The Nelson River Hydroelectric Project refers to the construction of a series of dams and hydroelectric power plants on the Nelson River in Northern Manitoba, Canada. The project began to take shape in the late 1950s, with the planning and construction of the Kelsey dam and hydroelectric power station, and later was expanded to include the diversion of the upper Churchill River into the Nelson River and the transformation of Lake Winnipeg, the world's 11th largest freshwater lake, into a hydroelectric reservoir. The project is owned and operated by Manitoba Hydro, the electrical utility in the province.
Overview
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 centres 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 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 km2 reservoir 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 (HVDC) 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 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 (10 feet), as opposed to the 10.6 metres (35 feet) envisioned in the original plan. The diverted water flows through the 9.3 km (5.8 mi) 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 (100 mi) 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 licence to divert 850 m3/s (30,000 cu ft/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 (Keeyask, Conawapa, Notigi) and HVDC Transmission.: Studies are continuing to permit eventual construction of new generating projects along the Nelson River. The Keeyask (formerly Gull) 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.