Sustainable Watershed Evaluation and Planning Process for Wet Weather Program Alternatives Development

Abstract

Local governments and utilities across the nation are starting to address the needs for implementing more sustainable stormwater and watershed management strategies. These needs are driven by the necessity to reduce stormwater contributions to combined sewer overflows (CSO), water quality and designated use issues, total maximum daily load (TMDL) requirements, numeric nutrient criteria, and flood risk reductions. The U.S. Environmental Protection Agency (USEPA) has recognized the value of more green stormwater management approaches and has encouraged CSO programs, municipal separate storm sewer system (MS4) National Pollutant Discharge Elimination System (NPDES) permittees, and wastewater NPDES permittees to more actively implement sustainable programs including green infrastructure (GI) and low impact development (LID). Many stormwater management engineers have been skeptical of the real benefits of GI and LID for stormwater management compared with traditional best management practices. However, stormwater programs including GI and LID have been successful in communities across the country, showing that sustainable solutions have a place in the stormwater management toolbox. The Municipal Sewer District of Greater Cincinnati (MSDGC) is leading a major program that is taking a holistic approach to stormwater management as part of its overall CSO management strategy. Project Groundwork, MSDGC's wet weather implementation program, is focused on meeting federal mandates for CSO and sanitary sewer overflow (SSO) management as well as on improving overall water quality and public health. Simultaneously, the program has been designed to consider enhanced social, economic, and environmental outcomes of implementing a combination of green and traditional grey stormwater and CSO management alternatives. Watershed planning efforts have been guided by a sustainable watershed evaluation process to help identify the most affordable, socially responsible, and environmentally effective plans for each watershed in the MSDGC service area. This process, the Sustainable Watershed Evaluation and Planning Process (SWEPP), has been revised and enhanced to provide guidance for future watershed planning efforts to ensure that sustainable strategies are efficiently developed and evaluated. In the Upper South Branch Mill Creek watershed, the SWEPP is being applied to identify alternatives for meeting CSO and SSO issues in this highly urbanized watershed. Sustainability of the suite of green and grey alternatives is being evaluated using a combination of water quantity and quality modeling, business case evaluations (BCEs), and web-based tools. Community involvement and interagency collaboration have been incorporated throughout the process to ensure local community needs and goals are addressed in the evaluation.