Describe the three stages of a river.

The three stages of a river are-

1. Upper course — At this stage, the river flows swiftly, for the gradients are steep. This course generally lies in a hilly area and the river flows a considerable distance over a steep slope.
   Along its course, it erodes its bed and banks, and carries large boulders of rock with it. The erosion action is swift and effective. V-shaped valleys and waterfalls are formed in the upper course of the rivers.
2. Middle course — At this stage, the gradient is reduced, and the river flows more slowly. In the middle course of the river, the energy required to transport the materials is just enough to drag large particles.
   The lateral cutting is more active and the volume of water in the river increases due to many tributaries joining it. Meanders and oxbow lakes are formed in the middle course of the rivers.
3. Lower course — In this stage, the river flows sluggishly and makes many landforms. All the ideal conditions for depositional landforms exist but the load-transporting capacity is drastically reduced due to the sluggish flow as well as division of a river into many distributaries.
   Deltas are formed in the lower course of rivers.