Pointe du Bois Generating Station


Description: Pointe du Bois Generating Station after Spillway Replacement project. (Photo taken October 2017)

Description: Centrale Pointe du Bois après le projet de remplacement du déversoir. (Photo prise en octobre 2017)

Submitted By: Jarrod Malenchak

City: Winnipeg

Region: Manitoba

Benefits to society [Translate]

The 75-MW Pointe du Bois Generating Station is located on the lower reaches of the Winnipeg River after it flows out of the neighboring province of Ontario (approximately 38 km northeast of Lac du Bonnet, Manitoba). It is the oldest hydraulic generating station still in operation on the Winnipeg River and was originally built by the city of Winnipeg to be the main supply of electricity to the booming prairie city that aimed to be the “Chicago of the North.” When the station went into service, many Winnipeg residents still cooked on wood-fired stoves and read by kerosene lamp or candlelight in the evening. In addition, the upstream reservoir is approximately 19 square kilometers in size which has provided premium recreational opportunities in Manitoba cottage country for over 100 years.

Economic benefits [Translate]

When Pointe du Bois first started generating power in 1911, it came from the first three units. As demand grew and equipment and funding became available, more units were added in stages. The final additional units were added in 1926, bringing the total number of units to 16. The per kWh rate for electricity from this station was set at 3.3 cents – a rate that remained unchanged until 1968. Much of the electricity this station produces – on average annually about 599 million kWh – is generated by some of the same 16 horizontal-shaft Francis turbines installed over 100 years ago. Manitoba Hydro acquired Pointe du Bois as part of its purchase of Winnipeg Hydro in 2002. Compared to modern equipment, the older turbines at Pointe du Bois mirror turbines on display in museums; however, the station still produces power and has paid for itself many times. It was originally built for $3.25 million, a huge amount of money at the time, but relatively inexpensive when compared to cost of a new hydroelectric generating station today. The original spillway, installed in 1911 and upgraded in the 1920s and again in the 1950s, was replaced entirely in 2014 at a cost of $560 million. Dam Safety studies done showed that despite repeated rehabilitation work over the previous decades, the old spillway no longer met modern Canadian Dam Association safety guidelines for flood capacity and stability. In addition, a new spillway would improve reliability as well as worker and public safety.

Technical merits [Translate]

The multi section dam included a 215 m rockfill dam and a 170 m concrete gravity dam. Spillway gates consisting of timber stop logs needed to be manually lowered and raised to control the water level in the forebay before the large 170 m powerhouse was constructed. Each generator under normal flow conditions, is driven by 3.6 million cubic meters of water a day with a waterfall drop of approximately 14 m.

The new spillway and associated embankment dams were substantially completed in 2014. The spillway structure was ultimately located on the far east side of the river which allowed for the entire spillway and most of the rock excavation to be completed in the dry. This eliminated many of the project construction risks associated with in-stream work, temporary cofferdam works, and in-the-wet construction activities. This location required curved approach and discharge channels which necessitated simultaneous hydraulic physical and numerical model studies to optimize the novel design. This 7-bay spillway design reduced the total amount of concrete required and established a local source of rock for the new dam construction and upgrades. The new spillway was designed to pass the entire river flow for the Inflow Design Flood (IDF) with no reliance on the Powerhouse flow. This was a significant upgrade from the original spillway and provided enhanced flexibility to accommodate various future alternatives for the ageing generating units. At present, Manitoba Hydro plans to continue operating the station including investigating options to replace a number of the generating units.

Historical background [Translate]

Construction began in 1907 and the first hurdle was getting construction staff and equipment to a site that at the time was surrounded by thick boreal forest and only accessible by a canoe or a small boat. To facilitate the need to transport workers, construction materials and heavy equipment, Winnipeg’s new electrical utility built a railroad to the site. The task was to construct a track, complete with two bridges over the Winnipeg River and Lee River, from the nearby town of Lac du Bonnet roughly 60 km away from the site.

The methods of heavy construction at that time, when compared to current methods, relied more on brute force than anything else. This included clearing the land of all trees by hand, and hewing trees that were used as railway ties or to build cabins for the work camp. Steam powered drills were used, and horses were kept on site to move materials. Work also continued during the grueling winter months when the river froze over.

First, the site and powerhouse had to be developed which was no easy job given its remote location from Winnipeg on the bare rock of the Canadian Shield. The powerhouse continues to house 16 turbine-generator units, including 15 double-horizontal-shaft Francis turbines and one GE Canada-made Straflo turbine-generator. The Straflo unit was commissioned on Nov. 2, 1999 and replaced one of the original Francis turbines. The Straflo unit helped increase the capacity of the generating station to 75 MW.

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