Section B: Rivers
The shape of river valleys changes due to the dominance of different river processes. How it changes depends on whether the erosion processes are dominant or deposition is dominant, which depends on the amount of energy the river has.
In the Upper Course, e river has plenty of energy as it is trying to reach its base level. It erodes downwards (vertical erosion) which produces a V Shaped Valley.
In the Middle Course, the river is closer to its base level so there is less vertical erosion. A lot of energy is used in transporting its load of eroded material and the river uses surplus energy to erode sideways (lateral erosion) which means the middle course is wider and flatter.
In the Lower Course, the river is closer to its base and carries a heavy load of eroded material. If the river slows down, it deposits materials.
Example exam question: Name the 3 different ways river and its valley change from source to mouth?
Upper course: steep sider, v shaped valleys
Middle course: wider channel, gentler valley slopes
Lower course: floodplain, low gradient as the river gets closer to the sea
A cross profile of a river: a diagram that shows the cross-section of the river channel and valley
A long profile of a river: a diagram that shows how the gradient of the river changes as you move downstream
Erosion Processes include:
-Hydraulic Action - the force of the water on the bed and banks of the river erodes the river martial away. It is particularly powerful in a flood because the river is flowing very fast with a great deal of energy so the force of the water will be very strong
-Attrition - parts of the rivers load bumps, rubs against each other and wears each other down into smaller, more rounded pieces
-Abrasion - the load carried by the river rubs against the bed and banks, wearing it away
-Solution - some rocks and minerals are dissolved in river water and are carried in the water
Transportation is the way in which the river carries eroded materials.
Transportation Processes include:
-Traction - large boulders are rolled along the river bed due to the force of the water
-Saltation - smaller pebbles are bounced along the river bed. This is because the force of the water pick up the little pebbles and then drop them again as the flow of the river changes
-Suspension - fine sand and silt particles are carried along in the flow. This gives the river its brown colour
-Solution - minerals like limestone and chalk are dissolved in the water and are carried along in the flow
Deposition is when the river loses energy (slows down) and drops some of its load. A river may slow down enough to deposit material if:
- If they enter a much larger body…