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

This lesson is all about rivers fieldwork, the kind of questions that you can ask if you're going to a river site, and the kind of techniques you can use to collect data when you're there.

We've got a lot to do today, so let's get started.

By the end of this lesson, you'll be able to collect both primary and secondary data in a river environment, and you'll be able to use that data to answer an inquiry question.

So there's a few keywords to think about today.

First of all, channel morphology.

This is the physical size and shape of a river channel, and it also includes the sediment or the bedload that it carries.

Then, there's the Bradshaw model.

You might have heard of this before.

This is a theory about how river processes change from source to mouth.

Finally, flood management.

These are the strategies that are used to prevent a river over topping its banks following a period of intense rainfall.

The lesson is in three parts today.

First of all, what inquiry questions can be asked about rivers, how do geographers collect data at river sites, and then, finally, we're going to think about what secondary data we can use to study river sites as well.

Let's start with that first one.

So it's really important to remember that rivers are dynamic features.

They have multiple channel morphology characteristics that are in constant states of change.

Now, these characteristics include things like the bankfull or the low flow width.

Now, don't worry if you don't know the difference between those two.

We're gonna go through that in a moment.

The bankfull or the low flow depth, the channel gradient, the flow velocity or the speed of the river, the size of the bedload, and the shape of the bedload.

Theoretically, the way these channel morphology characteristics change from the source of the river to its mouth is described in the Bradshaw model, and you can see that in the table here.

So from source to mouth, we would expect the channel width and the channel depth to increase, but the gradient to decrease.

In other words, it goes from steep at the source of the river to quite shallow closer to its mouth.

The flow velocity will increase, the river will increase in speed as it flows along, and the size of the bedload will decrease, and it will become less rough.

In other words, it will become smoother as it gets closer to the mouth.

Geographers frequently like to test this model on real-life rivers, and though this model predicts how the characteristics will change, in a real river, there'll be degrees of agreement.

Geographers may also try to answer inquiry questions which test two of these characteristics against each other, so kind of pair the characteristics up and see how they fare.

For example, Alex is interested in the relationship between channel depth and velocity.

To what extent does the velocity of a river's flow increase with increased channel depth? Now, according to the Bradshaw model, the deeper the river, the faster it should flow, but is that gonna be the case in real life? That's what Alex is trying to find out here.

Let's check our understanding so far.

Which of the following inquiry questions could be asked about channel morphology? Remember, that's all about the shape of the river channel.

First of all, to what extent does the River Frome follow the Bradshaw model from source to mouth? How does the shape of the channel affect river processes along the River Frome? How does the geology of bedload change from source to mouth along the River Frome? Or to what extent does the course of the river affect water pollution levels along the River Frome? Pause the video now and have a think about each of those questions again.

Which of these could be asked about channel morphology? Okay, let's see what you thought.

So you might have noticed there's actually two right answers here.

The first one about the Bradshaw model and how it changes from source to mouth, that's all about channel morphology, and the processes, and how they change.

That one's definitely going to be included here.

And then the second one talks about how the shape of the channel affects processes, so that's definitely also going to be about channel morphology.

Hope you got those right.

But focusing on channel morphology characteristics does not highlight all the ways in which a river is dynamic.

The main processes, erosion, transportation, and deposition, can also be observed, and to some degree, they can be measured when one visits an actual river in real life.

Channel processes affect the size and shape of the channel morphology characteristics, and it's also the characteristics of the channel will affect the river processes.

So both happen in both directions.

Geographers can ask inquiry questions that highlight both directions of that relationship.

So how processes affect characteristics, and how characteristics affect processes.

Geographers can also ask inquiry questions about flooding, how it's managed, or how it could be managed.

So these questions could focus on the placement of management structures, such as barrages.

You can see one in the picture there, the Thames barrier, or the use of schemes, such as land use zoning.

It is really unlikely that you'll be able to see flood defences actually stopping a flood in real time.

The chance of you visiting a field site on the very day that it floods, well, we really wouldn't want that anyway, but it's very unlikely to happen.

Inquiry questions could instead look at the impact the defences themselves have had on local people's lives, on their businesses, maybe even on local ecology.

So here, we've got a question.

What have been the social impacts of the flood gates? Or you could ask, which areas of Upton are most vulnerable to flooding? So not about the flood itself, but about the structures that are around it.

So let's check our understanding of those ideas.

True or false? River channel morphology characteristics affect river processes.

Pause the video and have a think, and choose is it true or false.

Now, hopefully, you've realised that that is true.

Well, remember, channel morphology characteristics affect river processes, and themselves are affected by river processes.

Remember that idea about the two-way relationship.

Your first practise task of this lesson, sort the inquiry questions into those about channel morphology and those about flood management.

You can see the questions have been given A, B, C, D lettering.

Write the correct letter code in the correct column.

Again, pause the video, have a think, maybe have a chat with somebody nearby as well, and see what you come up with.

Okay, let's see what you got.

So first of all, channel morphology is question B and C.

B is talking about bedload size and channel depth, so that is all about size and shape.

And C is talking about the width of the river, so that's definitely also going to be about channel morphology.

Question A is mentioning dredging, which is a flood management scheme, which some places use, and it's talking about the impact of that, so yeah, that's gonna be that column.

And then D, although it's focusing on modern housing estates, really what it's talking about is its vulnerability to flooding, so that's yes, gonna go in that second column as well.

Hope you got those right.

Let's look at the second part of the lesson today.

How do geographers collect data at river sites? The cross-sectional area of a river channel is its width multiplied by its depth.

Now, geographers can measure the channel width and depth in two ways.

You might remember these phrases from earlier.

First of all, there's the bankfull.

This refers to the width or depth of the water if the channel were full, so if the water was right up to the top of the bank.

The other way of thinking of it is the low flow.

So this refers to the width or depth of the current water level.

So the low flow will always be at a lower level than bankfull.

Channel width is measured by stretching a tape measure taut across the channel.

The depth measurements are then taken at regular intervals across the channel using a metre stick, and you can see that in the picture here.

From these, you can then calculate the mean depth.

So at bankfull, it would be where the tape measure is sitting on the metre stick, and low flow would be where the water level is on the metre stick.

You can also measure the wetted perimeter.

This is measured by anchoring a tape measure at the edge of one bank.

You can see it on the left-hand side of the cartoon here, and then you tread along the tape until you reach the other bank.

So the tape will fit the form of the bottom of the channel, and then when you take the tape measure out and measure the section which is wet, that is your wetted perimeter.

Okay, let's check our understanding so far.

So Jacob has measured a section of a river and has recorded the following data, and you can see it there in the table.

We've got the distance across the channel, and he's taken a number of readings there, and he's got the bankfull depth and the low flow depth.

But what mistake has he made? Let's take a look at some options.

He has recorded the depths in metres rather than centimetres.

He has mixed up the bankfull and low flow depths.

He has not taken enough depth readings.

Which one of those would you think is a mistake that Jacob has made? Pause the video now, and then I'll come back to you.

Well, let's look at each of these in turn.

So he's recorded the depths in metres rather than centimetres.

Now, although yes, these measurements, some of them are quite small, 0.

1 metres, some of them, it doesn't actually matter whether it's metres or centimetres.

The fact is he's been consistent, and that's important.

He's not taken enough depth readings.

Well, we don't know what his question is, so actually we don't know whether that he's gonna be accurate enough in his readings, whether he's taken enough, so we can't really judge that one.

But B, he's mixed up the bankfull and the low flow depths, let's just look at that.

So the bankfull depth, he's got at 0.

10 metres, and his low flow at the same point, he's got as 0.

25 metres.

Now, that's impossible because what he's saying is that the top of the bank is lower than where the river is actually sitting, so he's actually got the two the other way round.

So that is the one which we're gonna say he's made a mistake on, and it's really easy to make those kind of mistakes in the field, so do double check as you are recording your data.

To measure river flow velocity, geographers record how long it takes for a float to travel a set distance on the river surface, and we use this calculation, velocity is calculated by distance, divided by time, to give a value in metres per second.

So the kind of floats you can use, they've gotta be easy to see, of course, and if they were to get lost, it's really important that they would not then cause harm to the local ecology of the river.

So things like an orange or dog biscuits, these make excellent floats.

They're both visible, and they're organic, so it means that if we do lose them, it's not going to cause any huge damage.

So let's look at how we would actually go about measuring velocity.

First of all, you measure out a five metre section of the river, and place a marker, like a ranging pole, you can see that's what we've got in the picture here, at either end of the section.

Then, you've got your float in hand, and you place the float at the foot of the marker that is upstream.

Then, you need to make sure that you're not standing in the way of the flow of the river.

In other words, you would act as a barrier, a block to the velocity of the river, so you wouldn't get a very accurate reading.

So making sure you're not standing in a way that impedes the flow.

You then just release the float at the same time as starting a timer.

You need to have a friend at the other end who's gonna be there to catch it.

So then you stop the timer when the float reaches the second marker, then you record the time that it's taken, and I would say you would want to repeat this at least twice more.

Now, if I was in the field and three of my readings were completely different from each other, I'd probably want to do another couple just to see if I can get a better average.

But if after three readings, all of the readings are roughly in the same ballpark, then I would be happy with my three.

Then, you can use the shovel on the surface of the river bed, so just kinda scraping the top layer, and that's a good way of sampling bedload.

So bedload that you've collected could then be measured along its longest length, or you could categorise it in terms of its roughness or smoothness using something called the Powers Index, and you can see a copy of that here.

So if it's categorised as really angular, you can see there's lots of sharp edges, all the way down to being well-rounded, where it's almost a smooth pebble.

You could also look at the geology of the bedload, and you could record that as well.

So let's check our understanding of that.

True or false? To measure the velocity of river flow, one should measure the distance a float travels in five minutes.

Is that true or false? Pause the video and have a think about the consequences of doing that.

So what do you think? True or false? Yeah, false.

But why? Well, if you think about it, in some rivers, releasing a float and letting it go for five minutes, it could actually go hundreds of metres away from you.

Might be quite difficult to then record it.

As it says, along most rivers, it would be extremely difficult to measure, and it could actually be quite hazardous for a geographer to go about it in this way.

Instead, we look at the time it takes for the float to travel five metres.

So we set the distance, and then we measure the time, rather than setting the time and then going and running after the orange and measuring the distance.

Geographers can look at a settlement's vulnerability to flooding as well.

They can also study how effective flood management is.

They can record the height of the land, and the different features, and they could use an altimeter for that, as well as the position of different flood defences.

You would then be able to estimate the amount of damage potentially that would be caused if the river were to flood to certain depths.

So by looking at the height of the land, you can say that the highest features, the highest points, are going to be least at risk of flooding, but there will also be some areas which are much lower down, and so you can actually estimate which areas would be most likely to flood.

Geographers can also carry out an impact survey, and this would measure how different forms of flood management might affect an area that has no protection.

So different defences like channel straightening, or lining a channel with concrete, building embankments, or afforestation, so planting trees along river banks, these would be kind of scored against different criteria, and you could really adapt these criteria for the location that you're working with.

So you might have criteria like: does this support local bird life, local aquatic life, does this flood management strategy create visual disturbance, does it allow access for recreational activities, things like fishing, does it allow riverside businesses to grow, or does it actually hamper their businesses.

So you could create a range of criteria that you can then measure the impact that potentially flood management strategies could have.

Let's check our understanding of those ideas.

Complete the sentences with the missing words.

Pause the video here, so you can have a read through the paragraph, and then I'll come back to you with the right answers.

Right, let's see what ideas you've got.

Geographers might study how vulnerable a settlement is to flooding.

They can record the height of the land, you might use elevation, that's fine as well, as well as the position of any flood defences using a map.

This allows them to estimate which areas are likely to flood and which would be protected.

Let's look at our second practise task of this lesson.

Izzy wishes to compare river discharge at three different sites along a river.

Let's remind ourselves discharge is the mean velocity multiplied by the cross-sectional area.

State three measurements Izzy will have to take at each field site as part of her data collection.

The second task is actually to go and practise with a ruler and a copy of the Powers Index, measuring bedload length and roughness.

Now, you don't have to be at a river, but choose somewhere that has a variety of rocks and pebbles for you to survey.

So I would say at least 10 would be a good way of doing this exercise.

Really important though, note down any ways in which your method is not as accurate as you might like it to be.

Where are the flaws in this method? Do note these down.

Now pause the video here, so you can have a go at those tasks, and I'll come back to you.

Right, so Izzy's trying to find the discharge of the river.

So she needs cross-sectional area, and she needs velocity.

Let's have a think about what she actually needs to do at her field site.

She would need to find the cross-sectional area, so she needs to have width multiplied by depth.

So the low flow channel width is one measurement she's going to need, and then she's going to need a number of low flow channel depths because she needs to repeat it across the channel, and then she can find the average depth or the mean depth.

She's also going to need velocity if she's going to find the discharge.

So she's going to repeat this three times, and then she, again, can calculate the mean velocity.

Now, in terms of measuring bedload using its length and the Powers Index as your measurements, there are some things which aren't always going to plan with that method.

So let's have a look at some of the things which you might need to think about.

Now, the Powers Index, it's a matter of opinion.

You're gonna pick up a piece of bedload, and then try to decide which of the six categories it falls into, and you might have one opinion, and someone else might think it falls into a different category, so there's some subjectivity around that.

Now, rocks aren't just uniformly going to fit into the category.

Sometimes the rocks might be smooth at one end, so they'd be in one category of the Powers Index.

They might be rough at the other end, and so they might fit into a different category.

So how do you decide where that rock will actually sit within the Powers Index? Then, you've got things like spherical-shaped bedload.

It doesn't have an obvious longest length, and even non-spherical pieces of bedload, sometimes you have to kind of take some time to work out which is the longest length of any piece.

And then when you're actually putting that piece of bedload against a ruler, sometimes it's not that easy to measure actually how many millimetres, to be most precise.

How well your ruler might be able to measure that is in doubt.

So it's probably going to be a little bit of guesswork as well on that part, so not as accurate as it could be.

Hope you've got a couple of those at least.

Now, we'll move on to the final part of our lesson.

We're going to think about secondary data that we can use to study rivers.

So first of all, maps and satellite images of rivers can provide really different forms of secondary data.

Old maps, you can look at the past position of rivers, and some aerial photographs, and you can see in the example here, you can actually see the scars in the landscape where the river channel once was.

And this particular example, you can see the river has been in many, many different positions compared to how it is today.

Maps also allow geographers to plot the position of their field sites in relation to human features, such as settlements, sewage works, anything which could affect channel morphology and processes.

You could also look at flood risk maps.

Now, these show the likelihood of flooding in certain areas, as well as historical data in relation to previous flood events.

You can also look at geology maps in relation to flooding.

So these can predict the future path of rivers that are able to flow naturally.

Rivers are likely to flow quickly and with more force through areas of soft rock.

They will also show where there's been silt buildup.

In other words, river sediment, the fine sediment which gets deposited when a river floods, it will show where those have built up over time.

Let's check our understanding there.

Complete these sentences with the missing words.

Pause the video, and I'll tell you the right answers in a moment.

Right, let's see what you got.

Geographers can use old maps to show the past position of river channels and features.

Aerial photography may show scars in the landscape where the river once was.

There is also flow data available for almost all UK rivers, certainly all the big ones, and this is held by an organisation called the National River Flow Archive.

This data can be used to study how flow rates vary at different times of the year.

Remember, when you're collecting primary data, you're only gonna be probably visiting the river once on one day.

So these kind of archives can give you a much more rounded picture of what the river is like.

You can use that data and compare it to the primary data that you've already collected, and you can also look at historical data, so how the river has changed its flow over time as well.

You can also look at the river basin management plans for most of the large UK rivers, and these highlight what has already been modified in river basins, their size, their ecological quality, and things like pollution levels as well.

Now, Aisha is using a river basin management plan to study a river she's later going to visit to collect primary data.

What secondary data might the management plan give her? Is it gonna give her data on the flow rates in different parts of the river, the size of the drainage basin, or the historical position of the channel compared to today? Which one of those would apply to a river basin management plan? Pause the video, have a chat with someone else if you need to, and then come back to me.

Well, well done if you've got this right.

Yes, it is the size of the drainage basin that the river basin management plan will show you.

If you want something on the data on flow rates, you'd have to go to the archive material, and then if you want historical positions of channels, then you'd be best looking at satellite imagery.

Now, our final practise task.

Jun is studying how the channel morphology and position of a river have changed over time.

So two elements there, channel morphology, the shape of the river, and the position of the river in historical terms. What sources of secondary data might support his inquiry, and what will they show? Pause the video.

This might take a little bit of thinking time, and then I'll give you some of my ideas in a moment.

So let's look at your ideas.

Your answers might include things like current and old maps to show the current path and the older paths of the river.

Having those sitting alongside each other, you can then make some really good comparisons.

Geology maps will show the depth and position of any old silt deposits, so that will tell you a great deal of information about where the river used to flow, as will satellite images and aerial photographs.

There might be river scars that you'll be able to pick out from those.

Historical flow data will also show how the river has changed over time.

For example, if the river is running faster now than it was in previous times, you'll know that it's very likely that the river is a lot larger and deeper, so that would account for that increase in velocity.

Let's summarise what we've learned today.

There are many geographical inquiry questions that you can investigate along the course of a river, such as how closely a river resembles the Bradshaw model.

Data collection methods can focus on channel morphology and assessing the impact and need for flood management.

Secondary data allows geographers to compare their river with others, and understand more about the factors that can create certain features in river systems. Well done.

There was a lot of information in there and a lot of ideas to think about, but I hope that's given you some renewed confidence to go out and try some river fieldwork.