🟨 SECTION 3: THE COURSE OF A RIVER

What are the three stages of a river?

The three stages are:

• Youth stage: Upper course.

• Mature stage: Middle course.

• Old-age stage: Lower course.

A river's gradient, valley shape, flow characteristics and landforms change along its course.

What is the upper course of a river?

The upper course is the section near the river's source, generally in elevated or mountainous terrain.

It is associated with:

• Steep slopes.

• Fast-flowing water.

• Vertical erosion.

• V-shaped valleys.

• Waterfalls.

• Rapids.

• Interlocking spurs.

These are characteristic features of the youth stage.

What is the middle course of a river?

The middle course is the section where the river generally flows through gentler terrain and its valley becomes wider.

It is associated with:

• Horizontal erosion.

• A wider valley floor.

• Gentle slopes.

• Meanders.

• A relatively narrow floodplain.

These are characteristic features of the mature stage.

What is the lower course of a river?

The lower course is the section nearer the river's mouth.

It is associated with:

• A very flat landscape.

• A broad and shallow river.

• Slow-flowing water.

• Wide floodplains.

• Meanders.

• Deposition.

• Oxbow lakes.

• Islands.

• Deltas.

These are characteristic features of the old-age stage.

What is a longitudinal profile?

A longitudinal profile shows how the elevation and gradient of a river change along its course, from its source towards its mouth.

The profile generally shows a steep upper course and a progressively gentler gradient towards the lower course.

Remember: A longitudinal profile follows the river along its length.

What happens to the gradient of a river from its source to its mouth?

The gradient generally decreases.

• The upper course usually has a steep gradient.

• The middle course has a gentler gradient.

• The lower course has a very gentle gradient.

The river descends from higher ground towards its mouth.

What is vertical erosion?

Vertical erosion is the downward erosion of the riverbed.

It deepens the river channel and contributes to the formation of a narrow, deep valley.

Main association: The youth stage.

What is horizontal erosion?

Horizontal erosion is the sideways erosion of a river's banks.

It widens the river channel and valley.

Main association: The mature stage.

How does a river valley change as the river develops?

The valley changes from a relatively narrow, deep valley to a wider valley with a broader floor.

Youth stage: Vertical erosion deepens the valley.

Mature stage: Horizontal erosion widens the valley.

Old-age stage: The river flows through a flatter landscape where wide floodplains and depositional features develop.

Why does vertical erosion dominate in the youth stage?

The river flows down a relatively steep gradient and erodes the riverbed downwards.

This cuts the channel deeper into the landscape and contributes to the development of a V-shaped valley.

Why is horizontal erosion important in the mature stage?

Horizontal erosion wears away the riverbanks, widening the river channel and valley.

This contributes to the development of a wider valley floor and allows meanders to become prominent.

Why is deposition important in the old-age stage?

The river flows over a flatter landscape and may lose the energy needed to carry some of its sediment.

The sediment is deposited, contributing to the development of wide floodplains, islands and deltas.