2011 Assiniboine River flood

After a heavy snowfall on April 29 and 30 over much of the Assiniboine River watershed the crest forecast for Brandon was revised upward well above the flood of 1976.

[5][6][7] Premier Greg Selinger requested from Prime Minister Stephen Harper troops from the Canadian military to help with the flood fighting efforts.

[9] This amount of water would overwhelm the dikes downstream, along the Assiniboine River, which were only built to allow for a channel capacity of about 10,000-11,000 cu ft/s before spilling over.

It was determined by the Manitoba government that the capacity could be increased to 32000-34000 cu ft/s by building up the banks of the Portage Diversion, depending on hydraulic resistance on bridges along the channel.

This option was chosen as opposed to risking an uncontrolled breach, which could release as much as 500 square kilometres (190 sq mi) with flows of up to 15,000 cu ft/s (420 m3/s), while over 800 homes would be affected by the waters.

[11] The resultant flooding was very slow moving and was expected to take several days to reach the La Salle River.

The waters intentionally spilled from the Assiniboine were expected to cover 185 square kilometres (71 sq mi) and flood a possible 150 homes.

Increasing the capacity of the Diversion put surrounding residences in danger of being flooded, also prompting an evacuation of Delta Beach on Lake Manitoba.

[10][16][17] A technical review of the 2011 flood completed in October, 2013 concluded that the net effect of artificial works (Fairford River improvements and the Portage Diversion) was a rise of 0.3 feet (0.091 m) on the lake.