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How A River Changes As It goes Downstream.

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How A River Changes As It goes Downstream A rivers course starts in the mountains or relatively highland area and ends up meeting the sea. As a river travels downstream it changes in many ways. Different features are made and different processes take place. These things take place in different stages of the river. There are 3 stages in total. The upper course, the middle course and the lower course. In the upper course, the start of the river is called the source. It is usually a small lake or spring. In the mountains there are also small tributaries that feed into the main river at the confluence. In this particular part of the course the width is small and the depth is very shallow. The channel gradient is very steep allowing the water to just trickle down the hill because it hasn't got enough water to flow. The velocity is also very minor. In this part of the course, erosion is the dominant process. The river may erode creating different features by any of the four erosion processes. ...read more.


The sharp boulders cut into the softer rock making the ground uneven and therefore the water flows more rapidly over the bumps. As the river flows downstream from the upper course to the middle course, the gradient over which it flows becomes less steep and the river is not as high above as its base level. The river also becomes wider and deeper. The river continues to erode vertically, but lateral or sideways erosion becomes more important. The middle course is where the most transportation takes place. There are again 4 types of transportation. Traction, which is when large boulders, simply roll along the riverbed. Saltation, which is when smaller pebbles, are bounced along the bed, picked up and dropped as river flow changes. Suspension, which is when the finer sand and silt particles are carried along suspended in the flow of water. The last one is solution, which is when calcium carbonate materials dissolve in water and can be carried along in the river flow. The transportation takes place in the lower course as well just like erosion does. ...read more.


The first one is connected with meanders. When the outer bend is eroded and the inner bend is deposited on an ox-bow lake is formed. The old meander is cut off and there is a straight channel. When the ox-bow lake dries up it is called a meander scar. Close to the estuary, which is where the river meets the sea, flood plains can often occur. A flood plain is a very flat area of land that lies next to the river. When floods occur the water spills over its banks and floods the plain. This land is very good for farming because there are lots of nutrients in the soil. One of the final features is where all the transported material gets deposited. This is in the mouth and it is called a delta. As more and more material gets deposited, a flat area of silt starts to build up. Sometimes in a delta the rain creates a small lagoon in the middle of it. Overall as a river travels downstream, the width increases, the depth increases, the channel gradient decreases, the valley sides obviously decrease and the pebbles, rocks and boulders decrease in size, become smoother and rounder. Sunday 6th October 2002 ...read more.

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