Meanders
Formation 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 Steep bank created on the outside of a river bend by the erosive effect of fast-flowing water undercutting the bank..
- 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 The river moves more slowly on the inside of the bend. It cannot carry the larger pebbles and these are dropped here (also called a slip-off slope). (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