A Resilience-Oriented Framework for Assessing Surface Pollution Exposure Caused by Sewer Overflow in Urban Drainage Systems: A Case Study of Xiamen Island, China

Urban drainage resilience assessments emphasize hydraulic performance or pollutant discharges at outfalls, with limited attention paid to street-level contamination following sewer surcharge and overflow. This study developed an event-based framework to quantify surface pollution exposure resilience. An integrated 1D pipe network–2D surface hydraulic-water quality model was implemented in InfoWorks ICM for Xiamen Island, China. Spatial analysis revealed a mismatch between inundation extent and pollutant concentration distributions, demonstrating that severe flooding does not necessarily coincide with high pollution exposure and hydraulic indicators alone cannot adequately represent pollution exposure risk. Therefore, an event-based performance function integrating overflow nodes, pollution exposure area, and exposure intensity under different designed storms was proposed. Results showed that hydraulic failure occurred rapidly after rainfall onset, whereas pollutant accumulation and spatial expansion exhibited delayed responses, reflecting different controlling mechanisms of drainage failure and pollution exposure. Sensitivity analysis indicated that hydraulic failure dominated resilience sensitivity to rainfall intensity, with node-focused weighting causing the largest decline (0.733 to 0.662), whereas pollution exposure determined the magnitude of overall resilience loss, which was consistently lowest under exposure area-focused weighting. These findings highlight the necessity of integrating hydraulic and pollution perspectives to understand urban drainage behavior and provide a scientific basis for targeted resilience-oriented management and urban renewal.