Shapes Of Valleys Formed At Various River Courses

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This blog entry is to basically help you understand more about the shape of the valleys formed at the upper course, the middle course and the lower course.

The river is generally divided into three courses, the upper course, the middle course and the lower course. And this is due to the rate of erosion and deposition occurring at each course and other factors, which have been described below, and therefore, valleys are formed.

The upper course of the river is usually the young part of the river, usually where the flow of water begins from or also known as the river mouth. The middle course is known as the mature stage and the lower course is as such known as the old stage of the river.

The Upper Course

The upper course is located usually at the top of the river and has the steepest gradient compared to the other parts of the river. Therefore, water flows quickly through the channel and over time, the sides of the channel get weakened by weathering processes and erosion occurs in a downwards direction. It is also known as vertical erosion. Slowly, the mass movement of materials occurs down the valley sides and creates a v-shape. Vertical erosion is the cause many other landforms and for the steep sloping v-shaped valley formed at the upper course. Vertical erosion usually occurs in form of abrasion, hydraulic action and solution. The overall energy present for vertical erosion to take place is very high and more than lateral erosion and as such, the river continues to cut down vertically. Also, very little deposition takes place at the upper course.

Middle Course

In the middle course, the river channel becomes wider and deeper as the river, as the channel has been eroded and it is also due to the many tributaries that have begun to branch out from the river. The velocity of the water flowing in the middle course is decreased as compared to the upper course as the gradient is lesser steep. Therefore, the surrounding valley has become wider and flatter and additionally, there is a more extensive floodplain present. Due to the unique pattern of erosion and deposition and bends in the middle course of a river, landforms such as meanders, slip-off slopes and oxbow lakes are formed. Wider lakes can also be found at the middle course of the river.

Lower Course

At the lower course of the river, water begins to run even more slowly as the gradient of the river becomes lesser steep. Therefore, lesser erosion and more deposition takes place. Usually a wide floodplain is formed here as such. And floodplains are also formed when there is a heavy rain and the river’s water level rises and the average speed of water flowing increases. And that causes the deposited material or other fine material to be in suspension. Then, due to the increased speed of water, the river overflows its banks and deposits its load. And slowly, a small layer of load is laid at both sides of the river. The layer of load or material is also known as alluvium and this eventually forms a level of land called a floodplain. The shape of the valley in a lower course river is usually the widest and in a u-shape.

Definitions of some of the key words used above:

Erosion: The group of natural processes, including weathering, dissolution, abrasion, corrosion, and transportation, by which material is worn away from the earth's surface.

Deposition: The act of depositing, especially the laying down of matter by a natural process.

Tributaries: A small river which eventually joins or branches out from the main river.

Floodplain: A flood plain is a level stretch of land found on both sides of a river in its mature and oldstages.

Done by:

Subha(:

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