Lesson video

Hi there, my name is Chloe, and I'm a geography field studies tutor.

This lesson is called Fieldwork: Presenting River Data.

And it forms part of a Unit of work called Rivers: How do rivers shape the land? In this lesson, we're gonna be looking at how we might present river data that we would collect in the field and how we could do it in both interesting ways and in ways that means that we will be able to answer our inquiry question with ease.

Let's have a look at that now.

By the end of this lesson, you will be able to present river data and be able to show correlations in the data itself.

Before we get started, let's review some keywords that we're going to be using.

First of all, a channel profile.

This is a graph that shows the shape of a river channel as if it was sliced from bank to bank.

Then there's something called the line of best fit.

This is a straight line drawn over the top of the data in a scatter graph to show any correlation.

And a correlation itself, is the relationship between opposing geographical variables.

There are two parts in this lesson.

We're first going to be drawing a channel profile, and then we're going to be using scatter graphs to see correlations.

We're now in the third stage of our inquiry cycle.

You can see it here, data presentation.

So the data from the river surveys can be summarised in a table.

You can see here that I have used the average depth, average bedload size, and the average flow velocity in my table here.

I haven't gone into the smaller detail about each of the measurements that I took in the field.

The averages are good enough at this stage.

Channel depth and channel width can be used together to draw a channel profile.

So here I have gone into more detail and I have actually pulled out the data for one particular site.

You can see all the channel depths that I took from one to 10 as I went across the channel.

To draw the profile, the full set of data readings are needed for each site that was surveyed.

There are a number of steps that we need to take in order to draw a channel profile.

First of all, we identified the maximum depth from the data set.

So you can see here at site number three, the maximum depth was 0.

54 metres at 0.

7 along the channel.

I then use this maximum depth and the channel width to draw a set of axes, with the Y axis extending below the X axis.

So you can see here channel width is my X axis.

It stretches up to 2.

4 metres, which is the width that I recorded in the field, and then my channel depth also in metres is going down to 0.

6.

So that would comfortably encompass my 0.

54 maximum that I identified in the last step.

Then I plot the depth readings below the X axis using a series of points.

You can see them here.

I then join the points by drawing a smooth line as this best represents the shape of the channel in real life.

In real life, the channel is not going to be angular, so we shouldn't be using a ruler and straight lines.

Let's have a look at our understanding so far.

Channel profiles should be drawn using a ruler to join the points.

Is that true or false? Should be easy now.

Pause the video and then come back to me.

Well, hopefully, yes you remembered that it is false, and why is it that we don't use a ruler? Yes, it's because a smooth line best represents the shape of the channel in real life.

The channel profile is not complete without a title, labelled axes, and units on the axes themselves.

You can see all three of those things are on my version here.

Andeep then says a really good point.

He says, "Now I've got to draw another five graphs to show the other sites." He's thinking this could be quite a lot of work.

What else could Andeep do instead? Andeep could plot all of his channel profiles on the same set of axes.

So you can see here, I've now taken the maximum channel width from all of my data and the maximum channel depth from all of my data in order to decide the size of my X and Y axis.

I then use different colours for the actual lines to show the different channels themselves.

Andeep says, "Using the same scale makes the profiles directly comparable." I can see here that the yellow channel is much, much smaller than the green one for example.

Andeep needs to make sure that the axes are large enough to include all of the maximum values for all of his data.

He then needs to distinguish between the different sites by using a colour, and if you're using colour, of course, then you have to also include a key.

Really simple one here, just using six different colours.

Let's check our understanding about channel profiles.

Look really carefully at the two channel profiles.

Which of the following statements is true? A, the channels are identical in shape.

B, channel A is deeper than channel B.

Or C, Channel A is wider than channel B.

Pause the video and have a really close look at those two profiles, then come back to me with your answer.

Yes, it's a little bit of a trick question this one.

You can see that actually the axes are slightly different in size.

They have the same values on them, but in channel A, the depth has been stretched out.

And then channel B, the width has been stretched, but actually the channels are identical in shape.

This is an important lesson to remember that this kind of scale that you use on your axes can really make your channels look quite different.

Now, your practise task for this part of the lesson.

Draw your six channel profiles for your data on the same set of axes.

Make sure your X and Y axes are large enough to include the maximum width and depth values from the whole data set.

So from all of your six sites that you've got measurements for.

Your channel profiles should include all the elements that make them both readable and correct.

Pause the video here.

This might take a little longer, and then come back to me with some beautiful channel profiles.

Here's what your channel profiles might look like.

You can see I've got all six on the same set of axes.

I've also checked that I've got a title.

I've labelled both of my axes.

And I've got units clearly marked as well.

Importantly, I've also included a key so I can see how the channel profiles change shape as I go from site to site.

Now let's move on to the second part of this lesson, which is looking at scatter graphs and how we can use those to see correlations.

Jun wants to find out if the relationship between channel depth and channel velocity in the local river matches the theoretical relationship he learned about in the Bradshaw model.

So if you remember in the Bradshaw model, it says that channel depth and velocity should both increase as you go from source to mouth.

At the moment, he's just got some raw data in a table.

To see if there's a relationship he decides he needs to draw a scatter graph.

Let's have a look at the different steps that you need to take in order to draw a scatter graph.

In your first step, you identify the maximum values for depth and velocity.

You can see them highlighted here.

You then make the axes large enough to include these maximums. Label the axes clearly with the units.

You can see here flow velocity in metres per second and channel depth in metres.

You then plot the points on the scatter graph using a neat little cross or a dot.

You do not need to identify which site is which when you've actually plotted them.

Izzy then says, "How can I tell what the relationship is between the channel depth and the flow velocity?" So in this stage you could say that the scatter graph is complete, but does it actually help Izzy to work out what the relationship is? She needs to include something else.

Geographers draw a line of best fit on top of their graph to show any relationship such as a correlation.

The line of best fit runs through the centre of all the points.

This means that an even number of points need to sit either side of the line.

Remember, your line of best fit must be a single straight line.

You can see here that three dots sit above the line and three of our points sit below it.

Let's check our understanding there.

What is wrong with the scatter graph drawn by Sofia? Is it A, the plots have been joined together with a line.

B, the axes have not been labelled correctly.

C, there are not enough plots.

Or D, she has drawn the line with a ruler rather than a smooth curve.

Look carefully at Sofia's graph there and then come back to me.

So what answer did you get? Really well done if you actually spotted.

There's two correct answers here.

First of all, Sofia has joined the points together with a line, she shouldn't have done that.

There should be a single straight line over the top being a line of best fit.

She's also not labelled her axis correctly.

Yes, her Y axis is labelled but her X axis is not, so we don't actually know what she's plotting against the velocity there.

It could be depth, it could be width, it could be something else entirely, so it must have a label in order for us to understand the graph.

Well done if you saw both of those mistakes.

The more plots there are on a scatter graph, the easier it can be to see what the correlation is and the potential direction of any line of best fit.

The plots at the moment seen on this graph don't really give us much of a clue as to what's going on, and what that relationship between channel depth and flow velocity might be.

But if we start to add more and more plots, we start to see a clearer picture of what that relationship is.

You can see now that actually it's a fairly clear positive correlation between them.

Lucas has produced this scatter graph with his results.

You can see the plots are all over the place.

What would your advice be to him about drawing a line of best fit? Hmm.

As the plots show no correlation and they are completely randomly scattered, Lucas should not attempt to draw a line of best fit.

There actually is no correlation in Lucas's data.

Let's check our understanding of those ideas.

Complete the sentences with the missing words.

Pause the video so you can have a look through the paragraph below, and then come back to me with the three missing words.

Right, let's take a look at what you got here.

The more plots there are on a scatter graph, the easier it is to identify any correlation.

If the plots are randomly scattered, a line of best fit should not be drawn.

Hopefully, you got those.

Now let's look at our final practise task of this lesson.

I'd like you to draw two scatter graphs.

The first one should be the average channel depth plotted against the average flow velocity, and the second one, the average channel depth plotted against the average bed load size.

Make sure your scatter graphs include all the elements that make them both readable and correct, and they should include a line of best fit if a correlation is identifiable.

You'll definitely want to pause the video here and take your time over these graphs to make them as accurate as possible.

Let's now review your answers.

Now, of course, your graphs may look slightly different to mine.

It depends on what kind of data you collected.

One thing is for sure, is that they should both have titles, their axes should be labelled, and the units should be really clear as well.

There should be a line of best fit if there is a clear correlation in the data.

Let's now summarise our learning.

Geographers often draw river channel profiles to show the size and shape of a river channel.

When drawn on the same set of axes, different channel profiles can be compared.

Correlations can be shown on a scatter graph where a line of best fit can indicate the nature of the relationship between two river characteristics.

Well done on all your efforts in that lesson.

The two types of graphs that we drew today, the channel profile and the scatter graphs are two very common graphs that we use in geography.

If you didn't quite get them right the first time, don't worry.

There will be plenty of opportunities to practise both reading these graphs and drawing them as you continue your studies.