This can erode the bank and slowly increase the size of the bend to form a large curve called a meander. How are Meanders Formed?Īt a bend in a river or stream, water flows against the outer river bank with increased force. Uvac River, Serbia and eastern Bosnia and Herzegovina What is a Meander Landform?Ī meander is where a river or stream makes a bend or curve, generally over 90 degrees. As the river migrates towards the direction of the eroding bank, the current ripples of the point bar will end up being deposited on top of planar lamination/dune cross stratification of the bank.Meander Landforms Have 2 Main Characteristics: The point bar of the river will produce current ripple lamination, due to the finer sediment and slower flow speeds. The coarser grained areas that result from a faster flow speed will have upper planar lamination or dune cross stratification. The different flow speeds within the channel, along with the different grain sizes, will produce unique sedimentary structures. The coarser grains will be present in the outer edges of the channel, while finer sediment will be along the inside of the channel. The different flow speeds will carry different sized sediment grains, which will produce a cross section that is asymmetrical. There are two distinct areas within the river channel that are characterized by different flow speeds and grain size, the outer edge and the inner bend of the channel. This is related to the concept of Reynolds Number, which measures whether sediment transport of a specific grain size will be able to occur based on the velocity of the water. The coarser grains will be transported to these parts of the river channel because the higher velocity is able to transport the heaver grains. This migration can lead to the creation of an oxbow lake, which is described further here: (Sumner)/Textbook_Construction/Floodplains_and_Oxbow_Lakes.ĭue to the higher velocity in the middle and outside bend of the river channel, coarser sediment will be deposited in those areas. As this cycle of erosion and deposition continues, the river will migrate in it's river valley. This allows sediment to settle out and be deposited. On the inside bend of the river, known as the point bar, water velocity is slower because it doesn't have to travel as far as the water on the outside of the bend. Erosion is caused by the increase in flow velocity, which has the force to erode and transport sediment from the bank. This area is referred to as the bank of the channel, and it is where erosion of sediment occurs. When the water moves around a curve, the velocity of the water is highest along the outer part of the channel. The bank of the channel is where erosion occurs, and is located on the outer bend of the river. There is a build up of gray colored sediment. The point bar, where sediment is deposited, can be seen in the inner bend of the river. There are distinct sedimentary structures that result from this process.įigure 1: Aerial photograph of a meandering river. There is a differentiation in flow speeds within a meandering river channel that produces areas of erosion and deposition. The bends in the river will migrate back and forth within the river valley. Meandering Rivers are located on flat terrain that reduces the flow speed of water, allowing the river to curve or "meander".
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