Why a flood of new ideas could help cities better manage storm-related sewage overflow

Tens of thousands of residents in the City of Toronto won’t soon forget August 7, 2018. On that night, some of the oldest and most-populous sections of Canada’s largest city were overwhelmed by up to 100 millimetres of rain over just a few hours. Due to the impenetrable urban landscape, the water had nowhere to go: it quickly flooded streets, basements and storm sewers. The rising water even trapped two people in an elevator. They were rescued by first responders with only about 30 centimetres of air space left to breathe.

Many days after the water has subsided, the debris left behind painted a troubling environmental picture. Several Lake Ontario beaches were closed to swimming due to high bacteria counts in the water. And along shorelines, rivers and creeks, residents discovered what some call a ‘toxic stew’ of solids: items such as toilet paper, condoms, tampon applicators and more.

“There’s no simple way to calculate how much untreated wastewater just washed into the ecosystem, but we can assume it was a significant amount based on the raw sewage debris that turned up Lake Ontario after the storm,” says University of Ontario Institute of Technology researcher Andrea Kirkwood, PhD. “The system couldn’t handle the overflow. Unfortunately, events like this are more common in older cities like downtown Toronto where storm and sanitary sewer lines are combined.”

The biologist with the university’s Faculty of Science says sewage overflow events can cause short-term problems in our waterways, such as making contaminated waters unsafe for swimming.

“Sewage overflows caused by intense storms transport unwanted fecal bacteria, nutrients and organic matter into aquatic ecosystems,” says Dr. Kirkwood. “Beyond the displeasing aesthetics of floating debris in waterways, these excess nutrients can contribute to local algal blooms. Too much organic matter can reduce oxygen levels, reducing habitat quality and causing fish mortality. Compounding the issue is climate change. With summer storms in Southern Ontario predicted to occur more frequently and with greater intensity, this puts increased pressure on aging municipal infrastructure.”

Dr. Kirkwood says many sections of newer communities, like those in Durham Region, tend to avoid major sewage overflow events.

“Fixing and replacing aging infrastructure would solve the problem in older centres, but the cost likely runs into the billions of dollars. Infrastructure investment over the past 30 to 40 years in Durham Region has ensured sanitary and storm sewer lines are built separately. Storm management facilities are newer and apply the latest technologies such as stormwater ponds and ‘low impact design’ in new developments, which allows storm water infiltration.”

Dr. Kirkwood’s lab works with the City of Oshawa to research how effective the local stormwater management system works. Past studies have monitored water quality in Oshawa’s creeks and storm-sewer system. Current research focuses on the role of plants in improving the water quality of Oshawa’s stormwater ponds. This study is one of several projects connected to Teaching City, a multi-partner collaboration that establishes the city as one focused on experiential learning, applied research and innovative partnerships to address urban issues.

“Since most people in Canada live in urban centres, most Canadians are directly or indirectly affected by the economic, environmental and health impacts of stormwater pollution. The City of Oshawa is being proactive on this issue by supporting research that aims to improve stormwater management in our growing city.”

Media contact
Bryan Oliver
Communications and Marketing
Ontario Tech University
905.721.8668 ext. 6709
289.928.3653
bryan.oliver@uoit.ca