River Landforms - Rivers And Flooding AS

AQA AS Geography

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  • Created on: 23-03-12 22:56
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LANDFORMS
EROSION
Head ward Erosion ­ Upper course
This is when a river flows in to a valleys dead end.
It makes the river longer, by through flow
Vertical Erosion ­ Rejuvenated land and the upper course
Deepens the river, making it straight.
High discharge conditions, from rain or snow melt
The rough channel causes turbulence, with a large angular bed load
This all causes intense erosion
So little deposition, just some larger load when energy decreases
Lateral Erosion ­ Lower and middle course
Widens the river, and makes turns
DEPOSTION
When a river loses its energy, mostly like in the lower course, or bends in a river
When it slows it doesn't have the energy to carry its load
Factors:
Not much rain fall, a small discharge so there for less energy
Increased evaporation or abstraction, (taking water out for human uses) lowers discharge
The river will slow down in narrow sections; the more deposition means the narrow it will become too
When the river meets the sea, slows the river down. ­ Alluvium fans are made
Reasons for erosion: - The faster and the more load carried the more erosion it will cause.
Hydraulic action ­ Pressure of the water slowly breaks up the bed and the banks
Abrasion ­ Eroded particles of rock scrape the bed and banks
Attrition ­ This is erosion of the load in the river, making them more rounded
Cavitation ­ Air bubbles in the water have an increased erosive power
Corrosion ­ The dissolving of rocks chemical
CHANNEL EFFICIENCY
Increase in power: gradient, drag (wind) and friction.
River flows fastest at the bottom as it has had time to build up more energy, and it's a wider and deeper channel
which is smoother so less friction
Rivers become more efficient in the lower course, with proportionally less contact with the bed and the banks, as
there flatter.
YAZOO STREAM ­ A river that is below the main river because of levees, so this small stream will run parallel, so
they'll never meet. As rivers can flow up hill over the levee
DELTA ­ In a low land area of a flood plain by the sea
Produced by deposition, at the mouth of a river at a lake or by the sea
When the river reaches the sea it slows down and deposits all of its load
This happens on the sea bed, until over time the alluvium will reach the surface
This blocks the river, forcing it to flow through/ over the alluvium deposits
Cuspate (single braiding), arcuate (braiding and lagoons) and birds foot
POTHOLE ­ A rounded hole in a river bed created by erosive eddies
LEVEES ­ These are natural raised embankments, when a river floods it deposits its alluvium on its banks
The whole flood plain will be covered in a thin layer of alluvium
The lightest load goes furthest, and the heavier larger load is deposited first on the banks
Over time this builds up creating a levee
MEANDERS AND OX BOWS

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As rivers go round slight corners they develop an even current
These corners are made by:
There has to start of with deep pools in the river bed
This alters the current, causing it to speed up and slow down causing deposition
The deposition makes riffles, shallow sections
The energy is made by the pools then lost by the riffles
This unevenness makes the erosion un even, so on alternating sides of the rifles erosion will occur
Over time this will become exaggerated, and the…read more

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