The water cycle is key to our everyday lives. We need this system to access the water that we drink, cook with, shower in and use to make crops grow. The drainage basin is a key topic within GCSE Geography and is where the water cycle takes place. This page will give you all the details you need to know about drainage basins!
A drainage basin is an area of land drained by a river and its tributaries.
The water cycle is the system by which water is evaporated from the sea, travels through the air and flows back to the sea through rivers or the ground.
The definition of a drainage basin above is what you’d be expected to write in an exam. It would be useful to copy this definition onto a flashcard or into your notes as you can expect to need it! While the definition may sound a bit complex, it simply means that any rain that falls within an area of land will end up in a certain river.
The water cycle has 4 key things that you should know in GCSE Geography:
- Inputs – water is put into the drainage basin
- Transfers – water is moved from one place to another
- Stores – water is stored in particular places
- Outputs – the water comes out again at the end
Let’s take a look at examples of each of these.
Components of the Drainage Basin System
|Input||Precipitation||There is only one input to the drainage basin and that is precipitation. This is any water that falls from the sky: rain, hail, snow or sleet.|
|Stores||Interception by vegetation||Leaves and grass catch the rainfall and store them. When leaves store too much water it falls to the ground.|
|Water that runs over the ground’s surface.|
Water that sinks into the soil.
Water that flows through the soil.
Water that sinks down through the rock.
Water flows slowly from the rock to the river.
|Water flowing away in a river.|
Water is turned into water vapour in the air and by plants through their leaves.
Features of a Drainage Basin
We have already covered the definition of a drainage basin. Now let’s look at the landforms and features that make it up.
|Source||The place where a river starts.|
|Tributary||A stream that flows into a river.|
|River mouth||Where a river meets the sea.|
|Watershed||A boundary between drainage basins – this is often marked by a ridge of high land.|
|Confluence||Where two streams or rivers meet.|
TOP TIP: Learn all of these definitions! It might seem like hard work but it will pay off in your exams! Any of these could be asked in a question worth 1 or 2 marks. You should revise the diagram above too as you will often have to fill in the gaps of something similar.
Changes Along a River Profile
Rivers can span for miles and miles, across mountains, through forests and even through cities. The profile of a river looks at its shape from the source to its mouth. Most rivers have the same changes along their profiles. Things that can change include the river’s gradient, depth, width, discharge and load.
The table below summarises what each of these means and how they change.
|Definition||The steepness of the slope a river flows down||The measure of the top of the water level to the riverbed||Distance from one side of the river to the other||Amount of water passing a point in a certain time||The material that a river carries (sand, stones, rocks and pebbles)|
|Changes moving downstream (away from the source of the river, towards the mouth)||Gets less steep||Gets deeper||Gets wider||Increases||Particles get smaller and rounder|
|Why does this happen?||River erosion at the source is downwards, at the mouth the river erodes the land sideways||The river erodes downwards as it travels down the slope||The river erodes sideways as it travels||More water is added to the river from tributaries|
Erosion of the bed means there is less friction and so water travels faster
|Particles knock against each other and break up|
Key Exam Question!
It is important to know that river discharge is often measured in a unit known as cumecs. This stands for cubic metres of water per second. This is often asked in exams.
The Bradshaw Model
The Bradshaw Model is a way of showing the changes along a river’s profile in a visual way. You’re more likely to come across questions on the Bradshaw Model in your Field Skills exam but it is still important to know!
The different changes along a river profile are represented by triangles going across the page. A triangle with a fat base going to a very fine point from left to right represents that something is getting smaller. For example the size of the particles that the river carries. A triangle that starts on the left-hand side of the page at a sharp point and moves to the right getting wider represents an increase in something. An example would be river discharge.
See the diagram below which shows what the Bradshaw Model looks like for these changes.
And that should just about cover it!
That should be all of the information you’ll need to cover on the drainage basin, but make sure to check your exam board specification before the exam in case any minor details have been missed!