Costing $8.74 billion, the Belo Monte Dam rising over the Xingu River in Amazonia will generate just 4,500 megawatts per year on average—or more than one-third of its 11,233-MW installed capacity—due to environmental restrictions that have reduced the reservoirs’ size. Still, engineers call it the most daring project under way in Brazil.

Advancing at four independent sites, the project is expected to enter into commercial operation in 2016. Once completed, Belo Monte would operate with the natural flow of the Xingu, and the amount of power to be generated is expected to be the equivalent of 10% of Brazil’s national energy consumption. In power effectively installed, it would be the third-largest hydropower complex in the world after Three Gorges, in China, with 20,300 MW, and Itaipu, between Brazil and Paraguay, with 14,000 MW.

The material excavated for the dam’s 20-kilometer bypass channel covers an impressive 126 million cubic meters, well over half the volume required for the original Panama Canal, which had piled up to 205 cu m at the time of its 1914 opening, according to the Panama Canal Authority.

The size of the bypass channel is equally huge, stretching 210 m wide at the base, 300 m wide on the surface and 25 m deep. Other works are advancing next to it for the preservation of existing channels and igarapes or small streams. In total, this work involves 28 embankments or levees, requiring around 27 million cu m of landfill.

The four construction sites are located 40 km to 50 km away from each other. During a recent hardhat visit, it was clear that one could not tour the enormous scale of these construction works in just one day.

Assembling a labor force big enough to tackle the job also is a feat. Norte Energia, the dam’s concessionaire company, employed a peak workforce of 33,000 in the middle of last year. Through late 2014, about 25,000 people could still be found on site.

The current project includes the construction of reservoirs covering 503 sq km. Initially, the flooded area was to cover 1,600 sq km; however, environmental and local regulators imposed reductions to reach the current size. Some experts call the decision paradoxical because Brazil faces the risk of power shortages in the coming years.

For years during planning, the dam’s site was picked as the most viable, both geologically—featuring as it does metamorphic rocks and granite—and from the water-use point of view, says Gleison Carmozine, engineer and superintendent of Consorcio Engenharia Proprietaria Belo Monte (EPBM), a consortium of engineering design consultants involved in the project.

Water flow also is favorable. The Big Bend of the Xingu, where the main hydropower plant is being constructed, is about 150 km long and drops some 90 m. "If you take all the Amazon River, in its more than 3,000 kilometers of Brazilian territory, you will find that it is very flat and maintains a level difference of 20 meters,” Carmozine says. “The topography and geology of the area, and the water conditions, were determinative in the site selection.”

On the construction side, the Consorcio Construtor Belo Monte (CCMB), led by Andrade Gutierrez, also includes Brazil firms Camargo Corrêa, Norberto Odebrecht, OAS, Queiroz Galvão, Contern, Galvão Engenharia, Serveng-Civilsan, Cetenco and J. Malucelli.