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UNIT 1C - RIVER PROCESSES (Drainage basins (A river's water can…
UNIT 1C - RIVER PROCESSES
Erosion
- Erosion is the process that wears away the river bed and banks. Erosion also breaks up the rocks that are carried by the river.
Hydraulic action
- This is the sheer power of the water as it smashes against the river banks. Air becomes trapped in the cracks of the river bank and bed, and causes the rock to break apart.
Abrasion
- When pebbles grind along the river bank and bed in a sand-papering effect.
Attrition
- When rocks that the river is carrying knock against each other. They break apart to become smaller and more rounded.
Solution
- When the water dissolves certain types of rocks, eg limestone.
Transportation
- The river picks up sediment and carries it downstream in different ways.
Traction
- large, heavy pebbles are rolled along the river bed. This is most common near the source of a river, as here the load is larger.
Saltation
- pebbles are bounced along the river bed, most commonly near the source.
Suspension
- lighter sediment is suspended (carried) within the water, most commonly near the mouth of the river.
Solution
- the transport of dissolved chemicals. This varies along the river depending on the presence of soluble rocks.
Deposition
- When the river loses energy, it drops any of the material it has been carrying. This is known as deposition.
shallow water
at the end of the river's journey, at the river's mouth
when the volume of the water decreases
Drainage basins
A river's water can fluctuate over time. Understanding the hydrological cycle is useful in order to understand how and why the amount of water fluctuates.
A drainage basin is the area of land around the river that is drained by the river and its tributaries.
Watershed
- the area of high land forming the edge of a river basin
Source
- where a river begins
Mouth
- where a river meets the sea
Confluence
- the point at which two rivers meet
Tributary
- a small river or stream that joins a larger river
Channel
- this is where the river flows
River profiles
Long profile
- A long profile is a line representing the river from its source (where it starts) to its mouth (where it meets the sea). It shows how the river changes over its course.
Upper course
- in the upper course, where the river starts, there is often an upland area. The river's load is large in the upper course, as it hasn't been broken down by erosion yet.
Lower course
- in the lower course, the land is a lot flatter. The river's load is fine sediment, as erosion has broken down the rocks.
Cross profile
- A cross profile shows a cross-section of a river’s channel and valley at a certain point along the river’s course.
A - as the river flows downhill there is an increase in vertical erosion. The channel is shallow and narrow because there is not a lot of water in the channel.
B – as the river flows into the middle course, there is some vertical erosion but more lateral erosion. The channel is wider and deeper as a result.
C - in the lower course there is a lot less erosion, with only some lateral erosion. The channel is at its widest and deepest.