As the river enters the middle course the gradient of the river becomes less steep. Lateral erosion becomes more important and the river starts to meander.

A  meander is a bend in a river as is shown opposite. As the water flows round the bend the flow is fastest on the outside of the bend where the river is deeper. Here the river erodes the outside bank of the river and undercuts it to form a River Cliff. On the inside of the bend the river is slow flowing and shallow. This causes deposition to take place and a slip off slope or point bar is formed. In fact the meander is caused by hydrocoidal flow and the water travels around the meander like a corkscrew - so if you have been on the ride at Alton Towers you now know what a small pebble feels like as it travels through a meander!

Meander Migration

This is where meanders move downstream. As the river continues to erode on the outside of the bend and deposit on the inside meanders continually change their position. As you can see from the diagram below, they help to form the flood plain and the ways they do this are:

• The meanders have got wider due to erosion on the outside of the bends

• The meanders have moved or migrated downstream

• A line of river cliffs has formed along the edge of the valley floor

• Deposition on the slip off slopes has built up alluvium (deposits) on the valley floor

• As the meanders get wider so does the valley floor or flood plain