One of the world’s largest run-of-the-river hydroelectric projects under construction is about to begin, installing unique bulb turbines that eventually will contribute 3,150 MW to Brazil’s energy grid.

The $9-billion San Antonio hydroelectric project will require 44 massive bulb turbines seven meters in diameter, considered the largest ever built. Each turbine has 7-m-dia rotors and is capable of producing 71.6 MW of power. The turbine parts are being manufactured by France’s Alstom and the Austrian-German Voith Hydro in São Paulo, then shipped to the jobsite by boat to be re-assembled.

The project on the Madiera River in the Brazilian Amazon is on track to begin providing power as early as December, says project manager José Bonifácio Pinto of Odebrecht-led Consórcio Santo Antonio Energia. “After the first turbine goes on line, we plan to add one or two every month after that.”

When construction is complete in 2015, San Antonio is expected to be the largest dam of its type ever constructed and one of the biggest in Brazil. But it won’t hold the title for long: The Jirau hydroelectric dam, almost 100 kilometers upstream and also a run-of-the-river project, will have an installed capacity of 3,300 MW when completed in 2016. The builders are GDF Suez SA and Camargo Correa S.

The San Antonio dam is located on the Madeira River just a few miles south of Porto Vehlo, a town of about 330,000 people, which is also the state of Rondônia’s capital.

Initially, Brazil planned to build a conventional dam on the river, but environmental concerns prompted a switch to a run-of-the-river scheme that relies on the flow of the river to generate power. The current dam is expected to create a reservoir approximately 260 sq km in size, a tenth the size of a traditional dam.

The project consortium includes Brazilian construction firm Andrade Gutierrez, Bardella S.A. Ind�strias Mecânicas, Areva Transmissão e Distribui�ão de Energia and Siemens Ltd. The group won the contract for the project when it offered to sell electricity to the Brazilian grid at $43.82 per MWh, approximately a third less than the capped tender price.

The work involves the excavation of more than 17.2 million cu m of material, more than a third including rock. More than 800 tons of cement will be used in the structure’s construction. Dam construction is expected to peak this year, with more than 10,000 workers employed on-site.

The work on the dam began in September 2008 as the river right bank, facing downstream near the Ilha do Pres�dio island, was isolated with cofferdams. After these were completed, the excavation for the portion of the dam housing eight turbines began.

Work on the opposite bank of the river, which did not require the instillation of cofferdams, began at the start of 2009. A total of 23 turbines in two groupings will be situated on this section as well as the dam’s primary spillway.

This summer, consortium officials plan to route the river through the spillway and then build cofferdams on its existing bed to start excavations for the final section of dam construction.

The spillway structure was built by simultaneously erecting pairs of the 40-m-tall pillars to allow the electromechanical work on each gate to begin more quickly. The consortium used sliding molds, which allowed casing up to 20 centimeters of concrete per hour.

Eventually, a transportation system will be installed to permit migratory fish to pass from the river to the reservoir and access breeding areas upstream. In addition, a log interceptor will be installed at the surface of the reservoir upstream from the dam to ensure the turbines won’t be damaged by large debris.