Rivers

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  • Created by: Sapphire
  • Created on: 11-11-12 18:09

Processes of erosion

  • Attrition - material is moved along the river bed, collides with other material and breaks into smaller pieces.
  • Abrasion - fine material rubs against the river bank, the bank is worn away by a sandpapering action.
  • Solution - rocks from the banks and the river bed are dissolved by acids in the river.
  • Hydraulic action - the sheer force of the water hitting the river banks.
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Processes of transportation

  • Traction - large rocks are rolled along the river bed.
  • Saltation - smaller stones are bounced along the river bed.
  • Suspension - small grains of sand are carried in the water.
  • Solution - material is dissolved and carried downstream.
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Deposition

The Finer --> The Fragments --> The Futher --> They Flow.

Deposition occurs when a river can no longer support material.

Material is put down when the river no longer has the energy to carry the load.

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River Basin/Drainage Basin

  • Watershed - a boundary that separates drainage basins.
  • Main channel - the main river.
  • Confluence - Where the tributary meets with the main channel.
  • Tributary - a small stream flowing into the main channel.
  • Mouth - where the river meets the sea.
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Factors affecting discharge

  • Slope/relief - the steeper the slopes, the faster the runoff, so more water in the river.
  • Rock type - impermeable rock will mean a surface runoff.
  • Soil - thin soil, less infiltration. Deeper soil, more infiltration.
  • Land use - rural areas with little tarmac/concrete or drains there will be a higher level of infiltration.
  • Precipitation - more intense rain, the shorter the lag time/more rain in the river.
  • Temperature - in the summer, dry soil, longer lag time as rain infiltrates. In the winter, frozen or saturated soil, shorter lag time as water cannot infiltrate so runs off quickly.
  • Previous weather - large amounts of rain, saturated soil, cannot allow any more infiltration so run-off increases.
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Flood Defence Schemes - Hard Engineering

  • Dams and Reservoirs - used to save/manage the flow of excess water. Some are used to generate hydropower.
  • Man-made Levees - stop water flooding over. Commonly used in rivers near the sea.

 

  • Straightening Meanders - Involves digging a shorter channel. This can cause flooding downstream.

 

  • Dredging Channels - Can allow importing and exporting. But can cause a mess in the sea traffic.
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Flood Defence Schemes - Soft Engineering

  • Do nothing - The natural habitat is left, doesn't interfere with the rivers flow, it's cheaper to maintain.

 

  • Flood warnings and preparation - Buildings will be saved and people will be prepared. However unexpected floods will mean the equipment won't be available.

 

  • Floodplain zoning - Identifies areas of varying flood hazards.

 

  • Re-afforestation/plant tree - Replacing of forests and woodlands that have been destroyed. Trees intercept the rain and slow down the run-off to the river.
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