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Workers install a temporary berm along Memorial Drive in Calgary on June 14.Jeff McIntosh/The Canadian Press

Experts say a decade of flood mitigation measures helped Calgary avert disaster after a bout of intense rainfall several weeks ago, but warn that the city remains vulnerable to a larger storm system that could overwhelm existing infrastructure.

Calgary entered a state of emergency on June 13 after water levels in the Bow and Elbow rivers surged due to intense rainfall. The city was on high alert for nearly four days. Ultimately, there was no flooding – in stark contrast to the downpour of June, 2013 that caused more than $5-billion worth of damage and left five people dead in southern Alberta.

New flood mitigation strategies implemented after 2013 were successful. However, future heavy rains may still cause flooding as the most significant piece of infrastructure, the Springbank Resevoir Project, is unfinished and six years behind schedule. Climate change may also make heavy rainfall more common, said Thian Yew Gan, a water supply expert at the University of Alberta and a lead author of the most recent assessment report from the Intergovernmental Panel on Climate Change, the world’s premier climate change research organization.

“I don’t think the city is ready for another big event, like what happened in 2013,” Dr. Gan said.

The response to the recent rain was prompt. People were warned to stay off Calgary’s two rivers. Several large downtown parks were closed, and the city constructed a temporary berm over Memorial Drive, one of Calgary’s most critical east-west corridors that runs adjacent to the Bow.

Reservoir to protect Calgary from floods gets NRCB approval

The city got lucky this time. Despite some downed trees and interruptions to power in parts of the city, there was no flooding. The state of emergency was lifted after 125 millimetres of precipitation fell over three days – far less than the more than 200 millimetres of rain that was predicted.

Francois Bouchart, director of the city’s water services, said that the city was able to quickly respond to the storm and mobilize its flood mitigation strategy due to upgrades to its forecasting systems.

“While in 2013, we had only hours of time to get ready before the event started, we now have, in some cases, several days of forewarning that a system is developing and we can see whether or not the system is intensifying or dissipating and react appropriately,” Mr. Bouchart said.

There were also a series of infrastructure upgrades made along the Bow and Elbow rivers to help better manage surges in the water level of both rivers, which played a role this year, he said.

These measures include a number of flood barriers erected near the city’s most at-risk neighbourhoods, many of which were badly affected in 2013. The Glenmore Dam, which sits along the Elbow River, had also been retrofitted to replace its old stop-log system with steel gates, effectively allowing the dam to block water levels 2.5 metres higher than before.

The provincial government also instated an agreement with TransAlta in 2016 to use some of the company’s hydroelectric reservoirs during storm surges to decrease water levels along the Bow and the Elbow. That agreement is in place until 2026, when it will be reviewed for renewal.

However, there are weaknesses in Calgary’s flood mitigation plan that challenge the city’s ability to make it through the future bouts of extreme weather without any major issues.

The most glaring shortcoming is the unfinished Springbank Reservoir Project (SR1), a massive development 15 kilometres west of the city to divert water from the Elbow River, has been planned for years but only started construction last month.

SR1 has been in the works since 2014 and was supposed to be completed in 2018. It has notoriously faced numerous delays due to challenges from local land owners and Indigenous groups. The province has since been able to get all parties to sign off on the project, and the reservoir is now expected to be operational in 2024.

When finished, the reservoir will be able to hold the liquid equivalent of 30,000 Olympic-sized swimming pools, and is considered a critical tool in Calgary’s strategy for preventing the type of flooding seen in 2013.

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A flooded street on June 21, 2013.The Canadian Press

Yet even with existing flood mitigation measures, Mr. Bouchart said that the city is at a 55 per cent state of preparedness for any flooding events, adding that SR1 will increase that number to 70 per cent when complete. By 2026, with the construction of additional reservoirs along the Bow River, the city’s preparedness could be as high as 90 per cent, effectively allowing Calgary to contain floods of the same or even greater magnitude than the one of 2013.

“I think what we saw last week was, in my view, exactly how we should have responded,” says Kim Sturgess, founder and CEO of WaterSmart Solutions, an organization that has advised both the city and province on water management since 2005.

In Ms. Sturgess’ view, last week’s storm demonstrated the efficacy of improvements Calgary has made to its flood mitigation system in the last nine years and communicated the need to continue with efforts to improve upon and fortify the city against severe flooding through a multi-faceted approach.

“We have so many more levers to pull, to be able to respond to a severe flood event, than we had previously,” she said. “It was nice to have a, a sort of test run, if you will, in a situation that that turned out to be serious, but not overwhelming.”

Dr. Gan is not as optimistic. He argued that weather events that were thought to occur once a century have been observed occurring at much more frequent rates in recent years, both domestically and globally. In addition to the 2013 flood in Calgary, Dr. Gan pointed to severe flooding in major Alberta cities as examples of mega-floods becoming more common, such as those in Lethbridge in 1995 and in Edmonton in 2004 and 2013.

Dr. Gan said that while investment in mitigation tools such as barriers and reservoirs are useful in preventing immediate flood damage, such measures do little to address the growing threat of severe climate change.

Ultimately, even with advanced flood mitigation projects like SR1, Dr. Gan said that climate change could cause untold levels of precipitation as more and more of the world’s snow and ice evaporates into the atmosphere. That includes Alberta’s mountainous glacial supply, which just last year was observed to be melting at three times its normal rate.

Rather than simply focusing on mitigation, Dr. Gan said all levels of the Canadian government must prioritize and accelerate the transition to renewable energy and sustainable transportation, making the case that North America and Alberta in particular are too heavily reliant on fossil fuels and cars. He urged that transportation and renewable energy projects, including miniaturized hydroelectric dams, should be constructed alongside flood mitigation projects in order to help curb the rise of global temperatures.

“Unless we drastically try to reduce the greenhouse effect of increasing concentrations of carbon, it will overwhelm the system. The system is not designed to handle the sort of external events that we could be seeing more of in years to come.”

Editor’s note: A previous version of this article referred to incorrect flood-barrier locations and an incorrect number of TransAlta hydroelectric reservoirs used to decrease water levels along the Bow and Elbow rivers.

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