The Manitoba government may be selling the idea that water from the Portage Diversion contributed little to 2011’s Lake Manitoba flood, but ranchers around the lake aren’t buying it.
“People are just mystified as to how on earth can (they) state that the Portage Diversion raised it roughly .09 feet, which is an inch,” said Joe Johnson, who farms near Langruth, Man.
“Where we are farming, you could stand four feet away from the water and watch it come toward you.”
On Oct. 16, the province released a technical report on the 2011 flooding of the Assiniboine River, Lake Manitoba and Lake. St Martin.
Manitoba transportation and infrastructure minister Steve Ashton said the water from the Portage Diversion, which moves water from the Assiniboine River to the south end of Lake Manitoba, didn’t flood farmland and residential property.
“What the report also shows is the degree to which the operation of the Portage Diversion had very minimal impact on the lake,” he said during a news conference.
“I think it had an impact, according to the report, of .09 feet.”
The 2011 flood around the lake’s perimeter inundated thousands of acres of ranchland, forced farmers to move their livestock to higher ground and damaged hundreds of cottages on Lake Manitoba.
In response, the province paid hundreds of millions in flooding claims to farmers and property owners for their losses.
Despite the compensation, landowners around the lake remain frustrated because the province has never admitted that it was an artificial flood.
Farmers insist that the province deliberately flooded Lake Manitoba by expanding the capacity of the Portage Diversion and directing billions of litres of water from the Assiniboine into the lake.
The provincial government report, which was audited by an independent engineering firm, rejected that notion.
“It is noteworthy that in spite of the significant artificial inflow to Lake Manitoba from the Portage Diversion, there was only a nominal artificial effect on the Lake Manitoba water level,” the report said.
Its authors based their conclusion on the assumption that water from the Assiniboine, which flows west to east and south of the lake, would have jumped its banks and flowed into Lake Manitoba even if the Portage Diversion didn’t exist.
“This means that during a large flood, a portion of the flows on the Portage Diversion are not artificial flows, as they would have occurred anyway under unregulated conditions,” the report said.
It said the lake would have been lower from June 22 to August 30, 2011, under natural conditions, or without flood control structures such as the diversion and the Fairford outlet at the north end of the lake,. but not much lower.
“The regulated peak water level was 817.05 feet on July 23, 2011, versus the computed unregulated peak water level of 816.75 feet on July 1, 2011,” the report said.
“The artificial increase in peak water level of .3 feet resulted in an estimated 24,000 additional acres around the lake being flooded.”
The report also said the province’s decision to excavate the Portage Diversion channel and expand its capacity from 25,000 cubic feet per second to 34,000 cubic feet per second contributed almost nothing to lake levels.
“Restricting the flows on the Portage Diversion to the design capacity of 25,000 cubic feet per second would have resulted in a peak water level that was only .09 feet lower.”
Johnson said the province’s conclusions about the flood are contradictory.
For instance, the report praises the diversion for sparing land and property downstream of Portage la Prairie.
“Under unregulated conditions, without the benefit provided by the Portage Diversion and other flood protection infrastructure, the potential damage on the lower Assiniboine River has been estimated to be $2.2 billion,” the report said.
However, Johnson said that means the province claims the diversion prevented severe flooding between Portage and Winnipeg but also that the diversion had no impact on Lake Manitoba.
“They release a report that states the water was so insignificant it raised Lake Manitoba an inch. How on earth could an inch of water on Lake Manitoba cause (billions) worth of damage elsewhere?”