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.