- Casiquiare canal
Infobox_River | river_name = Casiquiare canal
caption = Location of the Casiquiare within the Amazon Basin
mouth = Rio Negro
length = convert|326|km|mi|abbr=on
watershed = convert|42300|km²|sqmi|abbr=on
The Casiquiare river is a
distributaryof the upper Orinoco, which flows southward into the Rio Negro. As such, it forms a unique natural canal between the Orinoco and Amazon river systems; it is the largest river on the planet that links two major river systems, a so-called bifurcation.
In 1744 a Jesuit priest called Father Roman, while ascending the Orinoco river, met some Portuguese slave-traders from the settlements on the Rio Negro. He accompanied them on their return, by way of the Casiquiare canal, and afterwards retraced his route to the Orinoco. La Condamine, seven months later, was able to give to the
Académie françaisean account of Father Roman's voyage, and thus confirm the existence of this waterway, first reported by Father Acuña in 1639.
But little credence was given to Father Roman's statement until it was verified, in 1756, by the Spanish Boundary-line Commission of
Yturriagaand Solano. In 1800 German scientist Alexander von Humboldtand French botanist Aimé Bonplandexplored the river. In 1968 the Casiquiare was navigated by an SRN6 hovercraftduring a National Geographicexpedition. [cite news |title= Graham Clarke|url= http://www.telegraph.co.uk/news/obituaries/1565257/Graham-Clarke.html|work= The Daily Telegraph|publisher= |date= 2007-10-07|accessdate=2008-07-14 ]
The origin of Casiquiare at the River Orinoco is convert|9|mi|km|0 below the mission of
La Esmeraldaat coord|3|8|18.5|N|65|52|42.5|W|region:VE-X_type:landmark|display=inline, and is about convert|123|m|ft|0 above sea level. Its mouth at the Rio Negro, an affluent of the Amazon River, is near the town of San Carlos and is convert|91|m|ft|0 above sea level.
The general course is south-west, and its length, including windings, is about convert|200|mi|km|0. Its width, at its
bifurcationwith the Orinoco, is approximately convert|300|ft|m|0, with a current towards the Negro of convert|0.75|mph|m/s|1|lk=on; but as it gains in volume from the very numerous tributarystreams, large and small, which it receives en route, its velocity increases, and in the wet season reaches convert|5|mph|m/s|1, even convert|8|mph|m/s|1 in certain stretches. It broadens considerably as it approaches its mouth, where it is about convert|1750|ft|m|0 wide. The volume of water the Casiquiare captures from the Orinoco is small in comparison to what it accumulates in its course.
flood-time it is said to have a second connection with the Rio Negro by a branch which it throws off to the westward called the Itinivini, which leaves it at a point about convert|50|mi|km|0 above its mouth. In the dry season it has shallows, and is obstructed by sandbanks, a few rapids and granite rocks. Its shores are densely wooded, and the soil more fertile than that along the Rio Negro. The general slope of the plains through which the canal runs is south-west, but those of the Rio Negro slope south-east.
The Casiquiare is not, as is generally supposed, a sluggish canal on a flat tableland, but a great, rapid river which, if its upper waters had not found contact with the Orinoco, perhaps by cutting back, would belong entirely to the Negro branch of the Amazon.
To the west of the Casiquiare there is a much shorter and more facile connexion between the Orinoco and Amazon basins, called the isthmus of
Pimichin, which is reached by ascending the Terni branch of the Atabapoaffluent of the Orinoco. Although the Terni is somewhat obstructed, it is believed that it could easily be made navigable for small craft. The isthmus is convert|10|mi|km|0 across, with undulating ground, nowhere over convert|50|ft|m|0 high, with swamps and marshes. It is much used for the transit of large canoes, which are hauled across it from the Terni river, and which reach the Negro by the little stream called the Pimichin.
*VARESCHI, Volkmar. "Orinoco arriba. A través de Venezuela siguiendo a Humboldt". Caracas: Ediciones Lectura, 1959
* [http://members.aol.com/ChrisChrz/humboldt.html Alexander von Humboldt and the Casiquiare River]
* [http://www.wikimapia.org/#y=2482133&x=-66423340&z=9&l=0&m=a&v=2 Wikimapia satellite image displaying locations of both the beginning (principio) and the end (desague) of the Casiquiare Canal.]
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