Geography AS Level - Rivers, Floods and Management

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  • Created by: charlotte
  • Created on: 21-10-13 21:19
How is the Middle stage of a river formed?
Lateral erosion and abrasion causing the river to widen. Deposition creates a flood plain on the valley floor. Rocks are smaller & smoother.
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How are V - Shaped Valleys formed? (Upper River Stage)
Vertical erosion creates narrow valley floors and steeply sloped sides. Mainly abrasion & some hydraulic action. Erosion occurs with high energy conditions e.g. high velocity & discharge after snow
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How is the lower stage of a river formed?
Wide valleys with gently sloping sides caused by deposition. Less erosion due to lower turbulence and particle sizes.
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How is a braided channel formed?
River splits into several channels separated by islands due to a variable discharge causing a very wide channel.
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How are floodplains formed?
An area of low lying ground adjacent to a river floods due to heavy precipitation leading to an increased discharge
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How are levees formed?
Type of dam running along the banks of a river that reinforce the banks, forms when sediment settles on the bank raising the level of land around the river
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How are deltas formed?
A triangular low lying landform that occurs at the mouth of a river caused by a lot of deposition due to low river energy
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How are meanders formed?
- Alternating shallow/deep sections caused by alternating deposits (bars) of sediment - Side to side flow means max velocity is directed at banks, resulting in erosion on outside of bend and deposition on inside as the flow is slower
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Meander formation continued..
- Meanders form due to helicoidal flow ( water moves like a corkscrew) - Fastes flow is downstream of the middle meaning erosion is greatest here so the meander migrates downstream
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What is river discharge?
Volume of water passing a measuring pint in a river in a given time (measured in cumecs)
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What is lagtime?
Difference between rainfall at it's peak and the peak of when it drains back
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What is a drainage basin?
The catchment area from which a river system obtains it's water
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name the input of the hydrological cycle
precipitation
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name the stores of the hydrological cycle
Interception, surface storage, soil water storage, vegetation storage & channel storage
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name some factors affecting discharge
land use/urbanization, intensity of a storm, soil type, (im)permeable rock types, precipitation, vegatation etc.
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What is vertical erosion?
- Runs downwards - Usually in upper reaches of land high above sea level
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What is lateral erosion?
- Runs sideways - In middle/lower reaches due to high energy
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Type of particle with lowest critical erosion
Sand due to needing a lower entrainement velocity to be picked up
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Velocity is influenced by..
channel shape in cross section, roughness of bed/bank & channel slope
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Rapids occur when..
There is a sudden change in channel slope
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How are potholes formed?
Vertical erosion, cylindrical hole are drilled in the bed by pebbles carried by high velocity water
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Waterfalls are formed by..
a sudden change in gradient due to rejuvenation, a resistant band of rock & edge of ledge
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What is rejuvination?
An increase in energy of a river due to a change relative to sea level giving the river more PE
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Other cards in this set

Card 2

Front

How are V - Shaped Valleys formed? (Upper River Stage)

Back

Vertical erosion creates narrow valley floors and steeply sloped sides. Mainly abrasion & some hydraulic action. Erosion occurs with high energy conditions e.g. high velocity & discharge after snow

Card 3

Front

How is the lower stage of a river formed?

Back

Preview of the front of card 3

Card 4

Front

How is a braided channel formed?

Back

Preview of the front of card 4

Card 5

Front

How are floodplains formed?

Back

Preview of the front of card 5
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