Hydropower in the Pan Amazon: Tucuruí and the Tocantins Cascade

The oldest hydropower facility in the Brazilian Amazon is the Tucuruí D&R complex (8.4 GW) on the lower Tocantins River, about 200 kilometers south of its confluence with the Amazon River delta. The dam and power plant were built between 1976 and 1984, and its capacity was doubled in 2007; current plans call for capacity to be expanded by another 2.5 GW over the next few years.

Tucuruí is owned by Electronorte, a subsidiary of Electrobras, which supplies most of the electrical energy consumed in the Brazilian Amazon. It was built before the environmental laws that required the completion of an environmental impact study, which allowed its proponents to discount the impacts of a reservoir covering 280,000 hectares and the relocation of an estimated 30,000 citizens, including several Indigenous communities. The massive reservoir flooded intact tropical forest and the subsequent methane emissions from rotting vegetation have been estimated at 2.5 million metric tons of carbon annually – a GHG footprint approximately equivalent to a gas-fired power plant.

The dam has radically altered the ecology of the river and caused massive disruptions to fish populations. Species richness has fallen by 25% below the dam and by 50% within the reservoir, changes that reflect the composition of fish communities and the decline of migratory species. Total fish catch in the reservoir increased in the years immediately following its impoundment but have declined over time, having stabilized at about 80% of the original value.

The Tocantins is the most heavily exploited watershed in the Brazilian Amazon. The Serra da Mesa, a D&R unit, was built in the headwaters near Brasília simultaneously with Tucuruí. These investments were followed by four large-scale D&R projects inaugurated between 2000 and 2010 (Lajeada /Luis Eduardo Magalhães, Cana Brava, Peixe Angical and Sao Salvador) and an R-o-R facility at Esterito in 2014. There are four additional sites on the central sector of the river that are candidates for large-scale dams: Marabá, just below the confluence of the Araguaía and Tocantins, followed by Serra Quebrada, Tuparatins, and Ipueiras.

The construction of these four dams is required for the development of the Tocantins waterway; none overlap with an Indigenous territory or conservation unit. The National Energy Agency (ANEEL) has identified 24 additional sites as candidates for medium-scale facilities (< 150 MW), all of which are located relatively high in the watershed. If all these proposed dams were completed, the total installed capacity of the Tocantins would increase from about 13.2 GW to 20 GW.

The Araguaía River, the western branch of the Tocantins basin, is free of dams between its mouth at Marabá and central Mato Grosso, although there are several projects planned for the upper watershed. Two controversial projects have been canceled by the environmental regulatory agency (Instituto Brasileiro do Meio Ambiente e dos Recursos Naturais – IBAMA) based on observations made during the environmental impact studies: Santa Isabela, on the lower between Goiás and Mato Grosso. There are no plans to establish any dams over the mid-section of the river, a broad flat floodplain that includes the Ilha do Bananal, a massive wetland complex that has been set aside as a protected area or Indigenous reserve.

“A Perfect Storm in the Amazon” is a book by Timothy Killeen and contains the author’s viewpoints and analysis. The second edition was published by The White Horse in 2021, under the terms of a Creative Commons license (CC BY 4.0 license).

Read the other excerpted portions of chapter 2 here: