How does a river profile alter with distance downstream?

A rivers long profile typically varies in accordance with the upper, middle and lower course.
The upper course typically has a steeper profile, a v shaped bottom, is narrower with faster flowing water. Waterfalls and gorges are common.
The middle course sees the development of a more gentle profile with a wider valley forming with a flatter bottom. River velocity slows.

In in the lower course the river widens and flood plains develop. Meanders, oxbow lakes and braided channels are all common features as a result of sediment deposition.