Hybrid Modeling Approach to Bridge Drainage System

The Ontario Line subway project in the City of Toronto is a 15.6 kilometer rapid transit line that connects downtown Toronto with the northeast part of the city. The Ontario Line lies within the Don River watershed in Toronto Region Conservation Authority jurisdiction, includes two crossings of the Don River. Two new railway bridges, each approximately 0.5 kilometers long, have been designed to route the transit line over the rivers.

The drainage from the bridges is required to capture and convey the 100-year flow to keep the bridge free from flooding. Flows along the bridge deck will be intercepted by scuppers, sending water to the pipe system running along and below the bridge deck, ultimately discharging to a vertical downspout along a pier, towards a raingarden.

The configuration of the conveyance system for the deck drains was required to address various physical constraints and criteria associated with as confined spaces, conflicts with other utilities, outlet pier location, and requirements for maintenance access. This resulted in a hydraulically complex drainage system consisting of low gradient pipes, multiple bends and junctions, and a vertical drop structure. The hydraulic models applied for the analysis and design were thus required to be highly sophisticated, but also highly efficient in order to quickly assess and guide design changes from the other engineering disciplines in the design of the crossing. The ultimate modelling applied a hybrid approach which combined FLOW-3D modelling for the drop structure with PCSWMM modelling for the deck drains and lateral pipes.

This presentation provides an overview of the process and rationale for the model selection, the approach applied to integrate the PCSWMM and FLOW-3D modelling for the hybrid approach, and key findings and lessons learned through the process.