Urban flood hazard and sewer system performance in New York City’s Tallman Island sewershed under extreme rainfall events

This study examines the hydraulic system performance of New York City’s Tallman Island sewershed in Queens, NY—one of 14 drainage areas and a critical component of the city’s combined sewer system. The sewershed, among the largest and most hydraulically constrained, conveys sanitary, industrial, and stormwater flows through a single network. As innovations in sewer monitoring are proposed for better adaptation, their performance under hydrometeorological extremes is vital to understand. The study analyzes sewer system behavior during flash floods from 1996 to 2024, focusing on flood hazard changes since 2011 and the impact of Hurricane Ida in 2021. Using rainfall data from three key stations (Central Park, LaGuardia, and JFK) within the SWMM–PySWMM framework, it evaluates the vulnerability of the city’s drainage system. In highly urbanized areas like Flushing and Astoria, drainage pipe fullness exceeded 80 %, and ponding durations surpassed 24 h due to a sharp rise in rainfall intensity after 2011. System-wide maximum velocity estimates show marked differences between Ida- and non-Ida-induced floods. Hurricane Ida heightened flood hazards in hydraulically constrained, high-impervious neighborhoods. The northwest and central Tallman Island zones repeatedly operated near full capacity, indicating chronic infrastructure stress. This framework offers a transferable approach for assessing evolving urban flood hazards and guiding resilience strategies in combined sewer systems. • A framework to assess urban sewer system performance in New York City is presented. • Short-duration, high-intensity rainfall is a necessary factor for major floods. • Hydraulic limits and high-imperviousness are the converging factors for impact. • The framework provides valuable insights for NYC’s sewer infrastructure upgrades.