Manitoba Hydro’s northern generation system is more complex than just dams in rivers. First, about 80 percent of the flow of the Churchill River is diverted southward into the Nelson River where the main generating dams are located.¹ This was deemed a cheaper way of harnessing the Churchill River than building generation dams on the river.

In order to divert the Churchill, Manitoba Hydro built the Missi Falls control structure at the eastern outlet of Southern Indian Lake–a lake which is essentially a widening of the Churchill River. (See maps.) The Missi Falls control structure raises the level of Southern Indian Lake by about 3 meters (10 feet) causing it to overflow southward through a man-made channel into the Rat-Burntwood River system which, in turn, empties into the Nelson River where the main generating dams are located.² This diversion augments the flow of the Nelson River by as much as 40 percent.³

Date
The diversion went into operation in 1976.⁴

Flooding 
Churchill River Diversion permanently floods 836.9 square kilometers of boreal forest at Southern Indian Lake and along the diversion route.⁵ That is an area almost a third the size of the Whiteshell Provincial Park.⁶                     

Unnatural Flows
Water flows along the roughly 300-kilometer-long⁷ diversion route are far greater than what they would be naturally. Average annual flows of the Burntwood River at Thompson are about 9.5 times greater than they would be in a state of nature.8

De-watering
Downstream of Missi Falls, the Churchill River and the lakes that are part of the river system are diminished in size. Three of the larger lakes along that stretch (Partridge Breast, Northern Indian, and Fiddler) have been reduced in area by 39 to 76 percent.9

35-year interim licence
Almost 35 years after Churchill River Diversion was completed, it continues to operate under an interim Water Power Act licence. A process is currently underway to finalize the licence.

See Manitoba Hydro’s description of the Churchill River Diversion project here. Or see Hydro’s 1970s booklet Power from Nelson which also explains the diversion.

Churchill River Diversion works in conjunction with another equally ambitious and grandiose project–Lake Winnipeg Regulation.

Notes

1.  Source: “Federal Ecological Monitoring Program (FEMP): Final Report,” Environment Canada / Department of Fisheries and Oceans, April 1992, Vol. 1, pp. 2 – 4, 2 – 5.
   
   According to this study, the estimated, long-term mean flow of the Churchill River at Missi Falls under natural conditions is 1,100 cubic meters per second and the projected long-term mean flow with diversion is 200 cubic meters per second, resulting in an average diversion of about 82 percent. The Manitoba Water Stewardship and Manitoba Hydro websites say long-term, natural outflows from Southern Indian Lake averaged 991 cubic meters per second but they do not provide average flows with diversion.
2. Source: Manitoba Hydro webpage on Churchill River Diversion (accessed Nov 2010).
3.  Source: Manitoba Hydro webpage on Water Regimes & Levels (accessed January 2011).
4. Source: Manitoba Hydro online timeline (accessed January 2011). Partial operation began in 1976 (less than the full discharge of water allowed by the licence) with full operation in 1977. Therefore, sometimes 1977 is listed as the first year it went into operation.
5.  Source: “Federal Ecological Monitoring Program (FEMP): Final Report,” Environment Canada / Department of Fisheries and Oceans, April 1992, Vol. 1, p. 2 – 7. Due to ongoing shoreline erosion, and the resulting disappearance of islands and expansion of lakes, the area flooded is likely greater than the figure given. Manitoba Hydro and the Manitoba Government have declined requests for data that would provide a current figure.
6.  According to the Government of Manitoba webpage about the Whiteshell Provincial Park, the park covers an area of 2,729 square kilometers.
7.  Estimate based on provincial transportation department map.
8.  Source: “Federal Ecological Monitoring Program (FEMP): Final Report,” Environment Canada / Department of Fisheries and Oceans, April 1992, Vol. 1, p. 2 – 8.
9.  Source: “Federal Ecological Monitoring Program (FEMP): Final Report,” Environment Canada / Department of Fisheries and Oceans, April 1992, Vol. 1, p. 2 – 5.