Vegetation in Assiniboine River affecting Manitoba flooding

A pair of canoeists paddle through high water on the Assiniboine River near the Forks in Winnipeg,...

A pair of canoeists paddle through high water on the Assiniboine River near the Forks in Winnipeg, Man. Sunday July 06, 2014. Brian Donogh/Winnipeg Sun/QMI Agency

QMI Agency

, Last Updated: 4:02 PM ET

WINNIPEG -- The Assiniboine River is higher than expected because it's full of plants.

Flood forecasters adjusted their predictions for the worst Monday, asking areas east of Portage la Prairie, Man., to dike for flood levels of 2011 plus one foot, and another two feet of freeboard to deal with waves.

"What we're finding is the Asssiniboine River efficiency is not as good as it was in 2011 due to vegetative foliage in the river," provincial flood analyst Steve Topping said.

He's finding that the faster the river flows, the more effect on the volume of the river that extra foliage is having.

"We are experiencing extremely high flows on the Assiniboine River. Record levels," Topping said.

In Russell, Man., 340 km northwest of Winnipeg, the crest is expected to be four feet higher than in 2011.

In most other places, including St. Lazare, Man., a crest one foot higher than 2011 should be accommodated by dike improvements since that flood.

But the river is still rushing east to Portage la Prairie, Man., where it's expected to crest below 2011 levels early July 9.

Then the 18,000 cubic feet per second of water will rush east, hitting Winnipeg's bedroom communities about 24 hours later.



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It's a critical 48-72 hours, Emergency Measures Organization Minister Steve Ashton said.

"We're mobilizing to minimize the impacts on people," Ashton said. "We realize this is a flood, but it's very much about its impact on people."

The Portage Diversion is being pushed to accept more water than it did in 2011, including raising the east dike embankments with aquadams. That's intended to keep water out of the Delta Beach channel, where that extra water flowed in 2011.

As a precaution, 15 homes have been evacuated in Delta Beach.

Hoop and Holler bend dikes still could be cut to save homes further east.

"If we did nothing -- doing nothing is not an option when you have this surge of water coming," Ashton said. "Historically, without the flood protection we have in place, you would have an uncontrolled breach in the Assiniboine River."

He noted that the Hoop and Holler bend was a natural break point for the Assiniboine during floods before the area was settled, with all that water flowing into Lake Manitoba and causing problems there.

If the surge isn't cut at Hoop and Holler, officials say, it's impossible to know where the surge would break onto land.

"So what we're doing here is controlling as much as possible of a very powerful surge of water," Ashton said.

Brandon, Man., crested just shy of 2011 levels at 10:30 a.m. Monday, with a second, smaller crest expected July 17-18.

 


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