Revision:The action of rivers

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• Rivers are the most widespread agents of denudation and deposition.
• The amount of erosion, transportation and deposition of the river is dependent on the energy of the river which in turn is dependent on:
  • The gradient of the slope
  • The volume of water
  • The shape of the channel
• Generally, the volume of the river increases from the source to the mouth. Exceptions may be such as when the river passes through a hot desert.

River Erosion

• River erosion involves 4 processes:
  1. Abrasion/Corrasion: The wearing away of the sides and the bed of a river by the impact of the load.
  2. Hydraulic Action: Erosion by the force of moving water.
  3. Attrition: The breaking down of the load by particles hitting against each other.
  4. Solution/Corrosion: When minerals dissolve in water.

River Transport

• The material a river carries is referred to as its load.
• A river transports its load in 4 main ways:
  1. Traction: The rolling of huge particles along the bed.
  2. Saltation: The bouncing of particles on the bed of the river
  3. Suspension: The movement of particles held up by river turbulence.
  4. Solution: The movement of particles dissolved in water.

River Deposition

• Deposition takes place when a river has insufficient energy to transport its load. It takes place at all stages of a river.
• Larger particles are deposited first.
• Deposition is greatest in the lower course of a river. It is also greater during floods.
• Deposition will occur when the speed of a river is reduced. This may happen in:
  • areas with a sudden increase in gradient
  • the inside of meanders
  • places where the river enters a sea/lake.

The Development of a River Transport System

• Surface run-off forms small streams.
• These streams join together to form larger streams.
• These larger streams join to form a river.
• The junction of 2 streams is called the confluence. When a smaller flow joins a larger flow it's called a tributary.

The Long Profile of a River

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