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The Features and Processes of a River along its Profile.

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Introduction

The Features and Processes of a River along its Profile Introduction Along the path of a river, from source to mouth, the river shows many different features and is affected by several different processes. These processes are going to be described and explained in the course of this essay and diagrams will be used to back-up and justify my ideas. A river can be simply divided into an upland or lowland river environment. Upland features and processes occur at a higher altitude, closer to the source of the river; lowland features and processes occur at lower altitudes near the mouth of a river. A river's course can be better divided into a young, mature and old stage. A simple map of a river showing the different stages is shown below: The main processes acting upon a river are: * Erosion * Transportation * Deposition These three main river processes can be further sub-divided into "sub-processes". Erosion, for example, wears rocks away through 4 sub-processes: * Corrasion or abrasion * Attrition * Corrosion or erosion by solution * Hydraulic action Transportation can be further divided into: * Traction * Saltation * Suspension * Solution A description of these processes and diagrams showing how they affect the river are shown below: Erosive Processes Corrasion or abrasion This is when smaller material which is suspended, rubs against the river banks. ...read more.

Middle

Meanders and Ox-bow lakes Description A Meander is a bend in a river. The bend increases over time to form an ox-bow lake, which is shaped like a banana. Explanation When a river is nearing its mouth, it is flowing over much flatter, with less of a gradient. At this point in the rivers profile, large bends often form, known as meanders. These meanders form when a piece of hard rock lies on the bank on one side of a straight river. As the water flows past the hard rock, the soft rock past it is eroded. This directs the flow toward the outside of the river, causing lateral erosion on one side of the river, causing a slight bend in the path. This slight bend is exaggerated as the water is thrown to the outside of the bend due to the centrifugal acting upon the water. So as the river approaches the meander, the flow is directed toward the outside of the bend, causing erosion on one side of the meander. This causes a reduction in friction, increasing the velocity of the river at this point. This velocity enables the river to transport more material in suspension, and this material erodes in the form of corrasion against the bank. This causes an undercutting of the bank, causing it to collapse, and retreat backwards like a waterfall would. ...read more.

Conclusion

The effect of weathering is to break up the rock or soil on the valley sides which then falls into the river. This "extra" material is then used by the river in abrasion or adds to the "load" of the river. Two important types of physical weathering include: * freeze-thaw * exfoliation Freeze-thaw occurs when water within cracks in a rock freezes and expands and then warms up and melts. Over time this can break up the rock into scree, which under the influence of gravity rolls down the valley sides into the river. This process would affect Britain in the winter months. Exfoliation or "onion" weathering This occurs when a rock heats up in the sunshine and then cools down at night. Over time the rock splits into layers and breaks up and rolls into the river. This process occurs in Britain during the summer months. If weathering continues valley sides will be worn down and more load will be added to the river. Human action This can affect rivers in many ways. Humans can alter the shape and course of a river by straightening the channel, building artificial banks, dredging the channel and building bridges, viaducts and locks. Humans also erode the sides of rivers by farming too close to the river's edge and walking along paths which follow a river. Humans can also pollute a river by dumping waste and chemicals into the water, killing fish and vegetation. Ends ...read more.

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