Paraguá (in the upper reaches)
Map of the Orinoco Basin ( see correction notes )
|location||Venezuela , Colombia|
|River system||Orinoco (and partially Amazon)|
|Headwaters||at Cerro Delgado Chalbaud
in the Sierra Parima
|muzzle||in the Atlantic Ocean
|Height difference||1047 m|
|Bottom slope||0.52 ‰|
|Catchment area||approximately 1,000,000 km²|
| MQ discharge
without delta area 33,600 m³ / s
|1330 m³ / s
35,000 m³ / s
81,000 m³ / s
|Left tributaries||Río Guaviare, Río Vichada, Río Tomo, Río Meta, Río Arauca, Río Apure|
|Right tributaries||Río Ventuari, Río Caura, Río Caroní|
|Big cities||Puerto Ayacucho , Ciudad Bolívar , Ciudad Guayana|
|Medium-sized cities||Curiapo , tucupita|
|Small towns||San Fernando de Atabapo , Puerto Carreño|
|Navigable||approx. 1600 km
(430 km for ocean-going vessels)
|In the upper course water loss to the Río Negro through the branching Brazo Casiquiare|
The Orinoco is with a water flow of 35,000 m³ / s the fourth largest river in the world and the second largest in South America . There, however, in terms of its length, the Orinoco 2010 km and the river system (from the headwaters of the Río Guaviare ) about 3010 km, the river is exceeded by three rivers ( Amazon , Paraná , Rio São Francisco ). The high volume flow of the Orinoco can be explained by the high rainfall in almost the entire catchment area , which ranges from 1000 mm / a to over 4000 mm / a.
The catchment area covers about one million square kilometers and is located just north of the equator. It is partially framed by the Andes and other mountains ( Sierra Nevada del Cocuy : 5330 m) and covered by tropical rainforest and wet savannas. About two thirds of it is on Venezuelan territory and about one third on Colombia .
The headwaters of the Orinoco are located in the southwestern mountains of Guiana in the Sierra Parima in the Venezuelan state of Amazonas near the border with the Brazilian state of Amazonas . Its further course describes a wide arc extending to the west around the mountainous region of Guayana northwards to the Atlantic . A distinction is usually made between four sections:
For this upper section, also known as Paraguá , which is generally west-north-west facing, there are lengths of around 800 km (from 710 km, up to 850 km are plausible). The Orinoco rises at a height of only 1,047 meters on Cerro Delgado Chalbaud and then flows through the predominantly steep, hilly mountainous region of Guayana in alternating narrow and basin-shaped valley sections. At a certain distance from the rock faces of prominent table mountains they are towered up to 2000 meters, such as the Cerro Duida near the former mission station Esmeralda.
The valley floor here is part of a network of valley sand plains, which is penetrated by individual granitic hills and rock formations. After the confluence of sedimentary tributaries from the higher mountains, the Orinoco leads cloudy water and forms not only islands here at its branches, but also a river bifurcation - which is very rare in the upper reaches of rivers ; it is considered the most important river branch in the world. The Brazo Casiquiare draws from the water of the Orinoco (1,400 m³ / s) between 12% at low tide and more than 25% at high tide and grows further towards the left source river of the Rio Negro , which in turn flows into the Amazon . The Alto Orinoco then increasingly acquires the characteristics of a black water river further downstream .
The uppermost section of the valley is one of the parts of South America with the least traffic and is the settlement area of the indigenous Yanomamo people. Large parts of the area are under the protection of the largest Venezuelan national park Parima-Tapirapeco and the national park Duida-Marahuaca . The Río Ventuari flows into a branching rapids from the right , which doubles the Orinoco with a water flow of more than 2,000 m³ / s ( Rhine near Emmerich: approx. 2,330 m³ / s).
The middle section of the river begins with the confluence of the largest Orinoco tributary , the Río Guaviare, which rises in the Colombian Andes . It surpasses the upper Orinoco not only in length (with around 1,760 km), but also in water flow (7,400 m³ / s including the Río Atabapó, which opened shortly before, compared to 4,750 m³ / s of the Orinoco). It is therefore not without good reason that it is pointed out (often from the Colombian side) that the Guaviare is the main stream of the Orinoco river system, which with it reaches a length of around 3,000 kilometers (according to other sources, 2,560 to 2,800 km).
With this confluence begins the section of the Orinoco, on which tributaries from the Andes flow in close succession from the left. In addition, it forms the border between Venezuela and Colombia over a length of 270 kilometers, up to the confluence of its third largest tributary, the Río Meta . In this section are also the largest rapids on the Orinoco, after 145 kilometers the Raudales de Maipures , after another 55 kilometers the Raudales de Atures .
The city of Puerto Ayacucho below the rapids is the upper terminus of the continuous shipping route on the Orinoco. The Río Meta flows a little below; it can be navigated much further upstream and is therefore the more important traffic route. Sometimes people speak of the lower Orinoco from here , but sometimes only from the confluence of the Río Apure, with which the series of Andean tributaries ends. Up to this point the Orinoco has become a clay-yellow white water river .
The beginning of the lower Orinoco is marked by the Puente Mercosur bridge between Caicara and Cabruta, which is still under construction (2015) . The current here has a water flow of 22,250 m³ / s.
In the last section of the course, the Orinoco receives its tributaries mainly from the right side, from the very rainy mountainous country of Guiana. In the catchment area of the Orinoco tributary, the Río Caroní , the second largest at 4,800 m³ / s , lies the world's highest waterfall , the Salto Ángel , and the Río Caura , the other major tributary on the lower Orinoco, forms the most powerful waterfall in Venezuela with the Salto Pará . The rivers from the Guayana mountains are again mostly dark in color (due to tannins from plant residues and humic acids ).
The settlement density is significantly higher in this section than above; here are the two large cities Ciudad Bolívar (with the oldest bridge over the Orinoco, the Puente de Angostura ) and Ciudad Guayana at the mouth of the Caroní (with the Puente Orinoquia ). As far as Ciudad Bolívar with its important ore loading facilities in Puerto Ordaz and Palua, ocean-going ships can go up the Orinoco.
The estuary delta is one of the largest in the world, with an area of around 19,000 km² and a width of 370 kilometers. By far the most important estuary , the Río Grande, flows east; the westernmost arm of the river, the Río Mañano, was largely fed through the Volcan dam to the Caño Macareo, the central main arm. Further interventions with risks for the habitats of the very species-rich amphibious delta landscape entail the development of the oil deposits there. The delta is inhabited by the Warao people.
The name Orinoco is said to have been borrowed from a term in their language for space for paddling ( boat area ) .
Spatial development of the river system
The course of the Orinoco river was only able to develop into its current form after the Andes began to unfold or rise en bloc in front of the much older continental cores ( cratons ) of South America , which were drifting westward . The northern part of the craton, the Guiana Shield, has been bulging since the beginning of the Tertiary against today's lowlands of the Amazon and Orinoco. Originally an arm of the sea, which for a time connected the upper Amazon basin with today's Caribbean Sea , separated it from the young Andean chains with their often poorly solidified rocks. From there, the rivers filled the inlet with extensive alluvial fans and have since accumulated along the line where the alluvial fans meet the rising Guiana shield. This drainage line, which runs around the base of the bulge, represents today's arched course of the Orinoco.
The Guiana shield is overlaid by very old and resistant sandstones, the island-like remains of which tower over the hill country as striking table mountains . The rivers can only remove a small amount of material from these rocks, which is why, in contrast to the Andean tributaries, which are rich in sediments, they have the character of clear water rivers or black water rivers. The river networks in the Guiana Mountains often reflect abrupt changes of direction and often reflect paths of former drainage directions.
The same applies to the headwaters of the Río Atabapó (tributary of the Río Guaviare, the valley line of the central Orinoco continuing upwards), whose former upper course has been lost to the headwaters of the Guainía of the Río Negro, leaving behind a dry valley. It is known under the name Isthmos del Pimichin as an alternative connection between the Amazon and Orinoco (earlier boat transport, parallel gravel road).
The annual rainfall in the Orinoco area decreases from about 3,600 mm in the south to about 1,000 mm at the delta root, and then increases again to 2,400 mm over the short distance to the coast. In the perhumid climate of the southern Orinoco Basin, tropical rainforests dominate with a few open islands, while the vast grasslands of the wet savannah extend to the north.
Exploring the Orinoco
In August 1498, on his third voyage of discovery , Christopher Columbus noticed that streams of fresh water poured into the sea with great force near Trinidad. He concluded from this that the corresponding river must have flowed through a large continent and was therefore encouraged to be on the coast of the large Asian continent. In fact, he was sailing off the northern part of the Orinoco Delta.
Antonio de Berrío sailed the Río Casanare in present-day Colombia in the 1580s up to its confluence with the Río Meta . From there he continued his journey across the confluence of the Meta and Orinoco to the Orinoco estuary and to Coro .
In 1800 the German researcher Alexander von Humboldt and the French botanist Aimé Bonpland undertook an expedition from the mouth of the Río Apure to the upper Orinoco valley. They collected important data on the flora and fauna of the river basin. According to today's data , Humboldt long afterwards denied the Río Guaviare's entitlement to the rank of the main hydrological river as an expression of "geographical ignorance", which has always been considered . Nevertheless, Humboldt was the first to prove the existence of the Brazo Casiquiare river bifurcation and to explain the hydrological peculiarities of the Orinoco in an understandable way.
The source of the Orinoco was only discovered by Venezuelan and French researchers in November 1951.
1988: The breadth of the river is reflected in the song Orinoco Flow by Enya , which reached number 1 in some charts.
- Orinoco - The River of Adventure , Arte Documentation, 2010.
The southernmost part does not belong to the Orinoco region, as shown, but to the Río Siapá (tributary of the Brazo Casiquiare).
River areas that drain into the open sea are also included in the east of the delta.
- Gustavo Silva León: La cuenca del río Orinoco: visión hidrográfica y balance hídrico . Revista Geográfica Venezolana, Vol. 46 (1) 2005, 75-108 (p. 79, measurement along the estuary of the Rio Grande). The length data in the literature range from 2010 km to 2560 km. Differences are particularly justified in the upper reaches with its strongly meandering sections of the route, which are measured individually and generalized. Information up to about 2150 km is plausible.
- The figures range from 925,000 km² to 1,032,500 km² (Gustavo Silva León: La cuenca del río Orinoco: visión hidrográfica y balance hídrico . Revista Geográfica Venezolana, Vol. 46 (1) 2005, 75-108). This can mainly be explained by different demarcations on both sides of the estuary delta, but also partly by widespread erroneous topographical water data, which the upper catchment area of the Casiquiare tributary Río Siapá has added to the Orinoco tributary Río Movaca.
- Gustavo Silva Leon: La cuenca del río Orinoco: visión hidrográfica y balance hídrico . Revista Geográfica Venezolana, Vol. 46 (1) 2005, 75-108 (p. 100, MQ in table for the discharge balance)
- Note: to Amazonas (206,000 m³ / s), Congo (41,800 m³ / s) and Meghna (Upper Meghna + Brahmaputra + Ganges : 36,500 m³ / s)
- Note: 40,200 km² are often incorrectly stated; however, this is the area of the state Delta Amacuro there .
- The epicontinental Amazon basin , Institute for Geography of the University of Innsbruck
- Alexander von Humboldt: Views of Nature , Berlin 1807 (chapter on the Orinoco waterfalls at Atures and Maipures )
- Jules Verne: The Proud Orinoco . Known and unknown worlds. Adventurous journeys by Julius Verne, volume LXXIII – LXXIV, Vienna, Pest, Leipzig 1899, pp. 5–17, 19–20.