This post is about the stages of the river and how they are formed.
1. Upper course
Most of the rivers begin from the top of the hills and mountains. Since the clouds move upwards air will cool down and form the rain, there will be a lot of rain. When rain falls on the land, some of the water will seep into the soil, and some of it stays on the surface. The water on the surface will flow down and form tiny streams. These streams will gradually join with other streams to form the beginning of the river. The beginning may be a spring, or a marsh or even a glacier. When the river flows down the steep and rocky sides of the hill or mountain, it will get faster and wilder as well as pick up and carries along with the large boulders and rocks. This wearing away of the land is called erosion.
2. Middle course
As the river continues on its journey the ground starts to have a gentler slope. The river carries on eroding the land, making the river wider and deeper. Bends and turns called meanders then start to form, as the water begins to wears away the sides. The volume of water also increases, as smaller rivers called tributaries also flow in.
3. Lower course
Fig 4. The lower course and end of the river
The river is very wide and deep by the time it reaches its final stage which is lower course. The surrounding land will have also flattened out, making the water slow down, and stones that have been carried along will drop down to the riverbed. It is also at this stage that the river meanders into large horse-shoe shapes, and this is where flooding is most likely to cause problems. When the river comes to an end, it will either flow into a loch or into the sea. This parts is known as the mouth of the river.
Done by Yu Jiacheng (25)
TO add on for jia cheng's part
ReplyDeleteV-shaped Valley, usually found at the upper course of river, due to the steep gradient there. Steep gradient means high erosion as water will be carried down faster. Also, downward erosion is stronger too.
However, a V-shaped valley may also be formed in the lower course of a river when its powers of downward erosion become renewed (rejuvenation - by a fall in sea level, a rise in land level, or the capture of another river)
Another point i want to elaborate on is the meander. Th erosion occurs on the outside bank of river, which accounts for the "wriggly" shape. Also, water at the inner bank flows slowly thus debris will be deposited there. This accounts for the shape too.
Delta occurs at the lower course as water flows slowly, depositing lots of debris and sediments there, forming delta.
Luo Yang (22)
http://www.americaswetlandresources.com/background_facts/detailedstory/RiverDelta.html
To add on to Luo Yang and Jiacheng
ReplyDeleteThat in the upper courses of the river another feature that is common is the waterfalls and the speed of the river is ((most of the times) fastest in the upper course but as it flows down is become slower.
Another feature that is found in the middle course are the OX-bow lakes, which are formed because of meanders. What happens is that when the meanders are formed, like the one shown above, the river would try to cut through the middle, as every time it flows it will first hit that turn over there. So over a period of time it will ultimately dig its way through it and the segregated part of the river is what we call an Ox-bow lake.
Hi everyone
ReplyDeleteI have something to add to Jiacheng’s entry. This is about a special type of river called subterranean river. It is a river that flow underground. A subterranean river does not have specific upper, middle and lower course, and it does not really possess the characteristic like V-shape, U-shape etc This kind of river is often found in limestone mountain.
I hope that the above information is useful.
Hieu
Just to add on to and elaborate Jia Cheng’s post and Luo Yang’s comment.
ReplyDeleteErosion:
There are two aspects of erosion: vertical and lateral. Vertical erosion lead to the deepening of the river channel, which occurs when rocks and sediments on the river bed are worn away. Lateral erosion leads to the widening of the river channel when rocks and sediments on the passageway, the sides of the channel, are removed by flowing water.
Vertical erosion usually occurs in the upper course of the river due to the force of gravity acting on the water, while lateral erosion takes place at the middle course and lower course.
Meanders:
Meanders are formed when there is an erosion, transportation and deposition of the sediments carried by the water along the river. Erosion occurs on the outer bank (also known as concave bank) of the river as the speed of the river is high due to lesser friction on the outer bank. The water then carries these sediments with the flow and deposits them along the inner bank (convex bank).
When loops of the meanders become more distinct, it is known as an Oxbow Lake. Referring to Fig. 3 of Jia Cheng’s post, the two meanders (at the far end of the picture) eventually meet due to the erosion, forming an “O” shape.’
Chelsia