![]() ![]() At different stages of the erosional cycle, the valley acquires different profiles.The extended depression on the ground through which a stream flows is called a river valley.A braided river, or braided channel, consists of a network of river channels separated by small, and often temporary, islands called braid bars. Braided streams occur in rivers with low slope and/or large sediment load. Braiding: the main water channel splitting into multiple, narrower channel. ![]() Vertical, Lateral and Headward Erosion (Kayau, from Wikimedia Commons) Headward erosion: erosion at the origin of a stream channel, which causes the origin to move back away from the direction of the stream flow, and so causes the stream channel to lengthen.Lateral erosion: the erosion of the walls of a stream (leads to valley widening).Downcutting (vertical erosion): the erosion of the base of a stream (downcutting leads to valley deepening).Corrasion or abrasion: solid river load striking against rocks and wearing them down.Attrition: river load particles striking, colliding against each other and breaking down in the process.Corrosion: chemical action that leads to weathering.Hydration: the force of running water wearing down rocks.Various aspects of fluvial erosive action include:.Fluvial Erosional Landforms are landforms created by the erosional activity of rivers.The landforms created as a result of degradational action (erosion and transportation) or aggradational work (deposition) of running water are called fluvial landforms.Over time a smallīeach of material builds up on the inner bend this is called a slip-off slope. Reducing energy), encouraging further deposition. This increased friction further reduces the velocity (thus further In contrast, on the inner bend water is slow flowing, due to it being a low energy zone, deposition occurs resulting in a shallower channel. Results in undercutting of the river bank and the formation of a steep sided river cliff.Ģ. Increase in energy results in greater erosion. Which deepens the channel, in turn the reduction in friction and This is due to water being flung towards the outer bend as it flows around the meander, this causes greater erosion Water flows fastest on the outer bend of the river where the channel is deeper and there is less friction. In lowland areas which results in lateral (sideways) erosion being moreĭominant than vertical erosion, causing the channel to cut into itsġ. Meanders form due to the greater volume of water carried by the river Meander scar - feature left behind when the water in an ox-bow lake dries up.Result in the straightening of the river channel and the old meanderīend becomes cut off forming an ox-bow lake. In the eventual cut through of the neck as two outer bends join. a lake formed when the continued narrowing of a meander neck results Slip off Slope - a small beach found on the inside of a meander bend where deposition has occured in the low energy zone.River Cliff - a small cliff formed on the outside of a meander bend due to erosion in this high energy zone.In cross-section with a more extensive floodplain.ĭistinctive features of the river in the middle course is its increasedĥ.Unlike the relatively straight channel of the upper course, in the middle course there are many meanders (bends) in the river. Its surrounding valley has also become wider and flatter The velocity of flow may be as fast as in the uplands.ģ. The river channel has become much wider and deeperĪs the channel has been eroded and the river has been fed by many
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