Lesson video

Hello, geographers.

My name's Mrs. Homigo.

I'm really looking forward to teaching you today.

I hope you're gonna enjoy the lesson and learn lots.

Let's get started.

Today's lesson looks at the interaction of human and physical factors in river landscapes, and by the end of the lesson you'll be able to explain how physical and human factors interact to affect river landscapes, sediment load, and flood risk.

There are four keywords for today's lesson.

Floodplain, which is an area of low-lying ground adjacent to a river, and it's formed mainly of river sediments and is subject to flooding.

Urbanisation, the process by which an increasing percentage of a population lives in cities and suburbs.

Deforestation, the clearing or thinning of forests by humans.

Sediment load, the total amount of sediment transported by a river.

There are three parts to today's lesson.

"What factors interact to affect river landscapes?" "What factors interact to affect sediment load?" And "What factors interact to affect flood risk?" Let's get started on the first learning cycle, "What factors interact to affect river landscapes?" River landscapes are the physical features and landforms found in and around a river as it flows from its source, its starting point, to its mouth, where it joins the sea.

These are examples here.

Meanders, floodplains, and deltas.

Meanders are often found in the middle and lower course of rivers, and floodplains and deltas in the lower course.

Human and physical factors interact to shape these river landscapes and they influence erosion, deposition, and the flow of water.

Here are a few human and physical factors that are interacting.

For the physical factors, we've got geology, so the type of rock.

Is it a harder or a softer rock? The climate.

Do we expect to have heavy rain? Is it a dry climate? The relief.

What's the shape of the land like? Are there steep slopes or is it quite flat, undulating ground? And then human factors, river management.

What flood defences or what management schemes have been put in place by people? Urbanisation.

Are there large areas of urban developments? Because that affects the impermeable surfaces.

And deforestation, the cutting down of trees by humans.

How do these factors interact to affect the river landscape? Let's have a quick check now.

Which of these are human factors affecting river landscapes? Is it A, dam building; B, heavy rain; or C, urbanisation? Pause the video and come back when you've decided.

Hopefully you chose dam building and urbanisation.

These are two things that humans can do to influence a river landscape.

Let's look first at these two factors, heavy rainfall or high rainfall and steep valley sides, so thinking about the relief, together with deforestation on valley slopes.

Alex has pointed out there, "Deforestation is the human factor." Well done, Alex.

If we look here at this image, we can see that there's been some sort of landslide, a big mass movement.

By taking away the trees on the valley sides, we are destabilising the slopes.

They are more prone to erosion because they're not protected from the rainfall by the trees, and so more water is running across the surface and into the river, and we can get increased erosion of river banks and valley sides as a result, which makes them steeper again.

Here we have an image of a levee, which is a river management scheme.

It might be called an embankment sometimes.

It's built to try to protect the surrounding area from flooding by increasing the capacity of the river channel.

However, it can interfere with the natural processes of deposition on the floodplains.

It can cause sediment buildup and raise the riverbed.

A river would naturally flood out onto its floodplain, depositing some of the load that it was carrying.

With these levies in place, it's unable to do that, therefore sediment can build up in the river.

And this will change how the river landscape develops over time.

Wide flat areas next to the rivers naturally flood and deposit sediments, building up floodplains.

Izzy's pointed out, "This is a physical factor." If we have urban development on these floodplains, this creates lots of impermeable surfaces.

Think about the tarmac and the concrete that you see in cities, and drainage systems. All of these factors increase the speed and the volume of the water returning to the river.

See here it says that impermeable surfaces mean rainwater can no longer infiltrate into the ground, which affects river landscapes because flooding may become more frequent and severe.

River erosion increases due to higher river velocity, so the speed of the river.

And river management schemes to protect or straighten the channel can create a more artificial landscape.

Here we have an image of a dam.

These are constructed sometimes in the upper course of the river and they have several purposes.

It provides an area to store water, which we can use for water supply or irrigation, or as a means of flood control by allowing us to control the flow of the water down the river when there are points of high rainfall or high discharge.

They can also generate hydroelectric power by using flowing water to turn the turbines.

And Lucas points out, "This is a human factor," that is affecting the river landscapes.

So rivers transport sediment.

This sediment is carried downstream and it's deposited and it can create many distinct landforms. At the coast, it will contribute to building up deltas and estuaries, and dams can interfere with it.

When a dam is built, it stops the river's flow as a reservoir is created behind the dam, and we can see that large area of water is called the reservoir behind the dam.

As the water isn't flowing, it has less energy, and sediment is deposited at the bottom of the reservoir.

The river below the dam transports less sediment and so landforms created by deposition of this sediment, for example, deltas near the coastline, may start to shrink or even erode and coastal areas may retreat.

So it has huge consequences further downstream.

A quick true or false for you now.

Human and physical factors interact to shape river landscapes by influencing erosion, deposition, and the flow of water.

Pause the video and come back when you think you've decided.

I hope you said true, but can you give an example of that? Pause the video and see if you can think of one.

It may have been something you've discussed as you were deciding whether it was true or false.

The example I've given is here.

Dam construction traps sediment upstream.

This reduces deposition downstream.

Urban developments on floodplains increase the volume and speed of water flowing into the river, which increases the river velocity and the erosive power of the river.

I hope you came up with something similar.

Let's move now to our first task.

This OS map extract shows the lower course of the River Eden.

Can you annotate the map to describe two examples of how human and physical factors can interact to affect river landscapes, and where this might take place? So remember, an annotation is more than just a couple of words.

It's an explanation next to your map.

Pause the video and have a go.

These are the annotations that I've come up with.

You may have these or something similar.

I've pointed here to this area at the mouth of the river.

Dam construction upstream can reduce sediment transported by the river, causing depositional landforms in the lower course to shrink or be eroded.

And that's pointing to the estuary of the River Eden.

Urban developments, so I'm pointing here to an area of Carlisle.

E.

g.

roads and car parks on floodplains create more impermeable surfaces.

This increases the river discharge and erosion in the river channel downstream.

Well done if you had something similar to that.

Let's move now to our second learning cycle and think now about, "What factors interact to affect sediment load?" So start by making sure we're confident with what sediment load is.

It's the material, and this can be soil, rocks, sand, gravel, and silt, that a river transports.

And if you remember, a river can transport things in different ways.

The bed load, the larger heavy material, like the pebbles and the stones, are rolled or bounced along the riverbed.

Suspended load, fine particles like silt and clay, are carried within the water, and that's often what makes the water look muddy.

And the dissolved load is the invisible minerals that are dissolved in the water.

For example, salts.

Here are some human and physical factors now that can affect sediment load.

The physical factors could be heavy rain, weak or loose soils, or steep relief.

Human factors, agriculture, construction and mining, urbanisation and deforestation.

Sediment load increases when human activities make the land more vulnerable to natural processes.

So let's look at that with a few examples.

Let's think first about the soil type being the physical factor and agriculture as the human factor.

So if we have sandy or silty soils, they erode easily, so when rain falls on them or wind blows across them, they're easily eroded.

When these soils are then ploughed or left bare during farming, rainfall causes higher sediment input into the rivers.

So these two factors interact to increase the rates of erosion and therefore increase the amount of sediment in the rivers.

Let's look now at heavy rain, a physical factor, and urbanisation, a human factor.

We've got here an image of very, very heavy rainfall in an urban area and you can see what's happening.

There's a huge amount of surface water.

Now that's linked to these two factors here.

We've got impermeable surfaces which stop the rainwater from soaking into the ground, and there are a lot of those in urban areas, and constructed drainage systems such as storm sewers which rapidly channel this runoff into rivers.

So this water is rapidly running down into drainage systems and back into the rivers much more quickly than if it was to move down through the soil and then back into the rivers.

Both of these increase the volume and speed of surface runoff during storms, which increases the erosion of channel banks and beds.

So we've got more sediment being added to the rivers.

Let's have a quick check now then.

True or false? Sediment load increases when human activities make the land more vulnerable to natural processes.

Pause the video and come back when you've decided.

Try to think also as to why you make your decision.

I hope you said true, and you may have come up with a reason similar to this.

Deforestation and frequent ploughing can make the soil weaker and more exposed to rainfall.

As a result, more sediment ends up being washed into the river, well done.

You may have considered the impact of urbanisation.

Right now thinking about steep relief as our physical factor and construction as our human factor.

Hills or mountain slopes make water run off quickly due to the pull of gravity.

If we build roads or houses on these slopes, as you can see has been done in this image here, this disturbs the soil.

Rainfall on disturbed sloped land leads to very fast rates of erosion and high sediment runoff into rivers, and as a result, the sediment load increases.

Let's look now at deforestation, our human factor, combined with heavy rainfall, our physical factor.

When trees are cut down or vegetation is removed to clear the land, as can be seen in this image here, we get a lot more rainfall hitting the soil directly.

As the rain hits the soil, it washes it into the rivers.

The trees are not there to intercept the rainfall or protect it.

As a result, during periods of intense or prolonged rainfall, we see a significant increase in the amount of sediment load of nearby rivers.

Let's have a quick check now.

What human and physical factors are interacting in these images that can lead to an increase in sediment load? So you'll need to think of a human and a physical factor for both of the images.

Pause the video and come back when you've had a go.

For the first one, you might have put steep slopes and construction.

The second one, heavy rain and urbanisation.

And the third, deforestation and heavy rain, well done.

Let's have a go now at your second task.

Can you complete this table to identify human and physical factors and how they interact to increase sediment load? One has been done for you.

The human factor is agriculture, with frequent ploughing, and the physical factor is weak or loose soils.

Let's think how they then interact to increase the sediment load.

The weak soil is weakened further by frequent ploughing, and so it's easily eroded and washed into nearby streams and rivers.

See if you can think of two more examples.

Come back when you've had a go.

You might have chosen these as your examples.

The human factor, deforestation, and the physical factor, heavy rainfall.

So without trees or vegetation to hold the soil together, rain hits it directly and washes the loose soil into rivers.

And for urbanisation and interacting with physical factor, heavy rainfall, you might have said impermeable surfaces increase the speed and volume of runoff, which increases erosion, so more sediment flows into the rivers.

Well done if you had similar answers to that.

Let's look now at our third learning cycle and consider, "What factors interact to affect the flood risk?" Flood risk is the probability of an area experiencing a flood event and how severe the consequences of that flood might be.

There are examples of factors that can affect a flood risk.

The physical factors could be climate change.

We're seeing more extreme weather events.

The frequency of those weather events is also increasing.

The geology, so the type of rock.

And heavy rainfall.

Human factors, urbanisation and deforestation.

Can you think now as to how any of these factors interact to increase the flood risk? You might be able to think back over what we've done already and think of some links between them.

Lucas and Sofia have had a go at this.

Lucas has said, "Deforestation means that during heavy rain there are no tree roots to absorb the rainfall, so more water returns to the river more quickly, increasing the flood risk." So he's identified deforestation as a human factor and heavy rain as a physical factor.

Well done, Lucas.

And Sofia says, "Urbanisation increases impermeable surfaces.

This means rainwater cannot infiltrate.

Instead, it flows as surface runoff.

And this means more water returns to the river more quickly, increasing the flood risk." So well done to Sofia, she's picked out urbanisation as a human factor and heavy rain as her physical factor.

Well done, maybe you came up with some ideas as well.

Let's have a little check now then.

Which of these are human factors that affect the flood risk? Pause the video and come back when you've had a go.

You probably ticked deforestation and urbanisation, well done.

Climate change is influenced by humans, but physical factors influence it as well.

Let's look now at climate change and urban development, and how do they interact? So climate change is causing an increase in storm intensity and rainfall, and more urban developments is happening on floodplains, so the flat areas in the lower course of the river, and this reduces permeable surfaces.

We can see here an image of Shrewsbury and the areas coloured blue are indicating the flood risk.

The darker the blue, the higher the chance of flooding.

So we can see here that by these urban developments taking place on the floodplains and more intense rainfall and more frequent storms, there is a much greater risk of flooding.

The Environment Agency collects data in order to show the flood risk for towns like Shrewsbury is significant and is increasing, and you can find out about your own town or towns nearby and the flood risk that they are facing.

Impermeable geology, for example, clay, and increased road and building construction drastically increases surface runoff.

So human construction and geology are interacting here.

The combination of natural and artificial impermeability increases the flood risk.

Let's have a check for you now.

Which human and physical factors could be interacting to increase the flood risk in Shrewsbury? Pause the video and come back when you've decided.

You probably came up with this.

Urban developments on the floodplains and more frequent heavy rainfall, well done.

Let's have a look now at your last task.

Can you explain two ways in which human and physical factors interact to increase river flood risk? Sofia says, "I must make sure I identify a human and physical factor for each way, and explain how they interact." Pause the video and have a go.

Your answer might have looked something like this.

Urbanisation, particularly on a river's floodplain, is a human factor that increases the flood risk.

Impermeable surfaces such as concrete prevent rainfall from infiltrating into the ground, which leads to more surface runoff.

Deforestation is another human factor which reduces the interception of rainfall and means more rainwater flows quickly into the rivers.

Climate change causes more frequent and intense storms, which is a physical factor, which when combined with the impact of deforestation and urban developments increases the chance of rivers flooding.

Well done if your answer was the same or similar to this one.

Let's have a look now at a summary of today's lesson.

Human and physical factors combine to shape river landscapes as natural features like steep slopes and rainfall interact with human actions like deforestation and construction.

Sediment load increases when physical erosion is intensified by human activities such as farming and deforestation.

And the flood risk rises when the influence of heavy rainfall and impermeable geology are intensified by urbanisation, deforestation, and climate change.

Well done today.

Lots of things to think about, but I hope now you feel more confident in how human and physical factors are interacting to affect river landscapes, sediment load, and flood risk.

I look forward to seeing you all again soon.