Winnipeg’s floodway gates face test due to ice build-up

Just as the Herculean work on the Red River Floodway around Winnipeg is nearing completion, the city has to confront the possible danger of flooding. Thousands had volunteered to pile sandbags to shore up the swollen river banks in Winnipeg and communities around.

This year the unusual amount of ice jamming poses a problem for opening up the intake gates that will allow water to be diverted into the Floodway. Normally the intake gates would not be opened while ice was upstream from the gates, but Manitoba Water Stewardship was warning that they might have to take the risk and open them up over the next few days if water upstream rises above the 6.1 metre (20-foot) mark. If not, the city could be at risk of flooding.

The problem is, if they open the gates and ice enters the floodway, there’s a small chance the ice could jam up at the narrower bridge crossings, thereby causing water to overtop the channel and flow towards the city. The first vulnerable point is St. Mary’s Road bridge.

A spokesperson with the provincial government, however, said the floodway would “easily” be able to meet Winnipeg’s flood protection needs now that the channel has been almost doubled in size. The expansion project started in 2005 has seen the floodway deepened and widened, so that it should be able to carry 4,000 cubic metres per second now, compared to the 1,700 cubic metres it could handle during the great flood of 1997.

The expansion project is a complex engineering feat involving not only widening the 1960s-era  42-kilometre trench, but also in re-engineering the many bridges, utility and railway crossings that span the channel. KGS Group of Winnipeg did the conceptual design, and they were part of the consortia that did the final design for the expansion. Other companies involved include Hatch, SNC-Lavalin, AECOM, Wardrop, Dillon, Barnes & Duncan, and First Canadian Engineers.

The critical floodway inlet control structure is to the south of Winnipeg, north of St. Adolphe. It was designed as pie-shaped steel gates, 11 metres high and 34 metres wide, which are submerged in the river channel. When they are raised, the water builds on the upstream side and is diverted into the floodway. The floodway itself has been expanded to an average width of 250 metres. Winnipeg is also protected on its southwest flank by the 34-kilometre West Dike.

Authorities were expecting the river to rise to 6.25 metres (20.5 feet) in Winnipeg if the ice was not moving freely by April 8. The crest of the Red River was expected to reach the Winnipeg area by April 16, but that time the ice should be gone.

This year a mid-March thaw followed by a late March freeze-up created ice jams, which force the water to rise unpredictably in certain places.