Hydrologic Risk and Sewer System Stress: Prioritizing Green Infrastructure for Flood Resilience in Pittsburgh, PA

Abstract

Combined Sewer Systems (CSS) convey wastewater and stormwater through shared pipes and remain the widespread primary infrastructure across U.S. cities. During precipitation events, CSS are vulnerable to flows exceeding pipe capacity, resulting in Combined Sewer Overflows (CSOs) that discharge untreated effluent into receiving waterways. Aging infrastructure, increasing precipitation intensity, and expanded impervious surface from urban development contribute to and exacerbate CSOs. Pittsburgh, PA, exemplifies these intersecting challenges due to its legacy CSS and uneven historic development. To mitigate the CSO threat, green infrastructure (GI) implementation is an emerging planning solution. This study assesses how hydrologic dynamics contribute to CSO occurrence, how CSO risks relate spatially with CDC social vulnerability index (SVI) scores, and identifies at-risk sites well-suited for GI. Results demonstrate a significant spatial overlap between neighborhoods with high SVI, elevated overflow potential, and limited existing GI. These findings highlight critical gaps in current stormwater management strategies and identify priority areas for equitable GI implementation.