Monitoring Blockage and Overflow Events in Small-Sized Sewer Network Using Contactless Flow Sensors in Hong Kong: Problems, Causes, and Proposed Solution

Effective monitoring and prediction systems for sewer overflow are essential for safeguarding public health and the environment. Flow sensors have emerged as valuable tools for understanding and measuring the hydraulic performance of sewer networks, enabling the detection of blockages and overflow events. However, previous research has predominantly focused on large-diameter sewer networks, leaving a gap in understanding the applicability and performance of flow sensors in small and medium-sized systems. Addressing this research gap and motivated by the need to improve the monitoring of small and medium-sized sewer networks, this study comprehensively assesses the performance of flow sensors in such networks, with a focus on detecting blockages and overflow. The study evaluates the performance of flow sensors in 12 locations within the Hong Kong sewer network and identifies challenges affecting accuracy. The findings reveal noteworthy shortcomings when solely relying on flow sensors, including inconsistent and unreliable observations. Notably, the correlation coefficient between the level and flow sensors was 0.36, and the average relative error in flow rate measurement was a substantial 72.14% compared to Manning’s equation. An in-depth analysis reveals key factors hindering flow sensors’ efficiency, such as inconsistent flow directions and pipe size variations. To overcome these limitations, the study introduces a new approach based on real-time measurement of vertical sewage velocities inside manholes. By incorporating level sensors and considering specific network characteristics, this alternative methodology provides a promising solution for detecting operational issues and improving the reliability of overflow monitoring systems.