🌊 Coast Flashcards
What is the coast?
Point at which the land meets the sea
What are the 4 types of coastal erosion?
- Hydraulic action
- Abrasion/ corrosion
- Attrition
- Corrosion
What is hydraulic action?
The sheer force of waves, especially when they trap air in cracks and holes in cliffs. When the wave retreats the air in the crack expands causing a minor explosion.
What is corrasion/abrasion?
Results from large waves hurling beach material at the cliffs
What is attrition?
When the wages cause rocks and pebbles on the beach to bump into each other and break down in size and smooth them over
What is corrosion?
Certain types of rock are dissolved by acids in sea, salt water eg. Chalk and limestone
Describe a wave approaching the coast:
Circular orbit in open water
Friction with the sea bed distorts the circular orbital motion
Increasing elliptical orbit so the top of the wave moves faster
Wave begins to break
Water from the previous wave returns as the wave rushes up the beach
What is swash?
The movement of the wave up the beach
What is backwash?
Movement of the wave back down the beach
What are 3 factors that determine the strength and power of a wave?
- Strength of the wind
- The length of time that the wind blows
- Fetch
The longer and bigger these are will result in bigger and more powerful waves.
What is fetch?
The distance of sea the wind has to cross
What are the 2 main types of waves?
- Destructive waves
- Constructive waves
What is the height of a constructive wave like?
Low in proportion to length
What do constructive waves do to the beach?
Build them via deposition
Describe a constructive wave’s swash and backwash:
Carries material up the beach in a strong swash. Material is then dumped as the weak back wash soaks into sand.
What is a constructive waves swash like?
Strong
What is a constructive waves backwash like?
Weak
When are constructive waves more common?
Summer
What do destructive waves do to beaches?
Destroy beaches (erosion)
What is the height of destructive waves like?
High and frequent in proportion to length
Describe a destructive waves swash and back wash:
Waves hit the beach and the strong back wash removes the material from beach (erosion)
Weak swash
What is a destructive waves swash like?
Weak
What is a destructive waves backwash like?
Strong
When are destructive waves most common?
Winter
What is the rate of erosion on coasts affected by? (8)
Wave type
Fetch
Rock type
Weather conditions
Wind speed
Shape of the coastline
Depositional landforms
Human activity
How are cliffs and wave cut platforms made? Process
- The sea attacks the cliff between high and low tide
- A wave cut notch develops in the zone of erosion between high and low tide
- The wave cut notch gets bigger and deeper through erosion, eg. Hydraulic action. There is a large area of unsupported rock above the wave cut notch
- The unsupported rock collapses and thus the cliff retreats. It leaves a wave cut platform and a new wave cut notch starts. The process repeats again
How are headlands and bays created?
They are caused by differential erosion
What is differential erosion?
Resistant rock and less resistant rock is eroded at different rates.
What is a discordant coastline?
Different bands of rock types run perpendicular to the coast
What is a concordant coastline?
Where the rock type is the same
How are headlands and bays formed? Process
- Headlands and bays are caused by discordant coastlines with perpendicular bands of hard and soft rock
- Wave attack, specifically hydraulic action, causes the cliff to retreat
- Differential erosion occurs where less resistant rock is eroded at a faster rate t o create bays. More resistant rock takes longer to erode forming headlands, where the harder rock sticks out
- The size of the bands of soft rock determines ones the size of the bay. During clam periods, deposition occurs in bays to form beaches
How are headlands eroded? Process
Crack, cave, arch, stack, stump
- The four processes of erosion begin to attack cracks and weaknesses in the headland
- Overtime the crack widens and deepens forming a sea cave
- As erosion continues the cave eventually erodes straight through the headland forming an arch
- As the arch gets larger, the rock above becomes unsupported and eventually falls, leaving behind a stack
- The base of the stack gets eroded and will eventually topple over leaving a stump remaining
This process repeats itself with a new cave being formed on the new headland
What is weathering?
The breakdown or erosion of rocks at the Earths surface by the action of rainwater, extremes of temperature and biological activity
What are the 4 types of weathering?
- Biological
- Wind, rain and waves
- Freeze thaw
- Chemical
What is biological weathering?
Roots find their way into cracks and expand the gaps forcing the rock to widen, become weaker and pieces fall off. Anima,s burrowing or walking over the surface of the ground can gradually wear it away or weaken it.
What is wind, rain and wave weathering?
The wind can blow tiny grains of sand against a rock which wears it away. Rain and waves can also wear away rocks over long periods of time.
What is freeze thaw weathering?
Water expands slightly when it freezes into ice. The formation of ice can break rocks. If water gets into a crack in a rock, freezes, expands, and pushes the drain further apart. When ice later melts, start can get further into the crack and the process repeats. This weekends the Rick, making the crack become so big that pieces fall off.
What is chemical weathering?
Chemical reactions breakdown the bonds holding the rocks together causing them to fall apart forming smaller pieces. Examples of this are oxidation, hydrolysis and carbonation
What is mass movement?
The downhill movement of large quantities of material under the influence of gravity.
What are the 4 types of mass movement?
- Rockfall
- Landslide
- Mudflow
- Rotational slip
What is rockfall mass movement?
Fragments of rock break away from the cliff face, often due to freeze thaw weathering
What is landslide mass movement?
Blocks of rock slide downwards
What is mudflow mass movement?
Saturated soil and weak rock flows down a slope
What is rotational slip mass movement?
Slump of saturated soil and weak rock along a curved surface
How does the sea transport material?
Solution
Saltation
Suspension
Traction
What’s traction?
Rolling heavy material along sea bed
What’s saltation?
Bouncing material along sea bed
What is suspension?
Finer materials being suspended by waves
What’s solution?
Salt and minerals are dissolved from rocks
What happens to material at any coastline?
Eroded, removed by sea, transported form the coat, deposited elsewhere
What is the transportation of beach material done by?
Longshore drift
What is longshore drift?
The transport of sediment along a stretch of coastline caused by waves approaching the beach at an angle
Describe longshore drift: (6 points)
- The direction of prevailing wind approaches the coast at an angle
- Swash washes the material up the beach at the angle of the prevailing wind
- Backwash pulls material back up towards the sea at 90 degrees to the sea front
- Overtime material gets removed from one end of the beach
- As the material moves along the beach it gets smaller via attrition
- Continuous transportation in the same direction adds material to the end of the beach
What is required for the formation of a spit?
- Longshore drift
- Change in the direction of the coastline
- A river mouth/estuary
What is a spit formed by?
Deposition at the coast and longshore drift
How is a spit formed?
- Prevailing winds need to be at an oblique angle to the beach causing longshore drift
- A change in the direction of the coastline is needed so the Longshore drift moves the material beyond a change in the coastline.
- As the material moves along, it is deposited and overtime it develops on length and may develop a hook as the wind changes direction, altering the shape slightly
- Waves cannot go beyond the spot creating a sheltered area where mudflats and salt marshes are formed
- The river flow prevents the spit from covering the estuary
Why doesn’t the spit reach across the whole estuary?
It is prevented by river flow
How are barrier beaches/ bars formed?
- Longshore drift moves material along the coastline
- The coastline changes direction
- Longshore drift continues out to sea
- Sand is deposited across the bay
- Once the sand reaches the other side, it completely cuts off the bay with a sandbank forming a lagoon
How is a tombolo formed?
- Longshore drift moves material along the coastline
- The coastline changes direction
- Longshore drift continues out to sea
- Sand is deposited creating a sandbank
- It reaches an island and the deposited sand builds up, forming a tombolo, connecting the coast and island
Why is there a beach at the back of a bay?
Wave refraction
What is wave refraction?
As a wave approaches the coast, it is refracted (bent) so that their energy is concentrated around headlands but reduced around bays. Waves then tend to approach the coastline parallel to it and their energy decreases as water depth decreases
What are the ingredients needed for a sand dune to occur?
Large tidal range
Large supply of land
Large, flat beach
Onshore wind
An obstacle, such as driftwood or plastic
How is the sand transported to the back of the beach to from sand dunes?
Creep
Saltation
Suspension
What is creep?
Heaviest particles are rolled along the beach by the wind
What is saltation?
Slightly lighter particles are bounced up the beach by the wind
What is suspension?
The lightest particles are carried in the body of the air up the beach
How is a sand dune formed? Process
- Obstacle at the back of the beach begins to trap the sand
- High velocity winds pick up sand grains on the windward side of the dune
- A crest is formed
- On the leeward side, wind speed drops and sand grains are deposited
- Layers of sand build up
- Dune migrates in the direction of the wind
How do sand dunes change as they move back?
More vegetation
Older as you go back
More nutrient rich soil
How do sand dunes develop?
Embryo dune, fore dune, yellow dune, grey dune, dune slack, mature dune
What can you decide on when it comes to coast erosion?
Doing nothing
Holding the line (protection at cliff face)
Advance the line (defences that reclaim area of land)
Where is Bournemouth?
South coast of Uk
East of Poole
North of swan age
East of forest coastline
Christchurch bay
Why is protection worthwhile in Bournemouth?
Tourism
Homes business
Livelihoods
What are groynes?
• Look like wooden “fences” that are built down the beach, at built at right angles to the coastline.
• They are designed to stop material being moved along the beach by long shore drift.
• They work by building up the amount of sand on the beach. The side of the groyne facing the waves suffers erosion, but the side protected from the waves allows deposition to occur and sand builds up there.
Positives of groynes:
• Groynes have a life span of approximately 20 to 30 years
• Relatively cheap at £5000 each as they are not needed as a continuous defence
Costs of groynes:
• Cause issues further downwind by starving the coastline of material
• Cause a barrier for beach users to cross
What are gabions?
• Large steel or stainless steel mesh cages that are filled with rocks.
• They run down the beach, at right angles to the coastline.
• The rocks absorb the energy from the waves so they cause less damage
Costs of gabions
• Only work on sandy beaches as shingle would break them down
• Can be very hazardous If not replaced when damaged
Positives of gabions
• Cheap at only £110 per metre
• Expected life span of 20 – 25 years if made from steel because they will rust. Stainless steel ones last much longer
What is rock armour?
• Large boulders, of 10 tonnes or more, are piled up along the shoreline to form a type of sea wall.
• The rocks are dumped on top of each other leaving gaps between them that allow water through. This disperses the energy of the waves and reduces their erosional power. They can be very effective.
• The boulders must be large, strong and resistant to erosion. Granite and basalt are often used. Small or weak rocks would not be able to withstand the impact from the waves and would quickly be erode
Positives of rock armour
Quick to build
Relatively cheap £1000-3000 per metreb
What is beach nourishment?
• Sand added to the beach to replace sand washed away, but it needs to be replaced regularly.
• This is done in the spring so tourists can enjoy the beach in the summer.
• Designed to absorb the energy of the wave and prevent it reaching the back of the beach
Positives of beach nourishment
• Natural appearance has little environmental impact
• Larger beach means more space for visitors during the summer, though during the process access is prevented
What are sea walls?
• Concrete wall built to protect the coast from coastal erosion.
• They stop the waves hitting the coastline so it stops it doing damage
Positives of sea walls:
• They stop the waves hitting the coastline so it stops it doing damage
• They give tourists a nice place to walk along the coast
Costs of sea walls
• They are expensive to build (around £5000 per metre)
• seen as ugly by many
• If poorly maintained collapse can occur, leading to huge amounts of damage (occurred in Dawlish 2014)
What is managed realignment?
• Creating a manmade (engineered) new position for the coastline, generally involving moving the coastal boundary inland
What is dune regeneration?
• The artificial creation or regeneration of sand dunes at the back of the beach
• Can be achieved by allowing sand to build up against fences
• Planting hardy Marram grass to trap material and improve growing conditions for other species
What is beach profiling?
• Following winter storms, the beach material at the base of the beach gets moved back up the beach as a protection
• No new material needs to be found or added it is just moved
• Doing this ensures the beach can absorb more of the wave energy and so protects the areas behind the beach
Costs of managed realignment
Relies on purchase of land and property to be flooded meaning people have to relocate
Lost habitats
Positives of managed realignment
Sustainable long term solution
New intertidal habitats
Costs of dune regeneration
Take years for dunes to be established
Walkways needed to avoid trampoline damage
Positives of dune regeneration
Cheap
Improved ecosystem
Gps for environment
Costs of beach profiling
Expensive
Beaches can seem artificial potentially deter ing visitors
Positives of beach profiling
Beach can abolish more wave energy
Why should we protect Bournemouth?
Coastal defences been present for 100 years
• Coastal erosion of 1m per year, huge damage will occur without the defences
• Tourism worth £472.8m per year, key to the local and regional economy
• Tourism employs 11 604 people in the town
• 3000 homes at risk from erosion so a huge amount of local public support for the protection schemes
• 100 businesses at risk
What are the coastal defences in Bournemouth?
New 17-year plan agreed in 2015
Total cost of the scheme is estimated to be around €50 million
• Replacement of the 53 groynes which currently protect the coast and have done since 1915
• Dredged material from the sea bed off the Isle of White will be spread onto the beach every 5 years
• ‘long groyne’ at the end of the beach to be replaced and prevent any material from moving further down the coast.
• Mainly funded by the environment agency with 19% contribution from local council
What effects are Bournemouths coastal defences having on Barton?
Barton on Sea is the next settlement down the coast from Bournemouth and has seen a noticeable loss of beach material and acceleration of erosion since groynes were first installed in Bournemouth in 1915.
Despite some localised rock armour erosion rates at Barton are up to 3m per year and homes and static caravans have been lost to the sea.
This is largely down to the lack of a beach to act as a natural barrier to the sea and absorb the energy from the waves.
The people of Barton argue Bournemouth should not be allowed to replace their groynes and starve them of sediment, but the fact that the area is of lower economic value means that their concerns are unlikely to be addressed.
