Historic Flood - 2014

In the summer of 2014, exceptionally heavy rains in the Upper Assiniboine Basin caused major flooding on the Assiniboine River. The unregulated peak flow at Brandon was the 2nd highest in recorded history, occurring only 3 years later than the record setting flood of 2011.

The summer flooding experienced in 2014 can be attributed to the amount of precipitation that occurred in the last four days of June as well as the accumulated precipitation that occurred during April, May and June.The earliest forecast for the summer 2014 event suggested that flows on the Assiniboine River upstream of the diversion would be between 1,360 cms (48,000) to 1,472 cms (52,000 cfs), but these were later revised to between 1,472 cms to 1,530 cms (52,000 to 54,000 cfs). This is similar to the 2011 event which saw peak flows of approximately 1,504 cms (53,100 cfs).

In response, the Province issued a Provincial State of Local Emergency on July 4th and on July 5th requested additional support from the Canadian Armed Forces to assist in flood protection preparations along the Assiniboine River. In a very short amount of time, Manitoba Infrastructure personnel worked with contractors and engineering service providers to undertake the following works along the Portage Diversion and along the lower Assiniboine River:

• Inspection, preparation and monitoring of the diversion channel dikes and related infrastructure for increased flows of 963 cms (34,000 cfs),
• Inspection, preparation and monitoring of the Assiniboine River dikes to handle flows of 510 cms (18,000 cfs),
• Preparation of the Hoop and Holler controlled breach site on the Lower Assiniboine River to alleviate flows above 510 cms (18,000 cfs) if required,
• Coordination of temporary flood protection efforts along the lower Assiniboine River beyond the Provincial Dikes to protect approximately 136 homes at risk of flooding.

The 2014 summer flood had two distinct flood peaks within a week of each other at Portage La Prairie. The first peak reached Portage la Prairie on July 9th with an estimated instantaneous peak inflow to the Portage Reservoir of 1,442 cms (50,050 cfs). Of that, 928 cms (32,800 cfs) was sent down the Portage Diversion, with the remaining 514 cms (18,150 cfs) allowed to flow through the bascule gates to the Lower Assiniboine river. On July 15th, a second crest arrived at Portage la Prairie with an estimated instantaneous peak inflow to the Portage Reservoir of 1,458 cms (51,500 cfs). Of that, 948 cms (33,500 cfs) was sent down the Portage Diversion, with the remaining 510 cms (18,010 cfs) allowed to flow through the bascule gates to the Lower Assiniboine River. The summer operation of the Portage Diversion lasted approximately 60 days (June 30 – August 28).

The flow volume diverted to Lake Manitoba was the second largest diverted volume since construction of the Portage Diversion. In 2014, the diversion contributed 2,720,000 cubic decametres (2,206,000 acre-feet) of water to Lake Manitoba, representing 24% of the annual inflow volume to the lake.

 

Portage la Prairie Operations Centre, 2014	Assiniboine River at P.R. 248, July 2014
Portage Diversion at Highway 1, July 2014	Portage Diversion Controlled Breach, July 2014
Overland Flooding, St. Francois Xavier, July 2014	Assiniboine River Control Structure