River processes

There are two types of question you might be asked about river processes. One is to explain the processes of the river. The other is to describe how the processes make landforms.

They sometimes overlap. You need to know what all the terms mean, and you need to be able to use them to describe processes.

The main processes involved in rivers are:

  • Erosion - the wearing away of the land and the stones carried in the river.
  • Transport - the movement of rocks, sand, and silt by the river.
  • Deposition - the dumping of rocks, sand and silt wherever the river slows down.

Erosion

The main ways in which a river erodes are:

  • Corrasion - wearing away of the river bed and banks by the load hitting against them.
  • Attrition - wearing down of the load as the rocks and pebbles hit the river bed and each other, breaking into smaller and more rounded pieces.
  • Hydraulic action - breaking away of the river bed and banks by the sheer force of the water getting into small cracks.
  • Chemical action (corrosion) - water dissolves minerals from the rocks and washes them away.

Transport

The main ways in which transport happens are:

  • Traction - quite large stones can be rolled or dragged along the river bed by the force of the water.
  • Saltation - small stones, which the water cannot lift, bounce off each other and are carried forward for short distances by the water above the river bed.
  • Suspension - if particles are small enough the river can lift them and carry them long distances.
  • Solution - when the river dissolves minerals from the rocks they are carried in the water itself.

Deposition

The main way in which deposition happens is:

  • Loss of Speed - when the river slows down on the inside of bends or when it meets deeper water, like a lake, it loses energy and cannot carry so much, so drops some of its load.