Combined sewer overflow (CSO) control in ageing urban areas is a costly and on-going issue. In addition, urban municipalities must deal with other daunting issues such as economics, sustainability, etc. In this paper, we show how decision makers might capitalize on the concept of natural capital or ecosystem services benefits, as well as other economic benefits in sewershed-scale green storm-water infrastructure (GSI) designs aimed at reducing CSO volumes. This concept is demonstrated on a sewershed within the City of Philadelphia using triple bottom line (TBL) estimates of benefits and continuous hydrologic/hydraulic simulations using EPA's Storm Water Management Model (SWMM) coupled with a simple genetic algorithm (SGA).Results are compared to existing conditions. Also explored are situations where property values are excluded from the analysis as a method of promoting economic equity in GSI placement.
INTRODUCTIONPlanning and developing structural best management practices (BMPs) at a watershed-scale to mitigate stormwater runoff is known to be an effective alternative to traditional practices that focus on individual on-site designs (Emerson et al. 2005). Many water resources managers and engineers identify near-optimal watershed-scale BMP designs and alternatives through coupling of computer-based models with evolutionary algorithms (EAs) with single or multiple objectives (e.g., minimize total construction and O&M costs). As members of the ASCE Task Committee on Evolutionary Computation in Environmental and Water Resources Engineering, Nicklow et al. (2010) provide a comprehensive overview of the recent use of EAs in water resources management. Another trend in the field has been a shift from traditional BMPs to low impact development or GSI that promotes sustainability (EPA 2007;Zhou et al. 2011). To address sustainability, TBL accounting is currently used by planners and managers, which considers social, economic, and environmental issues and not just the cost-effectiveness of GSI controls.