Reliability- and resilience-based performance assessment of urban drainage infrastructure

Efficient urban stormwater management is crucial to prevent floods and reduce health risks from polluted runoff. Urban Drainage Systems (UDS), designed from past rainfall records, often fail under extreme rainfall, requiring continuous evaluation. This study introduces a framework assessing UDS performance via a composite reliability index and multi-dimensional resilience approach, in three stages: (1) basin-scale resilience assessment in hydraulic, environmental, and socio-economic domains; (2) rainfall-runoff modeling and a reliability index combining occurrence, volumetric, temporal, and flow velocity metrics; (3) evaluating adaptive scenarios: BMPs, channel-enlargement, and auxiliary channels. The framework uses hybrid MCDM (SAW and PROMETHEE) with uncertainty analysis. Applied to an urbanized catchment in northern Tehran, Iran, results show a resilience index of 0.48-0.53 (medium level), with SAW and PROMETHEE in close agreement. BMPs proved the most effective adaptive scenario for this catchment. The study offers a practical tool for budget allocation and resource management to improve urban flood resilience.