What is a Meander?
The term ‘meander’ is one which refers to a winding curve or bend in a river. Meanders are typical landforms at the middle and lower courses of a river. Meander gradients are usually more gentle and they experience lateral (sideways) erosions which widen the channel of the river at the middle and lower courses of a river. Usually, the energy accompanying flow water in a river decreases progressively from the upper course of the river to the lowest course of the river.
Therefore, as water flows from the upper course of a river at very high energy, the impact it has on the landform on which the river is situated elicits erosional, transportation and deposition processes. Thus, during low flow conditions, straight river channels develop bars of sediment on their beds which leads to an eventual formation of deeper pathways which ultimately allow more flow of water and consequent formation of a sinusoidal flow of water.
As a result of the erosion on the outside portion the bend of flowing river water, erosion occurs, coupled with deposition on the inside portion of the sinusoidal curve. Thus the curvature of the pathway of river water flow increases, and the shape of the meander changes over time. The deposition process cuts off the original meander, leaving a horseshoe-like feature known as an oxbow lake. Meander geometry or median planform geometry is engaged in the technical description of meanders.
Some associated landforms include: Cut banks, Meander cutoffs, Incised meanders, Oxbow lakes, Scroll bars, and Slip-off slope.
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Formation of Meanders
Meanders are usually exhibited at the middle course of rivers. The major contributors to the creation of meanders include erosion, transportation, and deposition processes. The following are processes which lead to the formation of meanders in river bodies. These processes can be categorized into the following stages:
During low flow conditions, straight river channels have bars of sediment on their beds. The flowing water weaves around these bars of sediment which in turn creates deeper pathways where most of the water flows called pools and shallow areas where less water flows called riffles. Ultimately, the river flow starts to swing from side to side.
In this stage, the river swings towards the bank lateral (sideways) erosion causes undercutting. At the opposite side of the channel where the velocity (speed of the flow of water) is lower material is deposited. Thus, the river does not get any wider. As a result of this stage, undercutting often occurs on the outer bank and deposition on the inner bank of the meander.
With persistent erosion along the outer bank, a river cliff or bluff is created as a result of hydraulic action and abrasion. Then, a point bar forms on the inner bank. The point bar or meander bar is a gently sloping deposit of sand, gravel, and pebbles. Just as the surface flow of water hits the outer bank it corkscrews, flows along the river bed then deposits eroded material on the inner bank.
This stage of meander formation eventually causes the neck of the meander to be breached by the river creating an ox-bow lake. A perfect example could be found in the River Derwent, North Yorkshire which is almost at the point of breaching.
Therefore, meanders are formed as a river goes around a bend in which most of the flowing water is pushed towards the outside portion of the water flow. The speed of water flow increases and the hydraulic action together with abrasion forces impacted results in increased erosion.
Usually, the meander formed is characterized by an inner bend which is slower in flow, making water flow to slow down considerably creating a gentle slope of sand and shingle as a result of deposition of the eroded material. More water is gained by the deepening bend as the river makes its way to the middle course of the river. A resultant increase in flow energy is also exhibited.
Due to lateral erosion, the river widens and the river water flows over flatter land to develop larger bends which are referred to as ‘meanders.’ The characteristic sinusoidal (sinewave-like or snake-like) flow of water is therefore exhibited after the complete formation of meanders at the middle course of river bodies.
10 Interesting Facts About the Meanders
Fact 1: The word ‘meander’ comes from the Meander River located in present day Turkey and known to the Ancient Greeks as ‘maiandros.’ Principal Turkish rivers that drain into the Aegean Sea are the Gediz and Büyükmenderes (ancient Meander); the many loops and bends of the Büyükmenderes gave rise to the term meander in English.
Fact 2: Typical of meanders are Oxbow lakes. The oxbow lakes are also known as ‘cut-off lakes’. These lakes are usually formed by the normal process of fluvial meandering. Just after the cutoff meander is formed, the river flows into its end from the river and builds a small delta which eventually results in the formation of oxbow lakes.
Fact 3: The term ‘incised meander’ refers to meanders of a stream or river which has cut its bed down into the bedrock. Incised meanders can be found in Glen Canyon, United States of America.
Fact 4: Point bars are also known as ‘meander bars’ are often formed by the slow addition of individual layers of non-cohesive sediment in the inside bank of a meander by the accompanying migration of channels toward the outer bank.
Fact 5: Meanders are popularly described by the Stochastic theory. This theory states that: The meander train is assumed to be a result of the stochastic fluctuation of the direction of flow due to the random presence of direction-changing obstacles in the path of a river.
Fact 6: The sharp bend in a river’s course, called a ‘meander’, is eventually cut off by a new channel that forms across the neck of land created by the meander. At the end of this process, the original meander is separated from the river, and its water stops flowing. At this point, an ‘oxbow lake’ is said to be formed.
Fact 7: Meanders are usually found in the middle course of rivers. They result from erosional and depositional processes at this level of rivers mainly due to the high energy and flow of water.
Fact 8: During the flow of river water which eventually leads to meander formation at the middle course, the fastest current is usually found on the outside of the bend, while the slowest current is found on the inside of the bend. This is due to the fact that the water on the outside bend of river water flow is deeper and runs faster than the water flowing at the inside portion of the bend.
Fact 9: Erosion, therefore, occurs on the outside of meander bends while deposition occurs on the inner side of meander bends (which might eventually lead to the formation of oxbow lakes).
Fact 10: Typically, meanders belong to a series of regular sinous curves, bends, turns, windings or loops in the channel of a stream, river or other watercourse and the zone within which a meandering stream moves its channel across either its valley floor or floodplain from time to time is known as the ‘meander belt.’
- Middle course of a River. Retrieved from: geography.learnontheinternet.co.uk/topics/river_middle_course.html
- River landforms. Retrieved from: https://www.bbc.com/bitesize/guides/ztpkqty/revision/2&hl=en-NG
- Meander floodplains. By: rgamesby. Retrieved from: coolgeography.co.uk/GCSE/AQA/Water%20on%20the%20Land/Meanders/Landforms%20Meanders.htm