Secondary Geography KS4

The lesson we are deconstructing is a KS4 lesson looking at hard engineering in coastal areas.

Coastal hard engineering

Geography

We've looked at the stunning Dorset coastline and it's landforms today. Now it is time to show how me how much you've learnt. Good luck!

Dorset is located...

Which is the depositional landform on the Dorset Coast?

Old Harry Rocks is an example of a...

Which is the name of Dorset's famous arch?

Headlands and bays form on which type of coastline?

Dorset Coast quiz.

﻿Hello geographers and welcome to today's lesson about coasts. We're going to be looking at how we can stop erosion and flooding on our coastlines using hard engineering. I was walking along the sea wall in Weymouth today. Lots of people enjoying the beautiful weather, lots of children riding their bikes, but it really made me think, how many of them actually understood why the wall was there, rather than just making for a lovely walk in a sunny afternoon. So for today's lesson, all you need is a pen and paper. In a second, I'm going to ask you to pause, get them and clear away all those distractions. Alternatively, you might choose to find somewhere else to make it easier for you to listen to listen today. Pause now and I'll see you back in a second. Excellent. So now you're ready, I'd like you to jot down the title so we're looking today at Coastal hard engineering. Underline it for me. So you've got two photos on the screen and I'd like you to take 10 seconds see if you can come up with two ideas why it's important for us to manage our coastline against coastal erosion and flooding. Five more seconds, what can you come up with? The photo on the left shows South Devon Railway sea breach. So you can see a wall along that image where there's a digger, but behind there, used to be a railway line. And in the February 2014 storms, the waves breached that wall and affected the railway line running. In the second photo at Happisburgh, you can see we've got some houses very close to the cliffs where they've been retreating so rapidly. We use our coasts for living, we use it for our jobs, and we use it for infrastructure and getting around. So if coastal erosion is happening rapidly, it's going to have large social and economic impacts. So therefore, in particular areas it's important we manage our coastline. We can manage our coastline in three different ways. And today, we're only going to have a look at hard engineering. We can also do this through soft engineering, and through managed retreat. So there's going to be a video on each of those if you want to pop back and have a look at those. But today, we're going to focus on hard engineering. Hard engineering is where we use artificial structures to defend land against natural erosion processes and flooding. So I'd like you to pause the video and get that written down because that's really important we know a definition. Hard engineering is kind of man-made. Our first hard engineering strategy is a sea wall. A sea wall is a concrete wall which acts as a barrier which reflects the wave's energy back to sea. They are very effective at preventing erosion and flooding. Often, they have a promenade on the top for tourists. And you can see how wide the wall is. This is for locals and tourists to be able to walk along the coast and enjoy the views. Some people think that they can look very ugly. And they are very expensive. They're one of our most expensive strategies. However, even though they can cost between £5 and £10,000 per metre, they can last up to 75 years. The sea wall in the photo has got a curved side. They've curved the sides more recently on sea walls to try and break down some of the energy of the waves. Previously because sea walls reflect the wave's energy back to sea, there was still a very powerful backwash. And that powerful backwash tended to erode the base and the foundations of the sea wall, which was called scouring. This means that sea walls need maintenance about every 10 years. Our next strategy is Rock armour. Rock armour is where large boulders... and they're always made of hard rocks, and sometimes Basalt, sometimes Granite, are dumped at the base of a cliff or on a beach to absorb the wave energy. As the waves hit the rock armour first, water trickles through the gap. And that means that the backwash is reduced, which can lead to a buildup of sand in front of them. They are effective at stopping erosion. They're relatively cheap compared to others and easier to maintain. However, they are expensive to transport in because you're needing to use hard rock they need to come from different areas. Alongside that, people worry about the environmental impacts of quarrying these rocks and having to transport them from other areas. Some people feel that it looks ugly, especially because they're often not of the same rock as the rest of the coastline. They cost between £5 to £10,000 per metre. Gabions next. These are wire cages filled with rocks that can be built up to provide a buffer against the sea. They're very flexible as they can be built on top of each other like bricks, or they could be assembled in a long line. These are very cheap and they're flexible to place. They will eventually become vegetated so vegetation, grasses, flowers eventually grew through them, and that makes them look more pleasant. They will only last five to 10 years before rusting. So the salt water causes corrosion, which again can make them look more ugly. The cost for Gabions is up to £50,000 per hundred metres, so a relatively cheap option. Finally, our fourth hard engineering strategy is groynes. Groynes are wooden barriers built out into the sea to stop longshore drift. This means that beaches grow as a result. Because they stop longshore drift they make the beach wider, which is good for tourism. So in this photo here, you can see that the beach is wider where this groyne has prevented the sand moving any further. And it's the same here, narrow to wider where the groyne has stopped it. Narrow to wider. Wide beaches are great for tourism and they're relatively cheap. But there are problems with groynes in that they starve the beaches further along. So because they trap all the sediment areas down the coast don't receive as much sand and we're going to look at that in more depth in a second. Their life expectancy is about 25 years. Their cost is around £150,000 each and they tend to be about every 200 metres along the coast. Sea defences are often not used in isolation. You can see in this image that there's a sea wall with rock armour in front. In summary, hard engineering is very effective at stopping erosion, but it can be very expensive. The sea will always tend to win in the end so they're often not long-term solutions. Your turn. Right. Those steel cages of rocks, what are they called? Five seconds you written it down? Gabions, so steel cages of rocks are Gabions. The hard engineering strategy that prevents longshore drift is? Five more seconds here to jot it down, groynes. So groynes are the one hard engineering strategy which prevent longshore drift rather than stopping erosion directly. Let's get stuck in, I want you to pause the video, you're going to match the hard engineering strategy to its explanation. You've got a definition for groynes, sea walls, gabions, and rock armour. And if you would like that extra challenge, I'd love for you to write down one advantage, and one disadvantage of each of those strategies. Pause the video now and I'll see you when you're done. Right, let's check these answers so give them a big tick for me if you have got a sea wall is a concrete wall which aims to prevent erosion. Could you highlight the word reflects for me? So sea walls reflect the energy back. Groynes are wooden barriers built out to the sea to stop longshore drift. Again, can you highlight longshore drift for me? I think that's the important bit to remember. Rock armour are large boulders dumped at the base of a cliff to absorb wave energy. So can you highlight the word absorb for me. And finally, we have gabions which are the wire cages which can be built up to provide a buffer against the sea. So they also absorb wave energy. Well done everyone. Think about where you want to highlight the key terms so it's easier for you when you go back and look through your notes. Referring to the diagram, how effective are groynes? We've had a quick summary of each of the engineering strategies. But let's see if we can use this diagram to give us any more information. So I'd like you now to take 10 seconds, how effective are groynes? In this diagram, it shows that they've put rock armour in here. It shows that they have put two rock groynes there. And the reason why they chose to put them there is because we have this village very close by. However, you can see that there's a wide beach before this groyne and a wide beach before this groyne. But after this final groyne you can see the beach is much narrower, it's disappeared. So this area of the coastline experiences increased rates of erosion. Let's just recap to make sure that it's clear in our head. So longshore drift transports material through swash and backwash in a zigzag motion along our coasts. When we put groynes in, groynes trap the sediment. That sediment builds up. So the other side of the groyne here, this sediment is transported along, but no longer is this sand coming in to replenish it. So this bit of the beach is going to get much wider, and this bit of the beach gets even narrower. Task time. Let's look at groynes in more depth. Can you now explain how groynes protect the coastline from erosion? I've given you four sentences that I would like you to write out now in the correct order to answer that question. Pause the video and I will see you when you're done. Let's have a look at how you got one. We answered, explain how groynes protect the coastline from erosion. Groynes are wooden barriers build at the sea. A tick telling me what it is. These prevent longshore drift. This makes the beach wider, which absorbs wave energy and so prevents coastal erosion. Hopefully you've got those right if you didn't just pause and take a couple of seconds to make sure you've got those down in the correct order now. Well done. Here's a photo of a groyne. And I want us to think about the fact that we know that groynes trap the sediment. So what does this look like in real life? If we look at one side of the groyne, we can see that on the right hand side the beach is longer. On the left hand side of the groyne, the beach is narrower. If we look at the sand pilled up as well on that right hand side, this sand does look higher. And if you look at this photo, we can see that the sand has come all the way up to nearly the top plank on that groyne. And that was actually a depth of 32 centimetres when I measured it. On the other side where the beach is narrower, there is a much larger drop, and this is a photo of the same groyne and here we've got nearly four planks worth of drop from the top to the bottom. So that tells us that that sand has been disappearing. This arrow here shows then that the sand is piling up against the right hand side of the groyne making the beach taller and wider. On the left hand side, the sand is disappearing, it's being transported by longshore drift, making the beach narrower and a lot lower. Let's have a look at some data now to see if we can use it to analyse how that groyne is working. I would like you to answer these three questions. So pause the video, take your time, have a look at the data and see if you can work out which way longshore drift is going. And think about how could a geographer make this data more reliable and more accurate? Tell me now, which way do you think it's going? To the east or to the west? Hopefully, you've said to the east side. So the sand is moving from the west side to the east side. If we have a think about that, it is moving from the west because there is only a small drop only 30 centimetres. So that means the sand has piled up here. The east side where there's a large drop, it means that the sand is being washed away by longshore drift, leaving the large drop. To make our data more reliable, that means repeatable, we could repeat that on maybe 10 groynes rather than just five. We might also want to measure the groyne in two or three places and take an average, rather than just choosing one location. To increase the accuracy, rather than just recording 30 centimetres, we should be really accurate down to the nearest millimetre. So the drop is 30.4 centimetres. We could use a very posh digital tape measure as well so we knew we were super accurate. Right, what can groynes change? I need you to drop down two of these. Groynes can change? Five seconds. They can change the beaches width and they can change the beaches height. We're now going to tackle a big task. And in a second, we're going to be answering, explain the advantages and the disadvantages of hard engineering strategies at the coast. This question is going to be worth six marks. What would make an answer successful is that you discuss two types of engineering, because it says hard engineering strategies, with an s. If it's six marks, we need to be developing our points. So we're looking for connectives like this means that and therefore, we need one paragraph about the advantages, and one paragraph about the disadvantages. So let's have a look at our model to help us now. Hard engineering strategies such as groynes have many advantages. In this first sentence, I've named a strategy so groynes and I've told everyone that this paragraph is going to be about advantages. For example, they prevent longshore drift. This means that the beach becomes wider which absorbs wave energy and so prevents coastal erosion. It is your turn now. I think you're going to be fabulous. To make it easy, I think you should try and do sea wall advantages. And then for paragraph two, I think an easy one to explain that we've looked in depth in this lesson is how groynes have disadvantages. So can you pause the video now, it should take you between six and eight minutes and I look forward to seeing how you've done. Let's have a look at these excellent answers. You're going to do sea wall advantages so here we go. Hard engineering strategies such as sea walls have many advantages. For example, sea walls reflect wave energy back to sea, tick. This means, coastal erosion is lessened, tick, resulting in the valuable land use behind being protected, tick. However, hard engineering can also have disadvantages. As groynes trap sediment effectively, tick it means that the coast beyond the groynes is starved of sediment, tick. Consequently, the beach slowly disappears and coastal erosion increases, tick. Pause the video if you need to jot anything down, have a read through your answers, check you've got those connectives there. Well, that brings us to the end of today's lesson. It wasn't actually that hard at all, was it? We've absorbed some excellent knowledge on hard engineering strategies. We've looked at how some absorb the wave energy, whereas groynes actually work by restricting longshore drift. Before you disappear though, I need you to click to the next page. Make sure you defend your learning and spend a few minutes completing that quiz so you can remember it. I look forward to seeing how you've got. Thanks so much for your time today. Take care. And I look forward to you joining me to have a look at what alternatives we have to hard engineering through soft engineering methods. Have a great day everyone.

This lesson we looked at the hard engineering strategies used to protect our coastline. Now it is time for you to show me how much you have learnt. Good luck!

Hard engineering...

The hard engineering strategy which stops longshore drift is...

Cages of rocks are...

Why do some people disagree with hard engineering?

Which is the disadvantage of sea walls?

Coastal hard engineering quiz.

In the lesson, we will look at the coastal hard engineering used on our coastlines.

ITT: Coastal hard engineering

Secondary Geography KS4

1. Original Oak Lesson