IGCSE- Coasts- Coastal Flooding and Hard Engineering

Match

Who's that landform?!

spit

salt marsh

raised beach

wave cut platform

ria

• spit

• salt marsh

• raised beach

• wave cut platform

• ria

​Lesson Objectives

​

• To identify and describe the main causes and impacts of coastal flooding.

• To explain how different types of hard engineering methods are designed to reduce the effects of coastal flooding.

• To assess the effectiveness of hard engineering strategies in preventing coastal flooding

Open Ended

What would cause the coast to flood?

​Causes of flooding

​Tsunamis – generated by earthquakes e.g. Indian Ocean 2004.

Storm surges - These are causes by abnormally low air pressure, which raises the height of the high-tide sea. Strong onshore winds then drive the ‘raised’ sea towards the coast. 

Global warming - high tide –  rising sea levels – Venice, Italy

​What the Textbook says

​Tsunamis

​Tsunamis are giant waves resulting from earthquakes, volcanic eruptions, meteor impacts, any sort of major displacement of water in the ocean. Tsunamis are incredibly dangerous since they travel quickly and are difficult to detect

​

Out at sea, close to the source of the tsunami, the amplitude of the wave is relatively low making it difficult to detect but it travels very quickly (over 800km/h). As it approaches the shore the wave slows down significantly but its amplitude increases exponentially without the wave breaking.

​

When the wave hits the coast it does so with an immense amount of energy and its amplitude continues to grow as it slows down even more. Tsunamis have so much energy that they can travel several miles inland.

Tsunamis flood vast expanses of land and cause immense amounts of damage due to the energy they impact the coast with and the fact that they collect debris as they inundate more areas.

Open Ended

Explain how a tsunami is formed

​Storm Surge

​

Storm surges are sudden rises in sea level caused by very strong winds, normally those found in hurricanes. The strong winds essentially push the water on an ocean’s surface on top of more water, increasing the sea level and flooding coastlines.
The conditions needed to create these strong winds are generally associated with low pressures, further increasing the sea level. The strong winds can create large and powerful waves that can overtop coastal defences so even if the rise in sea level doesn’t flood the coastline, the resulting waves likely will.

Open Ended

What damage is caused by storm surges?

Open Ended

https://timeforgeography.co.uk/videos-list/coasts/challenges-sea-level-rise-and-coastal-management/

1. In what two ways is the sea level increasing?

   By how much is the sea level rising each year?

   Why are the Somerset Levels vulnerable to sea level rise?

   What happens to the sea surface in low weather pressure systems?

   What does the IPCC stand for?

   By how much does the IPCC predict the sea level will rise by the year 2100?

​

1. In what two ways is the sea level increasing?

   • Ice at the poles and mountainous areas is melting and water in the oceans in expanding (thermal expansion)

2. By how much is the sea level rising each year?

   • 2 millimetres

3. Why are the Somerset Levels vulnerable to sea level rise?

   • Because the elevation of the land is either at or below the current high tide level.

4. What happens to the sea surface in low weather pressure systems?

   • It rises up

5. What does the IPCC stand for?

   • Inter-governmental panel on climate change

6. By how much does the IPCC predict the sea level will rise by the year 2100?

   • 50cm

Open Ended

What are the impacts of coastal flooding

Open Ended

What can governments do about coastal flooding?

Open Ended

1. Storm surges are one cause of coastal flooding. Name two other causes of coastal flooding.

2. Describe how coastal flooding can be predicted.

3. Explain how the risk of coastal flooding can be reduced by:

a) planning

b) education

​Lesson Objectives

​

• To identify and describe the main causes and impacts of coastal flooding.

• To explain how different types of hard engineering methods are designed to reduce the effects of coastal flooding.

• To assess the effectiveness of hard engineering strategies in preventing coastal flooding

​What we need to know

Open Ended

Why does the coast need protecting?

​The people or businesses located near the coast are in an area that is at risk of flooding or erosion. This means that governments have to protect the coastline, however, it is not possible to protect the whole coastline

​Why does the coast need protecting?

​

• All sea defences come at some cost

• Not all the land is worth saving – some of the coastline might have no people living there or businesses.

• Some areas are not at risk 

Multiple Choice

How long is the UK coastline? (including the islands)

• 40,500 kilometers
• 31,368 kilometers
• 15,200 kilometers
• 25,000 kilometers

​

In the UK the Department for Environment, Food and Rural Affairs (Defra) is responsible for the protection of the coastline. 

In order to make these decisions more manageable, coastlines are divided into areas called sediment cells. 

​

In England and Wales, there are 11 sediment cells. Each cell is divided into sub cells to create smaller units for planning. A shoreline plan is then developed for each sub cell.

It would be too expensive to protect the whole coastline and it would change the whole of the coastal environment so Defra  have to decide

• Which parts should be protected

• Which methods should be used to protect different areas.

​A shoreline management plan (SMP) recommends how each sub cell should be managed.

​

• Hold the line – maintain the existing coastline by building defences

• Advance the line – New defences are built further out to sea in an attempt to reduce the stress on current defences

• Managed retreat (coastal realignment) – allow the land to flood and construct a new line of defence inland.

• No intervention – allow natural processes to shape the land.

Match

Match the following

• maintain the existing coastline by building defences

• New defences are built further out to sea in an attempt to reduce the stress on current defences

• allow the land to flood and construct a new line of defence inland.

• allow natural processes to shape the land.

Hold the line

Advance the line

Managed retreat (coastal realignment)

No intervention

• Hold the line

• Advance the line

• Managed retreat (coastal realignment)

• No intervention

​There are two types of coastal engineering..

​Hard Engineering and Soft Engineering.

Open Ended

What do you know about hard engineering and soft engineering?

​Hard Engineering

​Involves building some type of defence, usually from rocks or concrete. It aims to protect the coast from erosion and the risk of flooding by working against the power of waves. E.g. groynes, revetments, sea walls, gabions and riprap

​Soft engineering

​Tries to work with natural processes. It makes use of the coastal system, such as beaches, sand dunes and salt marshes. E.g. beach replenishment, cliff regrading, ecosystem rehabilitation and revegetation and managed retreat)

​

All management techniques have disadvantages. It is up to the government to decide which one they are willing to invest (put money) into. This might anger locals as some of the methods are not aesthetically pleasing (nice to look at)

​Sea Wall

​

A concrete barrier between waves and the land. Recurved walls are more effective as they reduce the chances of water over topping the wall, but are more costly.

• Some locals might not like the way it looks

• Waves can bounce off the walls and remove lots of material from the beach

• Gives people a physical sense of security

• Protects the area behind the wall

• They can restrict peoples access to the beach

• If well maintained, they can last for many years (75), however is costly to maintain if needed

• Helps to prevent flooding

• Very expensive (£5000- £10,000 per metre)

• Powerful backwash can scour the base of the sea wall

​Groynes

​

• Wooden structures built perpendicular to sea, 50m apart, to trap sand being moved by longshore drift. This then builds up the beach on the up drift side of the groyne.

Open Ended

What might be some disadvantages of groynes?

​Helps to build up beaches in areas that are suffering from coastal erosion – tourism – bigger beach

• Groynes are barriers which impede walking along a beach. They are also dangerous, as they have deep water on one side and shallow on the other. This is a particular hazard to children who might climb on them. 

• £1000 per metre– relatively cheap

• May prevent sand being deposited further downstream and cause more erosion in other areas

• Don’t require much maintenance and can last 30 years

• Ineffective during a storm

• Rock groynes can offer recreational opportunities e.g. fishing

• Considered unattractive

​Rock Armour/ Rip Rap

​Large rocks piled or placed at the foot of dunes or cliffs with native stones of the beach. This is generally used in areas prone to erosion to absorb the wave energy and hold beach material.

​

• Limited lifespan as wave energy moves the rocks

• Some locals might not like the way it looks

• Relatively cheap £1000- £4000 a metre

• Reduces the destructive power of the waves

• Access to the beach may be difficult – injury

• Rocks need to be transported – added cost. Might not blend into the local geology. 

• Can be used for fishing. 

​Gabions

​

• Strong wired baskets filled with stones. They eventually will have grass and sand on them. They act as a small wall against the coast, absorbing the wave energy.

​

• Some locals might not like the way it looks

• £5,000 -£50,000 per 100 metre – relatively cheap and easy to construct

• Can not use them on rocky beaches as the pebbles erode the gabions.

• Creates ecosystems

• Reduces the destructive power of the waves

• In a damaged state, they are dangerous as people may fall over them

• May last 5-10 years – corroded - rust

• They blend in better than other hard engineering methods

​Revetments

​

Wooden or concrete structures that are built slanted to the waves.

• Reduces the power of the waves, reducing the rate of erosion

• Strong waves can damage the structures

• Don’t require much maintenance

• Some locals might not like the way it looks

• £1000 per m.

​Offshore Breakwater

​

• Offshore concrete walls that break incoming waves, meaning their erosive power is reduced when they reach the coast.

• £2000 per m. 

• Very effective as they cause the waves to break before reaching the beach

• Easily destroyed in a storm

• Some locals might not like the way it looks

• Disturbed ecosystems

Match

Match the following

Groynes

sea wall

revetments

gabions

rock armour

• Groynes

• sea wall

• revetments

• gabions

• rock armour

​Lesson Objectives

​

• To identify and describe the main causes and impacts of coastal flooding.

• To explain how different types of hard engineering methods are designed to reduce the effects of coastal flooding.

• To assess the effectiveness of hard engineering strategies in preventing coastal flooding

Homework