Breach best of bad choices

JOHN WOODS / THE CANADIAN PRESS Enlarge Image

A crew tops up the main 18th Street dike protecting Brandon from the rising Assiniboine River.

Manitoba will punch a hole in a dike along the south side of the Assiniboine River east of Portage la Prairie and risk flooding 150 homes rather than take the chance an uncontrolled flood will swamp many more.

That was the grim choice flood officials were left with Monday as they faced an unprecedented tide of water from western Manitoba.

Enlarge Image

Soldiers from C Company, Second Battalion Princess Patricia's Canadian Light Infantry help with sandbagging just outside Poplar Point on Monday. (JOHN WOODS / THE CANADIAN PRESS)

At a Monday evening news conference that capped a day spent furiously finalizing plans, provincial flood officials said the controlled release of water will prevent the Assiniboine from spilling its banks east of Portage la Prairie.

An uncontrolled spill could send a rush of water -- 15,000 cubic feet per second -- into the La Salle River, flooding 500 square kilometres of southern Manitoba and up to 850 homes in communities such as Sanford, La Salle and Starbuck.

The unusual plan to punch a hole in the side of the Assiniboine dike, reminiscent of the last-minute construction of the Brunkild Z-dike during the 1997 Red River flood, would create a lot less damage.

The province expects a controlled spill into the La Salle watershed to flood 225 square kilometres of land south of the CN Rail main line in the RMs of Portage and Cartier, flooding 150 homes.

The dike breach will be made as early as Wednesday. The province has yet to determine how it will make the cut.

During the next few days, the province will also attempt to increase the capacity of the Portage Diversion, which sends most of the Assiniboine River's flow into Lake Manitoba. It hopes to send as much as 32,000 cubic feet per second into Lake Manitoba, even though the artificial channel is designed to handle only 25,000 cfs.

At the same time, members of the Canadian Armed Forces will tend to newly shored-up dikes along the Assiniboine between Portage and Headingley to see if the river can handle even more water -- probably an additional 2,000 cfs.

Depending on the success of these two gambits, from 2,000 to 6,000 cfs of water will be allowed out through the controlled breach in the dike southwest of Portage la Prairie, between the hamlets of Southport and Hoop and Holler Bend.

"We have been doing everything possible to minimize the need for any controlled release of the water," Emergency Measures Minister Steve Ashton said last night.

But the province felt it was out of options.

"The worst that can happen is an uncontrolled breach of the dike, because you can lose control of the water and where it goes," Premier Greg Selinger said.

The deliberate breach will flood land within the La Salle River watershed along the Elm River, the Elm River Channel, the Elm River Relief Channel, the Scott Coulee, the Scott Drain and the La Salle River downstream of the Elie dam and reservoir.

The 150 homeowners at risk of flooding were to be notified almost immediately by their municipalities that they will be evacuated. The province said it will do all it can to protect their residences. Homeowners will qualify for compensation if their houses are damaged.

With the Assiniboine River already at high levels, a big rainstorm forecast for southern Manitoba and ending Wednesday is adding to flood fighters' sense of urgency. The rain is expected to bring 20 to 40 millimetres and some localities in western Manitoba could get 70 mm.

To deal with the imminent flood threat, the Manitoba government has declared a provincial state of emergency for the city of Portage la Prairie and the RMs of Portage, Woodlands, Rosser, St. Francois Xavier, Headingley, Cartier, Macdonald and Grey.

The controlled spill will increase the La Salle River's flow into the Red River at St. Norbert, but this will have no effect on the City of Winnipeg's flood-protection efforts, said Grant Mohr, the city's flood-protection engineer.

A controlled spill into the La Salle may increase the Red River's level in Winnipeg about two feet, but city properties are already protected to that level, Mohr said.

A slight increase in the Assiniboine River's flow to Winnipeg also won't affect flood-protection efforts on the west side of the city, he added.

The province is fortifying dikes between the Portage Diversion gates and the railway bridge 1.6 km north of the Trans-Canada Highway. Crews are also working on the embankments to increase channel capacity.

larry.kusch@freepress.mb.ca,  bartley.kives@freepress.mb.ca

Making the cut

The arithmetic behind the province's unusual plan to avert an uncontrolled spill from the Assiniboine River into the La Salle River watershed, by deliberately cutting a hole in an Assiniboine dike:

UNCONTROLLED SPILL

• Flow of water into La Salle River watershed: 15,000 cubic feet per second.
• Area to be flooded: estimated at 500 square kilometres
• Flooded-out homes: About 850
• Flooded areas: St. Eustache, Elie, St. Francois-Xavier, Poplar Point, High Bluff, Bernard, Fortier, Starbuck, Sanford, La Salle and surrounding areas.
• See a map (PDF)

DELIBERATE BREACH

• Flow of water into La Salle River watershed: 2,000 to 6,000 cubic feet per second
• Area to be flooded: estimated at 225 square kilometres
• Flooded-out homes: About 150
• Flooded areas: Elm River, the Elm River Channel, the Elm River Relief Channel, the Scott Coulee, the Scott Drain and the La Salle River downstream of the Elie dam and reservoir.
• See a map (PDF)

Republished from the Winnipeg Free Press print edition May 10, 2011 A3