IGCSE Geography / River environments
Drainage basins and their features
Edexcel International GCSE Geography (4GE1), chapter 1: River environments, specification point 1.1b. Free lesson.
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A drainage basin is the area of land drained by a river and its tributaries. Knowing its features and how water enters and leaves helps you explain why it is an open system.
What is a drainage basin?
A drainage basin is the area of land drained by a river and its tributaries. It is also called a catchment. It means the land, not the river itself or the place where the river reaches the sea. A tributary is a smaller river or stream that flows into a bigger river.
What are the features of a drainage basin?
A river begins at its source and flows towards its mouth. Tributaries join the main river at confluences, forming a channel network across the basin. Watershed: the ridge of high land around the edge of a drainage basin. It separates it from the next basin. Source: where a river starts, such as at a spring, lake or bog. Main channel: the largest river in the basin, which the tributaries feed into. Channel network: all the streams and rivers in the basin, considered together. Mouth: where a river ends by flowing into the sea or a lake. Drainage density measures the…
Why is a drainage basin an open system?
A system has inputs, outputs, stores and transfers. The whole water cycle is a closed system, but one drainage basin is an open system because water enters it from outside and leaves it. The input is precipitation: rain, snow or hail falling on the basin. Water leaves as river discharge flowing out to the sea, and as evapotranspiration, which returns water to the air from the ground and plants. Water is stored in places such as soil and rock, and transferred between stores. The amount of water in the basin changes, so the river's flow rises and falls too.
How do you describe the watershed accurately?
The watershed is the boundary of the drainage basin, not the area of land it contains. It is a ridge of high land, shown on a map as a line along the hilltops. Rain falling on one side of the watershed drains towards one river. Rain falling on the other side drains towards a different river.
More lessons in River environments
- The hydrological cycle: a closed system and its stores
- Transfers in the hydrological cycle
- River regimes and what controls them
- Storm hydrographs
- How rivers erode
- Weathering and mass movement in river valleys
- How rivers carry and drop their load
- Long profile and cross profiles
- How a river changes downstream
- V-shaped valleys, interlocking spurs and waterfalls
- Meanders and oxbow lakes
- Flood plains and levees
- Case study: the River Tay from source to mouth
- Water: uses, rising demand and supply
- Water quality and pollution
- Storing and supplying clean water
- Case study: river management in Spain
- Case study: river management in China
- Case study: managing the Blue Nile in Ethiopia
- Why rivers flood
- Predicting and preventing river floods
- River fieldwork: collecting the data
- River fieldwork: results, conclusions and evaluation