I would say the waterfall and the rapids are the most prominent features of a narrow V - Shaped valley where the stream profile drops rapidly.
Velocity
cuts mainly side to side
gravel sized particles
channel size<lies
Stream erode their channels by abrasion, grinding, and by dissolving soluble material.
barchan dunes
Lowering the land.
longitudinal dunes
The main channel of a stream divides into several smaller creeks. Occasionally, deposition causes the main channel of a stream to divide into several smaller channels called distributaries.
..decreasing from top to bot..