More than 90 percent of the electricity produced in Brazil comes from hydropower. It has been argued that the national debt would be much higher without this saving on the costs of imported fossil fuels.

At first, hydropower developments targeted river basins near big cities, such as the basins of the Parana and São Francisco. As Brazil's energy needs grow, sources of hydropower are sought in the more remote interior areas, particularly the Amazon river basin.

For much of this century the vast and unexploited Amazon Basin has been seen as a major resource for economic growth in Brazil. Its timber could be exported, and the cleared land used for cattle-raising. Now the region provides hydro-electric power to further the country's industrial development.

Over the past few years, however, a passionate dispute has emerged about the long-term cost of exploiting the fragile Amazonian ecosystem for short-term economic advantage. Deforestation is often considered the main issue. The building of a large dam does contribute to the reduction of natural forest, but it also affects the human and natural environment in several different ways.

Critics of Amazonian dams point to a variety of adverse impacts:

• The lives of indigenous people and ethnic minorities are irrevocably disturbed by displacement and changes in the environment
• The habitats of unique fish, animals and plants species are destroyed
• The change in water quality affects fauna, flora and human populations for long distances downstream
• Disease-bearing mosquitoes breed in the large reservoirs behind the dams
• Migration is encouraged into otherwise untouched areas
• Dam reservoirs may contribute to "the Greenhouse Effect"

The Amazon River Basin

6,771 kilometers long, the Amazon is the world's second longest river. With a mean flow of 200,000 m³/second it is the source of 20% of the freshwater discharged into the oceans. The Amazon has

Map of the Amazon River Basin (Opens in new browser window)

the world largest and most complex river basin, having a drainage area of about 7,000,000 km².

The Amazon basin is entirely tropical, and is primarily covered by rainforests. It is possibly the richest river basin in terms of aquatic biodiversity.

Its source is in the Andean mountains in Peru and its mouth on the Atlantic coast of Northern Brazil. Throughout its course it is fed by a great number of large tributaries. Most of the river basin is situated in Brazil (58%), but it also drains Peru (16%), Bolivia (10%), Venezuela, Colombia, Ecuador, Suriname and the Guyanas.

The Amazon river is extremely wide for most of its length, so the potential dam sites are located in its tributaries. These are also very large rivers; the Tocantins river basin covers an area of 803,250 km², and has a maximum annual flow of 65,000 m³/sec. The massive volumes of these tributaries can generate megawatts of electricity, but this benefit can be offset by the distance it must travel for consumption in industrialised areas.

Several other large dams are under construction or planned in the Amazon basin. The potential impacts of some of these projects, in particular on the Xingu river, are subjects of growing controversy.

The Tucuruí Dam

Completed in 1984, the Tucuruí dam is located on the Tocantins river, 300 kilometers south of the city of Belem. It was the first large dam built in a tropical rainforest and its reservoir is the largest artificial lake created in such a zone.

Its purpose is solely hydropower generation, it is not used as a source of irrigation. The recent completion of Brazil's North-South electricity transmission grid means that Tucuruí power can be sold nationally rather than just regionally and gives further impetus to the exploitation of Amazonia's hydro potential.

With a capacity of 110,000 m³/s, Tucuruí has the world's largest spillway discharge. The dam wall is 77.5 m high, and its reservoir has an area of 2,875 km². It has an generating capacity of 4200 MW (1st phase), 8,000 MW (total). The total cost of construction was an estimated US$5.5 Billion

Key Issues in the Case Study

One of the interests of this case study that it gives an opportunity to discuss and clarify benefits and costs of dam building in the Amazon and how it compares with the alternatives. Natural gas from the Amazon Basin and from Bolivia, for example, has postponed most hydro development in Brazil for at least the next decade.

The Tucuruí dam was primarily built to power bauxite smelters near Belem, which produce aluminium for export. While Brazil has realised much economic benefit from this industry, the region has suffered negative social and environmental impacts due to the Tucuruí reservoir. There has been a major loss of intact forest, downstream fisheries have been depleted, mosquitoes have proliferated and some 40,000 people have been displaced.

An issue of high controversy concerning Tucuruí (and the neighbouring dam at Balbina) is the emission of greenhouse gases. The gradual decomposition of the forest flooded by the reservoir produces methane, although how methane is released into the atmosphere is still a matter of conjecture. This issue goes beyond these dams, as it challenges the widespread opinion that hydro dams are environmentally cleaner than power stations that burn coal or oil.