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, "The Influence of sediment transportation and deposition on coastal landscapes".

We're going to explore the different types of sediment transportation and how deposition features like beaches, spits, bars, and tombolos are formed.

Grab the resources you need for today's lesson and let's begin our learning.

By the end of today's lesson, you'll be able to explain the role of sediment transportation and deposition play in forming coastal deposition landforms. Before we can begin our learning, we need to be able to define the keywords that we'll be using throughout today's lesson.

Keywords that we'll be using throughout today's lesson are water column, prevailing wind and deposition.

Water column refers to the vertical section of water from the surface to the seabed.

Prevailing wind.

This is the most frequent wind direction a location receives.

Deposition.

This is the sea dropping sediment or material being carried by water at the coastline.

Fantastic.

Now we've defined these keywords, we can begin with our learning.

The first question that we're going to be exploring in today's lesson is how influential are transportation processes.

Coastal transportation simply refers to the movement of sediment, whether it's sand, pebbles, or rocks along the coastline by waves.

There are four main processes when we talk about transportation at the coast.

This is traction, saltation, suspension, and solution.

Longshore drift is also a really important transportation process in moving material along the coast.

Traction refers to the rolling or dragging of large heavy particles like pebbles and boulders along the seabed.

Imagine a bulldozer slowly pushing rocks along.

This is similar to how traction moves large particles.

Saltation.

This involves the bouncing of medium sized particles like sand and small pebbles along the seabed.

When the wave in the current hit the particles, they're going to be temporarily lifted into the water column, moving them in short jumps like you can see on the image.

Think of it a bit of like salt bouncing off of food.

Saltation is similar.

Particles bounce along the seabed.

Suspension.

This occurs when fine light particles like silt or clay are carried in the water column.

The particles will remain suspended and are transported by water over really long distances.

Suspension is like dust floating in the air.

Similarly, these light particles remain in the water as they travel over time.

Solution.

This is the transportation of dissolved materials like salts and minerals in the water.

The minerals are dissolved in the water and they're carried in the solution.

We can't see it, but they do contribute to coastal erosion and transportation.

Think of it a bit like sugar dissolving in tea.

The minerals are there, but they're invisible and they'll be carried by the water.

Fantastic.

Let's test our knowledge.

Let's define traction.

Is it a, the rolling or dragging of large, heavy particles like pebbles and boulders along the seabed? B, when fine light particles such as silts and clay are carried by the water column? C, the bouncing of medium-sized particles, sand and small pebbles along the seabed? Or d, the transportation of dissolved materials like salts and minerals in the water? Pause the video here whilst you decide and press play when you're ready to continue.

Fantastic.

The correct definition is a.

The rolling or dragging of large, heavy particles like pebbles and boulders along the seabed.

True or false? Saltation is a movement of dissolved materials in the water.

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

Excellent.

The statement is false.

Are you able to explain why? Pause the video here and press play when you're ready to continue.

Excellent.

The reason why this statement is false is because saltation is the bouncing of medium-sized particles, sand, and small pebbles along the seabed, whereas a solution is the movement of dissolving materials in the water.

Well done.

Longshore drift is the process of sediment moving along the coast in a exact pattern and it's caused by waves approaching the beach at an angle.

Longshore drift is really important in shaping our coastlines because it helps to create features like spits and bars.

The way longshore drift works is constructive waves will approach the shore at an angle due to the prevailing wind.

Remember, the prevailing wind is the most common wind direction a location receives.

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

This process is repeated over time and eventually the material will move along the coastline.

Longshore drift does cause beaches to get narrow at one end and wider at the other.

A way in which we stop this from happening is by building groins, like you can see in the image on the screen.

Groynes are constructed to reduce the movement of sediment along the beach due to longshore drift.

It helps to prevent the beach from narrowing at the updrift end.

This is the direction from which the sediment is being transported from.

Let's test our knowledge.

Which of these arrows is showing the prevailing wind? Remember, the prevailing wind is the most common wind direction a location receives.

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

Fantastic.

The arrow that shows the prevailing wind is D.

Well done.

I would now like you to explain one way in which sediment is transported at the coast.

Before we begin this, let's listen to some feedback that we've got from some of the students.

Izzy says, "This is one of those questions where you must name the process and then explain exactly how it transports sediment along the coastline." Sam has correctly identified that solution, suspension, saltation and traction are the four main ways in which sediment is transported.

Sam is also correctly identified that longshore drift is also a transportation process moving sediment along the coast.

Pause the video here whilst you tackle this question and press play when you're ready to continue.

Excellent.

Do any of your answers match the ones that we'll be reading on the screen now? Traction refers to the rolling or dragging of large heavy particles.

For the example, pebbles and boulders along the seabed.

Saltation involves the bouncing of medium-sized particles.

For example, sand and small pebbles along the seabed.

Suspension occurs when fine, light particles such as silt and clay are carried in the water column Solution refers to the transportation of dissolved material.

For example, salts and minerals in the water.

Longshore drift involves a swash of constructive waves carrying sediment up the beach at an angle due to the direction of the prevailing wind.

The backwash then moves the sediment straight back down the beach, creating a zigzag movement along the beach.

Well done if you managed to answer this question correctly.

The next question that we're going to be tackling in this lesson is how influential are depositional processes? Transportation processes and sediment deposition work together to create a number of different coastal landforms including beaches.

Remember calmer waves, constructive waves, deposit material which build up beaches over time.

They also build spits, bars and tombolos.

The first coastal deposition landform that we'll be looking at today are spits.

Spits are formed through long shore drift.

Constructive waves at the coast are going to approach it at an angle due to the prevailing wind and they'll be carrying sediment along the shoreline.

If the coastline suddenly changes direction or a river mouth is reached, the longshore drift continues to transport sediment out into the sea where it is being deposited.

As the sediment builds up, it extends out from the coastline into the sea.

The longshore drift then carries more sediment along it, and over time a narrow stretch of sand or shingle develops and that is known as a spit As you can see in the image.

If the wind direction changes over time, the spit will develop a curved end.

Think of it a bit like a finger of sand pointing out to the sea.

The spit will then create a sheltered area from the sea and this will allow mud and silt to settle.

Over time, this is going to build up and salt tolerant plants are going to grow, eventually a salt marshal form in the calm protected waters.

Let's test our knowledge.

True or false? Spits form whenever longshore drift transport sediment along the beach.

Pause here whilst you think and press play when you're ready to continue.

Fantastic.

The statement is false.

Are you able to explain why? Pause the video here and press play when you're ready to continue.

Excellent work.

The reason why this statement is false is because spits do form when longshore drift transport sediment along a beach, but there needs to be a sharp change in direction of the coastline in order for the longshore drift to continue to deposit sediment out to the sea to form a spit.

Well done if you managed to explain why that statement was false.

I would now like you to rearrange the statements to show how a spit would form by numbering them one to five.

Number one must be the first stage.

Pause the video here and press play when you're ready to check your answers.

Excellent work.

Let's check our answers.

Number one should be longshore drift moves sediment along the coast.

Number two should be sediment is deposited where the coastline changes direction.

Number three, a spit extends further out into the sea as more sediment is deposited.

Number four, sediment builds up in the sheltered area behind the spit leading to the formation of salt marsh.

Number five, a hook forms if there is a long term change in wind direction.

Well done if you managed to correctly identify the stages of how a spit is formed.

We're now going to be looking at how bars and lagoons are formed.

Bars form when longshore drift moves sediment across the bay.

The sediment deposited will connect two headlands creating the lagoon behind it.

An easy way to remember it is like this.

Think of a bar closing off access to people.

In the same way bars close off bays trapping water behind it leading to the lagoon forming.

Let's test our knowledge.

True or false? Bars form when a spit extends from the mainland but does not connect the two headlands leaving the bay open.

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

Excellent.

The answer is false.

Are you able to explain why the statement is false? Pause the video here and press play when you're ready to continue.

Excellent.

The reason why the statement is false is bars form when longshore drift moves sediment across bay through longshore drift.

The sediment deposited will eventually connect two headlands trapping a lagoon behind it.

Well done.

What coastal feature is created when a bar is formed? Is it a, a lagoon? B, a cove? Or c, a bay? Pause the video here whilst you decide and press play when you're ready to continue.

Excellent.

The coastal feature that is created when a bar is formed is a, a lagoon.

We're now gonna be looking at tombolos.

Tombolos are formed when waves lose their energy and when there is an island that is close to the coast.

When the waves lose their energy, they deposit sediment in the sheltered area between the island and the coast.

The longshore drift will move sand along the coast and as the waves lose their energy, the sediment will be deposited in the sheltered area between the island and the coast.

Eventually, the buildup of settlement will create a land bridge forming a tombolo.

Let's test our knowledge on tombolos.

Which statement do you think correctly describes how a tombolo is formed? Is it a, a tombolo forms when waves erode the coastline creating a land bridge to an island? B, a tombolo is formed when longshore drift deposits sediment to connecting two islands? Or c, a tombolo forms when a spit grows across water to link the mainland to an island? Pause the video here whilst you decide and press play when you're ready to continue.

Excellent.

The statement that correctly describes how tombolo is formed is c.

A tombolo forms when a spit grows across water to link the mainland to an island.

Well done.

I would now like you to add the missing labels to this diagram.

Pause the video here whilst you attempt this task and press play when you're ready to continue.

Excellent work.

Hopefully you manage to label them all.

A is the direction of longshore drift.

B is a tombolo.

Remember, this is when an island is connected to the mainland.

C, a bar.

This is when sediment is transported to connect one headland to another.

A lagoon is formed behind the bar.

Salt marsh, and a spit.

Well done on this task.

I would now like you to explain the formation of a spit.

When you're tackling this question, Aisha has made a really important comment that you need to consider when you're answering this.

This question is asking for a step-by-step process of how the landform is formed.

And Jun has said that he's going to make sure he uses geographical terms in his answer, like prevailing wind.

Remember, prevailing wind means the most common wind direction a location receives.

Pause the video here whilst you attempt this task and press play when you're ready to continue.

Excellent work.

Your answer could include some of the following points about how a spit is formed.

A spit forms through the process of longshore drift.

Waves approach the coast as an angle due to the prevailing wind and move sediment along the shoreline.

When the coastline changes direction, longshore drift does not follow the new direction, but it continues to move sediment out into the sea where it is deposited.

Over time, the spit extends further out into the sea as more sediment accumulates.

If a long-term change in wind direction occurs, the spits may developed a hooked end.

This answer is fantastic because it includes geographical terms like prevailing wind and longshore drift and has given a clear step-by-step process in how a spit is formed.

Fantastic.

We've now come to the end of our lesson and you've done brilliantly in learning about the influence of sediment transportation and deposition on coastal landscapes.

Before we finish this lesson, let's summarise everything that we've learned today.

Coastal transportation is simply the movement of sediment along a coastline through waves.

The coastal transportation processes that we know of are saltation, suspension, traction and solution.

Saltation bounces small particles along the seabed.

Suspension keeps fine sediment afloat in the water, traction rolls larger rocks or pebbles along the seabed and solution carries dissolved minerals that we can't see in the water.

Longshore drift is also a transportational process and it moves sediment in a zigzag pattern along coastlines due to the prevailing wind, the most common wind direction.

It reshapes the shoreline by transporting sediment up the beach.

We use groynes to stop longshore drift from starving one section of the beach and making another wider.

Transportation and deposition processes all work together to create distinctive coastal landforms. Landforms that we learned about today are beaches, spits, bars, and tombolos.

You've done excellently in today's lesson.

Well done.

I look forward to learning with you again very soon.