Toronto’s storm trunk sewer will reduce basement flooding during severe storms

By ES&E Staff

In what is Toronto’s most ambitious basement flooding prevention project to date, city workers have started work on a large storm trunk sewer that will be part of a system to collect, store and move stormwater from the Fairbank-Silverthorn area to Black Creek.

The three-part $380-million project is part of the 2021 council-approved basement flooding protection program and is funded in part by the federal Disaster Mitigation and Adaptation Fund. Following the creation of the new tunnel, workers will install 17 kilometres of new storm sewers and 320 inlet control devices (ICDs) to manage stormwater flow to catch basins.

With major storm events on the rise, the project is expected to reduce basement flooding and sewer backups for more than 4,645 homes across four city wards. It is estimated to reduce 40 million litres of annual combined sewer overflows into Black Creek and other local waterways. The new storm trunk sewer will have the capacity to convey up to 9,500 litres of stormwater per second to Black Creek.

“It is also designed to serve as temporary storage during heavy rainfall and will slow down the release of stormwater to Black Creek,” states a backgrounder on the project.

Overall, the Fairbank Silverthorn Storm Trunk Sewer System project will provide flood protection to a 140-hectare area. The ICDs restrict rainwater from entering the combined sewer system through catch basins, reducing combined sewer overflow and the risk of basement flooding. As a result, the devices may increase temporary surface ponding on streets.

Toronto’s investigation into chronic basement flooding picked up steam in 2010, following an environmental assessment. The city also has a basement flooding protection subsidy program, which offers homeowners a subsidy of up to $3,400 per property to install flood protection devices.

The main tunnel will be created using a Bessac tunnel boring machine that uses rotating disc-shaped cutting wheels to bore through soil and install pipe segments to create tunnel walls. It typically excavates eight to 10 metres per day. Crews will construct a three-kilometre long, 4.5 metre-diameter storm sewer.

The first section of the 270-tonne tunnel boring machine will be lowered into a 40-metre-deep shaft inside Fairbank Memorial Park, located on Dufferin Street south of Eglinton Avenue West. This project is expected to be completed by 2026.

Earlier this year, Toronto officials spent $9 million to rescue a microtunnel boring machine that became ensnared by steel wires while constructing a new storm sewer.