The Tocantins River is a river in Brazil, the central fluvial artery of the country. In the Tupi language, its name means "toucan's beak". It runs from south to north for about 2,450 km. It is not really a branch of the Amazon River, since its waters flow into the Atlantic Ocean alongside those of the Amazon. It flows through four Brazilian states and gives its name to one of Brazil's newest states, formed in 1988 from what was until then the northern portion of Goiás. The Tocantins is one of the largest clearwater rivers in South America.
Course
It rises in the mountainous district known as the Pireneus, west of the Federal District, but its western tributary, the Araguaia River, has its extreme southern headwaters on the slopes of the Serra dos Caiapós. The Araguaia flows 1,670 km before its confluence with the Tocantins, to which it is almost equal in volume. Besides its main tributary, the Rio das Mortes, the Araguaia has twenty smaller branches, offering many miles of canoe navigation. In finding its way to the lowlands, it breaks frequently into waterfalls and rapids, or winds violently through rocky gorges, until, at a point about 160 km above its junction with the Tocantins, it saws its way across a rocky dyke for 20 km in roaring cataracts. Two other tributaries, called the Maranhão and Paranatinga, collect an immense volume of water from the highlands which surround them, especially on the south and south-east. Between the latter and the confluence with the Araguaia, the Tocantins is occasionally obstructed by rocky barriers which cross it almost at a right angle.
Downstream from the Araguaia confluence, in the state of Pará, the river used to have many cataracts and rapids, but they were flooded in the early 1980s by the artificial lake created by the Tucuruí dam, one of the world's largest. When the second phase of the Tucuruí project was completed in November 30th, 2010, a system of locks called Eclusas do Tucuruí was established with the goal of making a long extension of the river navigable. In total there are five dams on the river, of which the largest are the Tucuruí and the Serra da Mesa dam.
Geology
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 elevation above sea-level, through which the rivers have eroded their deep beds. Around the estuary of the Tocantins the great plateau has disappeared, to give place to a part of the forest-covered, half submerged alluvial plain, which extends far to the north-east and west. The Pará River, generally called one of the mouths of the Amazon, is only the lower reach of the Tocantins. If any portion of the waters of the Amazon runs round the southern side of the large island of Marajóinto the river Para, it is only through tortuous, natural canals, which are in no sense outflow channels of the Amazon.
Discharge
The Tocantins River records a mean discharge rate of 13,598 m³/s and a specific discharge rate of 14.4 l/s/km². The sub-basins have the following specific discharge rates: Tocantins, Araguaia, Pará and Guamá.