AQA Water on Land 5.1 reading over the AQA Geography A textbook and making notes :) boring but it works! this is 5.1... I will make more up to 5.7 which is the whole water on land topic...but im a bit lazy so may take a while!

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How and why do river valleys change downstream?

Why? -Because of erosion, transportation Deposition and long and changing cross profiles.                             Erosion

1) Hydraulic action- the force of water against the bed and banks, when the ater is moving fast this occurs frequently.

2) Abrasion/Corrosion - The beds and banks are worn down by the rivers load. The river throws these particles against the bed and banks sometimes at  high velocity.

3) Attrition - The stones and rocks carried by th river bump into each other and are smoothed and broken down into smaller particles.

4) Solution - The acids in the river from rainwater can dissolve the rocks on the bed/ banks of the river esp. if chalk and limestone.

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How and why do river valleys change downstream?

Transportation    4 WAYS TO TRANSPORT....

Traction - large boulders roll along the river bed because they are heavy.

Saltation - Small stones move by bouncing along the bed as the flow of the river changes.

Suspension - fine particles such as sand and silt are carried in the flow.

Solution - Dissolved load which only occurs with certain rock such as limestone and chalk are carried in the flow but are not visable.

Affecting rate of erosion? -  Human facors, buildings deforestation changing landscape. Environmental steepness (fancyword gradient) bed load and river speed.

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How and why do river valleys change downstream?


The river dumps material it has been carrying - The heaviest objects first.

  • The smaller the load the further it can be transported.
  • the river deposits objects when there is less water and the speed is slower.
  • It useually deposits as the river enters a lake or near the foot of a mountain



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How and why do river valleys change downstream?

Long and Changing cross profiles

Long profile - looking at it from  a birdseye perspective from source to mouth.

Cross profile - as if to cut the river in half and look at it from one side if the bank to the other....that doesnt really make sense...you need to see a diagram!

At the start of the river it is:

  • Narrow
  • shallow
  • High
  • Hydraullic action and attrition abaration are occuring due to fast moving water
  • Depositation of large materials
  • some trationa and salation occur
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How and why do river valleys change downstream?

Continued... Middle section of river:

  • Wider seeper channel
  • smaller load
  • Depositation more visable
  • lots Suspension occures
  • some saltation and traction

 Lower section of river:

  • widest point
  • flat land
  • less erosion - slower water
  • Depositation of fine materials
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