Drainage basins and the water cycle Cambridge IGCSE Geography revision
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In plain words
Rain that falls on a hillside has to go somewhere. Some soaks in, some runs off, some goes back into the air. The area of land that feeds all its water into one river is that river's drainage basin.
8 things to know
- A drainage basin is the area of land drained by a river and its tributaries. Its edge, a ridge of high land, is the watershed.
- The source is where a river starts and the mouth is where it enters the sea or a lake. A tributary is a smaller river that joins a larger one, at a confluence.
- Water enters a drainage basin as precipitation. Interception is when leaves and branches catch it before it reaches the ground.
- Infiltration is water soaking into the soil. Percolation is water moving down from the soil into rock. Throughflow is water moving sideways through soil, and groundwater flow is water moving slowly through rock.
- Overland flow (surface runoff) is water running over the surface. Channel flow is water flowing in the river.
- Water leaves by evaporation from surfaces, and transpiration from plants. Together these are evapotranspiration.
- Discharge is the volume of water passing a point each second. Velocity is the speed of flow. The wetted perimeter is the length of bed and banks in contact with the water.
- The Bradshaw model shows how a river changes from source to mouth. Discharge, width, depth and velocity increase. The size of the load and the gradient decrease.
Worked example
Heavy rain falls on a drainage basin covered in forest, and on another covered in concrete. Explain why the second river rises faster.
- In the forest, trees intercept the rain, and much of it infiltrates the soil and reaches the river slowly as throughflow.
- Concrete is impermeable, so there is no infiltration. Almost all the rain becomes overland flow.
- Overland flow is the fastest route to the river, so the discharge rises quickly.
Tips and tricks
- Infiltration is into soil. Percolation is from soil down into rock. Examiners expect the right word for each.
- The Bradshaw model surprises people: velocity increases downstream, because a bigger, deeper channel has less friction for the amount of water it carries.
It lands in your notebook with its questions as flashcards.
Drainage basins and the water cycle: 6 questions and answers
These are the quiz’s questions. Do the quiz first, then come back here for the ones that got you.
What is a drainage basin?
All the rain falling in it drains towards one river.
What is the boundary of a drainage basin called?
It is a ridge of high land.
What is infiltration?
Percolation carries it further down, into rock.
What is discharge?
It is measured in cubic metres per second.
According to the Bradshaw model, what decreases downstream?
Attrition wears the load down as it travels.
What is evapotranspiration?
Water returning to the air from surfaces and from plants.
Quiz
6 questions
Tap an answer and you’ll see straight away whether it’s right, and why.
Worksheet
3 questions, 8 marks. Write your answers on paper, then check them.
Drainage basins and the water cycle
Cambridge IGCSE Geography 0460 · 8 marks · papermunch.org
Name ______________________________ Date ______________
Define the terms watershed and confluence.[2]
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A watershed is the ridge of high land that forms the boundary of a drainage basin. A confluence is the point where two rivers meet.
Describe three ways in which water moves from the land surface to a river.[3]
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Overland flow: water runs over the surface. Throughflow: water moves sideways through the soil. Groundwater flow: water moves slowly through rock.
State three ways a river changes downstream, according to the Bradshaw model.[3]
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Discharge increases. The channel becomes wider and deeper. The size of the load decreases. (Also: velocity increases; the gradient decreases.)
Answers: Drainage basins and the water cycle
- 1. A watershed is the ridge of high land that forms the boundary of a drainage basin. A confluence is the point where two rivers meet.
- 2. Overland flow: water runs over the surface. Throughflow: water moves sideways through the soil. Groundwater flow: water moves slowly through rock.
- 3. Discharge increases. The channel becomes wider and deeper. The size of the load decreases. (Also: velocity increases; the gradient decreases.)