Coasts

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Key vocabulary

Coastal area: interface between the land and the sea where marine and terrestrial processes combine to produce a variety of chaning landforms

Coastal ecology: ecosystem and habitat present at the coast

Coastal structure: How the rock beds lie in relation to the land

Coastal Zone: 2 zones- offshore (37km) and inshore (60km)

Geology: Rocks and soils of earth

Relief: Height and slope of the land

Sub-aerial: Work to break down material above HWM

Topography: Shape of the coast

Fetch: The distance of water winds blow. The longer the fetch the more powerful waves

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Eustatic and Isostatic

Eustatic: the global change in sea level.

Result in submergent features:

-Rias e.g. Australia - drowned steep sided river valley 

-Fjords e.g. in Norway - drowed V.steep sided U shaped glacial valleys 

-Estuaries e.g. Exe estuary - low level river valleys flooded

Isostatic: the change in height of the land relative to the sea

Result in emergent features:

-Raised beach 

-Bars/spits e.g. Slapton Sands and Dawlish Warren

-Ancient shore platforms e.g. Hallsands

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Destructive and constructive waves

Destructive waves - Erosional processes 

High frequency- 13-15 per minute

Plunging motion which means more swash and less backwash

Results in a net loss of material

Constructive waves - depostitional processes 

Low and flat

Wavelengths up to 100m

13-15 waves per minute

More powerful swash, less backwash

Forms beach ridges and berms

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Marine erosion.

Processes of marine erosion:

Attrition: Process of erosion where the collisions between parts of the load lead to communition

Abrasion: Degradation of the land through the scouring actions on rock by material carried by the sea

Corrosion: A chemical reaction between alkali rock and acidic sea

Hydraulic action: Water entering cracks in the rocks compress air and as the water retreats the air expands explosively enlarging cracks

Wave pounding: Physical weight of the water breaks away rock; 1 cubic metre of water weights 1 tonne

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Mass movement

Movement of material under the influence of gravity, caused by the presence of water

Rock fall: rocks become loose due to freeze-thaw action and fall due to gravity. Hard rock such as sandstone and chalk particularly susceptible such as Pennington Point at Sidmouth

Landslide: Rock pieces are lubricated by water and slide down the slope when the downward force is greater than the resistance eg: Lyme Bay

Mud flow: When fine cliff material becomes saturated and heavy in storms so weight causes it to flow down the slope eg: clay at Charmouth

Rotational slip: Weaker rocks become saturated and slump along the slip plane especially if the cliff has been undercut eg: clay at Budleigh Salterton

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Weathering

Weathering: The breakdown of rocks in situ

Physical - Freeze-thaw: Water enters cracks in the rock and as it freezes it expands by 9% enlarging the crack and Unloading: When pressure has been removed by the overlying weight being removed and this change in pressure causes rock layers to expand and they crack

Chemical -Hydration: Minerals in the rock absorb water and expand. This exerts an internal stress on the rock until it cracks and Carbonation: insoluble calcium carbonate reacts with carbonic acid in the rain forming soluble calcium bicarbonate

Biological - Plant roots grow into cracks and expand them

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resultant landforms of erosion

Headlands and bays: areas of alternating soft and more resistant rock. This causes differential erosion. The headland causes wave refraction which concentrates the erosion around the headland rather than bays

Wave cut notch: Wave energy is at its greatest at the foot of the cliff. Marine erosion undercuts the cliff

Wave cut platform: Continual undercutting by marine erosion increases stress and tension so cliff collapses and retreats. The platform widens as cliff retreats meaning the waves break further out so reduces wave energy on the cliff

Cliff profiles: soft rock- gentle slope hard rock- steep slope

Lines of weakness in the rock are exploited - These lines are weakness are expanded by processes of marine erosion and weathering, causing the rock to be worn away. Eventually this forms a cave- Parsons cave (a recess within a cliff face created formed as a result of material being gradually removed by erosional processes)

If part of the cave roof collapses due to a combination of weathering and marine erosion a Blowhole is formed. - If the whole of the cave roof collapses a Geo is produced (inlet in a cliff)

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Old Harry

If marine erosion wears away through the cave an arch is produced- Durdle Door, along the Purbeck coast in Dorset. The roof of the arch is prone to sub-aerial processes and when this collapses a stack is produced- Old Harry

The stack is undercut until it becomes so top heavy it collapses into the sea- Old Harry’s Wife which fell into the sea in 1896.

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Depositional processes

How can deposition occur?

Supply must exceed removal

There must be a supply of material

Sheltered area

Traction: Large rocks are rolled along the sea bed

Saltation: Smaller pebbles are bounced along the sea bed

Suspension: Particles are carried by the flow of water

Solution: Soluble particles dissolve in the water

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Depositional landform - Beach

Beach: accumulation of sand or shingle material at a coast or fringe of a body of water due to deposition. Beaches can be highly effective at reducing erosion. They are the best form of sea defence so management strategies aim to build the beach. E.g Dawlish Warren- sandy beach

The particles are packed tightly together, meaning a low rate of percolation. The compacted wet surface creates little friction and backwash is therefore strong. A gentler, flatter beach profile is the result. Sidmouth- shingle beach which is located in East Devon.

Gaps between the particles allow water to percolate through. High friction also means that the backwash is weak. Material builds up creating berms and a steep beach profile.

Features of a beach include:

Berms which are a ridge of material formed by constructive waves. They mark the stages of tidal levels from spring to neap.

Bars are markers where waves begin to break

Sand ripples are marks in the sand caused by wave action and tidal current

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Depositional landform - Bar

Bar: A sand or shingle bar above high tide parallel to the coastline and separated from the mainland by a lagoon

Eg: Slapton Sands which is located along the South Devon coast between Plymouth and Exeter. It is 100m wide and 9km long

It was a beach created by LSD 18 000 years ago when sea levels were 120m lower.

As sea levels have risen, by eustatic change, the beach has been rolled backwards until it reached the mainland. However it separated a body of water from the sea, which is now called Slapton Ley.

86% of the bar is made from flint which is provided by offshore sediments deposits 20 miles east of the bar in the English Channel.

It came to rest 6000 years ago.

The sheltered coastline ensures supply exceeds depletion.

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Depositional landform - Spit

Embankment of sand which juts out from the land, often across a river mouth.

Eg: Dawlish Warren (sand spit) which is located in South Devon 19 miles South of Exeter. It sits at the mouth of the River Exe.

Material eroded from Langstone rock is carried SW in the direction of LSD to spit.

When the orientation of the coastline changes larger shingle and pebbles deposited in slacker water in lee of the headland.

Storm waves throw up larger material above HWM making landform more permanent.

Curved end is caused by change in the PW direction

Spit can only extend to a certain point due to the fast flow of the river Exe and also the greater depth.

Prevailing SW winds pick up sand from the beach to form sand dunes on the spit.

Gentle, low-energy waves entering the sheltered area behind the spit deposit silt and mud which create a salt marsh.

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Depositional landform - Tombolo

Eg: Chesil Beach located in South Dorset. It connects Dorset mainland with the Isle of Portland. It is the longest shingle ridge in the British Isles at 18 miles long. consealse a lagoon - The Fleet

Constructive waves form a beach, 20 000 years ago when sea levels were 100-120m lower.

Post glacial sea level rise 12 000 years means constructive waves have rolled the structure towards the coast- swash aligned.

It settled in its current position 6000 years ago due to the nature of the coast and the coastline becoming shallower. This meant the waves had less energy to move the structure past the Isle of Portland

LSD provides material for the landform and the SW prevailing wind means the material is deposited at the tombolo.

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Geology - JACHS

Joints- lines of vertical weaknesses in the rock so rocks with lots of joints are more prone to sub-aerial processes

Alignment- where bands of hard and soft rock lay side by side the hard rock will produce a discordant coastline Liquorish allsorts

Composition- greater cohesion in the rock composition the rock particles are tightly bound

Hardness- the harder the rock the more it resists coastal processes

Structure- where bands of hard and soft rock lay side by side the hard rock will produce a discordant coastline Liquorish allsorts

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Geology

Simplest rock can be divided into 2 categories, whether rocks are:

Hard and resist coastal processes eg: sub-aerial/ marine erosion

Tighter crystal structure so few lines of weakness. It will hold its shape cause steep cliffs and steep landforms.

Soft and wear quickly and easily away due to coastal processes

Unconsolidated particles are loosely joined together. They are weak and easily eroded, they weather easily and water able to percolate easily so cannot hold steep cliff profiles.

There are two types of sedimentary rocks:

Coherent which have interlocking crystals strongly cemented particles and few lines of weakness, resist erosion and support steep angled slopes. Eg: chalk or limestone

Incoherent which weak, fine rocks. They form low- angled cliff profiles which are undercut and eroded easily eg: clay/sands

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Rock profiles

Chalk: Sedimentary rock, Alkali, hard rock. - Weathering: Physical- freeze thaw Chemical- carbonation Biological- plant roots. - Erosion: corrosion, hydraulic action -  Mass movement: rock fall

Clay: unconsolidated rock loosely joined together - Weathering: Physical- hydration - Erosion: Abrasion, wave pounding - Mass movement: rotational slip and mudflow

Boulder clay: sand and clay loosely joined together and boulders deposited during the last glacial period. (Unconsolidated particles) 

Limestone: Sedimentary rock - Weathering: Chemical- carbonation Physical- freeze- thaw - Erosion: corrosion, hydraulic action - Mass movement: rock fall

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Geology - scientific names

Sedimentary rock: formed in layers from microscopic organisms called cocoliths

Igneous: bound by heat and pressure, permeable eg: granite

Metamorphic: sedimentary rock bound by heat eg: marble (originally limestone) and slate

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West Purbeck coastline: concordant

Durdle Door- Eustatic change meant attacked joints and breeched the limestone. Differential erosion and wave refraction result in clay being eroded to form a cove. More resistance limestone forms a bar headland. Wave refraction attacks both sides of the headland and causes the cave to become an arch.

St Oswalds Bay- It is a Double Bay The clay eroded as far back as chalk, lateral erosion eroded through to next bay. Man o’ war rocks are the remnants of headlands.

Stair Hole- Folding due to tectonic activity means there are greater lines of weaknesses to increased surface area for sea to attack by marine erosion and weathering

Lulworth Cove- Fluvial erosion from east Lulworth river has helped weaken limestone ( river valley formed in peri-glacial period) Arches have collapsed to form a bar headland due to Differential erosion between clay and limestone. Chalk at the back of the landform has resulted in lateral erosion  as is harder and has a higher gradient.

Worbarrow Bay- Double Bay Arish Mell is dry river valley formed peri- glacial period. Low point has a smaller surface area so is easier to erode. Used to be an island in between but once island was eroded a double bay was left.

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Key vocabulary

Lithology: the mechanical and chemical properties of rocks

Wave refraction: the waves being defected around the headland, so energy is concentrated around a headland but reduced around bays

Differential erosion: variations in rocks causing rock to be worn away at different rates. Leads to a discordant coastline.

Discordant coastline: Bands or rock are perpendicular to coastline. If some rocks are less resistant they will be eroded more rapidly to form bays and leaving headlands to jut out into the sea

Concordant coastline: When rock type is running parallel to the coast. The sea can still find weaknesses and break through the rock

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Why manage coasts?

Coasts need to be protected because humans have built on them as if they are static features

however due to coastal processes they are dynamic

Conservation eg: DW - petalwort/ marsh orchid/ ringed plover, Energy eg: gas terminal at Easington/ nuclear power station Hinkley Point Somerset, Historical reasons, Industry eg: Swanage Bay barage, Settlement protection eg: Sidmouth population of 15 000/ Mappleton- 50 properties, Tourism: DW and Transport: A379 on Slapton Sands and Great Western Railway at Dawlish

60% of the world’s population live within 60km of the coast

2/3 of the world’s largest and fastest growing cities are located on the coast

Coastalisation is the process of people moving to settle by the coast.

19% of the population of UK is OAPs

32% of East Devon population is over 65

8% increase in eastly storms in last 25yrs

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Holderness

It is a concordant coastline - East Yorkshire Coast. It is 61km long. Erosion is 15x faster than the average coastline at 1-2 m per year. This is due to the long fetch and deep sea so less friction. This means there is lots of energy. Atlantic currents increase erosional power. The North Sea is enclosed so energy cannot disperse. It instead dissipates onto Holderness eg: storm 1967 which eroded 10m. Since Roman times 4km has been lost- a total of 29 villages. Most of eroded material is carried out to sea and the rest is carried by LSD to Spurn Point so beaches become narrower so more vulnerable. Destructive waves have a stronger swash than back wash.

Flamborough Head- is a chalk headland. It is a harder rock so less easily eroded.- Bridlington- sand and shingle beach - Hornsea- 20km North of Mappleton. Economy dependent on tourism, fishing and recreation. - Mappleton- village lies on top of the cliff- 50 properties are at risk of erosion. The access road B1482 is only 50 from the edge of cliff. Sandy beaches - WithernseaEasington- gas terminal which requires protection otherwise thousands of jobs could be lost.- Spurnhead- Sand spit with a lifeguard station and wildlife habitats behind spit protected by it. Good migration spot. Needs a constant supply of material. - HullRiver Humber- to the South is a fluvial input to the Holderness coastline.

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Why manage coasts - Agreculture

Steep land by sea so used for pastoral farming

Mild climate

Fertile soil at coast

Can use land vulnerable to erosion for arable- cheaper

+ Manure fertilisers the soil

+ Increased infiltration

+ reduced erosion- roots bind soil together

Pastoral farming increases erosion

Fertilisers can run into rivers (leaching) and seas and pollute water- cause eutrophication

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Why manage coasts? - settlements

Settlement- Sidmouth located on the English Channel in East Devon, SW Uk. At the mouth of the River Sid.

Aesthetically pleasing

Pleasant climate

High environmental quality

Lower than average crime rate

Accessible ½ hour from Exeter by A379- 15 miles SE of Exeter

Access to employment opportunities

Numerous amenities

Average house price £300 000

Slow pace of life attracts OAPs 40% over 65

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Why manage coasts? - energy

Nuclear power. Plenty of water for cooling, remote so reduce population affected if pollution occurs. Large amount of space, takes up 165 acres once in operation. Hinkley Point B near Bridgewater in Somerset on the Bristol Channel coast SW UK. It is owned and run by EDF energy. Commissioned in 1976.  A new 3 260 MW Hinkley Point C was given planning consent on 19th march 2013.  It would generate 92, 5 £/megawatt-hour.  Hinkley’ s power contribution rise by 7% of UK overall power total- 5 million homes an area twice the size of London.   + Benefits- low cost land, low cost water cooling, low transport costs, large energy yield, no CO2 emissions (9 000 000 tonnes of CO2 avoided), cheaper than fossil fuels and  creates 25 000 new jobs during construction / - Costs – radiation risk to population, price, interferes with wave processes and changes sediment balance, visual pollution, air pollution and heat contamination of sea water.

Wind - windy at the coast as no interference with buildings, exposed, large amount of space. Gunfleet sands, over 4 miles off Essex. 48 turbines each 85m tall and blades 52m in length. 3x as much as onshore site to build. Completed in 2010. Covers 17.5 square km of sea bed and powers 120 000 houses. Run and built by Dong energy for its 25 year life span .  - Only works in windy conditions, Noise and Visual pollution however less of an issue as it is far out to sea, Expensive and difficult to construct and Affect natural habitats- damage sea bed ecosystem / + No air pollution, Renewable- sustainable, Created 70 000 new jobs and Cost effective once built as minimal maintenance needed

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Why manage coasts? - conservation

Conservation- Dawlish Warren

Protect animal species that live in the area

+ Provides an income for 40 businesses

+ Nature reserve with endangered species eg: petalwort

Provide conflict between tourists and conservationists

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Why manage coasts? - industry

Port Talbot Steelworks is an integrated steel production plant in Port Talbot, South Wales. It is capable of producing 5 million tonnes of steel slab per year making it the largest in UK and one of the largest in Europe. It is owned by Tata, India

Raises concerns about waste disposal and pollution

+ provides 4000 jobs however indirectly creates a total of 18 000 jobs

+ It is worth £3.2 billion to Welsh economy

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Why manage coasts? - tourism

Dawlish Warren relies on tourism- 40 businesses 800 000 tourists a year.

The caravan and camping parks at 15 000 people to the population in the summer months

+ Tourists bring in money to the area

+ Development

Traffic congestion

Litter

Air/ noise pollution

Conflict

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Managment

1:8 for every £1 spent on coastal defences it must protect land with an economic value of at least £8

There are 4 decisions made to:

Retreat the line, Hold the line, Advance the line OR Do nothing

For a management strategy to be considered successful –

Does it work as it was designed to?

For Who?

For where? Local/national/global

For when? Present/ future

Sediment cells = section of coast within which movement of sand is self contained 

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Beach pumping: hard engineering, beach

Purpose: Increase the natural rate of sedimentation

How is it done? Drainage pipes are installed into the beach 2-3m below the surface and backwash energy is reduced as more water soaks into the sand. This allows sediment to build up.

+ Natural method- doesn’t interrupt natural sediment cells

+ aesthetically pleasing as pipes aren’t visible

Disruptive to underground ecosystem

Not easy to put system in

Pump costly

Beach closed to install

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Rock armour/rip rap- hard engineering, cliff foot

Large boulders of igneous rock piled up against cliff foot

Designed to absorb wave energy and decrease erosion eg: DW with rocks imported from Scandinavia

+ Natural materials are more aesthetically pleasing

+ Increase the life of existing defences, lowers ongoing maintenance costs

Cost of shipping experience

Reduces safe access for beach users

As they break down they contribute to abrasion and increases erosion

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Cliff pinning- hard engineering on cliff face

Material is pinned through shear planes in the cliff. This helps to secure the structure

+ stabilises the cliff

+ Widely applicable in the UK

If it is done wrong it will exacerbate the problem

Expensive

Not very effective- mostly applied to clay and clay moves very easily

Difficult to do

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Managed retreat

Breaching existing coastal defences such as the sea wall or embankment allowing land behind to be flooded by incoming tide

This land is left to be colonised by salt marsh vegetation which disperses wave energy

+ sustainable

+ Cheap

+ Creates new habitat

Low population density needed

Displaces human activity

Loss of land for building

Unpopular

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Dawlish Warren- Why was management needed?

Sand was being lost at a rate of 1-2m a year

Protect the low lying estuary villages eg: Topsham, Cockwood and Lympstone

Protect sand spit ecosystem and rare species Petalwort and Ringed Plover

Dawlish Warren is worth £158 million

Who manages Dawlish Warren?

Said to lost 100 000 tonnes sand over 15 yrs to Exmouth.

SSSI= Local Teignbridge district council, DEFRA, environment agency also involved- EDDC, RSBP DW trust, SAC= Natural England and SAP= Funding – EU

What are the current management strategies?

Breakwater/ beach nourishment, Cliff stabilisation, Sea wall, rock armour, Concrete revetment, Gabions and Groynes

Ecosystem management-visitor centre, information signs, buffer zone, boardwalks, wooden fences, replanting marram grass, sand dune stabilisation (Christmas trees)

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Sea defences in place before 1992 DW

Sea wall

Rock armour revetment (built in 1917 to protect the railway)

Rock platform

Concrete revetment (built in 1972)

Groynes (between 1972-1973 18 built)

Gabions built in 1972

Effect of the storm in 1990? - Boulders had become rounded and smaller due to erosion so were easier to roll away onto the foreshore. They had also moved over the years and were no longer interlocked. Limestone boulders had broken up. The layer of smaller rocks which should have filtered water from backwash of waves had been washed away.

Promenade was undermined

Sands behind rock armour was washed out.

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what was done after 1992 DW

Work took place from Jan-July 1992 costing £1.5 million as a result of a report produced in 1991 by consulting engineers “Posford Duviver” who recommended a new sea defence for damaged areas.

Main features include- rock armour revetment with a wave return sea wall, rock armour imported from Norway, concrete sea wall faced with local limestone and a new promenade constructed behind

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2014 storm effect on DW

February 6th- 7th 2014 storm Hercules:

Effects- 100 000 tonnes of sand moved by storms, 44 000 houses lost power wind speeds at coast reached 90mph. 25years worth of erosion. Storm surge 2.5m undercutting occurred higher upon cliff. High rainfall in winter 2013-14 weakened the cliffs so they were more susceptible to erosion and mm, sand dune ballasted was washed away 50 houses were evacuated and those on Riveria terrace, sea lawn terrace evacuated to DW leisure centre.

Stretch of rail line between  Dawlish and DW damaged (mainline to SW) foundation of sea wall railway runs on wash washed away lost business by closure for 2 months amounted to £30 million a day, more lost by public perception.  650m of track costing £35 million to rebuild and using 6000 tonnes of concrete and 150 tonnes of steel.

+ erosion and landslides revealed new fossils including a 5ft long dinosaur.

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successful strategies of managment? DW

YES- reduced erosion of Langstone rock, businesses protected eg: Langstone cliff hotel and Boathouse pub, beach still accessible, nature reserve protected. Settlements haven’t been flooded like in 90s & 80s. Improvements to railway line protects transport link.

NO- Built static but coast is dynamic, 1-2m of spit eroded each year, only short term and local. Reduced supply from SW to NE from DW to Exmouth therefore sand lost from the beach resulting in a loss of amenity for beach users. Offshore dredging needed for Exmouth. Frequent closure of Red Stone Rock at Langstone… due to waves breaking over rock armour and sea wall. In the future sea level (50cm rise by 2100) rise may break through DW. In 2010 a 1% chance of coastal flooding and in 2050 a 10% chance of coastal flooding 

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Future for DW?

“Dawlish Warren and Exmouth beach management scheme” delivered by Teignbridge, Enviro agency and EDDC and costs £14 million

Involves beach recharge, repair and renew groynes on beach and possibly extend, remove gabion baskets in some areas, maintain the sea wall and revetment and build a new flood defence scheme inland across warren to reduce tidal flood risk to properties 

Possibly move the railway line inland along former Teign Valley branch line which would cost £250 million. It would go from Okehampton to Plymouth via Tavistock through parts of Dartmoor. It would take 5 years to build however it may be needed as 1 in 100 storms happening annually. However it would avoid the coastal stretch but may mean more less people visit the area so less business.

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Holderness Coast management strategies

Skipsea: Gabions stabilise the shore and concrete revetment protects residential area

Hornsea: Wooden groynes build up beach. Sea wall, beach nourishment and rock armour at the base of sea wall dissipate wave energy

Mappleton: Beach nourishment, sediment starved and until 1991 £2 million was spent on rock revetment, rock groynes and cliff regarding. Up until 1990 erosion was 4m per year

Withernsea: 2 rock revetments, £6.3 million spent on sea wall, protecting properties. However it has resulted in noise and visual pollution

Easington: Rock revetments, small scale beach drainage and granite boulders

Lincolnshire: 1983 66 hectares of salt marsh reclaimed at Freiston Shore for arable farming. The cost of maintaining the sea defences was unjustifiable at £2.5 million over 50 years. In 2002 the flood embankment was allowed to breach and the flood embankment and arable farming behind was destroyed by the sea. Through succession 66 hectares of new salt marsh was created a 15 hectare saline lagoon were created. After 13 months 60-70% of the area had been colonised by 11 species of salt marsh plant and 8 fish species. There has been an increase in bird species and new arrivals eg: avocets. Feiston has also become a visitor attraction with 57 000 visitors a year bringing in £150 000 for the local economy providing employment.

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Holderness Coast- strategies successful ?

YES: Lincolnshire is sustainable and is successful for local providing jobs and national providing more taxes to government. It is successful for the present as the salt marsh absorbs the energy and the land is not needed by humans for building. It needs little money or management.

NO: At present most material is removed from the beaches out to sea rather than supplying Spurn Point sand spit which protects habitat behind it. Therefore defences such as groynes are starving it of material

In the future due to GW sea levels will rise and may breach coastal defences. Increased easterly storms by 8% so greater marine erosion for example wave pounding. Increased water so beach drainage may be less effective so greater amount of material removed from the beach. Beach more vulnerable and less able to protect gas terminal

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Sidmouth management strategies

Chit rocks behind wave cut platform

Seawall with rock armour

2 offshore breakwaters

165 000 tonnes of beach nourishment

2 large rock groynes to trap shingle

Cliff collapse- managed retreat

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Sidmouth management successful

YES: Protects in order of highest to lowest land value- offshore break waters protect historical value properties whereas agricultural land and Pennington point where coastal path is- managed retreat. This ensures the areas that bring in money to Sidmouth by tourists are protected- shops, promenade and beach.

NO: Create visual pollution. Properties on Pennington point at risk as cliff collapses. Rocks are thrown up by the sea in storms onto the promenade and road- cause damage. Due to the sea defences it has caused increased erosion at Pennington Point as sea energy is diverted there instead. The beach there is now unsafe to use and coastal path has had to be diverted. In the future global warming sea levels will rise and will increase marine erosion therefore weaken sea defences more easily.

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open coastal system

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nature of coast model

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Holderness map

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Perbeck map

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Management hard to soft

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rocks hard to soft

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Bedding plane

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Erosional processes

Corrasion/ abrasion - Bits of rock and sand in waves grind down cliff surfaces like sandpaper.

Attrition - Waves smash rocks and pebbles on the shore into each other, and they break and become smoother.  

Corrosion -  Acids contained in sea water will dissolve some types of rock such as chalk or limestone.

Hydrolic action - . Air may become trapped in joints and cracks on a cliff face. When a wave breaks, the trapped air is compressed which weakens the cliff and causes erosion.

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Transportation

eroded from cliffs

transported by longshore drift along the coastline

brought inland from offshore by constructive waves

carried to the coastline by rivers

Waves can approach the coast at an angle because of the direction of the prevailing wind. The swash of the waves carries material up the beach at an angle. The backwash then flows back to the sea in a straight line at 90°. This movement of material is called transportation.

Continual swash and backwash transports material sideways along the coast. This movement of material is called longshore drift and occurs in a zigzag

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Hallsands

fishing village +159 inhabitance by 1891 37 houses + chapel and pub on site since 1506 - protected by pebble beach + from south westerly wind by cliffs. 

1900 - beach fallen 7-12 ft

From 1897 - 1902 660 000 tonnes of shingle had been removed - said it would naturally be replenished but he had removed 1/2 shingle from area and State point prevented any new sediment from reaching Hallsands. 

26th Jan 1917 strong easterly gale + high tide resulting in defences being breached 24 houses fell into the sea. 

enquiry 1917 did not find Jckson responsible - consided act of god

BECAUSE - 1890 naval dockyard Devonport (near Plymouth) should be expanded - requiring 1000's tonnes of concrete.  Jan 1898 contacted Sir John Jackson . = dredged shingle to make concrete. Villagers were not informed. 

Now cliffs being eroded 0.5m a year and areas N finding their shingle beaches are also srinking

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synoptic links

sea temp + 0.6'c and the inetrgovernmental panel on climate change predict sea level rise will be 0.18 to 0.38m by 2100 most optimistic sanartio 0.26 to 0.59m most pesamistic 

sandbanks - a spit in poole harbour = 4th highest land value in world nearly £10 000 per sqm. - growing pop more pressure and also economic value of coastal land high

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