Tucuruí Dam: The Amazon Basin's First Major Hydroelectric Dam

**Tucuruí Dam** on the Tocantins River in Pará State is the first and one of the largest hydroelectric dams in the Amazon basin, with an installed capacity of **8,370 MW** across two powerhouses. Completed in its first phase in 1984, with a second powerhouse added in 2010, Tucuruí was built primarily to power the Carajás iron ore mining complex and the Albrás aluminium smelter in northern Brazil.

Introduction

The dam's construction in the heart of the tropical lowlands was unprecedented at the time and demonstrated both the enormous hydroelectric potential of Amazonian rivers and the severe ecological costs of damming them. The reservoir flooded **2,850 km²** of tropical forest, creating a vast artificial lake dotted with thousands of dead tree trunks that still protrude above the water surface decades later.

Engineering & Structure

• Type: Concrete gravity dam
• Height: 78 meters
• Crest Length: 12,500 meters (including earth dams)
• Turbines: 25 total (12 + 11 main + 2 auxiliary)

Tucuruí's dam complex extends over 12.5 kilometers including earth wing dams on both flanks. The concrete main dam is 78 meters tall — modest by international standards — but the enormous volume of the Tocantins River, one of Brazil's largest, provides the flow needed for massive power generation even at this relatively low head. The first powerhouse contains 12 turbines rated at 350 MW each, while the second houses 11 units of 375 MW.

The dam's spillway is one of the most powerful in the world, designed to pass the Tocantins' extreme wet-season flows of up to 100,000 cubic meters per second. The tropical climate means there is no dry season in the conventional sense — rainfall is heavy year-round, with a pronounced wet season from December to May when the river swells dramatically.

Geographic Setting

• River: Tocantins River
• Location: Tucuruí, Pará State, Brazil
• Coordinates: 3.83°S, 49.65°W
• Reservoir Area: 2,850 km²

The Tocantins River flows 2,450 kilometers from central Brazil's cerrado highlands to the Amazon estuary near Belém. At the dam site, the river passes through a region of dense tropical lowland rainforest, with a nearly flat terrain that required extensive earth dams to contain the reservoir on its flanks. The surrounding landscape is classified as transitional between Amazon rainforest and cerrado savanna.

The reservoir extends approximately 200 kilometers upstream, flooding a vast area of tropical forest. Over 1,600 islands were created in the reservoir, many of them formed by hilltops that remained above the waterline. The stagnant water in the flooded forest created ideal breeding conditions for mosquitoes, and malaria rates in the surrounding area spiked dramatically after the reservoir filled.

Hydroelectric Power

• Installed Capacity: 8,370 MW
• Annual Output: ~40 TWh
• Primary Users: Carajás mining complex, Albrás aluminium smelter
• Grid: Brazilian North-Northeast interconnected system

Tucuruí generates approximately 40 terawatt-hours of electricity per year, making it one of Brazil's most productive hydroelectric stations. The majority of its output was originally dedicated to the Carajás iron ore mine (the world's largest) and the Albrás aluminium smelter, both highly energy-intensive operations. Aluminium smelting alone consumed roughly 30 percent of the dam's first-phase output.

The addition of the second powerhouse in 2010 significantly increased the dam's capacity and allowed more electricity to be directed to the public grid rather than exclusively to industrial consumers. Transmission lines connect Tucuruí to the cities of Belém, São Luís, and Fortaleza, extending the dam's reach across northern and northeastern Brazil.

Environmental & Social Impact

• Forest Flooded: 2,850 km² of tropical rainforest
• People Displaced: ~25,000
• Greenhouse Emissions: Significant methane from decomposing biomass

The flooding of 2,850 square kilometers of tropical forest made Tucuruí one of the most environmentally destructive dam projects of the 20th century. The submerged vegetation decomposed anaerobically, releasing enormous quantities of methane — a potent greenhouse gas — for years after filling. Studies in the 1990s suggested the reservoir's greenhouse gas emissions were comparable to a fossil fuel power plant of similar output.

Approximately 25,000 people were displaced, many of them indigenous and riverine communities who depended on the Tocantins' fisheries for their livelihoods. The dam blocked the migration of several commercially important fish species, devastating downstream fishing communities. Malaria cases surged after construction, and the town of Tucuruí experienced rapid, poorly managed urbanization as workers flooded into the area.

Key Facts

• Tucuruí was the first major hydroelectric dam built in the Amazon basin.
• Its reservoir flooded 2,850 km² of tropical rainforest.
• The dam's 8,370 MW powers Brazil's largest iron mine and aluminium smelter.
• Decomposing flooded vegetation released significant methane emissions.
• The second powerhouse, completed in 2010, nearly doubled capacity.

Fun Facts

• Thousands of dead tree trunks still protrude from Tucuruí Reservoir decades after flooding, creating an eerie landscape visible from satellite imagery.
• The reservoir's islands have become refuges for wildlife, including species that swam or were rescued to higher ground during the filling.
• Tucuruí was originally built without fish passage facilities; a fish ladder was added much later in 2010 but has had limited effectiveness for most species.

Final Thoughts

Tucuruí Dam pioneered large-scale hydroelectric development in the Amazon basin and demonstrated both the enormous energy potential and devastating ecological costs of tropical river damming. Its methane emissions and rainforest destruction have made it a cautionary case study in the environmental assessment of hydroelectric projects.