Historic Flood - 1976

The flood of 1976 was the largest flood on the Assiniboine River since the flood of 1882.  The flood developed due to high soil moisture conditions going into the fall of 1975, higher than normal snowpack in the Souris River Basin (300 to 400 percent of normal) and the Assiniboine River Basin (200 to 300 percent of normal), and a very rapid snowmelt.

The flow along the Assiniboine River just upstream of Portage La Prairie peaked at 1,388 cms (49,000 cfs) in 1976. At peak discharge the Portage Diversion was used above its maximum design capacity to divert 736 cms (26,000 cfs) to Lake Manitoba. The Lower Assiniboine River dikes extending from Portage La Prairie to east of Baie St. Paul were reinforced to prevent major overland flooding. A peak flow of 668 cms (23,600 cfs) was recorded in the Assiniboine River at the Southport bridge on April 21st. Plywood flashboard was installed along the top of the dikes, in order to contain the high flows at the peak for a brief period of time. Flows above 510 cms (18,000 cfs) in the Lower Assiniboine lasted for about one week.

The volume of water discharged into Lake Manitoba from the Portage Diversion in 1976 was 1,750,000 cubic decametres (1,420,000 acre-feet). This makes up 39% of the total annual inflow volume of water into Lake Manitoba in 1976.

Overland flooding along the Lower Assiniboine River	Overland flooding along the Lower Assiniboine River
Poplar Point Bridge	Reinforcing Assiniboine River Dikes
Preparing Sandbags	Flash Boarding along Assiniboine River Dikes