Meanders

Image demonstrating how a river changes over time, from pools and riffles, to helicoidal flow, and eventually a meanderFormation of a meander

  • In a straight river channel pools and riffles will develop as water twists and turns around obstructions such as large boulders. This results in areas of slower and faster water movement.
  • Pools are areas of deep water and greater erosion (energy build-up due to less friction). Riffles are areas of shallow water created by deposition of coarse sediment.
  • Once pools and riffles have developed, the river flows from side-to-side in a winding course.
  • A corkscrew-like flow of water called Helicoidal Flow moves material from the outside of one meander bend and deposits it on the inside of the next bend.
  • 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 hydraulic action, corrasion and corrosion.
  • Water moves slowly on the inside of the bend and the river deposits some load, forming a gently sloping river beach (also called a slip-off slope).
  • Continuous erosion on the outer bank and deposition on the inner bank forms a meander in the river, which will migrate downstream and change shape over time.

Meanders