A section of a river or stream that diverts from the main channel and rejoins it downstream.
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An anabranch is a section of a
river or
stream that diverts from the main
channel or
stem of the
watercourse and rejoins the main stem downstream. Local anabranches can be the result of small
islands in the watercourse. In larger anabranches, the flow can diverge for a distance of several or even hundreds of kilometers before rejoining the main channel.
Word usage and related terms
The term anabranch, in its
hydrological meaning, is used more frequently in
Australia than in the rest of the English-speaking world.
The term anabranching river describes a
river with many anabranches, whilst an
anastomosing river is an organic-rich subset of this
river type.[1]
The term
braided river describes
watercourses which are divided by small
islands into multiple channel threads within a single main channel, but the term does not describe the multiple channels of an anabranching river.
A
distributary is a branch of a
river that does not rejoin the main channel; these are common on and near
river deltas.
An anabranch that gets cut off from the main channel becomes an
oxbow lake, known in Australia as a
billabong.
Examples
The
Magdalena River, in Colombia, bifurcates in
El Banco in two branches: Brazo de Loba (Shewolf Branch in Spanish) and Brazo de Mompox. The first one, Brazo de Loba is the main navigable channel and is 177 km long. Brazo de Mompox is thus the anabranch. There are several other branches that join those two main branches, interconnected by swamps ("ciénagas"), the main ones being Quitasol, Chicagua and La Victoria. Between Brazo de Loba and Brazo de Mompox is the island of Mompox or Margarita Island, a sunken geological block of 2.200 square km between the
faults of Chicagua and El Romeral.[2]
In the
Lower Simpson Desert, in
South Australia,
Kallakoopah Creek is an anabranch of the
Warburton River that flows during major Warburton floods of over 5 m in depth. The Kallakoopah is approximately 400 km long and members of the Lake Eyre Yacht Club and others have used it to sail a circular route to
Lake Eyre by traveling down the Kallakoopah and returning via the Warburton.
The
Bahr el Zeraf in southern
Sudan splits from the Bahr al Jabal section of the
White Nile and flows for 240 km (150 mi), before rejoining the White Nile proper upriver from
Malakal.
Approximately 15 km out[4] of
Charters Towers (
Queensland/
Australia) is a section of the
Burdekin River known as 'the anabranch'. This strip of water is separate from the main flood way, and is typically dry during the sunnier months. Once there is consistent rain, it will meet up with the river again and flood with fresh water. It is well known for barramundi fishing.
Probably because waterways played an important role in infrastructure, anabranches and the resulting river islands are often found in old cities as with the
Île de la Cité in Paris.