Lesson video

Hello, my name's Ms. Gilyeat and I'm going to be your geography teacher for today.

In today's lesson, we are going to be learning about drainage basins, which is the second lesson of the rivers topic, let's get going.

Our lesson outcome for today is that you can describe features of a river system and explain how water flows through a drainage basin to reach a river.

We've got two learning cycles.

So first of all, we're gonna learn about what some of the key features of a drainage basin are, and then we're gonna learn about how precipitation gets to the river.

So let's start with learning about what the key features of a drainage basin are.

Now we've got five keywords for today's lesson.

So we've got drainage basin, which is the area of land drained by a river and its tributaries, a watershed is the boundary of a drainage basin, a tributary is a smaller river that joins the main river, a confluence is the point where two rivers meet and the mouth is where the river enters the ocean.

These words are highlighted in bold throughout the lesson if you need to refer back to them at any point.

Okay, so geographers use specific terminology, so that's words, for talking about rivers, okay? So let's learn a few of them.

A drainage basin is the area of land that a river and all its tributaries drain, okay? So on the slide here, we've got a picture of a drainage basin, okay? So it's an area of land where all the rivers and all the small rivers, all the tributaries eventually flow into one main river, which will eventually enter either the ocean or a large lake, okay? So that is the drainage basin.

The source is the start of a river.

Now, actually within a drainage basin, you are not just gonna have one source.

There will be multiple ones, okay? So if we have a look at this diagram here, we can see where all the little blue lines start.

All of those are separate sources of different tributaries, which again, eventually lead to the main river.

The watershed is the boundary of the drainage basin, okay? So that's highlighted here in an orange dotted line.

And we're gonna learn in a minute about how you can tell where a watershed is, okay? But basically it's the defining point from one drainage basin to another.

A tributary is a smaller river that joins the main river, and the mouth is where the river enters the sea, sometimes, not always just to the ocean, but it can sometimes also mean where the river enters a large lake as well.

But in general, we mean where the river enters the ocean.

Okay, let's see if you can remember what I've just told you.

So can you add the labels to the features identified on the diagram of a drainage basin, okay? Pause the video and see if you can name them all.

Okay, let's have a look then.

So you've got the source at the top, but there's loads of different sources on there, the mouth where the river enters the sea, the watershed is the orange dotted line, and a tributary is any of those smaller rivers.

So well done if you've got those right.

Okay, so a watershed will often follow a high ridge of land where raindrops falling close to each other may travel into different rivers.

Okay, so if we have a look at the picture that I've got on the board, that ridge line is the watershed, okay? So if you imagine if you have a mountain ridge like this, if rain falls on one side of the mountain, it will eventually flow down into one river.

But if it was just to fall a couple of metres away on the other side of the ridge line, that water due to gravity will flow into a different river, okay? So a watershed is a ridge line which separates two different drainage basins.

Water can fall on one side, go into another, fall on the other side, and it goes into a totally separate river.

I find that quite cool actually.

So yeah, that's a watershed, okay? So rain falling either side of this ridge will travel into different rivers.

The source of a river is where it begins and the furthest point from the mouth.

So many river sources are at a spring where groundwater is forced to the surface.

So often sources of rivers can be quite hard to spot 'cause they might just be kind of like a pool of springy bog water if you like, okay? So here's an image that we've got on the slide which says the source of the River Lune, okay? So they're often in mountainous or hill environments.

There can be multiple sources for a drainage basin, but it's where those tributaries start and will eventually all of that water will flow into the main river, into the ocean, okay? Yeah, so there they start in mountainous areas.

A tributary is a smaller river that joins a larger river.

And the point where the two rivers meet is a confluence, okay? So the slide or the picture that we've got on the left here, it shows a confluence and a tributary 'cause you've got two rivers joining, but that smaller river that enters the larger river is known as a tributary.

So it's like, basically a small river, small, okay? Both these pictures show confluences, so that's where you've got two rivers joining.

Okay, let's check our understanding.

So true or false, all of the rain that falls in the UK eventually flows into one river.

That's false, why? There are lots of rivers in the UK taking water from the hills and mountains to the sea, okay? So there's not just one drainage basin of the UK.

There's multiple, lots and lots of different drainage basins, okay? A confluence is? Which one of those is a confluence? B, the point at which two rivers meet.

Well done if you got that correct.

Okay, so next keyword, the mouth is where the river meets the sea.

This can create an estuary where salt water will mix with fresh water, okay? So the mouth of the river is where it enters the ocean.

Now sometimes these are called estuaries as well.

If we have a look at the slide, the picture on the right, you can see that actually there's been lots of deposition in this area because the water has slowed down.

So often at estuaries you have mud flats or kind of marsh land where there's lots of deposition and they can create quite unique environments because you've got fresh water mixing with salty water, which leads to lots of really cool plants and animals living there.

Okay, let's check our understanding.

Choose two correct statements.

A, the mouth of a river could be a mix of salt water and fresh water, the mouth of a river is where it begins, the mouth of a river is where it meets the sea, and the mouth of the river is where two rivers meet, which two of those are correct? Okay, so the answers are the mouth of a river could be a mix of salt water and fresh water, river meets the ocean, and C, the mouth of a river is where it meets the sea.

So well done if you got that right.

Now this aerial image shows a drainage basin system.

All of those fine blue lines are tributaries leading to the main river, okay? So we can see here that the rivers have been highlighted in blue so we can see them better.

And all the really faint ones are the tributaries and that like kind of more obvious blue line is the main river, which eventually flows out to the ocean.

And you can see there in that estuary there has been quite a lot of deposition there.

So what other features can you spot from looking at that satellite image? Okay, so I'll pause the video and let you have a quick look at it.

So you've got the mouth there, many different sources, a tributary, okay? Now river features can also be identified on OS or Ordnance Survey maps.

So we're gonna look at some examples here, right? So if we look at the one on the left, first of all, here we've got the mouth of a river, okay? On the right we can see a source.

In fact, we can see a couple of different sources there, but there's one that's been pointed out for you, okay? And you've also got a tributary, a smaller river which is joining a larger river, okay? If we have a look at the extract from a map on the left, you have got a tributary, a small river.

You've also got a few different sources on there.

You might be able to spot, they're a little bit hard to see, okay? And you've got confluence where two rivers are joining.

Now, if we look at the right, we can see a few different things.

Now I can see tributaries, sources, but also, okay, there is a watershed here, right? Now, the reason that we can tell it's a watershed, because that's the highest point in the land there.

So if you were to look at it in a lot more detail, you can see that the contour lines show a ridge of high land and then it gets lower.

It's very, very steep as well, actually, we can also see there's a path over the top of the ridge line, okay? So that shows a watershed, right? Where you've got a ridge line, because water that would go on the left side of that watershed would flow into the rivers, such as the Anafon, okay? But then on the right they'd go into some of the other rivers that you can see there.

Okay, let's check our understanding.

So I've got three extracts of Ordnance Survey maps here.

What I'd like you to do is see if you can match the key feature with each of the parts of the Ordnance Survey map which has been circled, okay? So pause the video and have a go at that task.

Okay, so let's have a look then.

So the mouth of the river is the middle one, the confluence is the map on the left, and the source that's been highlighted is on the map on the right.

So well done if you got that right.

Okay, let's go onto our first task.

So the first thing I'd like you to do is describe the different river and drainage basin features, okay? So you are basically just describing what they are.

Now I've done one for you to get you going.

So watersheds will often follow a high ridge of land where raindrops falling close to each other may travel into different rivers.

So pause the video and have a go at completing the one for the source.

Okay, and now you can have a go at these ones, okay? So a confluence is, and the mouth of a river is.

Now your second task is I'd like you to match the OS map images with the correct feature on the diagram, okay? So it's been labelled to make it easier for you there.

So point A, B, C, and D.

And then can you match which map feature goes with it, okay? So it pause the video and have a go at matching the diagram with the Ordnance Survey map.

Okay, let's check our understanding.

So the source of a river is where it begins.

Many river sources are at a spring where groundwater is forced to the surface.

So well done if you got that right.

A confluence is the point that the two rivers meet.

The mouth of a river is where river meets the sea.

This can create an estuary where salt water will mix with fresh water.

So well done if you've got those correct.

Okay, so let's go through the answers to here.

So the diagram on the left, A is a source, point B is a confluence, C is the watershed, and D is the mouth.

So well done if you got those right as well.

Okay, we're gonna move onto our second learning cycle, which is learning how precipitation gets to the actual river.

Now, very little of the precipitation that falls in a drainage basin will land directly into the river.

Now let's just double check.

So precipitation is all forms of water that fall from the sky.

So that includes rain, snow, hail, and sleet, okay? So yeah, very little of that will actually fall directly into the river.

So let's learn how it actually gets to the river, okay? So I want you to have a quick chat with the person you are sat next to.

How do you think precipitation that falls on the ground could travel to a river? Okay, so let's find out.

Precipitation that falls on the land will go through a series of stores and flows before reaching a river.

This is part of the drainage basin water cycle, okay? Now a store of water is where water can be kept or stored on earth.

So imagine a bucket of water.

So examples of stores of water on earth include oceans, lakes, and in the ground as well, there are lots of different stores, okay? A flow is how the water moves from one of those stores to another, okay? So for example, how does it get from the lake to the ocean? Or how does it get from the ocean to the atmosphere? Those are the flows.

Okay, true or false, a store of water is how water moves within a drainage basin? That is false, and can you tell me why? A store of water is where water can be kept or stored on earth, it's not about how it moves, okay? So well done if you've got that right.

Now, the drainage basin water cycle is an example of a physical system.

Precipitation that lands in the drainage basin flows through this system to get to the river, okay? So I've highlighted precipitation there, which includes snow, rain, sleet, and hail, okay? So we're gonna learn how it moves through that system to get to the river channel.

Now, in the drainage base in water cycle, we can identify a few different things, okay? Inputs of water are things that are going into the system, okay? So I'm going to highlight those in this nice green colour to see them more clearly.

So inputs to the system are in green, outputs of water is how they leave the drainage basin system, okay? And those are highlighted in purple.

So how it leaves a drainage basin is either through evaporation or evapotranspiration, which is evaporation of vegetation, which we'll learn about in a minute.

Or it can also leave the system from a river, so channel flow, it can leave that area through the river.

Stores of water are highlighted in an orange colour here.

So this is where water is kept within the system.

So it might be kept on the leaves of plants, and this is known as interception, surface storage, so water on the surface of the earth, it can be stored within the soil, it can be stored within the groundwater, but it can also be stored within the river as well, okay? So that is where the water is kept within the system.

Now, flows of water is how it's moving between those different stores.

So I've highlighted in black here where water is flowing and moving within the system.

So we're gonna learn about what these are in a little bit more detail.

So don't worry if you feel a little bit overwhelmed right now.

So infiltration, percolation, surface runoff, through flow, groundwater flow, and also channel flow, which is the water moving within the river, okay? So you'll notice here that the river system has got inputs, outputs, stores, and flows.

The actual river can be counted as basically all of them apart from an input, okay? The only input is rain coming or precipitation coming into the system.

Now, water that reaches the ground may be stored in puddles as surface storage or flow to the river as surface runoff, okay? So here we've got here, it can be stored on the surface of the earth, for example, in a puddle, or it can flow to the river, which is known as surface runoff, and that's it.

Moving between the store of surface water to the river channel.

Water that flows on the surface often moves to the river quite quickly, okay? Precipitation can be intercepted by trees and plants.

From here, it may be evaporated back into the atmosphere through a process called transpiration, also known as evapotranspiration, okay? Now, if you imagine the vegetation on the surface of the land and it's got lots of leaves, flowers, et cetera, when that water from the sky falls down, sometimes the leaves collect that rainfall, okay? And that is known as interception, okay? It's intercepted the rain, and therefore, because it's landed on the vegetation, it doesn't reach the surface of the earth, okay? If it stays on that piece of vegetation, that piece of vegetation is storing it.

Storing it is where it's keeping it, okay? Some of that water might eventually get to the surface of the earth and then be surface storage.

Some of it will evaporate straight off, known as transpiration or evapotranspiration, okay? So there is water that has been intercepted, and if it comes off that plant, it's known as transpiration.

Some water may infiltrate, sink into the soil, and flow as through flow to the river, okay? So rainfall comes in here.

When it absorbs into the ground, okay, it's known as infiltration.

If water moves within the soil to the channel, that is known as through flow, okay? Some water may percolate into the rock to be stored as groundwater.

This may flow to the river as groundwater flow, which can take a very long time, okay? So rainfall, it infiltrates, but then when it starts to go through the rock, that's known as percolation, okay? So it's how it's going further down, okay? But if it moves within that ground rock, it's known as ground water flow.

Okay, let's check our understanding.

Can you label what processes are missing from this diagram? Okay, so we've got infiltration through soil and percolation when it goes into the ground rock.

So well done if you got that correct.

Now, as I said earlier, the river is a store of water, so it's where it's kept, it's a flow of water because it's moving water within the drainage basin system, but it is also an output of water because eventually it is taking water away from that drainage basin, whether that flows it into the ocean or into a lake, okay? So it's all three of those things, okay? Right, we're on to our task B for this lesson.

So what I'd like you to do is fill in the table describing the stores and flows, okay? So I've done the first one for you.

So the description of surface storage water is water that has reached the ground, which may be stored in puddles or lakes as surface storage.

And then for the second column, you need to say, how will water flow to the next store, okay? So for example, for surface storage, water will then either flow on the surface, known as surface runoff, or it will absorb into the soil known as infiltration, okay? So pause the video and have a go at filling in the table.

Okay, let's check our understanding.

So that's the first one that we did together.

Okay, so we've got surface storage, so water that reaches the ground may be stored in puddles or lakes of surface storage, and water will then either flow on the surface known as surface runoff, or it will absorb into the soil known as infiltration.

So for soil storage, water is absorbed in the soil.

This can make the soil saturated, which means that it's filled with water, the water will then either flow through the soil, known as through flow, or it will percolate into the ground rock below.

Groundwater storage is water that can be stored underground in cracks and caves.

This may flow to the river as groundwater flow, which can take a very long time.

The river stores water on the land, but rivers all eventually flow to the ocean.

So it pause the video to double check that you got those right.

Okay, so here's a summary for today's lesson.

We've got quite a lot here.

Now, a drainage basin is an area of land drained by a river, and the watershed separates each drainage basin.

The key features of each are a river's source, mouth, tributary, confluence, and estuary.

The water cycle is the constant flow of water around the land, sea and atmosphere involving evaporation, condensation, and precipitation, and precipitation that falls on the land will go through a series of stores and flows before reaching a river.

It may be intercepted by vegetation or be stored on the surface in the soil or rocks.

Precipitation will flow into the river as surface runoff, through flow or groundwater flow.

Right, that's it from me, so well done.

There's loads of stuff to learn there.

So you've done a brilliant job.

I'll see you next time.