eq2

• the coastline as an open system

  where matter & energy can be transferred from the system into the surrounding environment

  eg. sediment may be inputted from rivers
• dynamic equilibrium 


  met if inputs & outputs of a system are in balance. flows continue but no overall change.

  eg a beach
• negative feedback


  where a subsequent effect decreases the previous effects of a system. this promotes the state of dynamic equilibrium (stability)

  • As the shore is eroded, the material makes the wave-cut platform wider
  • This can absorb wave energy and reduce the impact at the base of the cliff
• positive feedback

  where a subsequent effect increases the previous effects of a system, promoting instability and moving the system further from its original state.

  • As waves erode the cliff, material is released
  • This material abrades the cliff which results in even more cliff erosion 
• what is a sediment cell?

  a length of coastline separated from other areas by well-defined boundaries (eg headlands and/or deep stretches of water)

  11 sediment cells on England & Wales coastline
• each sediment cell illustrates a system with:

  • inputs- sediment put into system
  • flows/processes- sediment transported within cell
  • stores- sediment stored within the cell in beaches, spits etc
  • outputs- sediment eroded by destructive waves will later be deposited by constructive waves (negative feedback cycle)
• inputs of sediment

  • rivers
  • cliff erosion
  • longshore drift
  • wind
  • glaciers
  • offshore sediment
• sediment sinks 


  an area where sediment accumulates due to deposition outweighing erosion

  eg a spit- Spurn Head on the Holderness Coast
• what is the sediment budget?

  • balance between inputs and outputs of sediment in the system
  • coastal systems should be in a state where the sediment budget is in a state of dynamic equilibrium
  • human activity & natural changes (climate change) can disturb this
• what are the main sources of energy at the coast?

  • wind (strength/duration/fetch)
  • waves (constructive/destructive/wave refraction)
  • tides (spring tide/neap tide)
• wind

  • main form of energy at the coast is waves- generated by wind
  • wind is the movement of air from one place to another (high to low pressure)
  • where bigger differences in pressure- strongest winds
• Factors affecting wave energy

  • strength of wind (determined by pressure gradient)
  • duration of wind (longer=more powerful)
  • fetch (distance of open water wind blows over)
• Where is UK's fetch longest?

  south-west of UK experiences a long fetch for 4000km across Atlantic Ocean

  south of UK has short fetch across English Channel
• destructive waves

  • strong backwash, weak swash= beach loss
  • erosion
  • steeper beach profile but will become increasingly gentle as sediment gets removed
  • tall wave height & short wavelengths
  • break frequently
  • common during storm conditions
• constructive waves

  • strong swash, weak backwash=beach gain
  • deposition
  • gentle beach profile but will become increasingly steep as sediment builds up
  • low wave height & long wavelengths
  • less frequent
• wave characteristics

  • most beaches subject to alternating cycle of constructive & destructive waves due to changes in weather
  • constructive waves build up the beach=steeper beach profile. over time, causes waves to be more destructive
  • with time. destructive waves erode beach , reducing beach angle so more constructive waves
• how do waves change as they reach the coast?

  open water- circular orbit

  as they approach coastline, begin to touch sea bed=friction on base of wave

  circular orbit changes into elliptical orbit

  this increases height & steepness, forcing crest to curve forwatd & form breaking wave
• wave refraction

  • occurs when waves approach uneven coastline
  • waves hit headland first so destructive power concentrated here. waves dissipate towards bay= deposition
• orthogonal waves


  high energy waves that travel towards the headland due to refraction
• tides


  periodic rise and fall in the level of the sea

  they're caused by the gravitational pull of the moon and sun
• tidal range


  difference between the high & low tides
• spring tides

  • sun, moon & earth are in a straight line= greater gravitational pull
  • twice a lunar month
  • greater tidal range
• neap tides

  • sun, moon & earth form a right angle= weaker gravitational pull
  • alternate weeks
  • small tidal range
• tidal surges/ storm surges

  • when weather conditions cause strong winds which can produce much higher water levels than those a high tide
  • funnelling- strong wins push sea water towards coast and has effect of piling up water against the coast
• Storm beach


  result from high-energy deposition of very coarse sediment during severe storms. resultant landform often a very steep beach.
• beach cusps 


  shoreline formations made up of various grades of sediment in an arc pattern.
• berms 


  nearly horizontal plateau found towards backshore, signifies highest point that waves can reach during high tide.
• runnels 


  dips in the sand that form parallel to shore line in foreshore zone

  formed due to interaction of tides, currents, sediments and beach topography

  form as simple drainage route for tides, as water flows in and out via them
• ripple


  relatively small, elongated ridges that form on the beach, perpendicular to the sea
• marine processes 


  process that are connected with the sea

  eg. waves, tides & longshore drift
• sub-aerial processes


  processes that operate on land, but still affect the shape of the coastline

  eg. weathering & mass movement
• the rate of coastal erosion is affected by a number of factors:

  • wave steepness: steeper=greater energy
  • wave breaking point: waves that break at cliff foot exert greater erosive power than those that break away from the shore
  • fetch: further=greater erosive power
• the rate of coastal erosion is affected by a number of factors:

  • sea depth: steep beach profile will create steeper & more destructive waves
  • coastline shape: uneven coastlines cause wave refraction so orthogonal waves concentrate power at headland
• the rate of coastal erosion is affected by a number of factors:

  • size of the beach: wide & flat beaches absorb & dissipate wave energy more
  • sediment type on beach: shingle beaches reduce wave energy via greater friction and percolation
  • human activity: sea defences reduce rates of erosion where they're built but can exacerbate erosion elsewhere
• Abrasion (corrasion) 


  sediment and stones are picked up by the waves and wear away at the cliff/headland
• hydraulic action


  this is the shear force of the waves forcing air at high pressure into cracks in the cliff over time this weakens the rock and causes the joint to widen
• corrosion/ solution


  weak acids in seawater dissolve the rock particles
• attrition


  as rocks are moved around by the water they knock into each other gradually becoming smaller and rounder
• weathering 


  gradual breakdown of rock, in situ. it's divided into biological, mechanical & chemical
• mass movement 


  downward movement of material under gravity