The land has been lifting against the meander against the river. The river has been down there for millions of years. Entrenched meanders tell that the land is lifting against the river. A subtle curve is becoming a more exaggerated curve. The meanders got established when the area was flat. It undercuts the riverbank and forms a river cliff, whereas the water travels slower on the inside bend, causing deposition to create a slip-off slope. As the water flows through the meander, it travels faster on the outside bend creating erosion through abrasion and hydraulic action. Meander is a slight bend in the river, and water will continue to flow down the river’s long profile from the upper course to the low cost. This can result in meander bends as the river diverts around obstacles. If the channel has rough surfaces or obstacles, such as large rocks or fallen trees, it can impede the flow of water, causing the river to seek an easier path. This can increase meandering as the channel adjusts to the changing flow conditions.Ĭhannel Resistance: The resistance offered by the river channel itself can also influence meandering. During high-flow periods, the river may have more energy and rapidly erode the banks. This sediment can then be deposited on the inner bank of the meander bends or downstream, contributing to the formation and growth of point bars and floodplains.įlow Variations: The river’s water flow is not constant but can vary depending on factors such as seasonal changes in precipitation or runoff from tributaries. As the river erodes the outer bank, it picks up sediment and transports it downstream. This sediment can act as an abrasive agent, further contributing to bank erosion. Sediment Transport: Rivers carry sediments, such as sand, silt, and gravel, as they flow. In contrast, harder materials like bedrock or consolidated soil are more erosion-resistant, resulting in a more stable river channel. If the banks are composed of softer, more easily erodible materials, such as clay or loose sediment, they are more prone to erosion. As a result, the river gradually shifts its course towards the outer bank, creating a meander bend.Įrodible Banks: The erodibility of the river banks plays a role in meander formation. This differential flow causes more erosion on the outer bank while the inner bank experiences sediment deposition. The force of the flowing water is typically stronger on the outer bank of a curve, where the water flows faster due to centrifugal force. Lateral Erosion: Rivers naturally erode the banks of their channels over time. Here are the main reasons why rivers meander: Rivers meander due to a combination of factors, including the flow of water, the characteristics of the river channel, and the erodibility of the surrounding land. The exaggerated curves also mean central Washington used to be flat. Humans can only develop these curves when an area is flat, like back east at the Mississippi. Eventually, the meander becomes so exaggerated that the curve is abandoned, forming an oxbow lake. As rivers age, they develop more and more exaggerated meanders. Hence, the speed of flowing water between the banks differs. River bends are asymmetric due to obstructions. So what causes a river to bend in the first place? All it takes is a little disturbance and a lot of time, which is plenty in nature. These bending, looping rivers are called meandering rivers. This imperfection will then cause turbulence near the edges of the imperfection, leading to further erosion, thereby creating the seed of a meander.Īlso, even if the walls were perfectly homogeneous, the slightest disturbance in the flow will cause the flow to oscillate leading to inhomogeneous forces on the walls and thus uneven erosion.Rivers that gently flow over sloping ground begin to curve back and forth. Therefore, even if you would start with a straight canal, some parts of the walls are preferentially eroded over others, causing the canal to no longer be straight. However, nature isn't as straightforward (if you pardon the pun), and rivers never start of perfectly straight, neither is the material ever perfectly homogeneous, and natural laminar waters are very rare. Theoretically it might be possible to create a perfectly straight and homogeneous canal, with perfectly laminar flow, and in that case you'd expect equal erosion on both sides of the river. On the origin of meanders, this is a more complicated matter. The first is indeed by erosion of the outside of the bends, and deposition on the inside of the bend, which is fairly easy to understand. I'm under the impression you're not asking why a meandering river will keep meandering, but why even a straight river will start to meander in the first place.
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