Rivers Flashcards

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Why does the channel cross-section of a river change downstream?
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In the upper course, the river erodes its bed by hydraulic action and abrasion. As the river flows downstream it is joined by tributaries, increasing the volume of water, velocity and therefore its erosive power. This enables it to cut a deeper channel as it flows downstream.

Downstream, the channel becomes wider as the gradient becomes more gentle leading to less vertical erosion. By the middle course of the river lateral erosion becomes the dominant type of erosion. The channel becomes wide because of lateral erosion.

Find out more about the cross profile of a river.

Why does the channel cross-section of a river change downstream?
What is soft engineering?
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Soft engineering involves working with nature and adapting to a river and learning to live with it.

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What is soft engineering?
Give three natural ways flood risk can be increased.
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Natural ways flood risk can be increased include:

  • heavy rainfall caused by depressions causing heavy, continuous rain which saturates the soil. The land can no longer absorb water as it is saturated increasing surface run-off, higher river discharge and flooding.
  • sudden downpours occurring following a very dry period can lead to flooding because the surface is baked hard. Surface run-off occurs as water cannot infiltrate leading to higher river discharge and flooding.
  • sudden snowmelt releases stored water that flows over the land as surface run-off
  • the loss of vegetation cover through drought or disease can lead to flooding as less interception occurs so more precipitation reaches the surface leading to increased surface run-off.

Find out more about human and physical causes of flooding.

Give three natural ways flood risk can be increased.
Identify two benefits of floodplain zoning.
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Examples include:

  • low-cost solution
  • reduces additional impermeable surface coverage of the floodplain
  • protects and conserves water meadows for wildlife and recreation
  • reduces insurance costs when property is flooded

Find out more about soft engineering.

Identify two benefits of floodplain zoning.
Identify one social cost of dams and reservoirs
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Social costs of constructing dams and reservoirs include:

  • the displacement of people due to flooding
  • the loss of cultural heritage
  • the resettlement of large numbers of people
  • the health and well-being of affected populations both upstream and downstream

Find out more about hard engineering.

Identify one social cost of dams and reservoirs




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