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Coasts - Coggle Diagram
Coasts
1.3
b.
rock type
- hard rock is more resistant to erosion (erodes slower) than soft rock
wave action
- wave - the movement of energy through water
- swash - the forward movement up the beach
- backwash - the retreating movement out to sea
- fetch - the distance of open water after a wave has travelled, driven by wind
constructive waves
- powerful swash - deposition - weak backwash
destructive waves
- break vertically - weak swash - strong backwash - erosion - caused by storms
geological structure
- concordant geology has the same type of rock, so erodes at the same rate
- discordant geology alternates between strata (bands) of hard and strong rock so you get differential erosion
- joints and faults
are naturally occurring weaknesses in the rock which can be made bigger through erosion (H.A.)
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a.
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deposition
- waves lose energy, so eroded material can no longer be transported and is deposited
weathering
chemical (chemical reactions)
- acid rain erodes rocks, such as limestone and chalk
biological (plants and animals)
- growing plant roots dislodge rock and break it apart
- burrowing animals + nesting birds dislodge rock
mechanical (physical)
- freezethaw - water gets into cracks in rocks, freezes and then expands
1.4
a.
caves, arches, stacks and stumps
- naturally occurring weaknesses erode to form caves
- two caves back into each other across a headland to form an arch
- arch collapses forming a stack
- stack collapses to form a stump (only visible at low tide)
wave cut platforms
- erosion at the base of cliff (undercutting) forms a wave cut notch
- wave cut notch (cave at the base of cliff)
- eventually, the top collapses
- process continues - cliff retreats
- wave cut platform - gently sloping, hard rock platform only visible at low tide. formed by process of undercutting and rock falls
headlands and bays
- discordant geology - differential erosion
- soft rock erodes quickly (low resistance) forming sheltered bay
- hard rock erodes slower (high resistance) forming headlands
b.
spits
- an extended stretch of beach material forming a deposition bar that projects out to sea. it is joined to the mainland at one end
- longshore drift occurs along the beach
- there is a change in the direction of the coastline
- longshore drift has momentum so it continues into open water
- deposition occurs as the waves lose energy
- deposition means that sediment builds up
- this forms a sandy ridge building out to sea
- spit stopped from growing any further due to river outlet removing material
- spits can become curved if the wind changes direction
- salt marches form behind spits as these are low energy zones - motionless water means that vegetation builds
bars
- created when there is a gap in the coastland with water in it (e.g. a bay). the deposited material joins the other side blocking the flow of water
- longshore drift continues when there is a change in the direction of the coastline
- like a spit
- a bar is formed as the spit grows across the bay
- continued longshore drift and deposition will eventually join the spit to the other end of the coastline
- this will often form a lagoon
- lagoon: an area of water dammed by the bar
- it will gradually be infilled by deposition
tombolos
- formed when a spit joins (connects) the mainland to an island - the spit will grow out from the mainland and join to the island and form a tombolo
beaches
- sandy beaches
- constructive waves deposit lots of materials
- destructive waves form steeper beaches due to erosion as they break vertically
- down the coastline from longshore drift areas
- in sheltered bays
- the profile of beaches is rarely smooth. they typically have a storm beach with smaller ridges called berms
- storm beach: a steep mound of large material at the back of the beach. formed during storms/high tides. large material that would normally be transported is deposited at the back of the beach
- berms: show the tidal movements. bumps/undulations/ridges going down the beach, mapping the retreating tide
- value of beaches: erosion buffer, good for tourism
1.5
a.
impacts
- social:
- north sea storm surge of 1953 - people killed and towns devastated
- 20mil people live on UK coast. 29 villages lost at Holderness
- Hallsands village destroyed by storms in 1917
- Seaton village in Devon will not be managed - houses and pub lost
- coastal recession affects transport - difficult to get to work and go about lives
- people migrate away from coast
- economic:
- north sea storm surge of 1953 - flood defences breached, property damage
- Seaton in Devon - campsite and pub will be lost, businesses deatroyed
- migration away from coast
- house values plummer
- insurance not available at high-risk areas
- environmental:
- cliffs that are being undercut and collapsing will retreat. larger wave cut notches
- north sea storm surge of 1953 - land lost/damaged
- soft coastline experiencing more erosion
- wetlands drained - wading birds and animals lose habitat
- cliff retreat - animals and birds lose breeding ground
- rubbish dumps and rubble washed into sea
- human activity - groynes increases erosion down the coast. dredging (excavating material from coastal areas) removes natural barrier. developing in vulnerable areas means that the vulnerable areas will become more heavy and erosion will happen faster.
- urbanisation - increases the amount of impermeable surfaces in an area
- growth of tourism also increases the amount of impermeable surfaces in an area
- deforestation - reduces the amount of rainfall intercepted
- burning of fossil fuels/enhanced greenhouse effect due to human activity means sea levels rise, so increased erosion
b.
hard engineering - costal management technique used to protect coast by absorbing the energy of waves, interfering with natural processes
groynes
- Physical barrier that intercepts sand moving along the shore due to longshore drift. Perpendicular barriers (to the sea)
- Halts longshore drift, preserving beaches (capturing sand), Relatively cheap and long lasting/ long lifespan (cheap relative to lifespan), quick to build
- Ugly, Interfere with natural processes and habitats - impact further down coast, Not effective in storms
revetments
- Wooden angled barriers at the base of cliffs. They dissipate energy, some water allowed through and some deflected back to seas
- Absorb wave energy, Cost effective, Cheaper and less intrusive than a sea wall
- Unattractive, Require space, Require maintenance, Shorter lifespan, Unstable during storms
sea walls
- A structure that is built to separate land and water areas. It is designed to deflect wave energy back out to sea.
- Secures settlements on coastlines - effective, Reflect energy
Long lifespan, Can be modified for local area, can have promenade
- Expensive, Destroy habitats/ interfere with biodiversity, Not aesthetically pleasing (eyesore) + can restrict access to beach, can increase erosion of beach
rock armour (rip-rap)
- Boulders piled on coastline to reduce erosion
- Cheap to maintain, Absorb energy - force waves to break thus dissipating their energy, Long lasting, quick to build
- Ugly - do not fit in with local geology, Safe?, Interfere with natural habitats, Expensive to obtain and transport boulders, Reduce recreational value of the beach, can impede access to beach
soft engineering - Managing coastal erosion sustainably, attempting to prioritise and preserve natural processes.
sand dune regeneration
- Securing sand dunes by planting more vegetation, stabilising sand dunes making them more resistant to erosion
- Preserves natural habitats, Cheap, Plants are good, Natural barrier between land and sea, maintains natural coastal environment
- Carefully managed to be effective, Protecting dunes limits tourism as areas have to be fenced off, takes time for vegetation to become established
managed retreat
- Controlling erosion in some areas and blocking it in others. Aims to prioritise natural processes where possible. Also called managed realignment
- Allowing flooding can produce natural animal reserves, Marshlands are a good barrier for erosion
- People need to be compensated if their land is allowed to flood, Not popular
beach nourishment
- Process of adding sand and sediment to beaches, replacing what has been lost through erosion
- Presents few problems to the beach, Minimal interference with animal habitats, Preserves beach biodiversity, beach can absorb more energy and protect coastline, blends in
- Expensive - not cost effective as needs constant maintenance, Needs to be done repeatedly to be long lasting, work often done in summer, disruption to beach users
shoreline management plans - different ways of protecting the coast/deciding what areas should be protected and how.
different plans:
- no intervention - no planned investment in defending against flooding and erosion
- managed retreat/realignment - allow the shoreline to change naturally, but manage the process - controlling erosion in some areas, but not others
- hold the line - maintain the existing shoreline by building new defences
- advance the line - build new defences on the seaward side (push sea back)
environmental impact of coastal defences
- reduce coastal erosion and risk of flooding
- but, also prevent coastline from evolving in response to natural processes
- railways, sea walls and groynes prevent longshore drift. can cause coastal squeeze - where coastal habitats are prevented from moving inland and so become smaller over time
- coastal defences are only ever able to defend against events that we are able to predict with reasonable accuracy - they are not able to adapt to changing conditions. instead we need to adapt to cope with the risk of flooding by adapting our homes and becoming more resilient to the impacts of flooding
1.6
a.
Dawlish Warren spit
- south coast of Devon
- extends 2km north-east
- next to River Exe estuary
importance of the spit
- economic
- fishing industry - seafood, mussels and oysters (jobs)
- tourism - 480,000 per year. in summer can reach 20,000 per day. 13% local employment
- small businesses on the spit
- water based activities - sailing, windsurfing, kitesurfing, water-skiing. walking and golf also played (jobs)
- environmental
- nature reserve - coastal species - birds, flowering plants. internationally important for wading birds and wildfowl. made a national nature reserve in 2000
- social
- public transport - trains, buses, ferries. footpaths for walking and a car park
- some residential properties on the spit
changes to the spit
- physical factors changing the spit
- in the 1930s, two sand spits (Inner and Outer Warren) joined to form one spit, enclosing Greenland Lake which had separated them
- the spit has continued to change due to erosion and deposition. erosion of the beach and dunes has caused the spit to retreat. storms have also caused the spit to retreat. 2013-14 storms approx. 5m of sand was lost from the southern face of the sand dunes. however, sands transported from S/SW of the spit helped rebuild areas and extend the spit to the east
- human factors changing the spit
- housing development. in the 1930s there were bungalows on the eastern end of the spit but at the end of the 1940s these had been washed away
- flood defences and transport links - 1917 first sea defence built on W end of spit. rip rap used to protect railway. after 1940s storms sand dune regeneration used, but this did not work. first wooden groynes installed 1959. 1970s coastal defences included: sea wall with promenade, gabions beneath sand dunes, 18 groynes. following 89 and 90 storms western end of spit repaired with 35,000 tonnes of granite
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