Riser Pipe and Port Design for the Toronto Ashbridges Bay Treatment Plant Outfall

The Toronto Ashbridges Bay Treatment Plant Outfall (ABTPO) project is anticipated to be the largest wastewater treatment plant effluent outfall in Canada. This paper describes the design criteria and design approach for a major component of the ABTPO: the riser pipes and ports. A 10-step construction sequence was established for efficient and safe riser pipe and port installation. Alternative materials were evaluated based on materials strength properties, flow resistance, constructability, and corrosion resistance. Biological fouling mitigation alternatives for the riser pipes and ports were evaluated for both microfouling (biofilm) and macrofouling (zebra mussels) potential. Other important design considerations include field investigations, geotechnical conditions, external and internal design pressure scenarios, pipe wall thickness selection, riser-to-tunnel connection details, and riser pipe and port joint connection methods. Performance requirements for marine construction methods such as marine navigation, drilling operations, surveying, riser pipe annulus grouting methods, and leakage testing were also established.