Editing Casiquiare canal (section)

==Geography==
[[File:Rio Orinoco e Canal do Cassiquiare, Venezuela.jpg|thumb|300px|The Casiquiare (bottom left) is separated from the Orinoco]]
The origin of the Casiquiare, at the River Orinoco, is {{convert|9|mi|km|order=flip}} below the mission of [[La Esmeralda, Venezuela|La Esmeralda]] at {{coord|3|8|18.5|N|65|52|42.5|W|region:VE-X_type:landmark|display=inline}}, and about {{convert|123|m|ft}} above sea level. Its mouth at the Rio Negro, an affluent of the [[Amazon River]], is near the town of [[San Carlos de Río Negro|San Carlos]] and is {{convert|91|m|ft}} above sea level.{{sfn|Church|1911a|p=787}}

The general course is south-west, and its length, including windings, is about {{convert|200|mi|km|-1|order=flip}}. Its width, at its [[river bifurcation|bifurcation]] with the Orinoco, is approximately {{convert|300|ft|m|-1|order=flip}}, with a current towards the Rio Negro of {{convert|0.75|mph|m/s|1|order=flip}}. However, as it gains in volume from the very numerous [[tributary]] streams, large and small, that it receives en route, its velocity increases, and in the wet season reaches {{convert|5|mph|m/s|1|order=flip}}, even {{convert|8|mph|m/s|1|order=flip}} in certain stretches. It broadens considerably as it approaches its mouth, where it is about {{convert|1750|ft|m|order=flip|0}} wide. The volume of water the Casiquiare captures from the Orinoco is small in comparison to what it accumulates in its course.{{sfn|Church|1911a|p=787}} Nevertheless, the geological processes are ongoing, and evidence points to a slow and gradual increase in the size of Casiquiare. It is likely that [[stream capture]] is in progress, i.e. what currently is the uppermost Orinoco basin, including [[Cunucunuma River]], eventually will be entirely diverted by the Casiquiare into the Amazon basin.<ref>{{cite book|editor=Quinn, J.A. |editor2=S.L. Woodward | year=2015 | title=Earth's Landscape: An Encyclopedia of the World's Geographic Features | volume=1 | pages=141–142 | isbn=978-1-61069-445-2 | last1=Quinn | first1=Joyce Ann | last2=Woodward | first2=Susan L. }}</ref><ref>{{cite journal |last1=Stokes |first1=Maya |last2=Goldberg |first2=Samuel |last3=Perron |first3=J. Taylor |date=25 May 2018 |title=Ongoing River Capture in the Amazon |journal=Geophysical Research Letters |volume=45 |issue=11 |pages=5545–5552 |doi=10.1029/2018GL078129 |doi-access=free |hdl=1721.1/140798.2 |hdl-access=free }}</ref>

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 {{convert|50|mi|km|-1|order=flip}} 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.{{sfn|Church|1911a|p=787}}

The Casiquiare is not 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.{{sfn|Church|1911a|p=787}}

To the west of the Casiquiare, there is a much shorter and easier [[portage]] between the Orinoco and Amazon basins, called the isthmus of [[Pimichin]], which is reached by ascending the Temi branch of the [[Atabapo River]], an affluent of the Orinoco. Although the Temi 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|order=flip|0}} high, with swamps and marshes. In the early 20th century, it was much used for the transit of large canoes, which were hauled across it from the Temi River and reached the Rio Negro by a little stream called the Pimichin.{{sfn|Church|1911a|p=787}}