Three stages of a river
A river flows from its source (where it begins) to its mouth (where it meets the sea). The flow of a river is divided into three stages: the upper course, middle course and lower course. A small river that flows into the main river is called a tributary.
Key idea
A river has three courses: upper (steep, fast, erosion), middle (meanders, wider) and lower (gentle, slow, deposition).
Features of each course
- Upper course — in highland areas, steep slopes, fast-flowing water, much erosion and waterfalls, V-shaped valleys.
- Middle course — gentler slopes, the river becomes wider and bends (meanders).
- Lower course — in flat areas, slow-flowing water, deposition occurs and a delta forms at the mouth.
Example
Waterfalls are often found in the upper course, while a fertile delta forms in the lower course near the mouth.
Importance of rivers
Rivers are important as a source of drinking water, for irrigating farms, as transport routes, for fishing and for generating hydroelectric power. Fertile river valleys are also suitable for settlement because the silt carried by the river makes the soil very good for farming. Since ancient times, many of the world's great towns and civilisations have been built beside rivers because of the water supply and fertile land they provide.
Remember
Erosion is greatest in the upper course; deposition is greatest in the lower course.