As the weather gets warmer and the risk of intense rainstorms increases, a hidden feature of McGill’s redesigned Y-intersection is about to come in handy.
A close look at the granite turtle shell mosaic unveiled last fall as the new centrepiece of McGill’s downtown campus reveals curved grates that surround the space. These empty into an underground rainwater retention basin.
Capable of holding up to 250,000 litres of water, the basin was installed directly under the former Y-intersection – now known as Tsi Non:we Onkwatonhnhets (The Place Where Our Life Force Emerges from the Earth) – as part of the renovation of Upper Main Road in 2024-25.
Urban sponge infrastructure
Jeremy Glenn, the lead professional on the Upper Main Road project, explained that the addition of the basin was driven by a new Montreal bylaw requiring rainwater management on private properties with over 1,000 square metres of impermeable surface.
“We’re seeing 100-year weather events happening more often and putting increased demands on city infrastructure,” said Glenn, who is a Senior Landscape Architect in Facilities Management and Ancillary Services.
According to Susan Gaskin, a civil engineering professor and researcher at the Brace Water Centre specializing in environmental hydraulics, “the initial drainage systems built in cities like Montreal can no longer handle the stormwater flows we’re seeing now.”
This is due to the long-term expansion of impermeable surfaces – like roads and sidewalks – and the increased frequency and magnitude of storms, said Gaskin.
“So, we have two choices: one is to dig up all the roads and make the pipes bigger – clearly that’s very expensive and disruptive. And the other is to get less rainfall into the stormwater drainage system during peak precipitation events.”
McGill’s new rainwater retention basin is designed to act like a sponge to help prevent the city’s drainage system from becoming overloaded, Glenn explained.
“The idea is that you’re retaining water on your site while the city is dealing with more significant water evacuation, said Glenn. “Then a day or two later you open up a valve and empty out your own sponge.”
In addition to the basin, the Upper Main Road project also replaced 500 square metres of old concrete sidewalks with new green spaces. This will help further increase water retention capacity on campus because “green surfaces are more of a sponge than hard surfaces,” Glenn said.
Combining design, art and function
A multidisciplinary team carefully integrated the water retention system into the larger plan for the reimagined Y-intersection, balancing drainage and grading requirements with sustainability and accessibility considerations.
Low-carbon-emission concrete was used to pour the basin and forest engineers were involved to ensure that tree roots would not be damaged.
“Those grates were also custom-made for the project,” said Glenn. “We needed to make sure that the grate openings were small enough to be wheelchair- and bike-friendly. But they also had to be big enough to accept a certain number of litres of water per second.”
Featuring a wave-like design, the grates were incorporated into the artistic vision for the space, which celebrates Indigenous presence, collaboration and reconciliation on campus.
Institutionalizing climate resilience
The installation of the basin is part of ongoing efforts to increase climate resilience on campus.
“Climate models show us how we expect the regional climate to change in the next 50 or so years. Climate resilience means being ready to handle those changes and not waiting to be caught off guard,” said Divya Sharma, Climate and Biodiversity Officer in McGill’s Office of Sustainability.
In 2023, McGill conducted an award-winning Climate Risk Assessment to identify critical risks that are likely to have an impact on the University, including extreme precipitation and prolonged heat waves, and suggest responses to those risks.
“One of those actions is to incorporate climate adaptation into existing policies and programs – to start thinking about how possible adaptation measures intersect with what we’re already doing at McGill,” said Sharma.
“This rainwater retention basin is a perfect example of that. The Y-intersection needed to be renovated and McGill incorporated climate adaptation into that plan.”