y11 geography 1 revision for year 11 for year 2012 2. coasts

1Y11 Geography

Revision for Year 11 for year 2012Revision for Year 11 for year 2012

2. Coasts

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The specification for this unitThe specification for this unit

• Physical processes give rise to characteristic coastal Physical processes give rise to characteristic coastal landforms.landforms.

• Processes: marine (wave characteristics and erosion; longshore drift; wave deposition); sub-aerial (weathering; mass movement).

• Land forms: erosional (headlands and bays; cliffs; wave-cut platforms; caves; arches and stacks); depositional (beaches; spits; bars).

• Role of geological structure, vegetation, people and sea-level change (estuaries and raised beaches).

• Distinctive ecosystems develop along particular Distinctive ecosystems develop along particular stretches of coastline.stretches of coastline.

• Coastal ecosystems and biodiversity (coral reefs and mangroves).

• Factors affecting the distribution of coastal ecosystems.

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The specification for this unitThe specification for this unit

• Management of both physical processes and human Management of both physical processes and human activities is needed to sustain coastal environments.activities is needed to sustain coastal environments.

• Coastal ecosystems are of value to people, but are threatened by tourism and other developments (industrialisation; agricultural practices; deforestation).

• Conflicts between different users of the coast and between development and conservation.

• Coasts as a natural system of interdependent places. Coastal retreat, flooding and natural processes. Coastal protection: soft and hard defences; management retreat. Different views on coastal protection.

• Case studies Case study of a located coral reef or a mangrove stand and its

management. Case study of a stretch of a coastline under pressure. Case study of one stretch of retreating coastline.

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Marine processesMarine processes

• What is the coast?• It is a narrow zone between the land and the sea

that is constantly changing due the effects of the land, sea and air acting upon it.

• You may recall the processes that create river landscape are Erosion Weathering Transportation Deposition Mass movement

• Well you will meet them again here but there are a few changes.

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Here they are at workHere they are at work• Including the usual

suspects there is Wave scouring - waves breaking at the base of the cliffs swirl around the base and result in the removal of loose rock

• Wave Pounding - breaking down of the cliff face due to the sheer force of the wave which can exert upwards of 30 tonnes / m2 when crashing on the cliffs.-

• These are both variations on hydraulic action

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How is energy transferred to How is energy transferred to create waves?create waves?

• 1. Wind creates friction on the waters surface;• 2. Frictional drag between the wind and the waters surface causes water

particles to rotate and energy is transferred forward; • 3. When the wave reaches shallow water, it slows down due to friction

between the base of the wave and the sea bed. The shape of the wave becomes increasingly elliptical;

• 4. The top of the wave continues to move forward as it is unaffected by the friction with the sea bed. It becomes steeper and steeper and eventually breaks;

• 5. Water moves up the beach as the swash;• 6. Water then returns back down the beach as the backwash.

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There are two main types of There are two main types of waves:waves:

• A constructive wave is• small in height• has a gentle angle: there is a shallow gradient between the waves

because there is a long gap between them and each wave is not very high

• has less energy• has a stronger swash than backwash (material is moved up the beach by

the strong swash).• So it is constructive because it is building the beach up – it is

constructing it

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There are two main types of There are two main types of waves:waves:

• A destructive waves is• large in height• has a steep angle: the is a steeper gradient between the waves because

there is a shorter gap between the waves and each wave is high• has lots of energy• has a weaker swash than backwash (beach is scoured and degraded as

the strong backwash pulls sand and shingle back down the beach)• So it is destructive because it is removing material from the beach – it is

destroying itCan you sort your constructive waves form your destructive ones?Try this: http://classtools.net/widgets/dustbin_0/uuQJ4.htm

http://classtools.net/widgets/dustbin_0/uuQJ4.htm

http://classtools.net/widgets/dustbin_0/uuQJ4.htm

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Diagrams you need to learn to drawDiagrams you need to learn to draw

• Make sure you include types of erosion, abrasion, hydraulic action …..in each of these formation diagrams

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Formation of a cove e.g. Lulworth, Dorset

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e.g. Flanborough Head

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A very useful diagram to explain long shore drift - a MUST MUST LEARNLEARN

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e.g. Spurn Head

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e.g. Chesil Beach

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This part maybe new? The role of This part maybe new? The role of sea level change in coastal features?sea level change in coastal features?

• An estuary• Is larger than a river

mouth, for example the river Thames, and resulted from a river that flowed out into the sea from a valley with low hills on either side. When the ice melted further north, the sea level rose causing an entry to the sea considerably wider than its former mouth.

This is a submergent submergent coastlinecoastline - together with the next 2 slides

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• A Ria• During the Ice Ages, the sea level

dropped as so much ice was piled up on the land, that there was less left in the sea, so the UK was joined to Europe and Alaska was joined to Russia.

• With the lower sea level, rivers that were still flowing eroded vertically making their flood plain at a lower level. When the ice melted and re-entered the sea the lower flood plains and the lower parts of the middle course were flooded, for example the River Tamar in Cornwall

• Where the valley was previously glaciated - scraped out by a glacier, leaving a flat bottomed U shaped valley, then fjordsfjords is left - see picture on page 41

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• Raised Beaches• Raised beaches are another way that show

that sea level has changed. A raised beach is an elevated area of sloping ground, sitting above the present tide line. In the past this area was at sea level.

• There are many examples of this feature throughout Britain, particularly along the West coast - this is because the area experienced the greatest weight of ice during the last Ice Age (about 20,000 years ago).

• During an Ice Age, the massive weight of ice bearing down on a landmass caused it to sink. Over time, as the earth's temperature rose and the weight of ice decreased, areas of land began to slowly rise back out of the sea. This ‘bounce back' motion - the localised change in sea level, relative to the land - is known as isostasy, or isostatic uplift.

• The picture of East Prawle in South Devon shows the old cliffs and the wave cut platform that was created at the time the land was lower than it is today.

This is a emergent coastlineemergent coastline

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The affects of geology on coastsThe affects of geology on coasts

• Summary:

• Hard rocks give high steep cliffs, with bare rock on the rock face and boulders and rocks at the base

• Softer rocks give gentler, less steep cliffs - the cliff face is smoother with evidence of slumping (slide 17 of rivers about weathering) with mostly sand and/or mud at the base.

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The affects of vegetation on coastsThe affects of vegetation on coasts

• Summary:• The longer the coast line has been

established, the more likely vegetation is to be there - so not on a cliff face that is forever changing, but yes on sand dunes and mangrove swamps.

• But be aware that only certain plants can withstand high salt content.

• The major impact of vegetation is that once established, it reduces erosion

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The affects of humans on coastsThe affects of humans on coasts

• Summary:

• 1. Settlements: coastal lowlands are very popular worldwide for settlement, especially protected bays and river mouth - they make good ports

• 2. Where economic development is possible along coasts, it will often happen - agriculture, industry, fishing, tourism and increasingly energy - wind turbines, wave and tidal power

• 3. Coastal management - man has sort to control the coastline over centuries - by reducing erosion with groynes, sea walls etc

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Beach ecosystems - coralBeach ecosystems - coral

• Are built up entirely of tiny living creatures, each of which have their shells - these shells form reefs.

• What do they need to survive?

• Sea temperatures that never go below 180C but are best 23-250C

• Light is needed for the corals to grow, so they are in sea less than 25 metres below the surface, but not be exposed to the air for too long if at all, as they dry out

• They can only survive in sea water.

• They need a lot of oxygen and so need strong wave action - lots of foamy white water.

• They clear clean water, so no sediment

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Why are corals under threat?Why are corals under threat?

• Primary impacts: Very pretty areas that attract tourists, reefs a great source of fish, farmers attracted by fertile coastal areas.

• Secondary impacts: development of ports, blasting by fishermen, pollution from farming, sewage all damage pristine conditions needed by coral, deforestation leads to silting of coastal fringe

• Tertiary impacts: coral declines, fish decline, tourists move on, local food supplies decline.

• One more addition to the pot of trouble - global warming leads to a rise in sea temperatures making it too warm for some coral and the sea is acidifying (more CO2 absorbed making carbonic acid) and this is damaging the delicate shells of the coral and another cause of reef bleaching and eventually death.

• 27% of coral reefs are highly threatened and another 31% under moderate threat.

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Case study of coral reef management Case study of coral reef management - St Lucia- St Lucia

• Where is St Lucia?• In the Caribbean just north of Venezuela• What is the problem?• 90km2 of coast was seriously threatened by human activity -

over fishing, tourism and coastal development, marine pollution and sedimentation form the land

• On the West coast around Soufriere, tourism and urban development resulted in conflicts of interest - between fishermen, divers and yachts all wanting to use the same areas

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Case study of coral reef management Case study of coral reef management - St Lucia- St Lucia

• The solution:• The Soufriere Marine

Management Area (SMMA) came up with a neat solution. They divided the coast up into 5 different zones - see the map.

• This way, everyone can make a living, while making sure that enough of the coral is protected, and they are working hard to make sure their ideas are sustainable through a variety of on-going research projects.

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Beach ecosystems - mangrovesBeach ecosystems - mangroves

• Most common in SE Asia - most found within 30 degrees latitude of the equator.

• They have 1 foot on the land and one in the sea.

• The shore needs to be soft and muddy enough for them to take root. The shoreline needs to be undisturbed for them to do well.

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Why are mangroves a good thing?Why are mangroves a good thing?

• They are a fish nursery, they trap silt and help create new land, but possibly most importantly in times of rising sea level, they protect coastal areas in times of storm surges that accompany tropical storms, e.g. cyclones.

• However they have been seen as disease-ridden and are therefore being cleared in many areas - what for? Nearly ½ are turned into fish farming areas, another ¼ for providing fuel and timber for construction.

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Case study of mangrove management: - Case study of mangrove management: - Bangladeshi SunderbansBangladeshi Sunderbans

• Bangladesh are one of the few countries to recognize the importance of mangroves as they are so susceptible to storm surges from cyclones and in particular due to the majority of their land being less than 10 metres above sea level. They also suffer from a grave shortage of land and high population density

• As part of its Coastal Zone Policy, as mangroves trap silt and stabilise shores, they have been planting mangroves in the delta sediments and have gained an extra 120 000 hectares of land as a result. This has been helped by the Sunderbans gaining World Heritage Status in 1998, which allows funds to flow in to help protect the area.

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Conflict between development and conservationConflict between development and conservation

• Each of the threats to the mangrove and the corals result from conflicts between human needs and conservation. In other words should these ecosystems be protected or should people be encouraged to make the fullest use of their resources and exploit the opportunities available? But conflicts between developers and conservationists are not the only issues. There are conflicts between different users or stakeholders, householders want good housing and a clean environment; business want space for offices, factories; farmers want the best land kept for them; fisherman want harbours and unpolluted sea; tourists want hotels, beaches and amusements.

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Case study of a stretch of a coastline Case study of a stretch of a coastline under pressure.under pressure.

• To manage the various pressures on the coastal zone, the concept of ‘integrated coastal zone management (ICZM)’ has been developed. ICZM has the following characteristics: It is a long-term approach involving the sustainable and

equitable use of resources (natural, cultural, economic) It seeks to bring together all the various organisations who

have responsibility for managing the coastal zone It recognises not only the need to protect the coast but

also the importance of recreation and commerce to coastal settlements

It provides a framework for managing and reconciling the various groups that have an interest in how the coastal zone is managed

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All the sites underlined in red will be saved but not the places in between

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THE HOLDERNESS COASTLINETHE HOLDERNESS COASTLINE a coastline under pressure.a coastline under pressure.

• Why does it erode so rapidly?• It erodes rapidly because the cliffs are made up of soft clay (called

‘boulder clay’) and sand. The clays and sands are unconsolidated which means they have not been compressed and hardened. The cliffs are not able to resist the force of the waves hitting them and frequently collapse. The sea then removes the debris and starts to attack the cliffs again. In this way, the cliffs recede (i.e. move inland) at a rate of around 2 metres a year.

• Geographer’s estimate that about 7,645,000 m³ of material has been lost from the Holdeness coast in 100 years. As the cliffs recede, villages close to the sea are under threat and historical records show that 29 villages have been taken by the sea since Roman times. 'Each year approximately 1 million m³ is eroded from the Holderness coastline and moved southwards. Only 3% of this reaches Spurn Head. The rest is either deposited in deep offshore areas (known as 'sinks') or is carried across or into the Humber estuary

• Around Flamborough Head, the cliffs are made up of chalk which is much more resistant. These cliffs have not receded as far as the clay cliffs which is why Flamborough Head forms a headland. (more detail on management of receding coastline)

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• Competing Interest Groups: • Different interest groups may have very different views as to the most

appropriate form of coastal defence. For example:• The Local Tourism Industry: Tourism is immensely important to this area.

It is important that the beaches are preserved but the less harsh on the eye the coastal defence measures are, the more appealing the beaches are likely to be to tourists.

• Farmers: Some areas of the coastline are only used for farming and spending money on defending them against the sea may not be economically viable. Farmers are unhappy, however, to see their land disappearing into the sea as they are not compensated for their losses.

• Local Authorities: They ultimately have to pay for coastal defence. They may not be able to afford the most effective and appropriate form of defence. However, it is in their interests that the area should be prosperous and one of the main forms of income is tourism, so this above some other issues, needs protecting.

• Environmental Pressure Groups/Organisations (e.g English Nature): In the case of Spurn Head, coastal defence measures such as groynes may have a strong negative impact on this bird sanctuary.

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• Conclusion - Integrated Coastal Zone Management• Local authorities such as in the case of Holderness, East Riding of

Yorkshire Council, have many other issues than coastal defence to consider. These include the promotion of tourism, fisheries and farming.

• In the case of tourism, they will want to promote tourism as it is so important to the local economy but also to maintain the environmental quality of the coastline.

• The litter that tourists bring not only has a negative visual impact, but may kill sea birds and dolphins, and smother rare coastal plants. Coastal areas such as Holderness that have clean beaches and water are given Tidy Britain Group Awards (distinctive yellow and blue Seaside Award flags, which are awarded for clean and safe beaches by the Tidy Britain Group) and Blue Flag awards. These are important as they demonstrate to both visitors and tourists that the area is clean and safe but they can be removed if the beaches and water are not kept clean.

• Integrated Coastal Zone Management looks at all of these inter-related issues and attempts to come up with a management plan that takes all of them into account.

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• The plan:Chalk cliffs (Flamborough Head to Sewerby)• The intent of management for this area is to allow natural processes to

continue.• Holderness cliffs (Sewerby to Kilnsea coast)• The intent of management for this area is to allow natural processes to

continue along the frontage whilst sustaining Bridlington, Hornsea and Withernsea as viable towns and seaside resorts. The draft policies intend to sustain the viability of the village of Mappleton and a strategic north-south transport link. The draft policies intend to sustain the Dimlington and Easington gas terminals while there is a strategic need for the site. The continued functionality of Tunstall Drain and Barmston Drain may be maintained.

• Spurn Head• The intent of management for this area is to allow the Spurn barrier to

evolve largely naturally with as limited intervention as is required to maintain the integrity of the Spurn barrier. The intention is to maintain access to the key facilities and assets at Spurn Point whilst causing minimal interruption to the natural environment, coastal processes and the functioning of Spurn Head and the Humber Estuary.

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THE HOLDERNESS COASTLINETHE HOLDERNESS COASTLINE Case Case study of one stretch of retreating coastlinestudy of one stretch of retreating coastline

• As we saw on slide 33 the Holderness Coast is retreating very rapidly. This is partly down to the geology but there are other issues involved too.

• (a) The weather: In winter there are frequent storms which produce stronger waves and higher sea levels. The rain also saturates the clay cliffs and they either slump or flow.

• (b) The waves attack the coastline. The dominant wind and thus wave direction is north-east. These waves have, therefore, a long fetch which causes very destructive waves.

• The approach of the dominant waves from the north-east causes longshore drift to move the material southwards. At the end of this stretch of coast where it meets the Humber, is a spit called Spurn Head. Each year it is estimated that 500,000 tonnes of material a year is moved towards the spit.

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Managing a retreating coastManaging a retreating coast• There are various strategies for defending the coastline. These can be divided

into ‘hard engineering’ strategies (sea walls, groynes etc) and ‘soft-engineering’ strategies (beach replenishment, sand dunes etc).

• HARD-ENGINEERING RESPONSES (some really useful diagrams of what these look like on page 59)

• SEA WALLS: • These are massive concrete structures which may either be straight or curved (a

'bull-nose sea wall’)• Advantages: They provide strong protection to the land immediately behind the

wall.• Disadvantages: Waves in storm conditions may break over them. They are

expensive to build and maintain.• GROYNES • These are wooden or rock structures (in which case they are called boulder

groynes) which run along the beach at right angles to the sea. They catch sediment that is being carried along the beach by longshore drift and prevent the removal of beach sediment downstream.

• Advantages: They maintain the beach and may therefore prevent coastal erosion of the land behind the beach.

• Disadvantages: They may catch so much longshore sediment that beaches downstream are deprived of sediment. They are unattractive to look at and so may put tourists off visiting a beach

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Managing a retreating coastManaging a retreating coast

• RIP-RAP (or ROCK ARMOUR)• This consists of boulders placed in front of a cliff or building to protect it.• Advantages: It is less expensive to build and maintain than sea walls. It is less

unsightly than sea walls.• Disadvantages: It is a less formidable barrier than sea walls. • SOFT ENGINEERING RESPONSES• SAND DUNES• Sand dunes can be an effective form of defence against storm waves. They are a

very popular destination for tourists and the dunes are easily eroded by people walking and riding bikes on them. It is important, therefore, that they are 'stabilised'. This means that there are schemes to plant grasses such as Marram Grass, which prevent the sand from being blown away and that areas are fenced off to protect them.

• BEACH REPLENISHMENT.• This is carried on numerous beaches, the beaches at Weymouth and Lyme Regis

being but two examples. It has the benefit that it may look natural, especially if the sediment is local but, on the other hand, replenished beaches require constant maintenance and so this may be an expensive solution.

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Managing a retreating coastManaging a retreating coast

• MANAGED RETREAT• The final response is to do nothing. The costs of resisting the

sea are sometimes questionable, especially if the defenses are only protecting farmland as is the case with long stretches of the Holderness coastline. This is, however, a controversial response and is, understandably often resisted by farmers.

• Conclusion: Possible coastal defence measures cannot be looked merely on the basis of whether they are suitable for the place in question. The bigger picture must be considered. Not only may defences such as groynes have knock-on effects on places downstream but coastal defence is just one of a number of issues such as tourism, waste disposal, economic development and pollution that local authorities have to take account of.

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• Various strategies have been adopted along the coastline to stop or slow down erosion.

• Hornsea is dependent on tourism and recreation and has a small fishing industry. Groynes have been used to protect the beach and behind that there is a sea wall. The authorities have also used rock armour (which is also called ‘rip rap’) to protect the esplanade behind it. The strong coastal defences have successfully reduced coastal erosion but have increased it to the south of the town.

• Mappleton consists of only about 50 properties but suffers from a rate of erosion of 2m a year. It needs to be defended, despite being a small hamlet, because the B1242 is a vital road (and is only 50m from the cliff at one point) and it would more expensive to re-route it than it is to protect the stretch of coast between it and the sea.

• In 1991 two rock groynes and a rock revetment were constructed (at a cost of £2 million), and as a consequence a substantial beach has accumulated. The groynes have, however, affected the movement of material down the coastline.

• The scheme has been moderately successful as the houses and the road seem to be safe. The cliffs are however showing signs of slumping.

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• Skipsea• At Skipsea, the authorities have placed cages filled with pebbles called ‘gabions’

along the sea wall to absorb some of the wave energy.• Easington• Easington Gas Terminal is owned by British Gas and together with nearby

Dimlington Gas Terminal provides 25% of Britain’s gas. The rate of erosion is 1 .8m a year.

• The defence of Easington presented huge problems as it is so close to Spurn Head which is a habitat for many species of bird and other fauna. The concern was that if they had built groynes this would have prevented sediment reaching the spit (Spurn Head) and would have increased its rate of erosion which in turn would have threatened the bird habitats. Therefore, they built a rock revetment (at a cost of £4.5 million) which protects the gas terminal but not the village.

• Spurn Head• Despite the presence of some old groynes, the spit is no longer defended; it has

been abandoned. The neck of the spit is so narrow that winter storms were washing over it and the spit was proving both impossible and very expensive to defend. It will be a loss if the spit is breached. Thousands of people visit it every year to appreciate its beauty and sense of isolation but also to bird-watch as it is an excellent place for ornithologists to observe migrating birds in Spring and Autumn.

y11 geography 1 revision for year 11 for year 2012 2. coasts

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