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In the USA, the Environmental Protection Agency (EPA) provides guidance to municipalities on managing CSO discharges and complying with the National Pollutant Discharge Elimination System (NDPES) through a CSO Control Policy. These discharges, known as combined sewer overflows (CSOs), transport washed-off atmospheric and urban surface pollutants along with the debris buildup in the CSS during dry weather periods and cause multiple adverse effects (e.g., WMO and GWP, 2008 Botturi et al., 2020). A very common type of sewer system in old urban areas is the combined sewer system (CSS), a network of pipes that collects both stormwater and wastewater and expels excess untreated water volumes into nearby water bodies. To protect city dwellers from the alterations to the hydrological cycle and its consequences (i.e., flooding and exposure to pollutants such as viruses, chemicals, and suspended solids carried by runoff), sewer systems collect and convey stormwater away from cities ( USEPA, 2014).
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Impervious surfaces, such as concrete or asphalt, prevent infiltration, encourage urban runoff, preclude natural groundwater recharge, and increase the occurrence of flash flooding ( WMO and GWP, 2008 Huong and Pathirana, 2013), among other negative impacts. Land cover change from its natural state to impervious surfaces resulting from urbanization introduces an array of disturbances to the hydrological cycle ( Saier, 2007). This case study demonstrates the regional CSO challenges posed by climate change and supports the use of GI as a mitigation strategy. The simulation results show that (1) current 100-year events generate CSO volumes similar to predicted 50-year events (2) CSO volumes could increase by 11–73% in 2070–2099 compared to 1970–1999 when no GI intervention is performed and (3) the installation of PP can reduce 2–31% of future CSO volume.
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This paper used the Intensity-Duration-Frequency (IDF) curves for current (1970–1999) and future (2070–2099) design rainfall scenarios, with four rainfall durations (1, 6, 12, and 24 hours) and four return periods (2, 10, 50, and 100 years). Using the Storm Water Management Model (SWMM), the performance of PP as a CSO abatement strategy was studied for the city of Buffalo, New York, USA. However, an understanding of the impact of climate change on CSO events and the effectiveness of GI practices is crucial for designing sustainable urban stormwater management systems. The installation of Green Infrastructure (GI) such as Porous Pavements (PP) is a resilient approach to mitigate CSO events. The impact of climate change on precipitation may result in an increase in the frequency and magnitude of heavy precipitation events, with a corresponding increase in CSO discharges.
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