Lesson video

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

In today's lesson, we are going to be learning about river processes, which include erosion, transportation, and deposition.

This is the third lesson of the river's topic.

We've got loads of interesting things to learn about, so let's get going.

Your lesson outcome for today is that you can explain the processes of river erosion, transportation and deposition.

We've got three key words for today's lesson.

So, the first one is erosion, which is the process by which the earth's surface, example rock or soil, is worn away and transported from its ordinal state and original location.

Transportation, is where rivers move sand, mud, and rocks.

And deposition is when sand, mud, and rocks are dropped by the river.

We've got three learning cycles.

Okay, so first of all, we're gonna look at how do rivers erode the land.

We're then gonna look at how do rivers transport that material.

And then finally we're gonna learn about how rivers eventually deposit that material.

So, let's start with our first learning cycle, looking at how the rivers actually erode the land.

So, river erosion is where the land is broken down and removed by a river.

Now that has a big impact on our physical landscape.

So, that's what the area of land around us looks like.

So, first of all, I want you to think why do you think rivers erode the land? So, why do they break the land down? Now there are actually four main types of river erosion, that is abrasion, hydraulic action, attrition and solution, okay? So, we're going to look at these four types of river erosion in a bit more detail, looking at how they work.

Now, just before we do that, I'm gonna make sure that we understand what these terms mean.

So, the banks of the river is the side bits of the river and the bed is the bottom of the river bed.

Now imagine this, as if you lying down in your own bed flat, okay, so the bottom of the river bed is the bottom, as if you are lying down in your own bed.

Now the first one we're gonna look at is abrasion.

So, abrasion is where rocks and sediment carried by the river scrape against the bed and the banks wearing them down and breaking off material, okay? So, sediment that might have been taken away from another form of erosion scrapes that bottom of the river bed or the banks.

And by doing that it can break off other material as it does it, okay? So, as we said there material carried by the river scrapes and grinds against the bed, a bit like sandpaper, wearing them a little bit smoother, okay? So, the bed or the banks of the river might become smoother because of this type of erosion.

Attrition is where rocks carried by the river collide and break apart.

So, over time the rocks will become round and smaller.

Okay, so two rocks hitting together, a little bit might break off, okay? So, as we've got here, they come together, bits break off, and the rocks over time become smaller and smoother.

Now you learn as you go further down a river, the material within the river tends to get smaller, okay? And smoother.

Now that's because of this type of erosion.

Okay, let's check our understanding.

Now which type of erosion is where rocks and sediment carried by the river collide with the bed and the banks causing bits to break off? Okay? So, it's about the bed and the banks of the river here.

Now that one is abrasion, okay? Because it's not the two bits of rock hitting together that would be attrition, it's about the bed in the banks becoming smoother.

Right.

Our next type of river erasion, it's called hydraulic action.

So, this is when the force of moving water hits the river bed and banks, dislodging and breaking rock and sediment, okay? Now what can actually happen, especially if there are cracks in the side of the river bed or the banks? Water can get forced into those and break bits off, okay? So, here we've got a diagram.

There's the flow of water and there's are little bits of rock which have broken off the bank of the river due to hydraulic action, okay? Now this type of erosion can happen when the river has a lot of energy.

So, looking at that photograph there, we can see that that river is moving quite quickly and there's a high volume of water, okay? So, hydraulic action, I always think big action, lots of energy within the river.

Okay, so solution is where the bed and the banks are slowly dissolved by slightly acidic river water.

Okay, so think of that word solution, sort of a chemical reaction happening there.

So, the actual river water, if it's slightly acidic, it can actually dissolve parts of the bed and the banks of the river, okay? Now this type of erosion happens especially with more alkaline rock types such as limestone because there's a greater difference in the pH here, okay? So, more of the rock is dissolved because you've got slightly acidic river water reacting with more alkaline rock.

Okay, let's see what you can remember.

Can you label the four different types of erosion there? Okay, so top left, we've got attrition, when they hit together and become smaller and smoother.

Hydraulic action, when the force of the water breaks away parts of the bed and the banks of the river.

Solution is when it dissolves it, and abrasion is when rocks at the bottom scrape and smooth the river bed.

Okay, so hydraulic action could be described as which of those four? Pause the video and see if you can figure out which one is hydraulic action.

It is C, the pressure of moving water against the bed and the banks causing erosion.

So, well done, if you got that correct.

And solution could be described as which of those four? It is D.

So, the water in the river chemically dissolving the bed and the banks of the river.

So, well done if you got that correct as well.

Okay, so we're onto our first task of the lesson.

So, first of all, I'd like you to label and describe each of the four types of erosion in the diagram.

So, annotate the diagram with the four types of erosion and write a quick sentence saying what they are.

Okay? Now an optional task, which might be fun to do if you do that first task super quickly, is to create an action for each type of erosion.

Show the actions to a partner and see if they can guess the correct erosion type.

So, I'll give you my favourite one.

When I do attrition, I go like this, (vocalising).

Okay, so two rocks hitting together and a little bit's breaking off.

Can you think of your own action for one of the four types of erosion? Okay, here's our feedback for this.

So, it might be worth pausing the video here and just checking that you've got similar answers to me.

So, attrition is when rocks collide with each other breaking into smaller rounder pieces.

Hydraulic action is when the force of the water breaks pieces off the river bed and the banks.

Abrasion is when material carried by the river scrapes against the bed and the banks wearing them down like sandpaper.

And solution is when slightly acidic water dissolves the banks of the river gradually eroding it.

Okay, so well done if you got those correct.

Right then, we are moving on to our second learning cycle now, which is looking at how do rivers transport material, okay? Now, rivers transport material as they flow downstream, okay? So, that basically means that they are moving the sediment within the river.

Now rivers carry different types of material from really fine particles that you can't even hardly see or larger rocks, okay? So, it ranges in between them all.

So, and, the different types of rocks will be moved by different processes depending on how much energy the river has.

So, we're gonna look at the different types of transport.

Now the flow of a river gives the water energy so that it can transport the material.

Now what do you think influences how much the river can transport? So, what do you think might influence how much material or how large material the river may be able to transport? Transportation is influenced by these things.

The speed of the river, the amount of water flowing and the size of the material.

Now there are four different ways that a river transports material.

So, traction is one.

Saltation, suspension and solution.

So, we're gonna look at these four types of transport in a little bit more detail.

Okay, let's check our understanding.

Can you remember the four different types of transport I've just told you? Okay, so we've got suspension, solution, saltation, and traction.

So, well done if you remembered those.

Now, larger rocks and boulders may be rolled along the riverbed as they are too big to be picked up.

This is called traction, and this requires a lot of energy from the river.

These rocks are called bed load, okay? So, large rocks, they're too heavy to be suspended in the water or to float along, okay? So, they roll or scrape along the riverbed, okay? But they still do require quite a lot of energy to be picked up because they are big and heavy.

If the rock gets a little bit smaller, okay? Smaller pebbles and rocks that can't be suspended, so that means they can't float to the water, may bounce along the riverbed and this is called saltation, okay? So, if a river, sorry, if a rock is able to bounce along, that is known as saltation, but it still does require quite of energy from the river.

Small sediment that is picked up and carried in the river is called suspension.

Sometimes sediment can be suspended for a long time and this is known as suspended load, okay? So, material which can kind of like float along if you like, it's in suspension, yeah, it's floating along the river and that's known as suspension or suspension load.

Material that has been dissolved and is transported in the water is called solution.

And this is called dissolved load.

So, a type, if the river has has eroded the banks or the bed of the river free solution, so it's slightly dissolved material, that material can then be transported in solutions.

So, they've got the same name here for the type of erosion and transport, okay? So, solution erodes, but they can also be moved in solution as well.

And that is when the sediment is actually dissolved within the river.

Okay, let's check our understanding.

So, which one of these is traction? So, that is D.

So, traction is where rocks and boulders are rolled along the riverbed.

Material that is dissolved and carried by the river is called? Solution.

Well done if you got that correct.

And can you match the transportation process with the correct description? Might be worth pausing the video here.

Okay, so traction, is large heavy particles like boulders and pebbles are rolled or dragged along the riverbed by the force of the water.

Saltation is when smaller particles such as sand grains are lifted off the riverbed and then fall back down after a short distance.

Suspension is when fine particles like silts and clay are carried in the water, suspended by the river's flow, often giving the river a muddy appearance.

And solution is when dissolved minerals and chemicals, such as calcium carbonate are transported in the river's water.

So, well done, if you've got those correct.

Okay, we're on to task B now.

So, first of all, you're gonna describe the four types of transportation.

Try and use these following words in your answer.

So, rolling, strong current, dissolved, sediment and bouncing.

Pause the video and have a go at describing the types of transport.

Okay, task two.

Tick the boxes in the table for the transportation types that may occur in each of these scenarios.

You can tick more than one box in each scenario or right, possibly where appropriate.

So, the first scenario is a storm increases the amount of water, speed and depth of the river making it incredibly powerful.

So, which types of erosion, or sorry, transportation are likely to be at play here? And the second scenario, a small, slow flowing shallow stream in an area made of limestone.

Okay, let's check our answers.

So, it might be worth pausing the video and making sure that you've got something similar to what I have written here.

So, traction is when large rocks and boulders may roll along the river bed.

This requires a strong current.

Saltation is when smaller pebbles and rocks bounce along the river bed.

Suspension is when small sediment is picked up and carried in the river.

And solution is material that is dissolved and is transported in the water.

So, well done if you got that right.

And for this one, so if you've got a storm happening, okay? It is likely that sediment is going to be able to moving the suspension, saltation, and possibly even traction, and a small shallow stream in an area made of limestone solution is likely to be at play here.

So, well done if you got that right.

Okay, we're moving on to our third learning cycle, looking at how to rivers deposit material.

Okay, so quick recap.

Deposition is when the river, lets go of the material, so it drops it back down.

Now rivers contain sediment of different sizes, we know that.

Deposition occurs when the material is dropped by the river at different times.

Okay? Now when we stir a glass of water with sediment inside, the material is given energy and it's transported around the glass.

So, if you were to get a glass of water and put some mud in it from outside and stir it around, that mud or sediment within the water will be uplifted and it'll move around within the water.

What happens to that material when we stop stirring? Have a quick chat with the person that you are sat next to.

When we stop stirring the water, it loses energy and the sediment is deposited at the bottom of the glass.

Which size sediment do you think would be deposited first? So, if we look here, larger sediment is deposited and then the smaller the sediment gets, the later it is deposited.

So, larger sediment is deposited in a river first as it is heavier, and as the water gradually loses energy, the fines sediment gets dropped off last.

Now deposition happens when the material transported by rivers is eventually deposited where there is no longer enough energy to continue to transport it.

Okay, so the river can't hold the material within the water anymore.

Now, if we have a look at this picture here, the material that we can see on the photograph has been deposited by the river.

So, at one point all of those bits of rock were being transported within the river's water.

But at some point the river hasn't got enough energy to hold it anymore and it's dropped it off.

So, when does deposition happen in a river? When the river loses energy? Well done if you got that correct.

Now there are different times when the river might lose energy.

So, we're going to have a look at a couple of examples of when this could happen.

Now, when rivers meet a lake or the sea, the water slows down and deposition of material occurs.

Okay, so if you imagine a river flowing to the sea, you've got water moving this way, but then you've got a big body of water stopping it here, so therefore the river actually slows down, slows down, it loses energy, it drops off material.

Now this is a lovely picture, a satellite image, and this shows that, because of that deposition, mudflats here have formed because all of the sediment that's been transported by the river has dropped, okay? So, lots of fine bits of material have been dropped off, near the mouth of the river.

Another type, or another time that river sediment can be dropped off is on a meander.

So, a meander is a river bend, okay? So, material is deposited on the inside of a meander bend where the water is shallower and flows more slowly.

Okay, so if we have a look at this image here on that inside of the bend, you've got a nice little river beach forming.

The reason that is formed is because the water there was flowing slower, okay? Because it's shallower, okay? And it therefore it's had to drop off some of that material.

So, why do rivers deposit material? Is when rivers lose energy and this can happen because the river slows down or the river is carrying less water, okay? Those are the reasons why material is dropped off.

So, let's check our understanding.

Which two scenarios are likely to lead to rivers depositing their load? Okay, slowing down at river estuary, and slowing down at the inside of a meander bend.

So, well done if you got that correct.

Okay, we're onto our final task for the lesson.

So, first of all, I'd like to use the images to explain why river deposition has taken place here.

So, pause the video and finish the sentences.

Okay, let's check our understanding.

I'm sure we've got the correct answers.

So, deposition has taken place here because the river meets the sea, the water slows down, loses energy, and therefore the river cannot hold the material anymore.

Deposition has taken place here because it is on the inside of the meander bend where the water is shallower and flows more slowly.

This leads to more material being dropped off.

Okay, so well done if you got those right.

So, here we've got a summary for today's lesson.

Rivers erode, transport and deposit material.

Erosion can occur through abrasion, attrition, hydraulic action and solution.

Transportation can occur through traction, saltation, suspension, and solution.

And deposition occurs when the river slows down in places such as the middle or sorry as the inside of a meander bend.

Right, that's it for today's lesson.

Good work and I'll see you next time.