Processes forming river landscapes - middle course

Formation of meanders and ox-bow lake in the middle course of a river.

Meander

Graphic explaining the formation of meandersFormation of a meander

  • Water twists and turns around stones and other obstructions resulting in areas of slower and faster water movement.
  • The river starts to flow from side to side in a winding course but still in a relatively straight channel.
  • Water moving faster has more energy to erode. This occurs on the outside of the bend and forms a river cliff.
  • The river erodes the outside bends through corrasion, corrosion and hydraulic action.
  • Water moves slowly on the inside of the bend and the river deposits some load, forming a river beach/slip-off slope.
  • Continuous erosion on the outer bank and deposition on the inner bank forms a meander in the river.
  • The meander will migrate downstream and change shape over time.

Meanders

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