The Branco River ( pt, Rio Branco; Engl: ''White River'') is the principal

affluent Wealth is the abundance of valuable financial assets or physical possessions which can be converted into a form that can be used for transactions. This includes the core meaning as held in the originating Old English word , which is from an I ...

of the Rio Negro from the north.

Basin

The river drains the

Guayanan Highlands moist forests The Guayanan Highlands moist forests (NT0124) is an ecoregion in the south of Venezuela and the north of Brazil and in Guyana, Suriname, French Guiana. It is in the Amazon biome. It encompasses an upland region with diverse fauna and flora, which ...

ecoregion. It is enriched by many streams from the

Tepui A tepui , or tepuy (), is a table-top mountain or mesa found in South America, especially in Venezuela and western Guyana. The word tepui means "house of the gods" in the native tongue of the Pemon, the indigenous people who inhabit the Gran S ...

highlands which separate Venezuela and Guyana from Brazil. Its two upper main tributaries are the Uraricoera and the Takutu. The latter almost links its sources with those of the Essequibo; during floods headwaters of the Branco and those of the Essequibo are connected, allowing a level of exchange in the aquatic fauna (such as fish) between the two systems. The Branco flows nearly south, and finds its way into the Negro through several channels and a chain of

lagoon A lagoon is a shallow body of water separated from a larger body of water by a narrow landform, such as reefs, barrier islands, barrier peninsulas, or isthmuses. Lagoons are commonly divided into ''coastal lagoons'' (or ''barrier lagoons'') a ...

s similar to those of the latter river. It is long, up to its Uraricoera

confluence In geography, a confluence (also: ''conflux'') occurs where two or more flowing bodies of water join to form a single channel. A confluence can occur in several configurations: at the point where a tributary joins a larger river (main stem); o ...

. It has numerous

island An island (or isle) is an isolated piece of habitat that is surrounded by a dramatically different habitat, such as water. Very small islands such as emergent land features on atolls can be called islets, skerries, cays or keys. An island ...

s, and, above its mouth, it is broken by a bad series of rapids.

Water chemistry

As suggested by its name, the Branco (literally "white" in Portuguese) has whitish water that may appear almost milky due to the

inorganic In chemistry, an inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds, that is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as '' inorganic chemist ...

sediments it carries.The Alfred Russel Wallace page
On the Rio Negro.
Retrieved 10 October 2017. It is traditionally considered a whitewater river, although the major seasonal fluctuations in its physico-chemical characteristics makes a classification difficult and some consider it

clearwater Clearwater or Clear Water may refer to: Places Canada * Clear Water Academy, a private Catholic school located in Calgary, Alberta * Clearwater (provincial electoral district), a former provincial electoral district in Alberta * Clearwater, Briti ...

. Especially the river's upper parts at the

headwaters The headwaters of a river or stream is the farthest place in that river or stream from its estuary or downstream confluence with another river, as measured along the course of the river. It is also known as a river's source. Definition The ...

are clear and flow through rocky country, leading to the suggestion that sediments mainly originate from the lower parts. Furthermore, its chemistry and color may contradict each other compared to the traditional Amazonian river classifications. The Branco River has pH 6–7 and low levels of

dissolved organic carbon Dissolved organic carbon (DOC) is the fraction of organic carbon operationally defined as that which can pass through a filter with a pore size typically between 0.22 and 0.7 micrometers. The fraction remaining on the filter is called particu ...

Alfred Russel Wallace Alfred Russel Wallace (8 January 1823 – 7 November 1913) was a British naturalist, explorer, geographer, anthropologist, biologist and illustrator. He is best known for independently conceiving the theory of evolution through natural se ...

mentioned the coloration in "On the Rio Negro", a paper read at the 13 June 1853 meeting of the

Royal Geographical Society The Royal Geographical Society (with the Institute of British Geographers), often shortened to RGS, is a learned society and professional body for geography based in the United Kingdom. Founded in 1830 for the advancement of geographical scien ...

, in which he said: " he Rio Brancois white to a remarkable degree, its waters being actually milky in appearance".

Alexander von Humboldt Friedrich Wilhelm Heinrich Alexander von Humboldt (14 September 17696 May 1859) was a German polymath, geographer, naturalist, explorer, and proponent of Romantic philosophy and science. He was the younger brother of the Prussian minister, p ...

attributed the color to the presence of

silicate In chemistry, a silicate is any member of a family of polyatomic anions consisting of silicon and oxygen, usually with the general formula , where . The family includes orthosilicate (), metasilicate (), and pyrosilicate (, ). The name is al ...

s in the water, principally

mica Micas ( ) are a group of silicate minerals whose outstanding physical characteristic is that individual mica crystals can easily be split into extremely thin elastic plates. This characteristic is described as perfect basal cleavage. Mica is ...

and

talc Talc, or talcum, is a Clay minerals, clay mineral, composed of hydrated magnesium silicate with the chemical formula Mg3Si4O10(OH)2. Talc in powdered form, often combined with corn starch, is used as baby powder. This mineral is used as a thi ...

. There is a visible contrast with the waters of the Rio Negro at the confluence of the two rivers. The Rio Negro is a

blackwater river A blackwater river is a type of river with a slow-moving channel flowing through forested swamps or wetlands. As vegetation decays, tannins leach into the water, making a transparent, acidic water that is darkly stained, resembling black te ...

with dark tea-colored acidic water (pH 3.5–4.5) that contains high levels of dissolved organic carbon.

River capture

Until approximately 20,000 years ago the headwaters of the Branco River flowed not into the Amazon, but via the Takutu Graben in the

Rupununi The Rupununi is a region in the south-west of Guyana, bordering the Brazilian Amazon. The Rupununi river, also known by the local indigenous peoples as ''Raponani'', flows through the Rupununi region. The name Rupununi originates from the word '' ...

area of Guyana towards the Caribbean. Currently in the rainy season much of the Rupununi area floods, with water draining both to the Amazon (via the Branco River) and the Essequibo River.

Citations

Notes

References

Encyclopædia Britannica Online.com: "Branco River"
. retrieved 19 September 2009. {{- Rivers of Roraima Tributaries of the Rio Negro (Amazon) Boa Vista, Roraima Guayana Highlands