Prevent overflow | Installing gates on the Shellmouth River would increase capacity by 1.5 metres and reduce flooding downstream
A water management expert says the Manitoba government needs to use the Shellmouth Reservoir to mitigate flooding rather than as a way to manage supply.
Alf Warkentin, who served as Manitoba’s senior flood forecaster for decades before retiring in 2010, said the historical record shows that excess water in the reservoir is a problem more frequently than a shortage.
Therefore, the reservoir, which is located near Russell, Man., should be managed accordingly.
“My evaluation shows there is far more risk of flooding in the last 40 years and very few risks of water supply problems,” he said.
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Warkentin, who recently wrote a report on the reservoir for the Assiniboine Valley Producers Association, said the provincial government could manage the Shellmouth differently by installing gates on the spillway, which would increase the reservoir’s capacity by 1.5 metres. Water now flows uncontrolled over the spillway when the reservoir reaches a certain elevation.
“This has been talked about for close to 10 years,” Warkentin said.
Spring rain, high soil moisture levels and a substantial snow pack have overwhelmed the reservoir in May and June for the last three years. As a result, millions of litres of water flowed over the spillway, inundating cropland and pasture between Russell and Brandon.
Producers with land in the Assiniboine River Valley lost an estimated 40,000 acres of land to flooding last year.
A gate on the spillway would have eliminated or reduced flooding downstream of the dam, Warkentin said.
“With that extra five feet of storage … in a lot of those floods there would’ve been enough storage to prevent the spillway (from flowing).”
He said the beauty of the gate option is it would increase the amount of storage for water supply and recreation on the reservoir but also provide the necessary flood protection.
In lieu of a gate, another alternative is to release more water in the springtime, Warkentin said.
“The operation during the runoff period is very important. There has been a tendency in the past to minimize the outflow and let the reservoir rise … to prevent flooding just downstream of the dam.”
Instead, the province should let more water out and flood land immediately downstream of the dam when the snow pack in Saskatchewan is significant,and there is a risk of exceeding the reservoir’s capacity.
“(Otherwise), the reservoir goes out of control and then you’re going to flood the whole Assiniboine valley all the way to Brandon,” Warkentin said. “That’s what happened quite a few times, such as 2012 in particular.”
Stan Cochrane, who farms near Griswold, Man., and leads the Assiniboine Valley Producers Association, agreed with Warkentin’s recommendation. He said it’s better to deliberately flood a stretch of the valley rather than drown out every producer from Shellmouth to Brandon if there is a serious risk of flooding on the Assiniboine.
“What we’re saying is in years like last year, if they would have flooded everyone from the dam to St. Lazare and compensated them for it, there wouldn’t have been a flood from St. Lazare to Brandon,” said Cochrane, who lost 1,500 acres of land to flooding in 2012.
His group submitted Warkentin’s report to the province this month, but Cochrane isn’t sure if it will have an impact.
“We seem to talk about what we’re going to do (differently) when it comes to operating the dam. Every year we just operate it the same. And we wind up with the same scenario — we get flooded.”
He said it’s hard to predict what will happen this spring, but the snow depths in eastern Saskatchewan mean it’s possible farmers in the Assiniboine River Valley will once again be flooded out.
Keith Pearn, who farms 5,500 acres near Virden, Man., and has approximately 2,000 acres in the valley, said it’s maddening that 40,000 to 50,000 of acres of land are regularly flooded and nothing is done about it.
“I’m still cautiously optimistic that it won’t be a real bad flood (this year),” he said. “(But) if this was the Red River Valley, it would’ve been fixed a long time ago.”
The Manitoba government did not respond to a request for comment before the April 22 press deadline for this issue.
