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Province lowers forecast for Assiniboine River water flow

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The province has again lowered its forecast for how much water is coming down the Assiniboine River.

In a flood briefing at noon today, officials said flows are now forecast to reach approximately 50,000 cubic feet per second (cfs) at the Portage Reservoir by about noon tomorrow. That’s down from a high of 54,000 cfs projected on Friday and 51,500 cfs on Monday.

Despite the lowered projection, the province has not ruled out making a deliberate breach of the Assiniboine River at the Hoop and Holler Bend south-east of Portage la Prairie.

The province said such action would only be a last resort if Assiniboine River dikes show signs of excess seepage and possible failure, and an uncontrolled breach.

To that end the Canadian Armed Forces has sent in a CP-140 Aurora surveillance aircraft that has specialized equipment that can detect, even at night, excessive moisture due to a failing dike. Currently, 500 military personnel are putting the finishing touches on protecting about 200 homes along the Assiniboine River from Portage la Prairie to Headingley and about 150 homes south of the Hoop and Holler Bend.

The army was called in late last week after province declared a state of emergency.

The province plans to divert up to 34,000 cfs through the Portage Diversion and 18,000 cfs down the Assiniboine River towards Winnipeg to handle the surge, which is expected to last about one day before levels begin to decrease. The Portage Diversion is currently operating with flows of 25,000 cfs. Flows on the Assiniboine River downstream of the diversion are 16,700 cfs.

Water from the diversion is funneled into Lake Manitoba. The forecast peak water level on Lake Manitoba is 814.6 ft. in early August.

Officials said the flood watch will remain for about another two weeks as a second surge is building up in western Manitoba in the Shellmouth Reservoir, upstream on the Assiniboine River. official said.

The water level on the Shellmouth Reservoir has increased to 1,415.7 feet. Inflows to the reservoir are approximately 18,370 cfs today while outflows from the reservoir are approximately 14,710 cfs.

Official said inflows to the Shellmouth Dam from Saskatchewan are forecast to peak at approximately 21,800 cfs on July 10 and the reservoir level is forecast to peak at approximately 1.416.1 ft. July 12. Peak forecast outflows of approximately 16,800 cfs are expected July 11.

That means a second summer crest on the Assiniboine River at Brandon July 17 to 18 at 31,000 to 32,000 cfs. This second crest will consist of flows from the upper Assiniboine and Qu'Appelle river basins.

The water moving through the second crest is runoff from last week’s rainstorms that drenched a large part of Saskatchewan and southern Manitoba.

Water levels between the Shellmouth Reservoir and St. Lazare will be higher than levels in 2011, official said. The forecast peak flow at St. Lazare is approximately 25,000 to 28,500 cfs July 14.

These levels will result in water flows below the permanent flood protection dikes, but approximately one foot higher than 2011 water levels. Several homes outside the permanent dikes are being monitored in case evacuations are needed.


Updated on Tuesday, July 8, 2014 at 6:07 PM CDT: Adds video.

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