Orinoco

For other uses, see Orinoco (disambiguation).

Orinoco River
Río Orinoco
256px Angostura Bridge over the Orinoco at Ciudad Bolívar, Venezuela
Countries	Colombia, Venezuela
District	South America
Source
- location	Cerro Delgado-Chalbaud, Parima Mountains, Venezuela
- elevation	1,047 m (3,435 ft)
- coordinates
Mouth	Delta Amacuro
- location	Atlantic Ocean, Venezuela
- elevation	0 m (0 ft)
- coordinates
Length	2,140 km (1,330 mi)
Basin	880,000 km2 (339,770 sq mi)
Discharge
- average	33,000 m3/s (1,165,384 cu ft/s)
Orinoco's watershed

The Orinoco is one of the longest rivers in South America at 2,140 kilometres (1,330 mi). Its drainage basin, sometimes called the Orinoquia, covers 880,000 square kilometres (340,000 sq mi), with 76.3 percent of it in Venezuela and the remainder in Colombia. The Orinoco and its tributaries are the major transportation system for eastern and interior Venezuela and the llanos of Colombia. The Orinoco is extremely diverse and hosts a wide variety of flora and fauna.

History

Map of Lower Orinoco 1897

The mouth of the Orinoco at the Atlantic Ocean was documented by Columbus on 1 August 1498, during his third voyage. Its source at the Cerro Delgado-Chalbaud, in the Parima range, was not explored by non-indigenous peoples until 1951, 453 years later. The source, near the Venezuelan-Brazilian border, at 1,047 metres (3,435 ft) above sea level ( ), was explored in 1951 by a joint Venezuelan–French team.

The Orinoco delta, and tributaries in the eastern llanos such as the Apure and Meta, were explored in the 16th century by German expeditions under Ambrosius Ehinger and his successors. In 1531 Diego de Ordaz, starting at the principal outlet in the delta, the Boca de Navios, sailed up the river to the Meta. Antonio de Berrio sailed down the Casanare to the Meta, and then down the Orinoco and back to Coro.

Alexander von Humboldt explored the basin in 1800, reporting on the pink river dolphins. He published extensively on the river's flora and fauna.

The first bridge across the Orinoco was the Angostura Bridge at Ciudad Bolívar, Venezuela, completed in 1967. In 2006 a second bridge was completed near Ciudad Guayana, Venezuela, known as the Orinoquia Bridge.

The first powerline crossing of the Orinoco was completed in 1981 for a 800 kV TL single span of 1,200 meters using two towers 110 m tall. In 1992, an overhead power line crossing for two 400 kV-circuits was completed just west of Morocure (between the cities of Ciudad Bolivar and Ciudad Guayana), north of the confluence of Routes 1 and 19. It had three towers, and the two spans measured 2,161 m and 2,537 m respectively.

Geography

The course of the Orinoco forms a wide ellipsoidal arc, surrounding the Guiana Shield; it is divided in four stretches of unequal length that roughly correspond to the longitudinal zonation of a typical large river:

• Upper Orinoco— 242 kilometres (150 mi) long, from its headwaters to the rapids Raudales de Guaharibos, flows through mountainous landscape in a northwesterly direction
• Middle Orinoco— 750 kilometres (470 mi) long, divided into two sectors, the first of which ca. 480 kilometres (300 mi) long has a general westward direction down to the confluence with the Atabapo and Guaviare rivers at San Fernando de Atabapo; the second flows northward, for about 270 kilometres (170 mi), along the Venezuelan - Colombian border, flanked on both sides by the westernmost granitic upwellings of the Guiana Shield which impede the development of a flood plain, to the Atures rapids near the confluence with the Meta River at Puerto Carreño,
• Lower Orinoco— 959 kilometres (596 mi) long with a well-developed alluvial plain, flows in a northeast direction, from Atures rapids down to Piacoa in front of Barrancas
• Delta Amacuro— 200 kilometres (120 mi) long that empties into the Gulf of Paría and the Atlantic Ocean, a very large delta, some 22,500 km² (8,700 sq mi) and 370 kilometres (230 mi) at its widest.

View of the Orinoco River in Mariusa National Park (Delta Amacuro)

Orinoco River, the second largest in South America, at its confluence with the Caroní River (lower left)

Rapids of the Orinoco River, near Puerto Ayacucho airport, Venezuela

The Orinoco River, here in Amazonas State, Venezuela

Orinoco River, in Amazonas State, Venezuela

At its mouth, the Orinoco forms a wide delta that branches off into hundreds of rivers and waterways that flow through 41,000 km² (16,000 sq mi) of swampy forests. In the rainy season, the Orinoco can swell to a breadth of 22 kilometres (14 mi) and a depth of 100 metres (330 ft).

Most of the important Venezuelan rivers are tributaries of the Orinoco, the largest being the Caroní, which joins it at Puerto Ordaz, close to the Llovizna Falls. A peculiarity of the Orinoco river system is the Casiquiare canal, which starts as an arm of the Orinoco, and finds its way to the Rio Negro, a tributary of the Amazon, thus forming a 'natural canal' between Orinoco and Amazon.

Major rivers in the Orinoco Basin

• Apure: from Venezuela through the east into the Orinoco
• Arauca: from Colombia to Venezuela east into the Orinoco
• Atabapo: from the Guiana Highlands of Venezuela north into the Orinoco
• Caroní: from the Guiana Highlands of Venezuela north into the Orinoco
• Casiquiare canal: in SE Venezuela, a distributary from the Orinoco flowing west to the Negro River, a major affluent to the Amazon
• Caura: from eastern Venezuela (Guiana Highlands) north into the Orinoco
• Guaviare: from Colombia east into the Orinoco
• Inírida: from Colombia southeast into the Guaviare.
• Meta: from Colombia, border with Venezuela east into the Orinoco
• Ventuari: from eastern Venezuela (the Guiana Highlands) southwest into the Orinoco
• Vichada: from Colombia east into the Orinoco

See also: Casiquiare canal-Orinoco River hydrographic divide

Ecology

The boto or Amazon river dolphin and the giant river otter inhabit the Orinoco River system. The Orinoco crocodile is one of the rarest reptiles in the world. Its range in the wild is restricted to the Orinoco River Basin.

More than 1000 fish species have been recorded in the river basin. Among these are species found in brackish or salt water in the Orinoco estuary, but also many restricted to fresh water. By far the largest orders are Characiformes and Siluriformes, which together account for more than half the fresh water species. Some of the more famous are the black spot piranha and the cardinal tetra. The latter species, which is important in the aquarium industry, is also found in the Rio Negro, revealing the connection between this river and the Orinoco through the Casiquiare canal.

Economic activity

The river is navigable for most of its length, and dredging enables ocean ships to go as far as Ciudad Bolívar, at the confluence of the Caroní River, 435 kilometres (270 mi) upstream. River steamers carry cargo as far as Puerto Ayacucho and the Atures Rapids.

El Florero iron mine

In 1926 a Venezuelan mining inspector found one of the richest iron ore deposits near the Orinoco delta, south of the town of San Felix on a mountain name El Florero. Full-scale mining of the ore deposits began after World War II, by a conglomerate of Venezuelan firms and US steel companies. At the start in the early 1950s, about 10,000 tons of ore-bearing soil was mined per day.

Tar sands

The Orinoco river deposits also contain extensive tar sands in the Orinoco oil belt, which may be a source of future oil production.

Eastern Venezuelan basin

Union of the Orinoco with the Caroní River.

Encompassing the states of Anzoategui-Guarico and Monagas states, the Interior Range forms the northern boundary and the Guayana Shield the southern. Maturin forms the eastern subbasin and Guarico the western. The El Furrial oil field was discovered in 1978, producing from late Oligocene shallow marine sandstones in an overthrusted foreland basin.

Recreation and sports

Since 1988, the local government of Ciudad Guayana has conducted a swim race in the rivers Orinoco and Caroní, with up to 1000 competitors. Since 1991, the "Paso a Nado Internacional de los Rios Orinoco-Caroní" has been celebrated every year, on a Sunday close to 19 April. Worldwide, this swim-meet has gained in importance, and it has a large number of competitors.

References

• Stark, James H. 1897. Stark's Guide-Book and History of Trinidad including Tobago, Granada, and St. Vincent; also a trip up the Orinoco and a description of the great Venezuelan Pitch Lake. Boston, James H. Stark, publisher; London, Sampson Low, Marston & Company. (This book has an excellent description of a trip up the Orinoco as far as Ciudad Bolívar and a detailed description of the Venezuelan Pitch Lake situated on the western side of the Gulf of Paria opposite.)
• MacKee, E.D., Nordin, C.F. and D. Perez-Hernandez (1998). "The Waters and Sediments of the Rio Orinoco and its major Tributaries, Venezuela and Colombia." United States Geological Survey water-supply paper, ISSN 0083; 2326/A-B. Washington: United States Government Printing Office.
• Weibezahn, F.H., Haymara, A. and M.W. Lewis (1990). The Orinoco River as an ecosystem. Caracas: Universidad Simon Bolivar.
• Rawlins, C.B. (1999). The Orinoco River. New York: Franklin Watts.

External links

• Map of Orinoco River that Includes Visible Islands and Tributaries at the Delta of the River, 1732
• Down the Orinoco in a Canoe at Project Gutenberg (Transcription of book from 1902)