An Analysis of Rainfall-Derived Infiltration and Inflow Using Water Level-to-Flow Conversion

During rainfall, the rise in groundwater levels, coupled with defects in pipe connections and manhole joints, increases Rainfall-Derived Infiltration and Inflow (RDII) in separate sewer systems. This results in exceedances of planned wastewater volumes and a surge in Separate Sewer Overflows (SSOs). To implement effective measures in the sewer system, it is crucial to monitor the long-term sewage flow under both dry and wet weather conditions to identify RDII sources within the sub-basins. However, because of the cost disparity between installing flow meters and water-level sensors, many municipalities opt for the latter, which is more economical but limits the accuracy of flow measurement. Therefore, this study developed a methodology to estimate flow rates based on measured water-level data, which were validated using adjacent flow measurement data. This water level-to-flow conversion method is expected to be utilized through the installation of water-level sensors owing to their ease of deployment, in addition to budgetary constraints that limit the use of flow meters. This approach enables the application of water-level data for flow estimation.