The use of Permeable Pavement as a form of Green Infrastructure has become increasingly popular, in part because it can be implemented without altering the original land use. However, few studies have attempted to quantify the effectiveness of PP for reducing the volume and frequency of Combined Sewer Overflows (CSOs), particularly at the city scale. In this study, a city-scale model for Buffalo, NY was used to evaluate PP effectiveness as a function of spatial configuration, including location within the sewer system and the possible grouping of individual installations into aggregated clusters. Several approaches to PP design were compared including trial-and-error, engineering judgement, and mathematical optimization using the Parallel Dynamically Dimensioned Search (PDDS) algorithm implemented in the public domain SWMM-OSTRICH software. Our case-study findings indicated that, despite the computational power and time required to develop a simulation-optimization-based design, formal optimization was the best approach to maximize the impacts of PPs on CSO abatement. In general, the optimal results varied accordingly to imposed budgetary constraints and did not indicate generalizable relationships associated with spatial aggregation or placement within the sewershed. These results suggest that while PP can be an effective strategy for CSO volume reduction, the optimal placement strategy is highly application-specific, and modeling is recommended to determine the most cost-effective design.
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