Despite Ottawa’s new purpose-designed stormwater tunnel opening in November 2020, a severe thunderstorm on Aug. 10 sent 316 million litres of stormwater and sewage overflow into the Ottawa River.
Marilyn Journeaux, water services director at the City of Ottawa, acknowledged that the unusually heavy rainfall had exceeded the tunnel’s capacity to handle the overflow.
“The intensity of the storm and the subsequent volume of rainfall surpassed the tunnel’s design capacity,” Ms. Journeaux told the Ottawa Citizen. “As a result, approximately 316,000 cubic metres overflowed to the Ottawa River, prompting notification to the Ontario Ministry of Environment, Conservation and Parks.”
The storm flooded roads, parks, and basements, as a result of 77 mm of rain over a six-hour period. Surface flooding was reported in the College, Knoxdale-Merivale, River, Capital, and Alta Vista communities of the city. Petrie Island East Bay and Petrie River beaches were closed from Friday through Sunday due to high levels of E. coli bacteria.
According to Environment Canada, the previous rainfall record for Aug. 10 in Ottawa was in 2004, with the city receiving 67 mm of precipitation.
The tunnel system can hold 43 million litres of rainwater facilitating its treatment before release into the river. When the tunnel officially opened, then-Ottawa mayor Jim Watson called the civic project an “engineering marvel.” The tunnel took four years to complete at a cost of $232.3 million.
The massive infrastructure upgrade was intended to address inadequacies that had previously caused millions of litres of untreated sewage to overflow into the river, costing the city more than $500,000 in fines.
Prior to the tunnel’s completion, Ottawa Riverkeeper, a charity dedicated to the environmental health of the Ottawa River, campaigned for real-time reporting of sewage overflows.
In October 2017, Ottawa Riverkeeper published a report that examined the data collected from five years of studying water quality. The report, “Brewery Creek and Beyond: The Problem with Combined Sewer Overflows in Ottawa and Gatineau,” said the water was contaminated and unsafe for recreational activity.
“Of the ten weeks that water quality test[s] were completed in 2017, only 4 results at the dam below Montcalm St. location showed E. coli levels that would be safe for boating and none that would be safe for swimming or wading,” said the report.
The city has encountered dozens of these overflow incidents annually. In 2017 alone, 1.6 billion litres of sewage-contaminated water entered the river.
