The Branco River (; 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 ...

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, the north of Brazil, and also within Guyana, Suriname, and French Guiana. It is in the Amazon biome. It encompasses an upland region with diverse fauna and f ...

ecoregion. It is enriched by many streams from the

Tepui A tepui , or tepuy (), is a member of a family of table-top mountains or mesas found in northern South America, especially in Venezuela, western Guyana, and northern Brazil. The word tepui means "house of the gods" in the native tongue of the ...

highlands which separate

Venezuela Venezuela, officially the Bolivarian Republic of Venezuela, is a country on the northern coast of South America, consisting of a continental landmass and many Federal Dependencies of Venezuela, islands and islets in the Caribbean Sea. It com ...

and

Guyana Guyana, officially the Co-operative Republic of Guyana, is a country on the northern coast of South America, part of the historic British West Indies. entry "Guyana" Georgetown, Guyana, Georgetown is the capital of Guyana and is also the co ...

from

Brazil Brazil, officially the Federative Republic of Brazil, is the largest country in South America. It is the world's List of countries and dependencies by area, fifth-largest country by area and the List of countries and dependencies by population ...

. Its two upper main tributaries are the

Uraricoera The Uraricoera (or Uraricuera) River is a river of Roraima state in northern Brazil. The confluence of the Uraricoera and Takutu Rivers forms the Branco River. Basin The river drains the Guayanan Highlands moist forests ecoregion. Part of the riv ...

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'') an ...

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 watercourses join to form a single channel (geography), channel. A confluence can occur in several configurations: at the point where a tributary joins a larger river (main ...

. It has numerous

island An island or isle is a piece of land, distinct from a continent, completely surrounded by water. There are continental islands, which were formed by being split from a continent by plate tectonics, and oceanic islands, which have never been ...

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

Discharge

Average, minimum and maximum discharge of the Branco River at near mouth. Period from 1998 to 2022.

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

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. Especially the river's upper parts at the

headwaters The headwater of a river or stream is the geographical point of its beginning, specifically where surface runoff water begins to accumulate into a flowing channel of water. A river or stream into which one or many tributary rivers or streams flo ...

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 Operational definition, operationally defined as that which can pass through a filter with a pore size typically between 0.22 and 0.7 micrometre, micrometers. The fraction remain ...

Alfred Russel Wallace Alfred Russel Wallace (8 January 1823 – 7 November 1913) was an English naturalist, explorer, geographer, anthropologist, biologist and illustrator. He independently conceived the theory of evolution through natural selection; his 1858 pap ...

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 1769 – 6 May 1859) was a German polymath, geographer, natural history, naturalist, List of explorers, explorer, and proponent of Romanticism, Romantic philosophy and Romanticism ...

attributed the color to the presence of

silicate 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 also used ...

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 fragile elastic plates. This characteristic is described as ''perfect basal cleavage''. Mica is co ...

and

talc Talc, or talcum, is a clay mineral composed of hydrated magnesium silicate, with the chemical formula . Talc in powdered form, often combined with corn starch, is used as baby powder. This mineral is used as a thickening agent and lubricant ...

. 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#Classification, river with a slow-moving channel flowing through forested swamps or wetlands. Most major blackwater rivers are in the Amazon Basin and the Southern United States. The term is used in fluvial ...

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