Casiquiare canal
Encyclopedia
Distributary
A distributary, or a distributary channel, is a stream that branches off and flows away from a main stream channel. They are a common feature of river deltas. The phenomenon is known as river bifurcation. The opposite of a distributary is a tributary...
of the upper Orinoco flowing southward into the Rio Negro, in Venezuela
Venezuela
Venezuela , officially called the Bolivarian Republic of Venezuela , is a tropical country on the northern coast of South America. It borders Colombia to the west, Guyana to the east, and Brazil to the south...
, South America. As such, it forms a unique natural canal between the Orinoco and Amazon
Amazon River
The Amazon of South America is the second longest river in the world and by far the largest by waterflow with an average discharge greater than the next seven largest rivers combined...
river systems. It is the largest river on the planet that links two major river systems, a so-called bifurcation. The area forms a water divide, more dramatically at regional flood
Flood
A flood is an overflow of an expanse of water that submerges land. The EU Floods directive defines a flood as a temporary covering by water of land not normally covered by water...
stage. Another river that links two river basins is the Echimamish River
Echimamish River
The Echimamish River is a river bifurcation in Manitoba. Like the better-known Casiquiare canal it has the curious property of flowing between two river systems, in this case, the Hayes River and the Nelson River. Located 50 or so miles northeast to the northern tip of Lake Winnipeg, it is about 40...
in Canada.
Discovery
In 1744 a Jesuit priest named Father Roman, while ascending the Orinoco River, met some PortuguesePortugal
Portugal , officially the Portuguese Republic is a country situated in southwestern Europe on the Iberian Peninsula. Portugal is the westernmost country of Europe, and is bordered by the Atlantic Ocean to the West and South and by Spain to the North and East. The Atlantic archipelagos of the...
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. Charles Marie de La Condamine
Charles Marie de La Condamine
Charles Marie de La Condamine was a French explorer, geographer, and mathematician. He spent ten years in present-day Ecuador measuring the length of a degree latitude at the equator and preparing the first map of the Amazon region based on astronomical observations.-Biography:Charles Marie de La...
, seven months later, was able to give to the Académie française
Académie française
L'Académie française , also called the French Academy, is the pre-eminent French learned body on matters pertaining to the French language. The Académie was officially established in 1635 by Cardinal Richelieu, the chief minister to King Louis XIII. Suppressed in 1793 during the French Revolution,...
an account of Father Roman's voyage, and thus confirm the existence of this waterway, first reported by Father Acuña
Cristóbal Diatristán de Acuña
Cristóbal Diatristán de Acuña was a Spanish missionary and explorer.He was born at Burgos. He was admitted a Jesuit in 1612, and afterwards sent on mission work to Chile and Peru, where he became rector of the college of Cuenca...
in 1639.
But little credence was given to Father Roman's statement until it was verified, in 1756, by the Spanish
Spain
Spain , officially the Kingdom of Spain languages]] under the European Charter for Regional or Minority Languages. In each of these, Spain's official name is as follows:;;;;;;), is a country and member state of the European Union located in southwestern Europe on the Iberian Peninsula...
Boundary-line Commission of Yturriaga and Solano. In 1800 German scientist Alexander von Humboldt
Alexander von Humboldt
Friedrich Wilhelm Heinrich Alexander Freiherr von Humboldt was a German naturalist and explorer, and the younger brother of the Prussian minister, philosopher and linguist Wilhelm von Humboldt...
and French botanist Aimé Bonpland
Aimé Bonpland
Aimé Jacques Alexandre Bonpland was a French explorer and botanist.Bonpland's real name was Goujaud, and he was born in La Rochelle, a coastal city in France. After serving as a surgeon in the French army, and studying under J. N...
explored the river. During a 1924–25 expedition, Alexander H. Rice, Jr.
Alexander H. Rice, Jr.
Alexander Hamilton Rice, Jr. was an American physician, geographer, geologist and explorer. He graduated from Harvard University in 1898 with an A.B. degree, and earned his medical degree in 1904 also at Harvard...
of Harvard University
Harvard University
Harvard University is a private Ivy League university located in Cambridge, Massachusetts, United States, established in 1636 by the Massachusetts legislature. Harvard is the oldest institution of higher learning in the United States and the first corporation chartered in the country...
traveled up the Orinoco, traversed the Casiquiare canal, and descended the Rio Negro to the Amazon at Manaus. It was the first expedition to use aerial photography and shortwave radio for mapping of the region. In 1968 the Casiquiare was navigated by an SRN6 hovercraft during a National Geographic expedition.
Geography
The origin of the Casiquiare, at the River Orinoco, is 9 miles (14 km) below the mission of La EsmeraldaLa Esmeralda
La Esmeralda is a small settlement in and the capital of Alto Orinoco Municipality in Venezuela’s Amazonas State. The name means “the emerald”...
at 3°8′18.5"N 65°52′42.5"W, and about 123 metres (404 ft) above sea level. Its mouth at the Rio Negro, an affluent of the Amazon River
Amazon River
The Amazon of South America is the second longest river in the world and by far the largest by waterflow with an average discharge greater than the next seven largest rivers combined...
, is near the town of San Carlos
San Carlos de Río Negro
San Carlos de Rio Negro is a town in Venezuela's Amazonas State.San Carlos de Río Negro is a small city of about 1200 inhabitants in the Venezuelan state of Amazonas. It serves as the administrative capital of the municipal district of Río Negro, inhabited primarily by Amerind people, in...
and is 91 metres (299 ft) above sea level.
The general course is south-west, and its length, including windings, is about 200 miles (321.9 km). Its width, at its bifurcation
River bifurcation
River bifurcation occurs when a river flowing in a single stream separates into two or more separate streams which continue downstream. Some rivers form complex networks of distributaries, especially in their deltas...
with the Orinoco, is approximately 300 feet (91.4 m), with a current towards the Rio Negro of 0.75 mile per hour (0.33528 m/s). However, as it gains in volume from the very numerous tributary
Tributary
A tributary or affluent is a stream or river that flows into a main stem river or a lake. A tributary does not flow directly into a sea or ocean...
streams, large and small, that it receives en route, its velocity increases, and in the wet season reaches 5 miles per hour (2.2 m/s), even 8 miles per hour (3.6 m/s) in certain stretches. It broadens considerably as it approaches its mouth, where it is about 1750 ft (533 m). The volume of water the Casiquiare captures from the Orinoco is small in comparison to what it accumulates in its course.
In flood
Flood
A flood is an overflow of an expanse of water that submerges land. The EU Floods directive defines a flood as a temporary covering by water of land not normally covered by water...
-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 50 miles (80.5 km) 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 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 easier portage
Portage
Portage or portaging refers to the practice of carrying watercraft or cargo over land to avoid river obstacles, or between two bodies of water. A place where this carrying occurs is also called a portage; a person doing the carrying is called a porter.The English word portage is derived from the...
between the Orinoco and Amazon basins, called the isthmus of Pimichin, which is reached by ascending the Terni branch of the Atabapo River
Atabapo River
Atabapo River is a river of Venezuela and Colombia. It forms the international boundary between the two countries for much of its length. It is part of the Orinoco River basin.-References:*Rand McNally, The New International Atlas, 1993....
, an 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 10 miles (16 km) across, with undulating ground, nowhere over 50 ft (15 m), 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 Rio Negro by the little stream called the Pimichin.
Hydrographic divide
The Casiquiare canal–Orinoco River hydrographic divide is a representation of the hydrographicHydrography
Hydrography is the measurement of the depths, the tides and currents of a body of water and establishment of the sea, river or lake bed topography and morphology. Normally and historically for the purpose of charting a body of water for the safe navigation of shipping...
water divide
Water divide
A drainage divide, water divide, divide or watershed is the line separating neighbouring drainage basins...
that delineates the separation between the Orinoco Basin and the Amazon Basin
Amazon Basin
The Amazon Basin is the part of South America drained by the Amazon River and its tributaries that drains an area of about , or roughly 40 percent of South America. The basin is located in the countries of Bolivia, Brazil, Colombia, Ecuador, Guyana, Peru, and Venezuela...
. (The Orinoco Basin flows west–north–northeast into the Caribbean
Caribbean Sea
The Caribbean Sea is a sea of the Atlantic Ocean located in the tropics of the Western hemisphere. It is bounded by Mexico and Central America to the west and southwest, to the north by the Greater Antilles, and to the east by the Lesser Antilles....
; the Amazon Basin flows east into the western Atlantic
Atlantic Ocean
The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...
in the extreme northeast of Brazil
Brazil
Brazil , officially the Federative Republic of Brazil , is the largest country in South America. It is the world's fifth largest country, both by geographical area and by population with over 192 million people...
.)
Essentially the river divide
Water divide
A drainage divide, water divide, divide or watershed is the line separating neighbouring drainage basins...
is a west-flowing, upriver section of Venezuela's Orinoco River with an outflow to the south into the Amazon Basin. This named outflow is the Casiquiare canal, which, as it heads downstream (southerly), picks up speed and also accumulates water volume.
The greatest manifestation of the divide is during floods. During flood stage, the Casiquiare's main outflow point into the Rio Negro is supplemented by an overflow that is a second, and more minor, entry river bifurcation
River bifurcation
River bifurcation occurs when a river flowing in a single stream separates into two or more separate streams which continue downstream. Some rivers form complex networks of distributaries, especially in their deltas...
into the Rio Negro and upstream from its major, common low-water entry confluence with the Rio Negro. At flood, the river becomes an area flow source, far more than a narrow confined river.
The Casiquiare canal connects the upper Orinoco, 9 miles below the mission of Esmeraldas, with the Rio Negro affluent of the Amazon River
Amazon River
The Amazon of South America is the second longest river in the world and by far the largest by waterflow with an average discharge greater than the next seven largest rivers combined...
near the town of San Carlos
San Carlos de Río Negro
San Carlos de Rio Negro is a town in Venezuela's Amazonas State.San Carlos de Río Negro is a small city of about 1200 inhabitants in the Venezuelan state of Amazonas. It serves as the administrative capital of the municipal district of Río Negro, inhabited primarily by Amerind people, in...
.
The simplest description (besides the entire area-floodplain) of the water divide is a "south-bank Orinoco River strip" at the exit point of the Orinoco, also the origin of the Casiquiare canal. However during the Orinoco's flood stage, that single, simply defined "origin of the canal" is turned into a region, and an entire strip along the southern bank of the Orinoco River.
Sources
- VARESCHI, Volkmar. Orinoco arriba. A través de Venezuela siguiendo a Humboldt. Caracas: Ediciones Lectura, 1959