How a river changes from source to mouth
How a River changes from source to mouth
The Long Profile
The long river profile is the changes in gradient at different stages in a river's flow.
In the Upper Course the flow is fast and load and water volume are slow.
In the Middle Course the river starts to slow and volume increases when tributaries join the river. The river erodes at this stage and the load increases.
In the Lower Course, the river slows down dramatically due the gradient being almost flat. The river deposits its load due to the lack of power and speed. The volume is the largest on the river's course. This part of a river is liable to .
The upper course is usually found in the mountains and hills where the river rises from its source. and are also sometimes found in this course. Water falls are caused when a river runs over alternating layers of hard and soft rock. The river in the upper course is usually fast flowing. There are lots of obstacles, stones and boulders for the water to flow over. As the river moves all the way through the upper course it cuts downwards. The steepness here is steep and the river channel is narrow. Vertical erosion in this highland part of the river creates steep sided V-shaped valleys and interlocking spurs. These are caused as the river erodes the landscape in the upper course, it winds and bends avoiding areas of hard rock. Therefore creating them they look a bit like the interlocking parts of a zip.
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The graphic shows how waterfalls and rapids are formed.
The graphic shows how V-shaped valleys are formed
V-shaped valleys are created due to erosion. This is because the river carries stones and rocks in its water. The force of the water (which is high in the upper course) and the grinding of rocks and stones cut down into the to carve out a V-shaped valley. The longer time goes on the more the river erodes and therefore the valley becomes deeper and wider.
The Middle Course
In the Middle Course loses velocity as the gradient lessens and volume of water increases when tributaries join the river. The river has had time to erode at this stage and the load it transports increases. The middle course also contains wider U-shaped valleys, the pebbles and stones are smaller and the river erodes vertically and laterally.
Meanders are created by the lateral erosion that the river undertakes. Water flows around the bend in the river and as it does so, it swings to the outside of the bend this means the fastest flowing and highest volume of water is concentrated on the outside of the bend thus having the most energy to erode the bank at this point. On the inside of the bend the flow is a lot slower and because of lack of energy, the river is depositing.
At the bend of a river the river's flow is concentrated on the eroding the bank, creating a landform known as a river cliff. On the inside, the deposition due to lack of energy creates a landform called a slip off slope. The river is therefore eroding laterally. This creates a large floodplain in the river valley. And as the lateral erosion is able to remove the truncated spurs are found here.
Ox bow lakes
Ox-Bow lakes are created by two River Cliffs are eroding towards each other. Ultimately, this will break and the water will flow along the straightened/faster course. In the river bend, the water stops flowing, and this loss of energy means the river deposits its load - this creates plugs at both ends of the meander and creates a lake.
2 - Ox-Bow Lakes (2)
At the lower course of the river, the river has a high volume and a large discharge. The river channel is now deeper and wider than before and the relief of the land round it is flat. But due to energy levels being low deposition takes place. The flood plain is now larger as the land is flat around the river. The river now erodes laterally and deposits bedland. A floodplain is the area around a river that is covered in times of flood. There is also a lot of silt at the lower course of the river. A build up of alluvium on the banks of a river can create which raise the river bank. Deltas are found at the lower course, they are found at the mouth of rivers. Finally the river meets the sea and where that occurs there is an estuary.
The flood plain is now larger as the land is flat around the river. A floodplain is the area around a river that is covered in times of flood. A floodplain is a very fertile area due to the rich deposited by floodwaters its good for agriculture.
A levee (from the French for "raised") is a natural or artificial embankment, usually earthen, which parallels the course of a river. It is made from High mounds of silt, which have deposited on the banks of a river during flooding and have frequently been increased by man to protect the floodplain.
Levees are the coarsest material which will be deposited when the river floods
An estuary is a semi-enclosed coastal body of water which has a free connection with the sea. This is where the sea water mixes with fresh water. The key feature of an estuary is that it is an interface between sea water and fresh water and there is an influence of the ocean tide creating a dynamic relationship between the two waters.
Deltas are found at the mouth of large rivers. A delta is formed due to the river depositing its material faster than the sea can remove it. This is because the sea doesn’t flow so the river stops flowing and loses its energy and can’t carry its load. So the load is deposited on the sea bed, this builds up to form a new piece of land in the river mouth. Because of this the river then has to divert its flow into smaller distributaries to reach the sea again. Once this has happened more load is deposited and this builds the new delta out into the sea, so the process repeats its self. There are main types of delta, named after the shape they create:
- Arcuate - the land around the river mouth arches out into the sea, the river splits many times on the way to the sea, creating a fan effect.
- Cuspate - the land around the mouth of the river juts out arrow-like into the sea.
- Bird's foot - the river splits on the way to the sea, each part of the river juts out into the sea, rather like a bird's foot.