AQA AS Geography Rivers: The Long/Cross Profile

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  • Created by: LucySPG
  • Created on: 22-08-13 20:09
Preview of AQA AS Geography Rivers: The Long/Cross Profile

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The Long Profile
A long profile shows you how the gradient of the river channel changes from the river's
source to its mouth by showing the height of the river bed above the base level for the
whole length of the river.
The base level is the lowest point that the river can erode to ­ usually sea level.
The total amount of erosion and deposition along the full course of a river are balanced.
But the rates of erosion and deposition change along the course of a river.
This can result in the formation of landforms such as waterfalls which make the profile
uneven.
Because the total amount of erosion and deposition is balanced, the rate of erosion of
landforms, like waterfalls, is equal to the rate of deposition elsewhere along the river.
This means that over time the long profile will change from being uneven to a smooth
curve.
This is called a graded profile but hardly ever happens.

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The Upper Course
The gradient is steep and the river is high above sea level which gives it lots of potential
energy.
Vertical erosion takes place.
The rough channel causes turbulence and the large, angular bedload is dragged along the
river bed causing intense vertical erosion.
Mainly large particles, such as boulders, are carried by traction or saltation during high-
energy conditions.
There is little deposition ­ mainly largest particles deposited in the river bed as energy
levels drop.…read more

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Downstream Changes
Discharge and Velocity
The velocity and discharge of a river increase as you go downstream from source to mouth.
Discharge increases as tributaries and more surface runoff join the main channel.
River velocity is influenced by gradient, discharge and channel characteristics ­ the shape
and the roughness.
Most of a river's kinetic energy is used to overcome friction ­ the rest causes erosion.
The more energy a river has available for erosion and transportation, the more efficient it is.…read more

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The Cross Profile
Upper Course Steep V shapes
Vertical erosion creates narrow valley floors and steep sloped
sides
Middle Course Wider valleys
Lateral erosion
Deposition creates a flood plain on the valley floor
Lower Course Wide valleys
Lateral erosion
Much wider flood plain cause by deposition…read more

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The Bradshaw Model…read more

Comments

Mr A Gibson

I find students often get mixed up with the profile changes along the course of the river - this document give a clear guide to the main points and uses effective diagrams to help with the explanations.

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