Daniel-Johnson Dam

Daniel-Johnson Dam, dam on the Manicouagan River in Quebec province, Canada, one of the world’s largest multiple-arch buttress dams. An iconic symbol of Québécois ingenuity, the impressive dam supplies water to the nearby Manic-5 and Manic-5-PA power stations to generate hydroelectric power for the greater Quebec area. The dam is located in the administrative region of Côte-Nord, some 800 km (nearly 500 miles) northeast of Montreal. The facility is owned and operated by Hydro-Québec, a public utility.

History and construction

In 1955, given improvements in long-distance electricity transmission and an increasing demand for electricity in southern Quebec, Hydro-Québec launched a five-year feasibility study for a hydroelectric dam on the Manicouagan River. The river was found to have exceptional potential, and Hydro-Québec undertook the ambitious Manicouagan-Outardes project to construct five dams on the Manicouagan and three on the Outardes. Eventually the multiple-arch buttress design by French civil engineer André Coyne was selected for the fifth Manicouagan dam, then christened Manic-5. Unlike solid gravity dams, this type of dam does not rely entirely on its own weight to resist the thrust of the water and thus requires less concrete to build. Construction began in 1959.

To divert the river, large tunnels were dug through the granite wall of the gorge and two cofferdams were built, one to divert the water into the tunnels and the other to prevent backflow into the construction site. With the river thus manipulated, a pit was dug between the cofferdams to remove the alluvial deposits and then filled with concrete as the final preparatory step. The first concrete for the dam itself was poured in October 1962. Concrete was poured day and night, with cessation for the freezing temperatures of winter, in an attempt to construct at least a rudimentary dam before springtime flooding. The deadline was successfully met, and the diversion tunnels were sealed off, allowing the seasonal flooding to begin filling the reservoir in early 1963, a task that was not completed until 1977. The dam itself was completed in 1968.

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Scheduled to be inaugurated on September 26, 1968, the dam was originally to be named Duplessis Dam in honour of former Quebec premier Maurice Duplessis. However, on the eve of the dam’s inauguration, Quebec Premier Daniel Johnson, Sr., died suddenly of a heart attack; he had been slated to preside over the opening ceremonies and had helped launched the dam’s construction as minister of water resources in 1959. The celebrations were postponed for a year, at which point Johnson’s successor, Jean-Jacques Bertrand, inaugurated the Daniel-Johnson Dam in his honour on September 26, 1969.

During and after its construction, numerous cracks formed on both the upstream and downstream faces of the dam, especially at the bases of the arches. The high-pressure injection methods that were used to grout the cracks frequently resulted in new or worsening cracks, and the work was halted in 1985 until an extensive behavioral analysis of the dam and its arches could be carried out. In 1997, armed with the findings of the study, the work was continued to reduce water infiltration into the concrete structure.

Dimensions and facilities

The Daniel-Johnson Dam is 214 metres (703 feet) tall at its highest point, making it the tallest dam of its type in the world. Its 14 buttresses and 13 arches span 1,314 metres (4,311 feet) across the reservoir. The two buttresses that form the central archway are 160 metres (530 feet) apart at their bases, while the remaining buttresses are each about 76 metres (250 feet) apart. The dam was constructed with 2.2 million cubic metres (more than 77 million cubic feet) of high-quality concrete meant to withstand repeated freezing and thawing.

The dam supplies water to power the turbines of two hydroelectric generating stations nearby. The first station, Manic-5, began operating its eight Francis turbines in 1970–71. The station was modernized in the 1980s, increasing its output dramatically, and its inlet valves were refurbished in 2019. The second station, Manic-5-PA, was built in 1989 and has four turbines. Together, the complex has an installed capacity of 2,660 megawatts.

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The dam impounds the Manicouagan River to form an immense reservoir covering about 2,000 square km (about 775 square miles). Situated at the site of an ancient crater impact lake, the annular Manicouagan Reservoir, also known as the Eye of Quebec, completely surrounds René-Levasseur Island, the second largest lake island in the world.