The spring flood on the Red River is now expected to approach the volume of the 2009 flood, which was the highest since the 1997 flood of the century, provincial forecasters say.
Provincial hydrologist Fisaha Unduche forecasts the Red River will crest around May 10 at a level slightly below that of the 2009 flood, which closed down Highway 75 for weeks and required the evacuation of some rural properties.
Under favourable conditions, this spring's crest will be somewhere between the 2011 and 2009 floods. Under a worst-case scenario, the flood could be even higher than 2009.
Under all three scenarios, the volume of water in this year's flood is expected to exceed that of the 2009 flood, but water levels won't be as high because ice on the river in 2009 drove up water levels, Unduche said.
This year's peak levels are not expected to be as high because all the ice has moved off the river, especially in Winnipeg, which is protected by the Red River Floodway, he said.
Nonetheless, a flood on the order of 2009 will be a significant event that will likely close most of Highway 75 for several weeks and require the precautionary evacuation of several dozen properties that may lose road access to emergency services, said Manitoba Infrastructure Minister Doyle Piwniuk.
Manitoba may be forced to detour U.S.-bound truck traffic to Highway 3 if North Dakota closes Interstate 29, he said.
As recently as March, Unduche had downgraded the prospect of a significant flood this spring. Then came unusual snows in April followed by unusual rains.
Four large precipitation systems moved through the province in April and forecasters are monitoring another major system expected to hit the region this weekend. It's expected to bring another 30 to 80 millimetres of rain to southern Manitoba.
"The probability of getting that rain in April was like one in 87 years," Unduche said.
Piwniuk blamed Colorado lows for bringing Manitoba so much moisture.
"If it's an Alberta clipper, there's not much moisture in that snow, and we got a lot of Alberta clippers over the winter. But when we get Colorado lows, that's the variable," he said.
"That's where we get a lot of moisture and that's where it sort of ties up with the Gulf Stream."
Every community along the Red River has flood-protection infrastructure built to handle the expected crest in May.
Every town and First Nation community along the Red in Manitoba is protected by a ring dike engineered two feet higher than the level of the 1997 flood.
Every property outside those communities that ended up getting damaged in the 1997 flood was required to raise its foundation as well.
As a result, only a handful of farms and acreages that could be cut off face possible evacuations, Piwniuk said.
The province is planning those evacuations by pre-registering people in the flood zone who may be affected, said Johanu Botha, the deputy minister responsible for emergency management.
Sandbagging machines have been delivered to communites throughout the Red River Valley and infrastructure officials are monitoring overland flooding, he said.
"Overall, our emergency response system has ramped up and we are well-positioned to respond to the events that might come our way," Botha said.
The City of Winnipeg is also expected to notify additional properties of the potential need to build sandbag dikes.
Unduche said with the floodway in operation, he does not expect the Red River to crest higher in Winnipeg than about 20 feet above normal winter ice level at James Avenue.
As of Friday, the Red in Winnipeg stood at 17.3 feet James. The river peaked at 22.6 feet James in 2009 mainly because of ice jams at a time when the floodway could not be operated.
The peak volume of the Red River at the floodway intake south of Winnipeg during the 2009 flood was 97,000 cubic feet per second.
Unduche said the Red is expected to crest south of Winnipeg at a peak volume this spring somewhere between 94,000 and 121,000 cubic feet per second.
The 1997 flood of the century crested at 138,000 cubic feet per second.