Management Planning for Combined Sewer Systems in Urban Areas under Climate Change Public
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Management of urban stormwater is becoming increasingly difficult due to an anticipated increase in precipitation and extreme storm events that are expected under climate change. The goal of this research is to develop an approach that effectively accounts for the uncertain conditions that may occur under climate change and to develop best management practices to manage stormwater in urban areas. This presentation focuses on management of stormwater and combined sewage in Worcester, MA, where approximately four square miles of the downtown area is serviced by a combined sewer system. The EPA Stormwater Management Model was used to determine the impacts of storms on the urban environment for future conditions. This model was used to simulate discharges of selected design storms associated with a range of climate change scenarios. Various design storms were simulated in SWMM for 2010, 2040, and 2070 under high, moderate, and low climate change scenarios. Alternative best management practices were assessed in terms of specific metrics that included flood volumes and combined sewer overflow volumes through the Worcester sewer system. Cost evaluations were used to identify appropriate best management strategies for managing the combined sewer system under future scenarios. A design cost approach and net benefits approach were used to analyze different options for managing stormwater under climate change. Both of these approaches utilize the concept of risk analyze to determine expected values of both costs and benefits for different options under different climate change scenarios. Results for the design cost approach indicate that providing upstream underground storage in select locations throughout the Worcester combined sewer system is the most cost-effective strategy. In addition, increased pumping capacity at the Quinsigamond Avenue Combined Sewer Overflow Storage and Treatment Facility (QCSOSTF) should be included for this option. However, it was determined that only select upstream storage is the most beneficial option under the net benefits approach as increased pumping capacity at the QCSOSTF was determined to be too costly due to the additional costs of CSO treatment required at the facility. The Worcester case study provides an ideal context for assessing the relative advantages of full treatment at the wastewater treatment facility, limited treatment at a centralized CSO treatment facility, decentralized storage options, and low impact stormwater controls. It also allows for an assessment of decision making methods for controlling flows and loads from the Worcester system. Comparisons between Worcester and other case studies provide a foundation for understanding how stormwater and combined sewer systems can be managed given climate change uncertainty.
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