Question

Describe the three stages of a river.

Answer 1

1. Upper Course (Youthful Stage): In the upper course, the river flows over a steep gradient with a fast flow. This causes the river to be mainly involved in downward erosion, cutting into the land and deepening its channel. Due to the strong erosional force, the river forms V-shaped valleys, waterfalls, and gorges. The river’s primary action is to cut downwards, leading to the creation of deep valleys.
2. Middle Course (Mature Stage): As the river moves downstream into its middle course, the gradient becomes gentler, and the river flow slows down. The river begins to erode laterally (sideways) rather than downwards. This results in the formation of meanders, which are winding curves in the river’s path. The river also deposits some of the material it carries, forming oxbow lakes and floodplains. The volume of water increases as more tributaries join, and erosion and deposition become more balanced.
3. Lower Course (Old Stage): In the lower course, the river flows very slowly on a gentle gradient. Here, deposition becomes more dominant than erosion, as the river has less energy to carry large amounts of sediment. The river deposits sand, silt, and other materials, leading to the formation of deltas at the river’s mouth, where it meets an ocean, sea, or lake. The river also forms distributaries, channels that split off from the main river to form intricate networks. Floodplains are wide and flat, created by repeated flooding and sediment deposition.