RTC Modeling for CSO Control in Ottawa

Written by Diana Qing Tao, M.Eng

Wallingford User Conference – September 2007

The City of Ottawa proposes to implement an automated flow control (Real Time Control) system as part of the upgrade of five major regulators that control flow from collector sewers into the central Interceptor Outfall Sewer (IOS).

The project aims to reduce the volume of combined sewer overflows to the Ottawa River and meet the requirements of the Ontario Ministry of the Environment’s Combined Sewer Overflow (CSO) Policy Guidelines which is to achieve system-wide capture of 90% of the total wet weather flow (WWF) volume.

A Real Time Control Feasibility (RTCF) Study, completed in February 2005, concluded that CSO control requirements could be achieved through the implementation of a more efficient operating strategy at the key flow regulators along the IOS. Under the pre-design phase, RTC modeling and performance evaluations were conducted with the objective of optimizing regulator upgrade requirements and cost as well as minimizing complexity and risks, while meeting the control objectives of 90% capture. Alternatives were considered with the primary intent to attain the CSO capture goal without significant and costly changes to existing regulators. The analysis applied a specialized RTC-enabled simulation software: InfoWorks CS from Wallingford Software. The application of local reactive controls and modulating gates at the key regulators was integrated in the network model to assess performance on an annual basis and fine-tune the system configuration.

Stress-testing of the preferred configuration in InfoWorks was also performed under multiple failure scenarios and for critical flooding events. This was to ensure that the control processes would continue to provide acceptable performance and to identify adequate automated safety protocols for continued operation under “degraded” modes, such as power failures, instrument and gate failures, etc.

This presentation will introduce briefly the development of the operating philosophy and process control narratives, and will present in detail the modeling activities and results of performance evaluation that were carried out with the InfoWorks RTC module in optimizing the preferred real time control approach.

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Diana Tao

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