Winnipeg Free Press - PRINT EDITION

Cold increases threat of ice jams on river

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Stubbornly cold weather is behind an increasing threat of ice jams on the Red River, including inside Winnipeg.

It has been so cold, river ice remains a metre thick on some portions of the Red River, provincial flood forecasters said Wednesday.

When flood water from the United States, where the Red River is already cresting, meets solid river ice at Winnipeg, ice could drive up river levels and create localized flooding.

"It's a backwater effect due to ice conditions," said Steve Topping, executive director, hydrologic forecasting and water management for Manitoba Infrastructure and Transportation.

Ice cover could induce a Winnipeg flood crest of 18.2 to 18.7 feet above normal winter ice levels at James Avenue -- officially, a moderate flood.

Winnipeg flood-planning engineer Grant Mohr said the crest will possibility require the construction of precautionary sandbag dikes around three Winnipeg properties -- two on Cloutier Drive in St. Norbert and one on Kingston Row in St. Vital.

The city plans to contact the property owners over the next two days in order to ensure dikes are in place by the weekend.

"They've had to sandbag in the past, so they're aware of what they have to do," Mohr said.

Ice jams may begin to form on the Red within the city as early as Sunday, Mohr added.

The flood situation this spring is somewhat similar to 2009, when ice jams on the Red River north of Winnipeg caused sudden flooding of Breezy Point.

The major difference this year is there's a lot less water flowing through the Red River drainage basin.

The U.S. National Weather Service expects the Red to crest at the Canada-U.S. border on Friday or Saturday as a minor flood. North of the border, Highway 75 is not expected to be closed, Manitoba Infrastructure and Transportation Minister Steve Ashton said.

Manitoba flood forecasters expect the Red to crest upstream of the floodway inlet some time between Easter Sunday and Tuesday. A peak flow of 40,000 cubic feet per second is expected, with 5,000 cfs carried around the city by the floodway channel.

The floodway cannot operate effectively unless the water and ice on the Red River is flowing freely. Nonetheless, some water spills into the floodway channel when the river is high, even when the floodway apparatus is not operated.

During the 2013 spring flood, floodway operations reduced the crest in Winnipeg to 18.8 feet James on May 1. Without the floodway, the river would have crested six feet higher inside the city, according to the 2013 floodway operation report.

In 2009, ice jams led the Red to crest inside the city at 22.5 feet James. This was the sixth-highest peak recorded since the establishment of the Red River Settlement in 1812.

Meanwhile, the Portage Diversion west of Portage la Prairie will continue to carry 5,000 cfs of Assiniboine River water to Lake Manitoba. This represents 20 per cent of the diversion's normal capacity.

The diversion is operated to reduce the risk of ice jams and flooding along the lower Assiniboine River, between Portage la Prairie and the Red. The aim is to maintain ice on the Assiniboine so Winnipeg does not see an "ice run" that compounds the potential for ice jams.

"We hope that ice will simply rot in place," Topping said.

Should ice jams occur in the city, the province's fleet of amphibex ice-breaking machines can respond as well as heavy equipment on the shore, he said.

"They've been fitted with propellers now, so they're mobile in the water," Topping said. "They can be moved very quickly if required within the city to address ice jamming at whatever location they may occur."

In the unlikely event ice recedes from the Red in Winnipeg before the crest arrives, the river is expected to peak between 16.2 and 16.7 feet James. A crest at this level would be considered a minor flood and would not threaten any Winnipeg properties.

bruce.owen@freepress.mb.ca

bartley.kives@freepress.mb.ca

Republished from the Winnipeg Free Press print edition April 17, 2014 A9

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