Rivers: Erosion, Transport and Deposition

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Erosion

  • This is the wearing away of the bed and banks in a river

Abrasion/Corrasion: Rock fragments carried by river wear down bed and banks of channel. Boulders scrape rock bed while sand and gravel smooth surfaces

Hydraulic Action: Sheer force of water on the bed and banks. Water pushes into cracks of bed causing pressure and then erosion

Corrosion/Solution: Dissolving of soluble materials in bed and banks by weak acids in river water. Chemical reaction so not dependant on energy

Attrition: Load particles coming into contact with each other as well as the bed and banks. Rough edges become smoothed and particles become smaller and more rounded

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Transport

Suspension: Smaller particles of clay, silt and sand are carried by river's turbulence

Solution: Material is carried along and dissolved in river water

Saltation: Small bedload eg pebbles is bounced along the bed of the river by turbulence in high discharge

Traction: Largest boulders are rolled long the bed in high discharge

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Deposition

The Hjulstrom Curve

  • Shows velocity needed to erode, transport and deposit different sized particles
  • The larger the particle the more energy needed to transport it
  • Erosion will need more energy than transport ie once something is lifted it requires more energy to keep it moving

Two Curves:

1. Pickup Curvespeed needed to pick up a particle

2. Drop Curve: speed at which there is no longer any energy to transport particles

  • For most of the graph, more energy the river has, greater its ability to erode and transport particles
  • As a river's energy increases, it is able to erode and transport increasingly large particles due to larger particles with greater mas requiring more energy both to erode and transport them
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