Author(s): Licheng Ye; Yu Qian; David Zhu
Linked Author(s): Yu Qian, David Z. Zhu
Keywords: Coastal city Sanitary sewer system Inflow and infiltration Defect location
Abstract: Inflow and infiltration into sewer networks can lead to various operational and maintenance issues, such as increased hydraulic loads resulting in reduced treatment efficiency at wastewater treatment plants, and increased risk of combined sewer overflows (CSOs) etc. This study conducted a 16-month field monitoring program of a prototype sanitary system in a coastal city in China. The groundwater infiltration (GWI) on dry weather days and the rain-derived inflow and infiltration (RDII) for representative rainfall events on wet weather days were quantified and analyzed. The proportion of monthly averaged GWI to total flow can be as high as 70% during the observation period mainly due to the high groundwater level. The results show that the ratio of RDII volume to total rainfall volume (defined as R-value) reaches a limited value of approximately 10% for the studied system when the total rainfall depth increases. A reference indicator Rlim for the limited R-value was proposed for assessing the conditions of sewer systems in term of RDII. The Rlim value depends on local sewer conditions and in general, a lower Rlim value represents a better performance on RDII and vice versa. This study also proposed a method for determining single-point source inflow and infiltration location in sewage pipes, which based on environmental hydraulics principles of convection and diffusion. This study enriches the case studies on the performance of a specific sanitary system on inflow and infiltration in a typical coastal city with exceptionally high groundwater levels, excess rainfall events in the monitoring season and possible typhoon events. The proposed method for locating single-point source inflow and infiltration provides a new insight for the study of determining inflow and infiltration location in drainage systems.
Year: 2025