Application of SWMM5 to Study Wet-Weather Operating Strategies in a Large and Complex Sewer System

The City of Columbus wastewater collection system includes both separate sanitary and combined sewers, interceptor sewers directing flow to two large wastewater treatment plants (WWTPs) and complex flow control structures. The potential benefits of modified system operation during wet weather, including potential real-time control (RTC), have been identified and are being investigated with regard to the performance of both the collection and treatment facilities. Prior to establishing an effective RTC system, a modeling assessment of sewer system performance is required to understand the system constraints and simulate various operating strategies. SWMM5 is being used as the modeling platform with which to perform these modeling assessments for the Columbus system.

CDM is currently assisting the City of Columbus to update their system-wide sewer model using PCSWMM.NET. SWMM5 – the computational engine in PCSWMM.NET – provides a number of advantages for modeling the operating strategies versus the previous models of the Columbus system that used SWMM version 4.4h. In particular, the ability to write control rules directly in SWMM5 is a significant advantage for modeling complex hydraulic structures and RTC strategies.

The interconnector sewer between the Jackson Pike WWTP and the Southerly WWTP is the central conduit that conveys flow from the upstream sewersheds into either the WWTPs or storage at the Whittier Street Storm Standby Tanks. In order to optimize wet-weather flow capture at the Whittier Street Storm Standby Tanks and at the two WWTPs, operating strategies for the interconnector sewer were developed. In the study, SWMM 5 was applied as a fully dynamic hydraulic model with approximately 1200 pipes/nodes, 11 pump stations, 28 orifices, and 48 storage/wet wells. Numerous control rules to operate the various gates and pump stations in the system were set up in the model. The SWMM 5 model simulated the flows in the interconnector sewer and the control rules are being iteratively adjusted to achieve an optimal solution. This presentation describes the approach to set up the various operating strategies in the hydraulic model and demonstrates the preliminary modeling results. As the on-going project develops, it is expected that the operating strategies will be expanded to include more sophisticated RTC strategies.