Madeira River

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The Madeira River is a major waterway in South America, approximately 3,380 km (2,100 miles) long. Madeira is the longest tributary of Amazon.

The mean inter-annual precipitations on the great basins vary from 750 to 3000 mm, the entire upper Madeira basin receiving 1705 mm/yr. The greatest extremes of rainfall are between 490 mm and more than 7000 mm. At its head, the Madeira on its own is still one of the largest rivers of the world, with a mean inter-annual discharge of 17,000 m³/s, i.e. 536 km³/yr, approximately half the discharge of the Congo River. The mean inter-annual contribution of the Bolivian Andes is 4170 m³/s, i.e. 132 km³/yr, representing 25% of the discharge of the entire upper Madeira basin.

Between Guajará-Mirim and the falls, the Madeira receives the drainage of the north-eastern slopes of the Andes from Santa Cruz de la Sierra to Cuzco, the whole of the south-western slope of Brazilian Mato Grosso and the northern slope of the Chiquitos sierras. In total, the catchment area is 850,000 km²^[1], almost equal in area to France and Spain combined. The waters flow into the Madeira from many large rivers, the principal of which, (from east to west), are the Guaporé or Itenez, the Baures and Blanco, the Itonama or San Miguel, the Mamoré, Beni, and Mayutata or Madre de Dios, all of which are reinforced by numerous secondary but powerful affluents.

All of the upper branches of the river Madeira find their way to the falls across the open, almost level Mojos and Beni plains, 90,000 km² (35,000 square miles) of which are yearly flooded to an average depth of about 3 feet (0.91 m) for a period of from three to four months.

From the falls, the Madeira flows northward forming the border between Bolivia and Brazil for approximately 100 km (60 miles). Below the confluence of the Rio Abunã, the Madeira meanders north-eastward through the Rondônia and Amazonas states of north west Brazil to its junction with the Amazon. At its mouth is Ilha Tupinambaranas, an extensive marshy region formed by the Madeira’s distributaries.

It rises more than 15 m (50 ft) during the rainy season, and ocean vessels may ascend it to the Falls of San Antonio, near Pôrto Velho, Brazil, 1070 km (663 miles) above its mouth; but in the dry months, from June to November, it is only navigable for the same distance for craft drawing about 2 m (from 5 to 6 feet) of water. The Madeira-Mamoré Railroad runs in a 365 km (227 mile) loop around the unnavigable section to Guajará-Mirim on the Mamoré River.

A subspecies of Boto (Amazon River Dolphin) is known to inhabit the Madeira river system.

In July 2007, plans have been approved by the Brazilian Government to construct two hydroelectric dams on the Madeira River, and is opposed by certain groups such as environmentalists for the environmental impact that the construction could have.^[2]

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