CHANGING COASTLINE (COASTS)

Key areas of study for this question:

  • Coastal processes and waves
  • Landforms created by coastal erosion
  • Longshore Drift
  • Landforms created by coastal deposition
  • Holderness Case Study
  • How do landforms and processes affect the lives of people living along the coast?
  • Coastal management

COASTAL PROCESSES AND WAVES

The sea is constantly changing the shape of the land. On stormy days, large waves crash against the shore and wear away the coastline by erosion. The sea transports the material it has eroded and deposits it in places where the water is calm. This ability of the sea to erode, transport and deposit large amounts of materials produces a variety of coastal landforms.

  • Hydraulic Action - Pressure of water being thrown against the cliffs by the wave. It also includes the compression of air in the cracks in the rock face – more pressure causes the rocks to break off.
  • Corrasion - Sand and pebbles carried by the waves are thrown against the cliff at force.
  • Corrosion (Solution) - Chemical reaction between certain rock types and the salt and other acids in the seawater.
  • Attrition - Wearing away of rocks that are in the sea. As the boulders in the sea continually roll around, they chip away at each other until smooth pebbles or sand are formed.

 

WAVES

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The size of a wave depends on its fetch. The fetch is the distance a wave travels. The greater the fetch, the larger the wave. Wind also has a significant effect on the size of waves. The stronger the wind the larger the wave. As a wave approaches a beach it slows. This is the result of friction between the water and the beach. This causes a wave to break.

 

Waves are classified into two groups: destructive or constructive.Destructive waves are more powerful and cause erosion, whereas constructive waves are less violent and encourage deposition.

CONSTRUCTIVE WAVES

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  • They are created in calm weather and are less powerful than destructive waves.
  • They break on the shore and deposit material, building up beaches.
  • They have a swash that is stronger than the backwash.
  • They have a long wavelength, and are low in height.

 

DESTRUCTIVE WAVES

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  • Destructive waves are created in storm conditions.
  • They are created from big, strong waves when the wind is powerful and has been blowing for a long time.
  • They occur when wave energy is high and the wave has travelled over a long fetch.
  • They tend to erode the coast.
  • They have a stronger backwash than swash.
  • They have a short wave length and are high and steep.

 

LANDFORMS CREATED BY COASTAL EROSION

You should be able to explain how these landforms are created as well as be able to draw and annotate a diagram.

HEADLANDS AND BAYS

Headlands are formed when the sea attacks a section of coast with alternating bands of hard and soft rock. The bands of soft rock, such as sand and clay, erode more quickly than those of more resistant rock, such as chalk. This leaves a section of land jutting out into the sea called a headland. The areas where the soft rock has eroded away, next to the headland, are called bays.
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CLIFFS AND WAVE CUT PLATFORMS

One of the most common features of a coastline is a cliff. Cliffs are shaped through a combination of erosion and weathering - the breakdown of rocks caused by weather conditions. Soft rock, eg sand and clay, erodes easily to create gently sloping cliffs. Hard rock, eg chalk, is more resistant and erodes slowly to create steep cliffs.

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  1. Weather weakens the top of the cliff.
  2. The sea attacks the base of the cliff forming a wave-cut notch.
  3. The notch increases in size causing the cliff to collapse.
  4. The backwash carries the rubble towards the sea forming a wave-cut platform.
  5. The process repeats and the cliff continues to retreat.

 

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CAVES, ARCHES, STACKS AND STUMPS.

These are formed in rocks that have a fault or line of weakness. The action of the sea will exploit the fault, through erosional processes such as hydraulic action. In time the fault will widen to form a cave. If the fault is in a headland, caves are likely to form on both sides. When the backs of the caves meet, an arch is formed. The sea will continue to erode the bottom of the arch. Weathering will also take place on the bare rock faces. As the sea undercuts the bottom of the arch, a wave-cut notch will form. It will collapse in time, as it is pulled down by the pressure of its own weight and gravity. This leaves behind a column of rock not attached to the cliff, known as a stack. Continued erosion and weathering will lead to the formation of a stump that is visible only at low tide.

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http://www.bbc.co.uk/learningzone/clips/old-harry-rocks-coastal-processes-and-landforms/3245.html

 

LONGSHORE DRIFT

Waves rarely approach a beach at right-angles. They usually approach at an angle that depends upon the direction of the wind. The water that rushes up a beach after a wave breaks is called the swash. The swash picks up sand and shingle and carries it up the beach. When the water returns down the beach it is called backwash. Due to gravity, the backwash and any material it is carrying tends to move straight down the beach. The result is that material is transported along the beach in a zig-zag movement. This is called longshore drift.

Longshore drift is usually in one direction only - that of the prevailing (main) wind. For example, the prevailing wind in Britain is from the south-west. This causes material to be moved from west to east along the south coast of England.

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LANDFORMS CREATED BY COASTAL DEPOSITION

 
The other type of wave which operates in coastal areas is a constructive wave. As it’s name suggests, this wave builds rather than destroys the coastal environment. It deposits sand and pebbles that form beaches.
Constructive waves form a number of landforms in coastal areas:
  • Beaches
  • Spits
  • Bars
  • Tombolo

 

BEACHES

A beach is an area of land between the low tide and storm tide marks and is made up of sand, pebbles and, in some places, mud and silt. They are formed by constructive waves, often in bays where the waves have less energy due to the gently sloping land and, as a result, deposit material. They can also be found along straight stretches of coastline where longshore drift occurs. Seaside resorts often build groynes to keep beaches in place and to reduce the effects of longshore drift.(See coastal management for more information on groynes)

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SPITS

A spit is a long, narrow stretch of pebbles and sand which is attached to the land at one end, with the other end tapering into the sea. It forms when longshore drift occurs on a coastline. When the coastline ends, the sea deposits the material it is transporting because the change in depth affects its ability to transport the material further. If there is a river estuary, then the meeting of the waves and the river causes a change in speed which results in both the waves and the river dropping their sediment. In time, the material builds up to form a ridge of shingle and sand known as a spit. On the land side, silt and alluvium are deposited and salt marshes form. The wind and sea currents may curve the end of the spit around. Spits are very dynamic, which means that their shape and form continually change. If spits are present on a coastline, it should be possible to determine the direction of longshore drift.
 
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http://www.bbc.co.uk/learningzone/clips/the-formation-of-spits/3246.html

 

BARS

If a spit develops in a bay, it may build across it, linking two headlands to form a bar. This is only possible if there is a gently sloping beach and no river entering the sea. In this way, bars can straighten coastlines. An example is Slapton Ley in Devon which also has the characteristic lagoon formed behind the bar where any run-off water is trapped and slowly seeps through the bar to the sea.

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HOLDERNESS CASE STUDY

The Holderness coast is in the north east of England. This is one of the most vulnerable coastlines in the world and it retreats at a rate of one to two metres every year.

The problem is caused by:

  • Strong prevailing winds creating longshore drift that moves material south along the coastline.
  • The cliffs are made of a soft boulder clay. It will therefore erode quickly, especially when saturated.

The village of Mappleton, perched on a cliff top on the Holderness coast, has approximately 50 properties. Due to the erosion of the cliffs, the village is under threat.

In 1991, the decision was taken to protect Mappleton. A coastal management scheme costing £2 million was introduced involving two types of hard engineering - placing rock armour along the base of the cliff and building two rock groynes.

  • Mappleton and the cliffs are no longer at great risk from erosion.
  • The rock groynes have stopped beach material being moved south from Mappleton along the coast. However, this has increased erosion south of Mappleton. Benefits in one area might have a negative effect on another.

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The increased threat of sea level rise due to climate change, means that other places will need to consider the sustainability of coastal defence strategies for the future.

 

HAPPISBURGH CASE STUDY

 
One village under threat from this policy is the village of Happisburgh which has a population of approximately 850. It is one of the fastest eroding areas in the world. The area was defended in 1958 with revetments which reduced the amount of erosion to about 50 cm a year. In 1995 the council stopped repairing the coastal defences which caused the rate of erosion to accelerate. Since this time, 25 properties and the village’s lifeboat  launching station have been washed away.
 
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HOW DO LANDFORMS AND PROCESSES AFFECT THE LIVES OF PEOPLE LIVING ALONG THE COAST?

Over 17 million people live within 10km (7 miles) of the UK coast and 40% of the country's manufacturing industry is on or near the coast. Coastal processes and their resultant landforms will therefore impact on large numbers of people and there are many different groups who have an interest in what happens in coastal areas including:

  • Residents
  • Environmental groups
  • Industrialists
  • Local councils
  • National governments
  • Tourist boards
  • National Park authorities.

Issues in coastal areas include:

  • Erosion threatens some coastal settlements
  • New tourist attractions proposed
  • Existing tourist resorts are in decline
  • People want to build new housing in the attractive coastal environments
  • Danger of flooding if sea levels rise
  • Problems with sewage and/or pollution

Each interest group may have a different view about what should be done to protect and manage the coastline.

COASTAL MANAGEMENT

 
COASTAL FLOODING - In England 2.1 million properties are at risk from flooding. Nearly 50% of these properties are at risk from flooding from the sea. There are a number of ways that the effects of flooding can be reduced.  Householders can be warned about a flood so that they can take precautions. This is done in the UK through a chain of events.
The Met Office predicts the likelihood of a coastal flood and gives information to the public through weather forecasts and news broadcasts on the television. 
On the Environment Agency website there will be information on the likelihood of a flood. This will be identified by a system of warning codes: flood watch, flood warning, severe flood warning and all clear.
 
Flood Warning Codes from the Environmental Agency:
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FLOODING AND DEFRA - DEFRA (The Department for Environment, Food and Rurall Affairs) has the responsibility for deciding which areas of the coastline are going to be defended against the risk of flooding. The Environment Agency then organises for the defences to be built and maintained. DEFRA provides the money for most of the work that is completed.
 
 
DEFENDING THE COASTLINE
 
Coastal defences can be classified as either HARD or SOFT engineering techniques.

HARD ENGINEERING: Hard engineering is a method of coastal management which involves major construction work, for example, seawalls.

SOFT ENGINEERING: Soft engineering is a method of coastal management which works, or attempts to work, with the natural processes at work on the coastline and to be unobtrusive visually. It does not tend to involve major construction work, for example, beach nourishment/replenishment.

 
HARD ENGINEERING (ADVANTAGES AND DISADVANTAGES)
 
  • Sea Wall - Placed at the base of a cliff to reflect the waves energy. They are very expensive at approximately £10,000 per km, but extremely effective at protecting areas from flooding. Environmentally ugly.
  • Gabions - Cages of wire filled with rocks to absorb the waves energy, they are effective and cheap but environmentally ugly.
  • Groynes - Can be made of wood or rock and are long vertical structures placed at right angles to the beach to trap sediment. This builds up the beach and protects the cliffs from erosion. They are effective at building up the beach therefore protecting cliffs from wave attack. Can result in areas further down the coast being starved of beach material resulting in more erosion! Only last 25-30 years.
  • Rip Rap (Rock armour) - Large rocks placed at the bottom of the cliff to absorb the wave energy, they are effective at dipersing the waves energy and cheap. Environmentally ugly and may put off tourists.

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SOFT ENGINEERING (ADVANTAGES AND DISADVANTAGES)

Soft Engineering is a less environmentally noticeable way of managing the coastline. 

  • Beach Nourishment - Large amounts of sand are added to beaches to build them up and help absorb wave energy. This protects tourism as well as the coast and is easy to carry out and fairly cheap. But it does not last very long as sand will continue to be transported along the coast by longshore drift.
  • Managed Retreat - This allows the natural erosional processses of the sea to occur, areas of low value land are allowed to flood hopefully protecting more important areas further down the coast.
  • Cliff Stabilisation - Cliffs are covered in matting and vegetation planted to help make them more stable and resistant to erosion.
  • Do nothing - Obviously the cheapest and most environmentally friendly option! However, you have to weigh up the COSTS (to people, tourism and buildings) against the BENEFITS (advantages of letting the area return to its natural processes). If the costs greatly outweigh the benefits e.g. by having to rehome many people or losing valuable tourist facilities then other options will have to be looked at.

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lesson-11-coastal-management-in-walton-on-the-naze.doc lesson-11-coastal-management-in-walton-on-the-naze.doc

 

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