Unit 1: The Coastal Zone

Check list

ü  Do you know the processes of erosion, transportation and deposition?

ü  Do you understand the processes of mass movement and sub-aerial processes?

ü  Can you draw a diagram and explain the formation of wave cut-notch and platform?

ü  Can you draw a diagram and explain the formation of bays and headlands?

ü  Can you draw a diagram and explain the formation of caves, arches, stacks and stumps?

ü  Can you explain the formation of a spit and salt marshes?

ü  Can you describe the special habitat associated with salt marsh?

ü  Using a case study can you explain how salt marshes can be managed in a sustainable way?

ü  Can you use case studies to explain the economic, social and environmental impact of cliff collapse?

ü  Can you describe the different  advantages and disadvantages of hard and soft engineering at the coast using case study examples?

Shaping our coasts

Coasts are shaped by the processes of erosion, transportation and deposition.

Waves are the main reason for coastal change. Waves are created as wind blows over the water causing friction; this causes the water to start to move in a circular orbit. The amount of energy is dependent on the wind speed, the length of time the wind has been blowing and the distance of open water it has been blown over (fetch).

There are two types of waves: -

Constructive waves: - these waves have a long wave length and are therefore flat and low (1 m high). These waves have a smaller backwash and a larger swash. They create gently sloping beaches with a berm.

Source: Geography-student

Destructive waves- Destructive waves are higher and have a smaller wave length. Destructive waves have much more energy and remove material from the beach with a strong backwash creating steep beach.

Source: Geography-student

Watch: BBC Class Clips

Erosion is the break down and removal of rock. Destructive waves erode our coast in a number of ways: -

• Hydraulic Action: - waves force air into the cracks and weaknesses in rocks, this acts like mini explosions forcing the rocks apart. 
• Abrasion: - waves pick up rocks and sand and rub them against the cliff face (like sandpaper)
• Attrition: - rocks that are carried by the waves hit into each other breaking chunks off
• Solution: - the chemical properties of the sea water make it more acidic, this dissolves some types of rock e.g. chalk

Coasts can also be subject to sub-aerial processes which are land based processes which also shape our coasts. This is a combination of weathering and mass movement. 

Weathering is the wearing away and breakdown of rock due to atmospheric processes and biota (plants and animals).

Examples of weathering: -

Mass movement is the movement of sediment down slope en mass.

Examples of mass movement: - 

Source: Geogify.net

Together these process produce the erosional landforms found along our coast.

Erosional Landforms

Wave cut-notch and wave cut-platforms
 

1. The waves erode the base of the cliff through the processes of hydraulic action, abrasion and solution. This forms a notch between the high and low tide mark.
2. The cliff face is weakened by weathering such as freeze thaw action. 
3. The notch continues to get bigger until it can no longer support the material above and it collapses. 
4. The cliff retreats inland leaving behind a wave cut-platform which can be seen at low tide. 

Headlands and bay formation

 

1. Headlands and bays are formed where there are alternative bands of more resistant (hard) rock and less resistant (soft) rock.
2. The waves erode the cliff face through the processes of hydraulic action, abrasion and solution. The less resistant rock is eroded at a quicker rate than the more resistant rock. This forms headlands, harder pieces of land which stick out into the sea and bays, curved inlets.
3. The shape of the coastline refracts the waves forming sheltered bays with sandy beaches. The destructive waves attack the headlands.
4. Eventually the coastline will become straight and the processes will start again. 

Dependent on the arrangement of rocks depends on the type of coastlines we get. If the layers of hard and soft rock are at right angles to the coastline you will get a discordant coastline. If the same type of rock is along the stretch of coast with a less resistant rock behind we get a concordant coast.

Caves, arches, stacks and stumps

Erosion and weathering can produce the erosional landforms of caves, arches, stacks and stumps.

The waves through the processes of hydraulic action, abrasion and solution erode cracks and weaknesses in the cliff face making them bigger, this forms caves. The processes continue until the erosion breaks through the headland, this feature is known as an arch. Over time the arch will get bigger and will not be able to support itself and due to gravity will collapse forming a stump. Over time the stack will be subject to erosion forming a stump.

Old Harry Rocks in Dorset stands at the tip of a chalk headland between the bays of Studland and Swanage and is an excellent example of a stack. He once had a wife who is now a stump. 

Link: Bitesize

Transportation

Once eroded material is moved along the coast by waves, this is known as transportation. There are 4 main processes by which material is transported by waves. 

These processes contribute sediment to larger overall processes called longshore drift (LSD). 

LSD is the zigzag movement of sediment along the beach. This process is reliant on the waves hitting the beach at an angle. These waves are driven be the prevailing winds. The swash carries sediment up a beach at an angle, and then due to gravity, the backwash pulls the sediment straight back down the beach. This process continues moving the sediment along the beach. Over time this can change the shape of the beach.

Watch: BBC Class Clips

Spit formation

Spits are a depositional feature formed through the processes of LSD. LSD carries the sediment along the beach until there is a change in the direction of the coast for example a river estuary. LSD carries the sediment in a straight line out into the sea. Deposition of the sediment will occur where the waves enter a sheltered or shallow area or where there is little wind. The sediment over time builds up and salt marshes can form in the sheltered area behind. The secondary wave direction can change the shape of the spit giving it a hook like appearance, these are known as laterals. The spit cannot form completely across an estuary as the river current is too strong. Our example is Spurn Point. 

If the spit grows across a bay it is known as a bar. A spit which connects an island to the mainland is known as a tombolo

Beaches

Beaches are common features of a coastline. Beaches are formed by constructive waves. The eroded material from the cliffs is deposited over time to form beaches. The shape on the beach is dependent on the type of material which it is made up of.

Sand dunes form were there are large quantities of sediment, a force to move it (winds and waves) and some kind of barrier (e.g. Marram grass, sea weed or a forest) 

Salt marshes

Salt marshes are an example of a specialised coastal habitat which forms in the inter-tidal zone. It is a marshy area that forms a transitional zone between land and salty (or brackish) water. They form in the sheltered area behind spits. The roots of the plants help to hold the deposited sediments together and over time the mud builds up. As the height of the salt marsh increases it spends less time out of the water.

 

The changing shape and height of the salt marsh forms bands of different types of vegetation, this is known as a vegetation succession. This is the evolution of plants from the pioneer species to the climax communities which are adapted to the changing conditions.

The mudflats are the lowest part f the salt marsh and are inundated with water on a regular basis.  Plants such as Cordgrass colonise the mudflats these are known as pioneer species. These plants must be adapted to be salt tolerant and cope with the tides. Cordgrass have a long and complex root network and are able to secrete the salt through special glands.  As the salt marshes get higher and more developed the fertility increases and the amount of salt decreases. This means more complex flowering plants can take over the pioneer species such as Sea Lavender and eventually trees and shrubs can grow such as ash and alder.

Example: Abbotts Hall Farm and Spurn Point 

Exam Questions

1. Describe how the sea erodes the coast. (3 marks)
2. Explain why deposition occurs at certain places along the coast. (3 marks)
3. Using diagrams describe the processes of long shore drift. (4 marks)
4. Describe the formation of a spit. (4 marks)
5. Describe the formation of a stack. (4 marks)
6. Describe the process of mass movement. (3 marks)
7. Describe the formation of wave cut-platforms. (4 marks)
8. Describe the formation of the landform in the photo. (4 marks) 

Flambourgh Head, Holderness Coast

Coastal management
 

There are different ways we can manage our coasts and protect property and businesses against the threats of coastal erosion. We can use hard engineering, such as sea walls or soft engineering, like beach nourishment. These techniques each have different advantages as disadvantages:

Soft	Advantages	Disadvantages
Beach Nourishment	-Creating a larger beach takes out the wave energy. -Looks natural so people can enjoy the beach -Relatively cheap	-Must constantly replace the sediment which is transported away which can be costly. -Using different sediments can alter the beach and erosion rates.
Planting Marram Grass	-Works with the natural system to hold sand dunes together to take wave energy out of the waves -cheap	- perhaps not as effective as hard engineering
Hard
Sea Wall	-Stops erosion at the base of the cliff -Can help prevent coastal flooding	-High cost to maintain -High cost to build -Can cause increased erosion of beach
Groynes	-Captures beach material to protect the cliff from erosion	-Can make access hard along the beach -stops sediment moving protecting other areas
Rock Armour	-disperses wave energy protecting the base of the cliff -relatively cheap to build and maintain	- doesn’t look very nice -can be expensive to transport boulders

In the past councils have attempted to protect one area by implementing hard or soft engineering techniques without thinking about the impacts elsewhere. Now engineers understand that when looking at coastal management we need to look at the coast as a whole, this is known as holistic management. The way councils attempt to do this is by creating Integrated Coastal Zone Management (ICZM), here they create a shoreline management plan for a whole sediment cell. There are different options: -

 

• Do nothing approach – let the sea erode the land
• Managed retreat – allow the land to erode however, they give compensation
• Hold the line – put in management strategies
• Advance the line – create new land, this is unusual as expensive

This type of management can cause conflict between residents, business owners and the council as to which parts of the coast to save.

Holderness Coast

Holderness is a lowland region of England that lies between the chalk hills of the Wolds and the North Sea. It is part of the East Riding of Yorkshire.

Holderness coast - Background

Ø  For centuries, erosion has been a problem along the coast of East Riding and Yorkshire (Holderness Coast).

Ø  It has the fastest eroding coastline in Europe (2m in an average year, up to 10m in a stormy year.)

Ø  It is eroding fast because: -

o   Geology (predominantly boulder clay)

o   The fetch – NE waves which is a relatively short fetch but combined with low weather systems causing, currents in an enclosed area producing powerful destructive waves and the sea floor is deep which means the waves are not weakened before the reach the shore.

o   Longshore drift – boulder clay produces particles which head out to sea easily and don’t accumulate at the bottom of the cliff. Small beaches are not effective at protecting the coast against wave energy. 

 

Ø  Cliff-erosion processes (sub-aerial processes, eg weathering of cliff face and erosion of the cliff foot) result in slumping. – Holbeck Hall

 

Holderness Coast- Management

Integrated coastal management – there is a move in recent year to manage the coast as a whole (holistic management), as actions in one area can have an impact elsewhere. This is because of sediment cells – these cells form the basis for shoreline management plans (SMP).

 

The Holderness coast is part of a sediment cell from Flamborough Head to The Wash. This whole cell is considered but it is broken into to sub cells. In SMP, all local interest groups are consulted and provide engineers with background information. The four options that can be considered are: -         

                  

·         Do nothing,

·         Hold the line

·         Advance the line

·         Retreat the line

 

An environmental impact assessment (EIA) and a cost-benefit analysis (CBA) are carried out to decide.

 

Terminal Groyne Syndrome: This is where the last groyne prevents long shore drift from bringing material to other areas along the coast, therefore moving the problem down the coat.

 

Impacts of erosion and cliff collapse on peoples lives: -

• Homes and properties are at risk from being lost to the sea such as Holbeck Hall Hotel 
• House prices have dropped e.g. a house near Aldbourough was valued at £300,000 but as the cliff  collapsed it was sold for £40,000
• People are unable to get mortgages or house insurance 
• Businesses are lost e.g. Ulrome 10 pitches a year at Sandy Beaches Caravan Park are lost. Valuable farmland is being lost e.g. the farmer at Aldbourough was losing an acre a year at the cost of £5000. 80,000m2 are lost along the Holderness Coast.
• Easington Gas terminal is at risk, this provides many jobs for the local area and 25% of Britain's gas supply (this is why there are now substantial coastal defenses)
• Loss of accesses to certain areas for example Spurn Point (now a movable road has been put in place).

 

Impacts of cliff collapse and erosion on the environment: -

• Threats to the salt marsh at Spurn Head due to increased erosion and lack of sediment (terminal groyne syndrome), this is an SSSI (Site of Special  Scientific Interest) and  is very important for in particular wading birds.

 

 

Sustainable management of the Holderness Coast - Watch the case study video

 

The erosion at the Holderness Coast is expected to get worse due to climate change.

BBC Class Clips 1953 floods

 

 

Climate change and changes in sea level

Sea level is continuously changing (tides), however, longer term changes have a significant implications coastal erosion and flooding.

There are two ways in which the sea can rise: -

Eustatic – an increase or decrease in the amount of water in ocean basins due to thermal expansions of the oceans and to a lesser extent the melting of the sea ice. Sea levels are have risen by about 15cm in the last 100years, and are expected to rise a further 30cm by 2100(IPCC range of predictions 11cm – 77cm). Global warming, resulting from an enhanced greenhouse effect, is currently responsible for sea-level change.

Isotactic – local tectonic movements of the Earth’s crust due to either plates moving or the retreat of an ice sheet which reduces the weight applied to the land and it “recoils” back.

 

Governments are increasingly worried that a repeat of the 1953 floods could again occur but with rising sea levels result in the flooding of the capital.

Thames Barrier

Watch BBC Class Clips Thames Barrier

Coastal flooding is a serious threat for the UK. Many British cities are situated on or near the coast, on low-lying land, together with 40% of the UK’s manufacturing industry. London is quiet vulnerable to flooding.

The city of London lies along the River Thames. The location and shape of this estuary means that storm surges sweeping down the North Sea are sometimes magnified by the time they get to the city. Indeed, London has been flooded, or nearly flooded, several times in the last two centuries, and after each event the level of the flood defenses has been raised. During the 1953 floods that killed 1,835 people in the Netherlands, London’s defenses were within a few cm of being overtopped, and the British Government responded with a major program of improvements in sea defense.  

Thames Barrier was completed in 1982 and is expected to protect London till 2013. The Thames cost over £500 million to construct and it must be maintained. It is important to protect London as the economic impacts of a storm surge could be phenomenal, not just in London but for the whole of the UK.

Ø  Banking and finance industry  located in London  creates 40% of the UK’s GNP

Ø  Insurance claims for damaged property would be huge

Ø  Transport – surface and underground rail

The Environment Agency (EA) and The Met Office supply flood warnings and GIS maps to show areas which are liable to flooding. The  EA is currently planning new flood defenses to deal with increased risk, they are also setting aside land where flooding will be permitted. 

Coastal Realignment Abbotts Hall Farm

Source: http://www.coastalwiki.org/wiki/Coastal_squeeze

Abbotts Hall Farm

 

The majority of sea defences in Essex were built to enclose saltings that were drained to provide improved grazing, rather than to protect existing dry land from flooding.

 

The erosion of saltmarsh and coastal squeeze (see diagram) are evident at many places on the Blackwater Estuary. At Abbotts Hall Farm there were 3.8km of sea walls along the north bank of the Salcott Channel with saltmarsh on the seaward side, which is subject to coastal squeeze.

 

When saltmarsh becomes eroded tidal and wave energies increase and the sea wall must be reinforced or rebuilt if it is to withstand the effects of the sea. This is hugely expensive and, where agricultural land is being protected, is of doubtful economic value to the taxpayer even without counting the environmental cost of coastal squeeze.

 

A managed retreat scheme was decided to be done here in 2002. They made 5 breaches in the current embankments which allowed the sea water to flood onto about 80 hectares of land (0.312 miles²- see above map). This made it into a salt marsh. Salt marshes are a natural coastal defence as they absorb water and take away the pressure of it.

This type of management is a hot topic at the moment particularly after the tidal surges which we have experienced this January. See BBC 

Exam questions

1.     Using case studies, describe the impacts of cliff collapse on people’s lives and the environment. (8 marks)

2.    Using a case study explain why a coastal habitat has distinct characteristics. (8 marks)

3.    Using a case study explain how coasts can be managed sustainably. (8 marks)

4.    Explain why areas such as the Holderness Coast use both hard and soft engineering. (8 marks)

5.    For a coastal environment that you have studied, describe the ways in which it is managed to ensure it is conserved, but used sustainably. (8 marks)

6.    Describe the impacts of continued coastal erosion. (4 marks) 

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