News / Ottawa

Last week's rain sent nearly 600 million litres of sewer overflow into the Ottawa River

The city is building a state-of-the-art sewage storage tunnel—but even that wouldn't be able to hold as much rain as Ottawa saw last week.

People walk past the flooded parking lot of the Pebb Building, located across from the Ottawa River, following a rain storm in Ottawa last week.

Justin Tang/Canadian Pres

People walk past the flooded parking lot of the Pebb Building, located across from the Ottawa River, following a rain storm in Ottawa last week.

Nearly 600 million litres of sewer overflow—comprising a mixture of raw sewage and rainwater—was pumped directly into the Ottawa River last week, as heavy rains soaked the capital and overloaded the drainage system. 

The bulk of that came during the heavy rainfall of October 29 and 30, when 515 million litres of sewage were pumped in. On November 2, a further 67.6 million litres ran into the river, followed by another 6.8 million, according to Meredith Brown, Ottawa’s riverkeeper. 

It’s a sign, says Brown, of the impact that climate change is having on the city. 

“These are exactly the problematic storms that we talk about with climate change that are inundating our municipal infrastructure.” 

The city recently began tunnelling work on the combined sewage storage tunnel (CSST), designed to mitigate the number of overflow events each year. But that tunnel will only provide 43 million litres in extra capacity. 

Zaid Ghadban, manager of the CSST project, said this isn’t a case of city infrastructure being ill-suited to the task—just that it is next to impossible to build a overflow storage system big enough to respond to the kinds of heavy rains Ottawa saw this week. 

“Those are unique situations, and we’re not designing for those situations,” he said. “We can’t design for those extreme events.” 

But with the impacts of climate change making those extreme events more common, it’s unclear how the city can best mitigate overflows.

“The ‘average year’ is kind of shot,” said Brown. 

This shouldn’t be read as a criticism of the city’s stormwater management efforts, which Brown says are quite advanced relative to other cities in North America.

Rather, she said, it illustrates the significant challenge that climate change will pose to municipal infrastructure. 

“The key thing here is that storm intensity is changing,” she said. “Are we really prepared for it?” 

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