River bifurcation (from Latin : furca , fork) occurs when a river (a bifurcating river ) flowing in a single channel 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 .
20-571: The Echimamish River is a river bifurcation in Manitoba , Canada . Located 70 kilometres (43 mi) northeast of the northern tip of Lake Winnipeg , it is about 60 kilometres (37 mi) long and runs east–west between the Hayes River and the Nelson River . It flows through nearly flat swampy country and has a barely detectable current. Flowing through peat bogs, the water acquires
40-399: A dam . Manmade restrictions to natural stream flow or temporary natural obstructions such as ice jams , vegetation blockage, or flooding of a lower stream can create backwater. If a river has developed one or more alternative courses in its evolution, one channel is usually designated the main course, and secondary channels may be termed backwaters. The main river course will usually have
60-549: A dark color, hence the old name of Blackwater Creek. Since it is shallow canoe navigation is helped by beaver ponds . Morse claims that it flows in two directions from a central beaver pond. On the Echimamish is the Painted Stone Portage. This is not the divide between the two river basins, but a short (20 paces) carry around a shallow and rocky section. The only other obstacles are beaver dams. The Echimamish
80-489: A result of river bifurcation, are important for the deposition and movement of water, sediment and nutrients from farther inland to the larger body of water that it empties into. Deltas are very important to humans, as the delta distributary regions provide homes to roughly half a billion people, and are exceptionally biologically rich. Bifurcated rivers are largely semi-permanent, and are subject to constant change in their configuration from evolving terranes and flow rates. As
100-431: A result of this, observation of the process by which rivers bifurcate and then gradually deteriorate has been poorly documented. The evolution of river bifurcations from single channel to multi-channeled and back again is largely dependent on discharge rate from the backwater regions of the channel. The bifurcation of channel systems begins when a single channel is forced to split when a bar of sediment causes initiation of
120-544: 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
140-489: A typical angle at which it is observed, with a critical angle of approximately 72º. However, observations and experiments show that many distributary channel bifurcations do not actually exhibit a bifurcation angle of 72º, but rather grow towards this angle over time after initiation of bifurcation. This implies that bifurcations that occur in deltas are semi-permanent, as many observed channels do not exhibit this angle due to their relatively recent initiation, or because some of
160-554: 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,
180-634: The Hayes River, the Echimamish and a portion of the Nelson River was designated part of the Canadian Heritage Rivers System . River bifurcation 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
200-432: The channels that do reach this bifurcation angle did not last to be observed. As is the case with river confluence , bifurcation is important in dividing land and morphological areas. Rivers are abundantly used as political boundaries, marking borders between regions of opposing countries, states and peoples, among other things. Sudden river bifurcation, even temporary, can disturb terranes that would otherwise be considered
220-436: The deposition of material required for various organisms to live, and thus has an indirect impact on surrounding ecosystems via flow patterns. Backwater (river) A backwater is a part of a river in which there is little or no current. It can refer to a branch of a main river, which lies alongside it and then rejoins it, or to a body of water in a main river, backed up by the sea tide or by an obstruction such as
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#1732772464038240-423: 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. This then leads to increased numbers of distributaries in deltas. Delta bifurcation has
260-536: The evolution of the braided system. Bifurcations move largely as a result of migration of the upstream channel. The configuration of the bifurcated system is also modified by the migration of bars within the system. This can cause sudden variations in channel widths, as well as width asymmetry in the system. Over time, the stable channel system will eventually deteriorate until only one channel receives flow from upstream, this then creates an unstable channel, one in which no flow passes through. River bifurcations impact
280-413: The expression a "cultural backwater". When a section of a river is near the coast or another feature that sets its base level , the section influenced by the conditions at its mouth is termed a backwater. If a river flows into a lake or sea, it is the region in which the slope of the river decreases because the lower water flux permitted at the mouth causes the water to back up. Where the river outlet
300-541: The fastest stream and will likely be the main navigation route; backwaters may be shallower and flow more slowly, if at all. Some backwaters are rich in mangrove forest . This results in a more diverse environment of scientific interest and worthy of preservation. Backwaters also provide opportunities for leisure activities such as canoeing and fishing. The term has been applied as a metaphor to physical and social areas that have been bypassed. It may apply to places that have been neglected in economic development, or in
320-430: The same region. Bifurcations are different from confluences in that many confluences are considered important sites for cities and trade. But due to the semi-permanence of most bifurcated rivers, and their uncommon occurrences, the concept of construction is not largely exhibited at sites of river bifurcation. Distributaries are common components of deltas, and are the opposite of tributaries. These distributaries, that are
340-466: The surrounding area in a plethora of ways, namely, redistributing flow of water, sediment and nutrients throughout a watershed and delta. In addition to this, migrating bifurcations and landforms can alter the terranes in a given region affected by this process. Sudden bifurcation initiation can cause small scale flooding of the surrounding area. The opposite, deterioration of a stable bifurcation to an unstable one, can have similar effects, as flow that
360-506: The two channel system, however, this does not always result in a system in which both channels receive flow. In braided systems, evolution of bifurcate systems is largely determined by the water level of adjacent branches of the system. The water level differences in braided systems are themselves caused by closure of branch entrances as a result of bar growth. In addition to bar growth, differences in direction of bifurcated river flows from compound bar shapes and backwater effects also influence
380-421: Was part of the voyageur route from Hudson Bay to Lake Winnipeg. Since most of the Nelson River is difficult, canoe and York boat brigades would take the easier Hayes and use the Echimamish to reach the upper Nelson and Lake Winnipeg. The first European to use the river may have been Joseph Smith in 1757. In 2006, the historic 600-kilometre (370 mi) route from York Factory to Norway House which includes
400-460: Was split through two channels now being directed through one can cause the stable channel to surpass bank-full stage, or the point at which the water level is above the river bank. This can also cause flooding, and is a prominent issue in regions where levees are in use. Bifurcations are a major distributor of nutrients and mineral particulates to biologically rich areas in deltas. Sudden deterioration or initiation of bifurcated systems can disrupt
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