Coasts Flashcards
What are properties of constructive waves?
- weaker winds
- short fetch
- low energy
- swash stronger than backwash
- deposition greater
- low waves
- long wave length
- 6-9 waves per minute
What are properties of destructive waves?
- strong winds
- long fetch
- high energy
- backwash stronger than swash
- erosion greater
- high waves
- short wave length
- 11-15 waves per minute
What is wave length?
The distance between wave crests
What is wave height?
The height from the wave trough to the crest
What is wave frequency?
The number of waves per minute
What is a crest?
The highest point of a wave
What is a trough?
The lowest point of a wave - the general sea level
What is fetch?
The distance in which waves are formed
What is swash?
Water rushing up the beach
What is backwash?
Water draining down the beach
What do the height and strength of waves depend on?
- wind speed
- the time the wind blows for
- fetch
How does longshore drift occur?
- waves approach the beach at an angle similar to that of the wind
- swash along the beach at angles - sea carrying sediment
- backwash at right angles to the beach
- beach material builds up
What is corrasion/abrasion?
The process where the coast is worn down by material carried by the waves - particles are thrown against the rock
What is hydraulic action?
When waves enter faults and compress air within the crack. When the wave retreats the air in the crack expands
What is attrition?
When material carried by the waves bump into each other so are smoothed and broken down
What is corrosion?
The chemical action of sea water where acids the salt dissolve rocks on the coast
What are the coastal processes involved in shaping the coast?
- wave erosion
- weathering (i.e. at top of cliff)
- mass movement (e.g. slumping, landslides, flowage)
- transportation (longshore drift)
- deposition
What types of weathering are there?
- mechanical
- biological
- chemical
Types of mechanical weathering?
- freeze thaw - jagged rock faces
* salt crystallisation
What is salt crystallisation?
- when salt crystal growth occurs in rock pores
* expanding crystals cause walls to crack
Where does salt crystallisation occur?
Only in coastal environments due to salt in the sea
Example of chemical weathering?
Acid rainwater - weak carbonic acid in rain dissolves rocks (solution)
Example of biological weathering?
Burrowing animals and plant roots cause rocks to loose and crack
What is mass movement?
The down hill movement of loose material under gravity
Case studies for coastal mass movement?
- landslip - Holbeck Hall Hotel, Scarborough
- rockfall - Beachy Head, Sussex
- slumping - Mappleton
- mudflow - Overstand, Norfolk
Details of the coastal mass movement case study in Scarborough?
- holbeck hall hotel
- 1993
- landslip
Details of the coastal mass movement case study in Sussex?
- beachy head
- 200ft high chalk tower ‘devil’s chimney’
- rockfall
Details of the coastal mass movement case study in Holderness?
- mappleton
* rotational cliff slumping
Details of the coastal mass movement case study in Norfolk?
- Overstand, Norfolk
* mudflow
Types of coastal mass movement?
- landslip
- rockfall
- rotational cliff slumping
- mudflow
What is a landslip?
- generic name for the downhill movement of a large amount of rock
- heavy rain drains through soil and into rock
- now heavier, mass falls away
What is a rockfall?
- when a cliff becomes unstable and collapses
- fragments of rock break away from cliff face
- wave cut notch at base of cliff
- freeze thaw weathering
- scree
What is rotational cliff slumping?
- curved surface
* material is rotated backwards into the cliff face as it slips
Where does slumping usually occur?
In places where there is no protection e.g. sea wall
What is a mudflow?
• groundwater seepage, rain goes into the ground
Where do mudflows usually occur?
Where vegetation is sparse so cannot hold the soil in place
How are headlands formed?
- discordant coastline
- hard and soft rock so there’s differential erosion
- soft rock retreats
- hard rock juts out
- wave refraction - tip of headland gets eroded slower and soft rock retreats more
What is wave refraction?
- the bending of waves
* concentrating erosion at the sides of the headland
How do waves wear away a headland?
- abrasion on either side of headland - wave cut notch
- caves - hydraulic action
- arches - weathering makes it collapse
- stacks and stumps - abrasion
- wave cut platforms
- attrition on fallen rock then transportation
What are discordant coastlines?
Coastlines where the geology alternates between bands of hard and soft rock
What is a concordant coastline?
A coastline which has the same type of rock along it
What do concordant coastlines tend to have?
Fewer bays and headlands
What is a spit?
A sand or shingle beach that is joined to the land but projects downdrift into the sea
Why are spits formed?
When the coastline suddenly changes shape or at the mouth of an estuary
What is a bar?
A ridge of sand or shingle that stretches from one side of a bay to the other - forming a lagoon behind it
Why are bars formed?
Longshore drift transporting sediment from one side of a bay to another
What are the characteristics of a spit?
- hooked end
- lagoon
- approx. 4km
- mudflats and salt marshes
How does a spit form?
- coastline changes shape, and waves begin to lose energy so there’s deposition at the near end
- long shore drift moves sediment along the beach
- hooks mark former ends of the spit
- pebbles become smaller near the end of the spit - attrition
- dominant wind causes far end to hook towards the land
What are beaches?
Areas of deposited sediment that lie between the high and low tide levels
When do beaches form?
When the swash of constructive waves is larger than backwash and deposition occurs
Why are the largest pebbles found at the back of the beach?
They get thrown to the back and therefore do not get reached by the tide and do not move as often
Why are larger rocks only found on one side of a groyne?
Only at one side will they be eroded by longshore drift
What affects the characteristics of a beach?
- the type of material
- how hard the material is
- the distance the material has traveled (rocks will be rounder)
What are the characteristics of a sandy beach?
- flat gradient
- constructive waves
- wide beach
- sand dunes at back of beach
- runners
- shingle at top of beach, fine sand at the bottom
What are runners?
Small water filled depressions formed at low tide, with rides either side
What are the characteristics of a pebble beach?
- generally steep
- destructive waves
- not as wide beach
- storm beach with large pebbles at back of beach
- smaller shingle at bottom of beach
What are the parts of the beach? (starting from the back of the beach)
- VERY BACK: dunes or storm beach
- back shore - usually dry
- foreshore - covered and uncovered by changing tides
- near shore - where waves break
- offshore - waves not breaking
How does a beach profile differ in the winter compared to the summer?
- steeper at the very back
- more destructive waves in the winter
- more material in back and fore shore moved
What is nearshore?
The breaker zone where waves break
What is backshore?
An area not usually affected by waves; sand usually dry
What is foreshore?
The intertidal zone repeatedly covered and uncovered y changing tides
What is offshore?
Fairly far out into sea where the waves do not break
What are sand dunes?
Coastal sand hills above the high tide mark
What are sand dunes shaped by?
Wind action
What is needed for a sand dune to form?
- large, flat beach
- large supply of land
- large tidal range (so there’s time for sand to dry)
- onshore wind to move sand to back of beach
- obstacle e.g. drift wood - for dune to form against
What are the three ways that wind moves sand?
- suspension
- saltation
- creep
How are sand dunes formed?
- heaviest grains of sand will settle against an obstacle
- ridge forms
- lighter grains settle on other side of obstacle
- area facing wind begins to reach a crest
- steep pile collapses and lighter grains fall down other side
- repeated - so dunes migrate inland
What is an embryo dune?
A newly formed dune closest to the sea
What is saltation?
How sand is bounced along by the wind
What is marram grass?
A plant found in the dunes that has long binding roots
What is a dune crest?
The top of a sand dune
What is a water table?
The upper horizontal limit of wet sand
What is dune slack?
When there is a trough or low point in a line of dunes
What is the Leeward side of a sand dune?
The slope that faces away from the wind
What is the windward side of a sand dune?
The slope that faces the wind
What is hard engineering?
When expensive artificial structures are used for procreation
What types of hard coastal management strategies are there?
- sea walls
- groynes
- rock armour
- gabions
What types of soft coastal management strategies are there?
- beach nourishment
- beach reprofiling
- sand dune regeneration
- managed retreat
What is a sea wall?
A costal defence that provides a barrier between waves and the land
Where are sea walls placed?
At the back of a beach
What do recurved sea walls do?
Reflect more waves
Advantages of sea walls?
- social - sense of security, cycling/walking route above
- economic - can last for years if well maintained
- environmental - don’t integer with transport of sediment
Disadvantages of sea walls?
- social - restrict access to beach, floods may occur if waves break over wall
- economic - expensive to build and for repairs
- environmental - ugly, can destroy habitats
Example of sea walls?
Hornsea or Easington
What are groynes?
Wooden or stone structures that trap sediment transported by longshore drift
Where are groynes placed?
The foreshore, at right angles to the beach roughly 50m apart
Advantages of groynes?
- social - some have concrete crests to walk on, windbreaks
* economic - cheap and can last if well maintained
Disadvantages of groynes?
- social - barriers that stop people walking on beach, dangerous due to deep water on one side and shallow on the other
- economic - problem is passed on down drift
- environmental - unattractive
Examples of groynes?
Bridlington, Hornsea or Easington
What is rock armour?
Boulders of hard rock that act as a barrier between the sea and land
How does rock armour work?
As water enters the gaps between boulders, pressure is released and reduces the waves’ energy
Advantages of rock armour?
economic - relatively cheap, quick to build and easy to maintain
Disadvantages of rock armour?
- social - restricts beach access and people climb over causing accidents
- economic - rock from abroad as oppose to from local quarries
- environmental - unattractive, litter gets trapped
Examples of rock armour?
Hornsea and Mappleton
What are gabions?
Cages filled with rocks
How do gabions work?
Water enters the cages and absorbs some wave energy - reducing the rate of erosion
Where are gabions placed?
At the back of a sandy beach
Advantages of gabions?
- economic - cheap and easily constructed, use local rock, quick fix
- environmental - blend in
Disadvantages of gabions?
- economic - only on sandy beaches as shingle would degrade them, need maintenance
- social - dangerous when damaged
- environmental - unattractive when damaged
Example of gabions?
Mappleton
Cost of sea walls?
£5000 per metre
Cost of groynes?
£5000 each
Cost of rock armour?
£1000-3000 per metre
Cost of gabions?
£100 per metre
What is beach nourishment?
Replacement of lost sediment
How is beach nourishment carried out?
- beach recharge - sediment is taken from a bay that is losing sand. dredger collects shingle from seabed and pumps it out
- beach recycling - sediment is taken from a down drift area which is building up and return it up drift
Cost of beach nourishment?
£300,000 to hire dredger
£3000 per meter
Advantages of beach nourishment?
- social - wider beach so more space for people
- economic - protect expensive properties, widened beach reduces sea wall maintenance
- environmental - blends in
Disadvantages of beach nourishment?
- social - during nourishment beach access is restricted
* economic - ongoing costs as it has to be redone
Example of beach nourishment?
Sandbanks, near Poole
What is beach reprofiling?
Artificial reshaping of a beach using existing material
Cost of beach reprofiling?
£200,000 per year
Advantages of beach reprofiling?
- social - residents are protected so feel safe
- economic - cheaper than hard engineering
- environmental - looks natural
Disadvantages of beach reprofiling?
- social - bulldozers restrict beach access
- economic - major reprofiling is expensive
- environmental - steep, high crested beach may look unnatural to tourists
Example of beach profiling?
Selsey in West Sussex
What generally costs more: hard or soft engineering?
Hard engineering
What is sand dune regeneration?
Artificial creation of new sand dunes or regeneration of existing ones
Cost of sand dune regeneration?
£2000 per 100 metres
Advantages of sand dune regeneration?
- social - protect land behind and can be used for walking/picnics
- economic - small planting projects use volunteers so costs are minimal
- environmental - help maintain habitat
Disadvantages of sand dune regeneration?
- social - when becoming established they’re fenced off to public
- economic - checked twice a year, costly systems in place to prevent trampling, boardwalks to reduce damage
- environmental - no guarantee dunes will be stable
Example of sand dune regeneration?
Studland in Dorset or Formby
What is managed retreat?
When the decision is made to no longer follow a ‘hold the line’ strategy
Cost of managed retreat?
£28 million
What are the costs of managed retreat for?
To relocate residents and demolish buildings
Advantages of managed retreat?
- social - reduce risk of flooding further down drift
- economic - cheaper in the long term
- environmental - enhance natural environmental, creates new intertidal habitats
Disadvantages of managed retreat?
- social - relocation of residents causes disruption
- economic - short term costs of relocation
- environmental - agricultural land lost, so are coastal habitats of birds so bird numbers will decline
Example of managed retreat?
Medmerry in West Sussex
What type of erosion is involved in creating caves?
Abrasion
Why do arches become thinner at the top?
Due to weathering at the top of the cliff e.g. freeze thaw
