The Manitoba government said it plans to divert water from the Assiniboine River into the La Salle River watershed in an effort to avoid a massive spill that would inundate 500 square kilometres of southern Manitoba.
Due to unprecedented flows on the Assiniboine, the province plans to send 2,000 to 6,000 cubic feet of water per second from the Assiniboine River into the La Salle River through a new channel southeast of Portage la Prairie, Emergency Measures Minister Steve Ashton told a news conference Monday.
The province also plans to send more water through the Portage Diversion into Lake Manitoba, even though the artificial channel west of Portage la Prairie was not designed to handle higher flows, he added.
The Assiniboine is expected to flow as much as 51,000 cubic feet per second at Portage la Prairie within days. Without intervention, it could spill its banks at a rate of 15,000 cubic feet per second in a huge spill that would threaten a dozen communities.
The new diversion southeast of Portage la Prairie is an attempt to control the spill and impact only 150 homes and 225 square kilometre of land, versus 850 homes and 500 square kilometres in an uncontrolled spill.
"The release will be through the south side of the Assiniboine dikes and will flood lands within the La Salle watershed adjacent to the Elm River, the Elm River Channel, the Elm River Relief Channel, the Scott Coulee, the Scott Drain and the La Salle River downstream of the Elie dam and reservoir. This controlled release is necessary to reduce the risk and severity of an uncontrolled breach of the dikes," the province announced.
The Manitoba government declared a state of emergency Monday as flood waters from the Assiniboine River threatened the city of Portage la Prairie and the rural municipalities of Portage, Woodlands, Rosser, St. Francois Xavier, Headingley, Cartier, Macdonald and Grey.
These high flows are due to much higher than forecast flows from Saskatchewan and an "unstable weather system" that could bring 20 to 40 mm of rain across much of southern Manitoba between now and Wednesday.
The city of Winnipeg is not threatened, officials said.
Meanwhile, Ashton said that flood forecasting is a difficult task when you’re dealing with unprecedented water flows as the province is in western Manitoba.
In May 4, the province was predicting a crest ion Brandon of 26,000 cfs in Brandon. By late Sunday, the Assiniboine reached 38,000 cfs in Manitoba’s second-largest city — and the crest has yet to arrive.
The province suggested on Friday that a faulty federal water gauge in the Qu’Appelle River at Welby, Sask., had thrown its forecasts off. But officials were backing away from that assertion Monday.