The Branco River (Portuguese: Rio Branco; Engl: White River) is the principal affluent of the Rio Negro from the north.
Basin
The river drains the Guayanan Highlands moist forests ecoregion.[8]
It is enriched by many streams from the Tepui highlands which separate Venezuela and Guyana from Brazil. Its two upper main tributaries are the Uraricoera and the Takutu.[9] 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.[10]
The Branco flows nearly south, and finds its way into the Negro through several channels and a chain of lagoons similar to those of the latter river. It is 350 miles (560 km) long, up to its Uraricoera confluence. It has numerous islands, and, 235 miles (378 km) 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.[5]
Year
Discharge (m3/s)
Year
Discharge (m3/s)
Min
Mean
Max
Min
Mean
Max
1998
5,664
16,435
2011
454
5,008
16,815
1999
1,792
9,538
22,576
2012
2,135
8,381
17,944
2000
2,506
9,725
28,697
2013
1,377
6,493
13,229
2001
788
6,551
17,791
2014
1,117
6,384
15,489
2002
1,271
5,219
18,760
2015
772
3,983
10,416
2003
640
4,375
13,320
2016
435
4,316
11,677
2004
756
4,244
11,959
2017
2,258
7,437
16,449
2005
729
7,868
19,893
2018
777
6,653
17,912
2006
2,457
9,899
22,644
2019
625
5,205
15,859
2007
845
7,271
15,118
2020
1,567
7,216
16,564
2008
2,739
7,630
17,280
2021
1,712
8,828
23,180
2009
486
4,318
10,735
2022
1,810
9,087
23,631
2010
278
2,754
8,040
278
6,469
28,697
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 sediments it carries.[11] It is traditionally considered a whitewater river,[12][13] although the major seasonal fluctuations in its physico-chemical characteristics makes a classification difficult and some consider it clearwater.[14][15] Especially the river's upper parts at the headwaters are clear and flow through rocky country, leading to the suggestion that sediments mainly originate from the lower parts.[11] Furthermore, its chemistry and color may contradict each other compared to the traditional Amazonian river classifications.[14] The Branco River has pH 6–7 and low levels of dissolved organic carbon.[15]
Alfred Russel Wallace mentioned the coloration in "On the Rio Negro", a paper read at the 13 June 1853 meeting of the Royal Geographical Society, in which he said: "[The Rio Branco] is white to a remarkable degree, its waters being actually milky in appearance". Alexander von Humboldt attributed the color to the presence of silicates in the water, principally mica and talc.[16] 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 with dark tea-colored acidic water (pH 3.5–4.5) that contains high levels of dissolved organic carbon.[15]
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 area of Guyana towards the Caribbean.[17] 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.[10]
^ abcde Souza kodra, A.; M.N. Fernandes; W.L. Paxiúba Duncan (2014). "Effect of clearwater on osmoregulation of cururu ray, Potamotrygon sp. (Chondrichthes; Potamotrogonidae), an endemic species from blackwater river". Scientia Amazonia. 3 (1): 15–24.
Brazil