OCR Geography B: River Processes

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  • Created by: Pipa
  • Created on: 17-02-13 09:58

Types of Erosion

  • Hydraulic Action: the force of the river against the banks/cliff can cause air to be trapped in the cracks. The pressure weakens the banks/cliff and wears it away.
  • Corrosion: Rocks carried along by the river wear down the river bed and banks.
  • Attrition: Rocks being carried by the river smash together and break into smaller, smoother and rounder particles.
  • Solution: Soluble particles are dissolved in the river and rub at the banks/cliff like sand paper.  
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Types of Transportation

  • Solution: When particles are dissolved in the water so you cannot see them.
  • Suspension: Very small particles are carried along in the water.
  • Saltation: Small stones and pebbles are bounced along in the flowing water.
  • Traction: Big boulders and stones are rolled and dragged along the bed.
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Meandering of Rivers

The shape of a river is always going to be affected by obstacles such as hills. However, the river always flows in a certain way, a corkscrew like pattern called helical flow. This helps to change the shape of the river channel becuase the current on the outside edge of the river is faster to more erosion takes place there than on the inside where it is slower.

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  • Birds Foot Delta: The flow of the river is STRONGER than the sea. E.g. Mississippi River
  • Arcuate Delta: The flow of the river is WEAKER than the the sea. E.g. Zambezi River
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When the river is in flood, the water picks up a lot of silt and once it reaches the lower part of the river, where things flatten out, the silt falls out of the flood water. Over many floods, layer apon layer of silt builds up forming a wide, flat plain of very rich soil; a lot of flood plain farming.

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  • Peak Rainfall: The highest amount of rainfall on a hydrograph.
  • Discharge: The amount of water at a given point in a river.
  • Lag Time: Time between peak rainfall and peak discharge.

If Lag Time is LONG the river is LESS likely to flood.

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Flood Prevention and Management

Hard Engineering:

  • Dams
  • Embankments
  • Straightening of the River

Soft Engineering:

  • Storage Areas
  • Land Use Zoning
  • Washlands
  • Afforestation
  • Warning Systems
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Case Study: Zambezi Flood Management


  • Longer and heavier rainy season
  • Deforestation
  • Climate Change

Management and how sustainable:

  • River Basin Initiative - Early Warning and resources - GREAT
  • Water Resource Management - Land Use Zoning - GOOD
  • Mphanda Nkuma Dam - 2.3 Billion + Clean Electricity - NOT GOOD
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Coasts - Wave Vocabulary

  • Fetch: The distance of open water over which wind blows.
  • Swash: The movement of water up the beach.
  • Backwash: The movement of water back down the beach.
  • Constructive: Flat, low, limited energy waves.
  • Destructive: High energy and high waves.
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Coastal Protection and Management

Hard Engineering:

  • Tetrapods
  • Groynes
  • Cliff Drainage
  • Concrete Sea Wall
  • Revetment
  • Gabions
  • Rock Armour/Rip-Rap

Soft Engineering:

  • Offshore Reef
  • Beach Re-profiling/Replenishment
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Case Study: Lyme Regis Coastal Management

  • Rock Armour: Rocks placed infront of the land to absorb energy.
  • Beach Replenishment: Moving sand from where it has accumulated to areas it has been eroded from.
  • Groynes: Wooden or boulder 'fences' designed to trap and accumulate sand.
  • Sea Wall: Deflects the waves.
  • Cliff Drainage: Removing water from the cliff quickly so it is less likely to slump.
  • Offshore Reefs: Built just out to sea to make the waves break on them and make it calmer closer to the coast.

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Case Study: Lyme Regis Coastal Management


Problem: Clay slumping off and into the sea becuase of layered on top of limestone.

Why Bother: Tourism, Money, 170 homes and 5,000 people.

Are The Chosen Strategies sustainable:

Sea wall: Yes; it will last for ages/ No; Very Expensive

Offshore Reefs: Yes; prevents cliff erosion/ No; Damages fishing nets and needs gates.

Beach Replenishment: Yes; Not very expensive

Land Drainage: Yes; It solves the underlying problem.

Rock Armour: Yes; Proven to be very effective.

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