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Water on the Land - Channel processes and landforms.

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Introduction

Geography Water on the Land Channel processes and landforms I. Distinguish between vertical and lateral erosion and examine where along the course of a river, each is likely to occur. (10 marks) Along the course of a river, there are various processes that take place, including several different types of erosion. Erosion is the wearing away of something over a period of time, and the two main types of erosion, upon which I will be focusing, are vertical and lateral erosion. Furthermore, there are four main processes of river erosion, which I will go into greater detail. Vertical erosion is specific to the upper course of a river, which is due to the high altitude and steep gradient of the source of the river, eroding in a downwards direction. It takes place at this point along the course of the river because the river is trying to find the quickest route to sea level and so cuts vertically through the rock in order to reach its mouth. Vertical erosion is a process which uses up a lot of the river's energy and so the structure of the river channel particular to this course of the river is generally very narrow and shallow, with large boulder strewn across it. The river channel generally does not increase in either width or depth as all of the river's surplus energy is used to erode vertically. The most common erosional process, which takes place in the upper course of the river, is corrasion. It is responsible for the vertical erosion of a river and corrasion is the term used for when pieces of rock are dragged along the riverbed by the flow of the water, and so in turn wear away the river channels bed and banks. The size of the load affects the amount of erosion, as larger pieces of rock create a more rapid rate of erosion, whereas smaller pebbles tend to round off edges of surfaces. ...read more.

Middle

The character of the material also influences the amount that can be carried, as finer particles such as silt and clay will be transported further in the state of suspension, than boulders or gravel. The Hjulstrom graph is model that shows different velocities are needed to erode, transport and deposit different types of material. The rock type of the land over which the water is flowing also has a lot to do with the size, type and amount of bed load found in a river channel along its course. Acidic water in the river channel has the ability to erode softer rocks such as Limestone and Chalk as the minerals in the rock are dissolved by the acidic components of the water. When the water is capable of eroding in this way, the minerals of the rock are carried by suspension and are moved along in the flow of water in a dissolved state. However, if the rock that the river is flowing over is of a much harder property, such as Granite, then corrasion will erode such rock and the transporting process of traction moves the larger rocks and boulders of Granite along the river bed. In certain circumstances, the larger of the boulders will only be capable of being moved in times of flood due to their size and the fact that a specific velocity is needed to transport them. Similarly, the factors of discharge and velocity play an important part in shaping the size, type and amount of load that a river carries. Discharge is the volume or flow of the water within the river channel, passing a particular point in the river at a specific time. Discharge therefore has an influence on the load that is carried by the river, as the greater the discharge, the larger the river's capacity to carry load. The velocity is the speed of the water's flow in the river channel and so has an effect on the load that the river can carry as the higher the velocity, the higher the amount of energy that the river potentially has to erode and transport. ...read more.

Conclusion

Deltas generally occur in calm, tideless seas such as where the Rh�ne enters the Mediterranean Sea. The periodic flooding of the river, which deposits further amounts of alluvium helping to build up lev�es, helps the formation of a delta. Finally, the process of flocculation, where river water meets the salt of the sea water has an electrical charge which causes molecules to stick to one another, increasing their mass and so causing them to deposit on the riverbed, helps to form the depositional feature known as a delta. There are two main types of deltas, and their shapes distinguish them. One known as a 'bird foot's delta, such as the Mississippi delta and the other is recognised as an 'arcuate' delta such as the Nile delta. A braided stream is a stream that has islands of build up deposited load within the river channel, known as eyots. Braiding tends to take place in streams where the load is made up of much heavier, coarser material such as sands and gravel's. The channel itself is generally straight in this course of the river, however, the eyots and smaller channels within this one river channel go through many changes in both shape, size and position. A characteristic of streams and rivers that have a varying discharge is the process of braiding and they tend to be very common in semi-arid areas or glacial-fed streams. Streams with high velocities and heavy loads are resultant of torrential downpours of rain, causing substantial overland flow, are typical of semi-arid areas. Evaporation and infiltration following the storm, lessening both the volume and velocity of the stream, cause the deposition of the load. Glacier-fed rivers have increased discharge due to the ice melting during hours of sunlight, however, at night and during winter, the discharge is noticeably less. During times of high flow, the river is capable of carrying and transporting a large load, though, when a stream's competence and capacity falls due to the decrease in velocity, the result is the load's deposition and over time, the formation of eyots. Joanna Lowe Page 1 Mrs Forkan ...read more.

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