New green infrastructure will be built in Winnipeg to slow and clean up flowing water before it enters the sewer system, as part of a broader project to reduce combined sewer overflows.
The city expects to design and build a “rain garden” with bio-retention and soil cell elements in 2025. The project will strategically select and plant vegetation that slows down, absorbs and helps clean water before it enters city drains.
“The different (types of) vegetation provide different treatment capacity to that runoff, in terms of nutrient capture and absorption… Water quality gets improved going through it,” said Patrick Coote, a senior project engineer in the city’s wastewater planning and project delivery branch.
Coote said the three types of green infrastructure would be integrated together alongside Leila Avenue, largely between McGregor and McPhillips streets, as part of an Armstrong combined sewer district separation project.
Slowing down the water flow is intended to decrease the peak flow into the sewer system.
“Initially, it will slow the runoff to those combined sewer systems and more of it will be stored and utilized by the trees… (and by) soil storage systems, so that will reduce runoff and correspondingly reduce (combined sewer) overflows. It also improves the water quality of the runoff that does get into the sewer system,” said Coote.
Certain nutrients in water can promote algae growth, which some plants can filter out.
The rain garden could also get saturated in wet weather and hold rainfall, he said, while underground soil storage cells are designed to let water slowly percolate through and drain.
A similar soil cell system was added to Broadway this summer to better support tree growth, Coote notes.
While a final green infrastructure design plan isn’t complete yet, Coote expects the green infrastructure elements in the Armstrong district will cost between $1 million and $2 million.
He said the city will conduct extensive testing to determine how the flow of water changes after the green infrastructure is added to determine how well it works. That data will help guide further builds in the Cockburn and Mission combined sewer districts, he said.
“Potentially all of them will be (adding) green infrastructure opportunities,” he said.
Overall, the city is required to devote $104.6 million to green initiatives in the city’s master plan to reduce combined sewer overflows. That plan also calls for about $870 million worth of sewer separation and millions more to store, screen and control the flow of sewage.
The entire master plan to reduce combined sewer overflows is expected to cost between $1.15 billion and $2.3 billion, with work continuing for decades.
Aging combined sewers collect both precipitation and wastewater in a single pipe. The pipes can overflow during heavy rainfall, which sends billions of litres of diluted sewage into Winnipeg rivers each year.
Coun. Brian Mayes, a former water and waste chairman, said he suspects the city is behind on using green infrastructure in the combined sewer overflows project and much more similar work should be underway by now.
“(The city) should be doing millions of dollars of that stuff already… I don’t see this as a great leap forward,” said Mayes (St. Vital).
The councillor said it’s not clear how much the city has spent on green infrastructure within its combined sewer overflow reduction work so far.
In an email, a water and waste spokeswoman said “significant” investment has been made to design green infrastructure, though the work is typically included in larger contracts and not priced separately.
“These designs lay the groundwork for multiple contracts that will lead to construction in the coming years. Each (combined sewer overflow) district requires a detailed assessment on potential green infrastructure locations,” wrote Lisa Marquardson.
Marquardson noted the city spent about $192 million on its overall combined sewer overflow reduction program between 2013 and 2023.
Meanwhile, Mayes said he’s disappointed so-called green back lanes, which use “permeable pavers” to divert storm water from sewers, don’t look set to be included in that work.
The city has tested the green lanes in the past. However, a water and waste report states the lanes require extra maintenance and could lose drainage benefits over time. The report also estimates it would cost more than $2.75 million to implement another pilot project on the idea.
Mayes said the first test failed to accurately measure how effective the lane was in diverting runoff and said it’s “ridiculous” to rule out the concept.
“(The pilot) took forever… and we can’t measure if it had any effect. I don’t think that forever answers the questions,” he said.
Coote said green back lanes aren’t the most promising option to slow down water flow, especially when replacing gravel lanes.
“It’s hard to come up with a cost-effective solution,” he said.
joyanne.pursaga@freepress.mb.ca
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Joyanne Pursaga
Reporter
Joyanne is city hall reporter for the Winnipeg Free Press. A reporter since 2004, she began covering politics exclusively in 2012, writing on city hall and the Manitoba Legislature for the Winnipeg Sun before joining the Free Press in early 2020. Read more about Joyanne.
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