Lesson video

Hello and welcome.

My name is Ms. Harrison.

I'm so looking forward to learning with you today.

Today's lesson is called "Wave Processes at the Coast." Grab everything you might need and let's begin our learning.

By the end of today's lesson, you'll be able to understand how wave processes shape the coast.

Before we can begin this learning, we need to define the keywords that we'll be using throughout today's lesson.

The keywords in today's lesson are: waves, erosion, destructive waves, and constructive waves.

Waves, these are ripples in the sea which is caused by wind blowing over the surface of the water.

Erosion, this is the action of water wearing away the rocks.

Destructive waves, these are high, steep waves and they're typically formed by local storms, and they remove sediment from beaches.

Constructive waves, they are low waves and they're typically formed by distance storms and they deposit sediment onto beaches.

Brilliant, now that we've defined these keywords, we can begin our learning.

The first question we are going to explore in today's lesson is what are the different types of waves? Waves play a really important role in shaping our coastline.

They erode, transport and deposit material along our coast.

The strength of the wave will depend on three main factors, the first being wind speed.

The stronger winds transfer more energy to ocean surfaces, and this generates larger, more powerful waves.

The second is when duration.

The longer the wind blows across the water, the more energy that can go into wave development and creating larger, more destructive waves.

Lastly, the fetch, the uninterrupted distance over which the wind blows across the water.

A longer fetch means a greater area for the wind energy to be transferred to the water.

A and B show winds from two different directions.

I would like you to pause the video here whilst you decide which is likely to generate the largest waves at the coast and explain why.

Press Play when you're ready to check your answer.

Excellent.

The answer is A.

Aisha has carefully noted that she thinks A would generate the most powerful waves because it has a much longer fetch.

Well done if you managed to explain that correctly.

True or false, the size and strength of the wave is related to wind speed only? Pause the video here whilst you decide, and press Play when you're ready to continue.

Excellent.

The answer is false.

I would now like you to explain why this statement is false.

Pause the video here and press Play when you're ready to continue.

Excellent, the reason why this statement is false is because the size and strength of a wave is related to wind speed.

Faster speeds will produce larger, more powerful waves, but wind speed is not the only factor.

Wind duration and the length of fetch are also important factors in deciding the size and strength of a wave.

Well done if you manage to explain that correctly.

Different waves have different characteristics.

This simply means different features.

There are two key characteristics that a wave has, swash and backwash.

A swash is the movement of water up the beach after a wave breaks carrying sediment and debris onto the shore.

Backwash, this is the flow of water returning down the beach after swash, pulling sediment back into the sea.

This can be called erosion.

On the video on the screen, you can see the swash is the movement of water up the beach after the wave breaks, and the backwash is the flow of water back into the sea due to gravity.

This process is repeated, bringing sediment up to the beach, through the swash and removing sediment from the beach through the backwash.

There are two types of waves that we find along the coast, destructive waves and constructive waves.

Destructive waves are high-energy waves that remove sediment from the beach, and they have specific characteristics.

They have a strong backwash and a weak swash.

This helps 'em to remove sediment because the backwash is much stronger, so it's pulling sediment off the beach or the coast, and the weak swash isn't able to bring all the heavy rocks, boulders back onto the beach, so this causes the coastlines to retreat.

The waves are really high.

They're usually over one metre, and they're very steep.

And they're very close together, 10 to 15 waves per minute, and this helps in eroding the coastline because these strong heavy waves that are breaking frequently are going to continuously put pressure on the beach or on the cliffs.

Constructive waves are low-energy waves, and they carry sediment onto the beach.

They also have specific characteristics.

They have a strong swash and a weak backwash.

This helps 'em to carry sediment onto the beach, and the backwash is so weak it's unable to bring that sediment back down so it helps to build beaches.

The waves are low, they're under one metre, and they're further apart.

They're between six to eight metres per minute.

I would like you now to define swash.

Is it A, the movement of water up the beach after a wave breaks carrying sediments and debris onto the shore? Is it B, the flow of water running down the beach due to gravity pulling sediments back into the sea? Or is it C, the flow of water up and down a beach pulling sediment along the beach in a zigzag pattern? Pause the video here whilst you decide which statement correctly defines swash, and press Play when you're ready to continue.

Excellent.

The statement that correctly defined swash is A.

It's the movement of water up the beach after wave breaks, carrying sediment and debris onto the shore.

Well done.

True or false, destructive waves build up beaches? Pause the video here whilst you decide if this statement is either true or false, and press Play when you're ready to continue.

Excellent.

This statement is false.

I would now like you to explain why this statement is false.

Pause the video here and press Play when you're ready to check your answer.

Excellent, the reason why this statement is false is because destructive waves cause erosion because they have a strong backwash which removes material and a weak swash.

Constructive waves, on the other hand, build up the beach as they have a strong swash which deposits material and a weak backwash.

Well done if you managed to explain that correctly.

I would now like you to compare the different characteristics of wave types.

You're going to be focusing on constructive waves and destructive waves, and you're going to have to identify the characteristics that each have for wave height, wave frequency, swash strength, backwash strength, and net impact on beaches.

Pause the video here whilst you attempt this task, and press Play when you're ready to check your answers.

Excellent.

Well done for attempting this task.

Let's now check our answers.

Your answers should include the following points.

For constructive waves, wave height should be low, under one metre.

The wave frequency is six to eight waves per minute.

It has a very strong swash, but a very weak backwash.

And their impact on beaches is that they build beaches by depositing sediment.

Destructive waves, their wave height is over one metre.

Their wave frequency is much higher with 10 to 15 waves breaking per minute.

Their swash strength is weak, but their backwash strength is very strong.

And their impact on beaches is that they remove beach sediment through erosion.

Well done if you manage to complete this task correctly.

The second question we are going to explore in today's lesson is how is sediment eroded at the coast? Waves do not just shape coastlines by creating beaches.

They also cause erosion which gradually wears away the land.

Waves erode the coastline through hydraulic power, attrition and abrasion.

Hydraulic power is the coastal erosion process in which waves compress air in cracks and joints and rocks.

This eventually puts pressure on the rock, and it will cause the rocks to fracture.

Like you can see on the image on the screen, the waves are smashing against the cliff face forcing air into the cracks, and this is putting pressure on the rock and eventually rocks will start to fracture away from the cliff face.

Attrition, this is the process where rocks and sediment collide and break into smaller, smoother pieces.

An easy way to remember this is attack is spelled A-T-T-A-C-K, and it has A-T-T at the start.

Attrition also has A-T-T at the start.

And with attack, rocks are being attacked the same way in attrition the rocks are attacking each other to make them much smaller pieces.

Abrasion, this occurs when sediment carried by waves scrapes against cliff faces wearing away the rock surface.

An easy way to remember this is abrasive means something that's rough.

So imagine your sponge in your kitchen sink, there's one side that is very rough, and you'll use that to rub against the plates that are really, really dirty to get the dirt off.

The same principle is happening here.

The rough rocks are robbing against the cliff face and wearing it away.

I would now like to test your knowledge.

Which statement best describes the difference between abrasion and attrition in coastal erosion? Is it A, abrasion is rocks colliding and breaking into smaller, smoother pieces while attrition is sediment in waves scraping against cliff faces? Is it B, abrasion, is the grinding of rocks against a cliff face while attrition is where waves compress air and rock cracks and rocks? Or is it C, abrasion is sediment in waves scraping against cliff faces while attrition in rocks colliding and breaking into smaller, smoother pieces? Pause the video here whilst you attempt this task, and press Play when you're ready to continue.

Excellent.

The answer is C.

The statement that best describes the difference between abrasion and attrition in coastal erosion is C.

Abrasion is sediment in waves scraping against cliff faces, while attrition is rocks colliding and breaking into smaller, smoother pieces.

Well done if you manage to identify that correctly.

True or false, hydraulic power is when water expands inside cracks and joints in the cliff face causing the rocks to break up over time? Pause the video here, and press Play when you're ready to check your answer.

Excellent.

This statement is false.

I would now like you to explain why this statement is false.

Fantastic, the reason why the statement is false is because hydraulic power is the coastal erosion process in which waves compress air and cracks and joints and rocks.

This puts pressure on the rock and eventually causes the rock to fracture.

Well done if you managed to explain that correctly.

I would now like you to complete the definitions of these coastal erosion processes.

Remember, we're focusing on hydraulic power, abrasion and attrition.

Pause the video here whilst you complete this task, and press Play when you're ready to continue.

Fantastic.

Let's now check our answers.

Your answers should look like this: hydraulic power, the definition of this is waves compress air and cracks and joints and rocks.

This puts pressure on the rock and eventually causes the rock to fracture.

Abrasion, this is sediment carried by waves, which scrape against cliff faces wearing away the rock surface.

Attrition, this is rocks and sediment collide and break into smaller, smoother pieces.

Well done.

We're now going to explore our final question in this lesson, which is how is sediment transported at the coast? Coastal transportation refers to the movement of sediment, whether it's sand, pebbles, or rocks along the coast through the action of waves.

Longshore drift is an example of how sediment is transported at the coast.

Longshore drift moves sediment along in a zigzag pattern, and it's caused by waves approaching the beach at an angle.

Waves approach the shore at an angle due to the wind direction.

The sediment is pushed up the beach with the swash at an angle, and then the sediment is then again pulled down the beach with the backwash.

This process is repeated again and again and again, and this forms that zigzag pattern that we were talking about.

This moves material along the coast over time.

Eventually, longshore drift will cause a beach to get narrower at one end and wider at the other.

In the photo on the screen, you can see groynes have been constructed.

They were created to reduce the movement of sediment along the beach due to longshore drift.

The groynes help to prevent the peach from narrowing at the updraft end.

The updraft end is the direction from which the sediment is being transported from.

I would now like to test your knowledge.

Which of these arrows is showing the backwash? Pause the video here, and press Play when you're ready to continue.

Excellent, the answer is C.

C is showing the backwash.

Remember, backwash is when the sediment is being pulled back down into the sea.

Well done.

True or false, longshore drift does not change the coastline? Pause the video here whilst you decide if this statement is either true or false, and press Play to continue.

Excellent.

This statement is false.

I would now like you to explain why this statement is false.

Pause the video here, and press Play when you're ready to continue.

Fantastic, the reason why this statement is false is long short drift is the movement of sand and pebbles along the coastline.

It's caused by waves hitting the shore at an angle.

This process moves sediment beach material in a zigzag pattern along the beach.

And as we know, longshore drift can cause one end of the beach to become wider and the other to become narrower.

Well done on this task.

I would now like you to explain how the process of longshore drift transport sediment at the coast.

You may use the image on the screen to help you.

Pause the video here and Press play to continue.

Fantastic.

Let's now check our answers.

Your answer might look a little bit like this.

"When waves approach a beach at an angle due to the wind direction, then their swash will carry sediment up the beach at the same angle.

The backwash then moves sediment straight down the beach due to gravity.

Then the swash of the next wave picks it up and moves it up the beach at an angle again, while it's backwash carries it straight down the beach.

Again, this zigzag movement along a beach is how long short drift transport sediment at the coast." Well done if you manage to include any of the following points in your answer.

We've now come to the end of our lesson, and you've done brilliantly in learning about wave processes at the coast.

Let's summarise everything that we've learned about in today's lesson.

We know that the greater the fetch and the stronger the wind speed, the larger the wave is going to be.

Constructive waves, which are gentle waves, help to build upon beaches, or destructive waves, which are stronger waves cause erosion.

Erosion processes include hydraulic power, which is water forcing air into cracks in rocks; abrasion, which is rocks grinding against the coastline; and attrition, these are rocks colliding and breaking into smaller pieces.

We also know that longshore drift helps remove sediment along the coastline.

It's driven by waves approaching the beach at an angle which causes sediment to move in as the exact pattern.

We know that longshore drift causes one side of the beach to become wider whilst the other becomes narrower.

Well done in your learning today.

I look forward to learning again with you very soon.