Southwestern Manitoba faces high risk of spring floods
Province says high soil moisture, winter precipitation to blame for elevated flood risk
Southwestern Manitoba is facing a high risk of spring floods, while otherparts of the province could also be in store for high watersafter the snow melts,the hydrologic forecast centre says.
High soil moisture, snow and winter precipitation levels could mean flooding in most parts of the province, Infrastructure Minister Blaine Pederson saidas a spring flood forecast was released Monday.
"We need to be aware of the potential for flooding with the understanding that we have a couple more months of winter weather and the uncertainty of the spring melt rate,"Pedersonsaid.
Southwestern Manitoba, including the Red, Pembina, Souris, Roseau and lower Assiniboine rivers, is at risk of major flooding this spring.
There are moderate to major flood concerns along the upper Assiniboine River, Winnipeg River and parts of eastern Manitoba. To the north, The Pas and the Saskatchewan, Swan and Carrot rivers are facing moderate to major flood risks.
The Interlake and Fisher River regions areat risk of moderate flooding.
Five variables determine flood conditions: soil moisture at freeze-up in the fall, channel capacity of rivers, moisture levels in snow, the rate of the snow melt and precipitation during the spring melt.
Parts of Manitoba broke weather records in January after a series of warm spells that included a few days of rain in Winnipeg earlier in the month.
"That kind of weather that hovers around zero and gives a fairly gentle melt can really help mitigate flooding throughout these basins," saidJayDoering, a civil engineering professor at the University of Manitoba.
Doug McMahon, assistant deputy minister of water management with Manitoba Infrastructure, said the revisedflood forecast builds on the province's predictions releasedin December.
The forecast now includes precipitation levels to date and factors in futureweather scenarios, but it's still "too early to say" whether flooding is a sure bet, McMahon said.
"There's certainly a lot of snow out there. I think everyone can see that, but that doesn't necessarily translate to future conditions. There's still a lot of winter left, and we'll have to wait and see how that unfolds."
Doering said he remains optimistic the spring will bring a mild melt that leads toa gradual runoff rather than the deluges that often precede floods.
"What's working in our favour is that having a relatively thick blanket of snow keeps the frost from penetrating particularly far into the soil," said Doering.
"The frost in Assiniboine and Red watersheds is normal to below normal depth. Sothat means the soil has an opportunity to thaw and some of what might otherwise be run-off if the soil was very deeply frozen can perhaps percolate into the ground."
Soil moisture levels this past fall resembled those in 2011, when high frost levels and spring rains left parts of southern Manitobasubmerged by overland flooding.
McMahon said levels on the Red River this spring could be comparable to those in 2010. Conditions on the Assiniboine River are similar to what they were in 2005, he added, "well within our flood protection levels."
The Red River Valley and Winnipeg are "well-protected" in the event of a flood because of the Portage Diversion and the Red River Floodway, Pedersonadded.
"The magnitudeof spring flooding potential is still very dependent on weather until the spring melt,"Pedersonsaid, adding the amount of frost, snow and spring rain to come could alter flood predictions, as could water levels on rivers that flow into Manitoba.
The province continues to work with municipalities as they prepare for what could be a very wet spring.
The province plans to release its full spring flood report at the end of February.
'It's just up to mother nature'
Biology professor and chief scientist of the Association of Lake Manitoba StakeholdersScott Forbes said it's unlikely the province will see flooding to the extent of 2011.
"But it doesn't have to be that bad to be bad," he said.
However, he said the province has been proactive particularly by emptying the Shellmouth Reservoir, which will store water from the Assiniboine.The province has also kept the Fairford water control structure at Lake Manitoba wide open, he added.
"That was by far the most important thing they've could done," Forbes said. "They've reduced the magnitude enormously by those two steps alone."
When it comes down to it, Forbes said it's too early to tell and we will just have to wait and see.
"We just don't know what's going to happen. We have to hope for favourable weather," he said.
"If we get one more big Colorado Low we could be in a lot of trouble. It's just up to Mother Nature now."
With files from Meagan Fiddler
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