Montreal experiments with urban water features that could protect the St. Lawrence River

With both feet sinking into damp dirt, urban planner Pascale Rouillé surveys a narrow strip of land that will soon be used to not only retain runoff, but also be bursting with greenery that the community can enjoy.

Tucked in next to a warehouse known as Bâtiment 7 in the Montreal neighbourhood of Pointe-Saint-Charles, near the intersection of Le Ber and Sainte-Madeleine streets, the terrain will become what has been dubbed a "blue-green alley."

Construction crews have been adding the finishing touches to a retention pond and park features to the 100-metre strip that will serve as a collection basin for the rainwater and snowmelt that would normally flow off the warehouse and into the city's sewer system.

That warehouse, once used for railway maintenance, now houses community groups and there has been a grassroots effort to build an outdoor green space that would help prevent overflow into the St. Lawrence River. 

Montreal already has an abundance of "green alleyways" — alleys behind or between homes that have been given new life with plants, gardens and outdoor space to socialize with neighbours.

Green alleyways reduce heat island effects, improve air quality and reduce vehicle traffic, the city says. But green alleyways aren't known for water retention, and that's where the blue-green alley comes in.

Each year, the equivalent of 1,200 Olympic swimming pools overflows the drainage network and ends up in the river, according to the city of Montreal's water service.

"In Quebec, we have thousands of overflows a year, which is really problematic for our natural environments like the St. Lawrence River," said Rouillé, president of Ateliers Ublo and member of the Alliance Ruelles bleues-vertes, which has been pushing for the project. 

"We were wondering what our solutions are to limit these overflows."

WATCH | Explore the blue-green alley coming to Montreal: 

She said all these overflows not only contaminate rivers, but could eventually lead to flooding, she said.

Over the past year, the warehouse's roof drains were disconnected from the sewer lines so as to direct water to a bioretention area — designed to collect runoff.

While some bioretention basins may filter water slowly through soil, these have a membrane at the bottom, allowing for the water to be collected and treated to promote the growth of plants known for absorbing large quantities of water.

The collected water can also be routed to gardens for more plant or food production.