What changes take place in a river during the three stages of its course?

A river's journey is often divided into three stages, each marked by distinct changes in its physical characteristics, flow, and the surrounding landscape. Here's a breakdown of the key changes in each stage:

1. Upper Course (Youthful Stage):

* Source: Rivers begin at a high elevation, often in mountains or hills. This is the source of the river, where water first collects and begins its journey.

* Steep Gradient: The upper course is characterized by a steep gradient, meaning the riverbed drops quickly. This leads to rapid and turbulent flow.

* Erosion: The high velocity and the large amount of sediment carried by the river cause significant erosion. This creates features like V-shaped valleys, waterfalls, and rapids.

* Limited Channel: The river channel is narrow and often confined by steep slopes.

* Low Discharge: The flow volume (discharge) is usually low in the upper course as the river is still collecting water.

2. Middle Course (Mature Stage):

* Decreasing Gradient: The gradient decreases significantly as the river flows towards lower elevations.

* Increased Discharge: As the river collects water from tributaries, its discharge increases.

* Lateral Erosion: The river begins to carve wider valleys and meander across the landscape, eroding laterally (sideways) rather than downwards.

* Floodplains: As the river meanders, it deposits sediment on the flat areas adjacent to the channel, forming floodplains.

* Formation of Oxbow Lakes: Meanders often become increasingly curved. Over time, the river may cut off a meander, creating a crescent-shaped oxbow lake.

3. Lower Course (Old Age Stage):

* Very Gentle Gradient: The gradient is very gentle, leading to slow-moving water.

* High Discharge: The river has the largest discharge at this point, carrying a substantial amount of water and sediment.

* Wide, Flat Floodplain: The floodplain is wide and flat, often covered with rich vegetation and sediment deposits.

* Delta Formation: As the river enters a lake or ocean, it loses energy and deposits its sediment load. This can lead to the formation of a delta, a fan-shaped landform at the river's mouth.

* Erosion and Deposition: The river continues to erode and deposit sediment, but the process is less dramatic than in the upper course.

Summary:

The river's journey through these three stages is a dynamic process. The river constantly changes its landscape, its flow, and its sediment load. From the turbulent torrents of the upper course to the slow, meandering flow of the lower course, the river's transformation reflects the powerful forces of erosion, deposition, and gravity that shape the Earth's surface.