The Tocantins River is the central fluvial artery of Brazil. The Araguaia River is also one of Brazil's major rivers and is almost equal in volume at its confluence with the Tocantins. The Araguaia-Tocantins watershed, in terms of energy production, is the second-largest in Brazil.
Tocantins-Araguaia River System
The Tocantins-Araguaia river system begins in the Brazilian Highlands and flows into the Pará River distributary channel, a navigable arm of the Amazon River delta, which empties into the Atlantic Ocean at Marajó Bay.
The Tocantins River gives rise in the Serra dos Pireneus, west of the Federal District. However, its western tributary, the Araguaia River, has its extreme southern headwaters on the slopes of the Serra dos Caiapós.
Though popularly regarded as a tributary of the Amazon River, the Tocantins-Araguaia is technically a separate system, since its waters flow into the Atlantic Ocean alongside those of the Amazon. Its drainage basin is more than 800,000 sq km (300,000 sq mi).
The Tocantins River is the central fluvial artery of Brazil, running in a northerly direction through the center of the country for approximately 2,640 km (1,640 mi) until it discharges into the Atlantic Ocean just south of the Amazon River. The Tocantins is one of the largest clearwater rivers in South America.
The river rises in several headstreams on the central plateau. It then flows northward through Goiás and Tocantins states after which it loops westward, along the boundary of Tocantins and Maranhão states. The river is of limited use for navigation as it is frequently interrupted by rapids and waterfalls.
Two tributaries, the Maranhão and Paranatinga, collect an immense volume of water from the highlands which surround them before the Tocantins' confluence with the Araguaia River. The combined river then turns northward again until it empties into the Atlantic Ocean.
There are five dams on the river, of which the largest are the Tucuruí and the Serra da Mesa:
- Serra da Mesa
- Cana Brava
- Peixe Angical
- Luiz Eduardo Magalhães (Lajeado)
The Araguaia River is one of Brazil's major rivers and is almost equal in volume at its confluence with the Tocantins River. It has a total length of approximately 2,627 km (1,632 mi). "Araguaia" means "River of the macaws" in the native Tupi language.
The Araguaia River's main tributary is the Rio das Mortes. Other important tributaries include the Bonito, Garcas, Tapirape and Formoso (or Cristalino) on the west; and the Pitombas, Claro, Vermelho, Tucupa and Chavante on the east.
The middle course of the Araguaia, in a marshland approximately 350 km (220 mi) northwest of Brasília, temporarily divides into western and eastern branches (the eastern branch is referred to as the Javaés River) to form the vast Bananal Island, an expanse of igapós or flooded forest, blackwater river channels and oxbow lakes called Cantão. The river also has approximately twenty smaller branches.
A large portion of the river's course is navigable all year but below the Cantão wetlands, the river is interrupted by rapids. The Araguaia joins the Tocantins after flowing northward another 1,000 km (600 mi).
Map of the Tocantins Watershed
Tocantins Basin (Araguaia-Tocantins Watershed)
The Tocantins basin, or Araguaia-Tocantins watershed, is a Brazilian river basin, whose main rivers are the Tocantins and Araguaia. The basin covers approximately 767,000 sq km (296,000 sq mi), which is approximately 7.5% of Brazil's national territory. In terms of energy production, the basin has the second largest in Brazil.
The basin extends to the states of Tocantins, Goiás, Mato Grosso, Pará and Maranhão, in addition to the Federal District. For water resource management purposes, it is inserted into the Tocantins-Araguaia hydrographic region.
The flat, broad valleys, composed of sand and clay, of both the Tocantins and its Araguaia branch are overlooked by steep bluffs. They are the margins of the great sandstone plateaus, from 300 to 600 m (980 to 1,970 ft) elevation above sea level, through which the rivers have eroded their deep beds.
Its length is approximately 2,500 km (1,550 mi) from its water source, in the Serra Dourada, to its mouth in the bay of Marajó (Pará). It has an elongated configuration, with altitudes varying generally between 350 - 500 m (1,150 -1,650 ft), although in some cases it reaches more than 1,000 m (3,280 ft).
The middle and lower basin of the river is in the Xingu–Tocantins–Araguaia moist forests ecoregion. This area is an integral part of the Amazon biome; however, the Araguaia River is not a tributary of the Amazon.
In its lower reaches the Tocantins separates the Tocantins–Araguaia–Maranhão moist forests ecoregion to the east from the Xingu–Tocantins–Araguaia moist forests ecoregion to the west. The river acts as a barrier that prevents the dispersal of flora and fauna between these ecoregions.
The basin is the home of several large aquatic mammals such as the Amazonian manatee, the Araguaia river dolphin and the tucuxi as well as larger reptiles such as the black caiman, the spectacled caiman and the yellow-spotted river turtle.
More than 350 fish species have been registered, including more than 175 endemics. The most species-rich families are Characidae (tetras and allies), Loricariidae (pleco catfish and allies) and Rivulidae (South American killifish). While most species essentially are of Amazonian origin, there are also some showing a connection with the Paraná and São Francisco rivers.
Several fish species migrate along the Tocantins to spawn but this has been restricted by the dams. Following the construction of the massive Tucuruí Dam, the flow of the river changed. Some species have been adversely affected and there has been a substantial reduction in species richness in parts of the river.
The São Domingos karst in the upper Tocantins basin is home to an unusually high number of cavefish species (more than any other region in the Americas).