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Winnipeg Free Press - PRINT EDITION

Thaw, not runoff, sinks river trail

By: Bartley Kives

Posted: 01/21/2010 1:00 AM | Comments: 0 (including replies)

DON'T blame the City of Winnipeg if you can't skate as far as you'd like this weekend.Part of the city's river trail is underwater because of recent mild weather, not street runoff or sewage outflows, says Manitoba's flood forecaster and chief expert in water dynamics.

The formation of thick river ice in early January, followed by mild weather later in the month, has caused water to run above the ice on the Assiniboine River, Alf Warkentin said Wednesday.

When thick ice forms on the river, there's less water in the liquid channel below it. That means there's no room for more water to flow below the ice during a mid-winter thaw such as the one experienced recently in southwestern Manitoba, Warkentin said. Increased flows in the Assiniboine River exert upward pressure on its frozen surface, but the ice can't move because it's frozen to the banks, so cracks form, allowing water to emerge on the surface, Warkentin said.

"We're doing more observing to see if this is what's happening, but it certainly appears to be the case."

The city has checked its systems and concluded there is no significant drainage -- never mind sewage outflows -- affecting city rivers right now, said city spokeswoman Tammy Melesko.

"It has to do with the (Assiniboine) River all the way back to Brandon and beyond," Warkentin said.

Water above ice on Manitoba rivers is not unusual, he added, noting it could happen anywhere along the Assiniboine River. He said it's possible extra-thick ice along the river trail contributed to the current phenomenon.

Warkentin's explanation makes sense, said Paul Jordan, chief operating officer at The Forks and the driving force behind the river trail. The purpose of clearing the trail is to create thicker ice, he said.

"We knew when we started making the trail this was the thickest ice we've ever run into. That cold spell with no snow froze things up really, really well."

The Winnipeg Police Service is asking people to stay off the Red and Assiniboine rivers, except for a section of approved river trail from The Forks to Hugo Dock.

bartley.kives@freepress.mb.ca

Republished from the Winnipeg Free Press print edition January 21, 2010 B1

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