Lake Manitoba flooding might have occurred without the use of the Portage Diversion, according to the authors of a report on the 2011 flood
Those looking for a clear answer on what caused flooding around Lake Manitoba in 2011 won’t find it in the newly released Manitoba 2011 Flood Review.
Completed in conjunction with a regulation review of Lake St. Martin and Lake Manitoba, the report makes 126 recommendations, including the construction of a second permanent outlet structure for Lake Manitoba.
But the question of artificial flooding on the lake was not part of the regulation review committee’s mandate, said chairman Harold Westdal.
“We did not study that, however, it was one of those top-of-mind issues that came up at every public meeting,” he said. “I think for the people around Lake Manitoba the answer is pretty simple. As far as they’re concerned there were measures that were taken that knowingly led to flooding on Lake Manitoba and Lake St. Martin.”
Experts consulted by the review committee indicated that it was possible excess water would have found its way into Lake Manitoba even if the Portage Diversion had not been used, following natural channels to the lake once the Assiniboine River overflowed or breached its dikes.
“There was approximately 53,000 cfs (cubic feet per second) coming down the system, the Assiniboine River could safely handle 18,000 cfs downstream of Portage la Prairie the other 35,000 had to go somewhere, and rather than trying to push it down the Assiniboine and having a catastrophic failure, the safe choice was to run it through the Portage Diversion,” said Flood Task Force chairman, David Farlinger.
During normal conditions, the diversion removes a maximum of 25,000 cubic feet of water per second.
During the flood of 2011, the diversion’s capacity was temporarily increased to 33,000 cubic feet of water per second, resulting in the emergency fortification of the diversion. Unlike years past, the diversion also ran for 100 days, rather than the roughly two weeks it usually operates.
Since 2011, $6 million of repair work has been done at the site.
“If that water had not been diverted through the Portage Diversion, there would have been, certainly, a catastrophic failure of the Assiniboine River dikes, some of that water would have found its way through natural channels into Lake Manitoba, but where the water would have gone is a bit of a moot point,” said Westdal.
“For the people who live around Lake Manitoba this is not a technical issue, this is a very emotional issue, they feel it very strongly, and they feel they have taken a significant hit for other people in the province.”
Steve Ashton, minister of infrastructure and transportation, said the province did everything it could with the tools available to minimize damage across Manitoba.
“I want to stress one thing; at no time was there any trade-off of protecting the City of Winnipeg versus rural Manitoba,” he said, adding that he could not say in technical terms whether the use of the diversion caused artificial flooding.
However, he noted overland flooding in 1892 caused significant flooding on Lake Manitoba without diversion structures.
The authors of the Regulation review of Lake Manitoba and Lake St. Martin describe the debate around flooding as, “partially technical (hydrologic analysis), partially semantics and partially perspective.”
A $260-million class-action lawsuit has been launched against the province in relation to the flooding of Lake Manitoba.
One thing all parties agreed on was that the flooding experienced in 2011 was unprecedented and unlikely to be repeated. Damage along some areas of Lake Manitoba was also linked to high winds that coincided with high water levels.
The report recommended lowering water levels on Lake Manitoba for the next five years to allow for the restoration of natural vegetation, as well as better forecasting technology, better communication, new water control structures, updated zoning regulations and new forecasting models.