Processes forming river landscapes

Oxbow lake

Formation of an Ox-Bow lakeFormation of an oxbow lake

  • The river is meandering across the valley.
  • The river is eroding laterally (from side to side).
  • The river flows faster on the outside bends and erodes them.
  • The river flows slowly on the inside bends and deposits material so its course is changing.
  • Continual erosion and deposition narrows the neck of the meander.
  • Often during a flood the river will cut through the neck.
  • The river continues on its straighter path and the meander is abandoned.
  • New deposition seals off the ends and the cut-off becomes an oxbow lake that will eventually dry up.

Oxbow lakes

Levée

Formation of a levee Formation of a levée

  • The river is on its floodplain with a very low gradient.
  • The river is mainly depositing (silt and sand).
  • When the river floods a lot of silt is deposited on the river banks and much less on the floodplain.
  • Frequent flooding continues this build up.
  • When the river is flowing normally it deposits in the river bed.
  • This raises the river above the floodplain.
  • Usually the built-up levées protect the plain from flooding.