New flood control outlets on Lake Manitoba and Lake St. Martin planned

Public open houses were held last week in Ashern, Manitoba, to present conceptual designs for new flood management strategies, including new outlet structures, on Lake Manitoba west of Winnipeg and Lake St. Martin, about 300 kilometres to the north.

After record floods in 2011 the Manitoba Government commissioned a task force to find ways of improving the control over flood water levels on both lakes.

The province says that adding new outlets from Lakes Manitoba and St. Martin will enable them to exercise greater flexibility in operating the larger provincial water control system, including benefiting the Lower Assiniboine river and the city of Winnipeg.

Infrastructure and Transportation Minister Steve Ashton said on September 18: “We are moving forward to implement greater flood protection by enhancing Lake Manitoba and Lake St. Martin outflow capacities as part of the larger flood management system that includes the Portage Diversion and the Fairford River Water Control Structure.”

Six options were presented for the Lake Manitoba outlet channel, of which two were recommended, based on their cost effectiveness and high environmental ratings. One recommended options is for an 11.6-km channel south of Pinaymootang First Nation to connect Lake Manitoba with Lake St. Martin. The work would include a new control structure and several bridges. The second recommended option was for a 22.8 -km channel following Birch Creek to connect the two lakes. The preliminary total costs are estimated to be in the range of $141 million to $238 million.

Either way, the designers recommended that the new channel capacity should be in the 5,000 to 7,500 cfs range, which would reduce the level of Lake Manitoba by between 0.24 m and 0.34 metres. Without a new outlet channel, the peak water level on the lake without wind in a 200-year event would be around 248.9 metres. The peak level in 2011 was more than that at 249.1 metres.

For the Lake St. Martin Outlet Channel, the province is recommending that an emergency channel that was constructed after the record flooding in 2011 should be expanded and made permanent, along with building a new control structure and permanent access roads. The preliminary cost of this work is between $142 million and $212 million.

KGS Group is the prime consulting engineer working for the Ministry of Infrastructure and Transportation on the studies and recommendations for flood mitigation in the province.

To see the report on the different options for flood management on Lake Manitoba and Lake St. Martin, click here.