak heavy rainfall with annual occurrence of 1.7 times scoured the sediments in the pipeline,making the combined sewer overflows became the prominent instantaneous pollution source in the upstream of the North Canal.The redundancy analysis results showed that the overflows were mainly affected by the cumulative rainfall and rainfall duration.To sum up,the rainfall characteristics were particularly important for the control of combined sewer overflows in the upstream of North Canal,and the control of sediment in the pipeline and total overflows in the main flood season should be paid more attention to.Therefore,weather forecasting has a particularly important guiding significance for the control of combined sewer overflows.