1) In the lower course of the river the gradient is gentler than in the upper course. The river has more energy and the volume amount of water is high.

2) In the lower course there is more lateral (sideways) erosion. The channel is wide and deep. The river has less friction to overcome which means that the river can flow faster.

3) As the river erodes sideways, it swings from side to side, forming large bends called meanders.

4) Over time the loop of a meander becomes tighter. If it becomes too tight the river may simply cut across the neck of the meander to form a straight river channel.The loop is cut-off from the main channel and forms an ox-bow lake.