|River Name:||Casiquiare canal|
The Casiquiare river is a distributary of 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 française an 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 Yturriaga and Solano. In 1800 German scientist Alexander von Humboldt and French botanist Aimé Bonpland explored the river. In 1968 the Casiquiare was navigated by an SRN6 hovercraft during a National Geographic expedition.
The origin of Casiquiare at the River Orinoco is 9miles below the mission of La Esmeralda at , and is about 123m (404feet) above sea level. Its mouth at the Rio Negro, an affluent of the Amazon River, is near the town of San Carlos and is 91m (299feet) above sea level.
The general course is south-west, and its length, including windings, is about 200miles. Its width, at its bifurcation with the Orinoco, is approximately 300feet, with a current towards the Negro of 0.751NaN1; but as it gains in volume from the very numerous tributary streams, large and small, which it receives en route, its velocity increases, and in the wet season reaches 5mph, even 8mph in certain stretches. It broadens considerably as it approaches its mouth, where it is about 1750feet wide. The volume of water the Casiquiare captures from the Orinoco is small in comparison to what it accumulates in its course.
In 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 50miles 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 Atabapo affluent 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 10miles across, with undulating ground, nowhere over 50feet 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.