Assessment and pathway determination for rainfall-derived inflow and infiltration in sanitary systems: a case study

Rainfall-derived extraneous flows in sanitary systems can create a variety of management problems. In this study, the quantity of stormwater entering sanitary systems in Jiaxing, China was investigated through flow surveys and flow balance analysis. The pathways of stormwater entering the sanitary systems were also discussed. The results indicated that rainfall-derived extraneous flow in sanitary systems was serious in Jiaxing. The pathway of rainfall-derived extraneous flow included the direct entering through illicit connections or misconnections, and indirect inflow and infiltration (I/I) through joints and breaches along the pipeline. The rainfall-derived inflow coefficients in residential areas R1, R2 and R3 was 0.29, 0.31 and 0.30 m(3)/mm center dot ha, indicated that illicit connections or misconnections in residential areas are probably the important pathway of stormwater entering the sanitary system. The results indicated that I/I also served as a pathway of stormwater entering the sanitary system and led to extraneous flows.