Determination of Block-Based RDII Monitoring Priority in a Separate Sewer System Using PROMETHEE

In separate sewer systems, rainfall-derived inflow and infiltration (RDII) cause operational problems such as sewage manhole overflow and overloading of sewage treatment plant capacity during rainfall events. Although various studies have proposed management strategies for RDII, objective methods for determining monitoring priorities under limited water-level monitoring resources remain insufficient. Therefore, this study proposes a methodology for determining monitoring priorities for middle blocks using the Preference Ranking Organization METHod for Enrichment Evaluations (PROMETHEE) to improve the efficiency of block-based water-level monitoring systems. Four evaluation criteria—pipe surface area, building roof area, average Soil Conservation Service curve number, and pipe age—were selected, and their weights were objectively determined using the entropy method. The calculated weights were applied to the PROMETHEE analysis to rank the monitoring priorities of the middle blocks. Furthermore, considering the limited number of available water-level sensors, a phased deployment strategy was proposed, in which sensors were first installed at the outlets of the middle blocks and then the remaining sensors were deployed sequentially to the sub-block outlets according to the calculated priorities. The proposed methodology enables the efficient utilization of limited monitoring resources and is expected to improve the identification of RDII occurrence locations and support effective monitoring and maintenance planning for separate sewer systems.