Canada Day storm a 1 in 200-year weather event with 167 mm of rain in some areas: City of Ottawa

The Ontario government says help for flood-stricken residents is coming, but there’s still no timeline for it. CTV’s Katelyn Wilson reports.

The Canada Day storm that flooded hundreds of basements and streets in Ottawa’s west end was a one in 200-year rainfall event, with some areas receiving more than 140 millimetres of rain, according to the City of Ottawa.

The clean-up continues after a series of thunderstorms hit Ottawa on July 1. The city has received 5,423 reports of basement flooding and collected more than 1,700 tonnes of storm waste since the storm. The city’s 3-1-1 line has received 5,423 service requests related to the flooding and extreme weather.

Environment Canada reported 118 millimetres of rain was recorded at the Ottawa Airport on July 1.

City council will receive an update on the city’s response to the Canada Day storm and flooding on Wednesday.

In a memo to council on Saturday, Infrastructure and Water Services general manager Tammy Rose said the city’s rain gauges show the rainfall totals varied across the city, from 15 mm at Trim Road in the east end to “as much as 167 mmm at the Britannia Station in the west end.”

“The highest rainfall amounts were concentrated in central and western Ottawa, including Britannia (167 mm), Colonnade (151 mm), Nepean (144 mm), Mooney’s Bay (117 mm), and St. Gabriel (114 mm), while many eastern and rural locations recorded substantially lower totals,” Rose said.

“This pattern demonstrates the highly localized nature of the storm, with some neighbourhoods receiving more than ten times the rainfall recorded at other locations within the city.”

According to the city, rainfall totals varied from 95 to 104 mm in Kanata, 104.4 mm at the Walter Baker Centre, 99 mm in Riverside South, 68 mm at Brewer Park, 61 mm at Lemieux Island, 48.4 in the Lees Avenue area and 15 mm to 19 mm in the east end.

Rose says a common storm in Ottawa between the spring and fall is often in the range of 5 to 15 mm of rainfall, with peak storm intensities of 5 to 15 mm per hour.

Rose notes Ottawa received a peak rainfall volume of 167 mm in five hours, with many areas experiencing a storm “close to or exceeding a 1 in 200-year event.”

By comparison, some areas of Ottawa received 107 mm of rain on Aug. 10, 2023 in five hours, which exceeded the 1 in 100-year event. A storm on Oct. 29, 2017 saw peak rainfall of 142 mm over 24 hours, which also exceeded the 1 in 100-year event, according to the memo.

Ottawa infrastructure

The heavy rainfall on July 1 caused flooding on roads and in basements and sent millions of litres of untreated sewage flowing into the Ottawa River from the sewer system.

Rose says the city’s drinking water system, wastewater treatment plant, pump stations and emergency response systems “continued to function and provide core services,” but the “extraordinary volume and intensity of rainfall” exceeded capacity.

“The storm sewer systems across the city were operating over capacity, resulting in some stormwater travelling across the surface rather than through the pipe system,” Rose said.

“This led to significant surface ponding in low-lying areas and a significant number of basement flooding incidents and substantial combined sewer overflow.”

Rose says there are “several possible entry points for water to enter basements,” including stormwater backing up through storm service connections, groundwater penetrating foundations through cracks and joints and surface water entering through doors and window openings.

The City of Ottawa has launched a “comprehensive review of this extreme weather event,” to look at system performance and identify opportunities for improvement, according to Rose.

The memo says staff will undertake the following activities and studies:

• Review previous flooding studies, historical flood records, and recommendations from past events.
• Document infrastructure and operational improvements that have been implemented and assess how they performed during this event.
• Prepare a summary report of flooding impacts across affected neighbourhoods, including an analysis of approximately 5,500 service requests. This will be supported by an engineering consultant, Rose said.

3-1-1 requests

Residents of College Ward and Bay Ward filed the most requests to 3-1-1 about flooding following the storm.

The city received 5,423 calls for service following the July 1 storm.

The data shows there were 2,282 service requests from Ward 8 (College) and 1,512 service requests from residents in Ward 9. There were also 684 service requests from Knoxdale-Merivale and 427 requests from residents in Kanata North.

Storm cleanup

The city says 1,700 tonnes of storm waste has been delivered to the Trail Road Waste Facility since the storm on July 1.

A second round of storm-waste collection will begin on Monday in all impacted wards.

The three-item garbage limit has been lifted for residents living in the area.

Information sessions on Sunday

The City of Ottawa is hosting a community information session at Ben Franklin Place on Sunday.

The city says residents impacted by the storm can drop by between 1 p.m. and 5 p.m. to speak with city staff, the Insurance Bureau of Canada and the Canadian Red Cross.

Information on the following topics will be available:

• Waste disposal
• Health and safety when cleaning flooded homes
• Building codes and permits
• Reporting basement flooding or damaged infrastructure
• Support programs
• Insurance processing

The city will also be holding community information hubs on Sunday from 10 a.m. to 4 p.m. at the following locations:

• Carleton Heights Community Centre – 1665 Apeldoorn Ave
• Nepean Sportsplex, Entrance 1 - 1701 Woodroffe Avenue
• Maki House – 19 Leeming Drive
• John G. Mlacak Centre – 2500 Campeau
• Ron Kolbus Centre - 102 Greenview Avenue