Province warned in 2010 floods could get worse

Report blamed climate change for peak flows

Provincial and city officials were warned three years ago that climate change could cause Calgary to suffer more frequent and devastating floods.

Despite the predictions of more intense rainfalls if carbon dioxide levels in the atmosphere increased, a 2010 engineering study suggested the worst-case inundation on the Bow and Elbow rivers still wouldn’t be as bad as previously predicted.

“It is anticipated that such changes in precipitation patterns could increase the frequency and intensity of extreme events,” the study said.

“There is no clear evidence that the patterns in magnitude or timing of flood peaks have changed significantly over the past 100 years.”

The $80,000 report — produced by Golder Associates consultants in Calgary for what is now Alberta Environment and Sustainable Resource Development — was supposed to guide emergency response planning and flood mapping efforts by the province and the city.

It’s unclear how the report was later used or whether it prompted complacency among local and provincial officials, who might have concluded from the findings that the risk of the sort of flood that Calgary witnessed four weeks ago was more remote than previously thought.

But for the hydrologist whose climate change research was cited in the report, the 2013 floods were no surprise.

“I kind of felt like saying ‘I told you so’ when it happened,” said Caterina Valeo, “because my work clearly showed flood- ing was likely to increase.”

Using the same computer model as Alberta’s river forecasters, Valeo and her team conclude in a 2007 study that climate change could cause peak flows on the Elbow River during spring floods to nearly double.

“Most of the big floods would be from intense rain events on already saturated soils,” she said.

“That report wa s supplied to the province, too, but I never heard anything back.”

The existence of the previously unreleased study by Golder Associates and some of the findings it contains about historic inundations in Calgary appear to contradict statements made by Alberta’s Con-

The bottom line is the reservoir just isn’t big enough HYDROLOGIST CATERINA VALEO

servative government in the wake of the recent floods.

“I want to stress that what Alberta has experienced in this past week was unprecedented,” Environment and Sustainable Resource Development Minister Diana McQueen told reporters on June 25.

“No report or recommendation looking at the lessons of the past could have prepared us for this event.”

But the 2010 study, like larger ones done previously for the province, show that the Bow River in Calgary was hit with estimated peak flows in both 1879 and 1897 that were 30 per cent higher than what the city experienced four weeks ago.

The highest flow on June 21 of 1,740 cubic metres per second was only slightly more than the downward-revised 1-in-100 year event that Golder Associates predicted and over 11 per cent smaller than what the province’s 1983 study said was probable once a century.

When asked for an interview Wednesday about her previous statements, McQueen deferred questions to department officials.

Environment and Sustainable Resource Development spokesman Nikki Booth said in a written statement that the 2010 report did not prompt a policy shift or alterations to the province’s flood maps.

“Since this study is about frequency analysis, we would want to include data from this latest event before we would make any changes,” Booth said.

While precipitation and river gauging records were sparse and uncertain a century ago, hydrologist John Pomeroy says his own research has found strong evidence of a rise in intense, multi-day rains across the Canadian Prairies over the past century.

“For Alberta to minimize flood damage and casualties,” said Pomeroy, “we need to improve flood forecasting and preparedness.”

Valeo said her team’s study on the Elbow River was focused on helping the city find out whether the Glenmore Dam could be managed better to moderate flows down stream to minimize flooding.

“The bottom line is the reservoir just isn’t big enough,” she said.

“Though it was never fully researched, we though the best solution might be containment areas farther upstream that could hold water during periods of peak flow.”

Indeed, city officials began emptying the reservoir four days before the recent flooding in anticipation of the heavy rains. But the swollen Elbow River soon filled it back up, overtopped the dam and caused heavy damage in downstream communities.

“The city is limited by geography and finances in what it can do to mitigate against these big floods,” Valeo said.

“The province is key to finding a solution.”