Several sites on the Nelson River, with potential of millions of horsepower, had been identified as early as 1911, but transmission of power to population centers in the south was beyond the state of the art of electric power transmission at that time. Between 1955 and 1960, studies were carried out to determine what resources would be available for future hydraulic generation in Manitoba. The stations at Kelsey, Kettle, Long Spruce and Limestone were built on the lower Nelson River to support both Manitoba load growth and export plans. Limestone, the largest generating station in Manitoba, is located on the Lower Nelson only 90 km from Hudson Bay. Long-term firm power sales contracts were signed with Northern States Power Company of Minneapolis, Minnesota. Control dams and excavated channels have transformed Lake Winnipeg into a 25,000 km2reservoir for the Nelson hydroelectric system. The great distance between generating sites on the Nelson River and load centres in southern Manitoba required the use of high-voltage, direct current electric power transmission lines to bring the energy to market. When these lines began operation as the Nelson River Bipole in 1972, they were the longest and highest-voltage direct current lines in the world. The Dorsey converter station is 26 km northwest of Winnipeg, Manitoba.
Generating stations
Churchill River Diversion
One of the key elements of the Nelson project was the diversion of much of the Churchill River into the Nelson watershed. The 1,609 km long Churchill River originates in northern Alberta and drains into Hudson Bay at Churchill, Manitoba. Currently the Missi Falls Control Structure at the mouth of South Indian Lake reduces the flow of the Churchill River to 15% of its natural flow. This causes South Indian Lake to rise 3 metres, as opposed to the 10.6 metres envisioned in the original plan. The diverted water flows through the 9.3 km South Bay Diversion Channel into the Rat River, which is in the Nelson River watershed. The outflow of Rat River into the Burntwood and subsequently Nelson River is controlled by the Notigi Control Structure. Before the construction of the Diversion, the Manitoba portion of the Churchill River was estimated to have 3 Gigawatts of hydroelectric potential. The river was however 160 km further north than the Nelson River, thus further from the major users of power in southern Manitoba. Jointly harnessing the water increased the flow of the Nelson River by 40%, while the flow of the Burntwood River is now 9 times pre-diversion levels. In 1973 Manitoba Hydro was granted an interim license to divert 850 m3/s of water from the Churchill River. Construction began the same year and finished in 1976. Diversion began 9 September 1976 with full planned potential reached on 20 August 1977.
New projects
New Hydraulic Generation and HVDC Transmission.: Studies are continuing to permit eventual construction of new generating projects along the Nelson River. The Keeyask station will have a capacity of approximately 630 megawatts. Final design and construction have started. The 1380 megawatt Conawapa project was initiated but postponed indefinitely in 1992 when Ontario Hydro elected not to purchase firm energy from Manitoba. Planning activities are continuing, but no construction commitment has been made and no environmental hearings are currently scheduled. The in-service date would be after that for Keeyask, with current estimated load growth requiring first power in 2021. The station at Notigi would be rated approximately 100 megawatts, but no in-service date has been set for this project.
More than 5000 MW of hydroelectric potential could be developed in Manitoba, which includes 1380 MW at the Conawapa site, 630 MW at the Keeyask site, and 1000 MW at the Gillam Island site, all on the lower Nelson river. Other sites have been assessed but are not currently under study for development. All of these developments would require a large increase in electric power exports, since Manitoba load growth will not require this capacity for a generation or more. All of these projects require additional HVDC transmission capacity from the North to the South. One such project, Bipole III, had been discussed with communities on the east side of Lake Winnipeg, but this area has been reserved by the provincial government, making transmission line construction infeasible. The government and Manitoba Hydro have currently rerouted Bipole III through the west side of Manitoba and construction has begun as of 2012.
Controversies and issues
Like any other large-scale activity, the Nelson River Hydroelectric Project has not been without controversy. In 1976, the Churchill River diversion project was set into operation. Flow was diverted by a series of channels and control structures into the Nelson River. Instead of developing hydroelectric sites along the Churchill River, water was diverted by control structures and an artificial channel into the Nelson, thereby increasing flow and saving cost of development. The effects of this diversion on pre-existing water levels and the indigenous Cree and Métis people continue to be felt to this day. Negotiations between the affected Northern communities and Manitoba Hydro continue, to discuss mitigation measures and compensation for loss of traditional resource areas and sites. The water level of Lake Winnipeg is now regulated by Manitoba Hydro as part of the energy generation operations. Some property owners on the southern edge of the lake feel that the levels are now maintained at a higher average level than would be natural, and attribute erosion of their property to the lake level. Manitoba Hydro has pointed out that the regulation project also allows lake level to be lowered, such as during the 1997 floods, thereby preventing significant property damage. Although development of the Nelson River system was intended to secure a reliable source of low-cost energy to promote industrial development in Manitoba, such development was not forthcoming. Concerns about the magnitude and cost of Hydro development led the provincial government to start an inquiry into the management of the company. The Commission of Inquiry into Manitoba Hydro reported in 1979 that Manitoba Hydro had not developed resources in the lowest-cost and most efficient way, and made many recommendations for the governance of Manitoba Hydro.
