Lower course – the final course of the river is where the land is a lot flatter. The river’s load is fine sediment, as erosion has broken down the rocks.
A – as the river flows downhill there is an increase in vertical erosion. The channel is shallow and narrow because there is not a lot of water in the channel.
B – as the river flows into the middle course, there is some vertical erosion but more lateral erosion. The channel is wider and deeper as a result.
C – in the lower course there is a lot less erosion and greater influence of deposition, with only some lateral erosion. The channel is at its widest and deepest.