Abstract

The Narragansett Bay Commission (NBC) manages a complex sewerage system that includes 65 combined sewer overflows (CSO). A model of the system was developed to determine in-system flows and CSO characteristics for use in conceptual design of CSO controls. The modelling approach successfully integrated six different SWMM models into a single system-wide model. The single system-wide model eliminated desktop approximations for boundary conditions and reflected the many inter-dependencies within the system. The model is stable and produces accurate numerical results. The estimated overflow volume is about 680,000 m3 (180 million gallons) during a 2-year design storm event. The model is currently being used to estimate the effectiveness and size of control alternatives. The alternatives include near surface storage facilities at strategic locations in the system and a deep tunnel scheme with drop shafts at major overflow locations.

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