![]() 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. 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. meandering portion of river when cross section criss-cross each other. The floodplain is the area of low relief that is level with the top of the stream’s channel. The valley consists of the sloping areas around the stream and has the distinctive V shape. 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. area with the measuring tool in the cross section plot. Looking at a stream in cross-section, three main components are visible: the valley, the floodplain, and the channel (Figure 8.1). 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". The build-up of deposited sediment is known as a slip-off slope close slip-off slope Gently sloping bank found on the inside of a river bend because of slow-flowing water, depositing sediment.There is less water on the inside bend of a meander so friction causes the water to slow down, lose energy and deposit the material the river is carrying, creating a gentle slope.The lateral erosion on the outside bend causes undercutting of the river bank to form a river cliff close river cliff Steep bank created on the outside of a river bend by the erosive effect of fast-flowing water undercutting the bank.and abrasion close abrasion When rocks carried by the sea water wear away the landscape, eg cliff face/headland.). The air in the cracks becomes compressed and then explodes outwards, breaking off bits of rock. This causes increased speed due to less friction and therefore increased erosion (through hydraulic action close hydraulic action Erosion caused by the force of river water hitting cracks in the side of the river bank. samples were obtained concurrently in wadable and non-wadable conditions at 20 evenly spaced increments within each cross section. Conceptual diagram, adapted from Furbish. As a river goes around a bend, most of the water is pushed towards the outside. Abstract River meander migration plays a key role in the unsteady conveyor belt of sediment redistribution from source to sink areas. ![]()
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