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Concept
Diffluence (hydrologie)
Résumé
River bifurcation (from furca, fork) occurs when a river flowing in a single stream separates into two or more separate streams (called distributaries) which then continue downstream. Some rivers form complex networks of distributaries, typically in their deltas. If the streams eventually merge again or empty into the same body of water, then the bifurcation forms a river island.
River bifurcation may be temporary or semi-permanent, depending on the strength of the material that is dividing the two distributaries. For example, a mid-stream island of soil or silt in a delta is most likely temporary, due to low material strength. A location where a river divides around a rock fin, e.g. a volcanically formed dike, or a mountain, may be more lasting as a result of higher material strength and resistance to weathering and erosion. A bifurcation may also be man-made, for example when two streams are separated by a long bridge pier.
River bifurcation occurs in many types of rivers. It is common in meandering and braided rivers. In meandering rivers, bifurcations are often unstable in their configuration, and usually result in channel avulsion. The stability of bifurcation is dependent on the rate of flow of the river upstream as well as the sediment transport of the upper reaches of the branches just after bifurcation occurs. The evolution of bifurcation is highly dependent on the discharge of the river upstream of the bifurcation. Unstable bifurcations are bifurcations in which only one channel receives water. Within deltas, these typically create channels with relatively large widths, and are also known as channel avulsions. Stable bifurcations are bifurcations in which both channels receive water.
In deltas, the directions of distributaries resulting from bifurcation are easily changeable by processes like aggradation, or differential subsidence and compaction. The number of distributaries that are present is in part determined by the rate of sediment discharge, and increased sediment discharge leads to more river bifurcation.
Source officielle
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