Coastal Systems (AQA A Level Geography)

• At the coast energy refers to the power behind any change or transfer in the system
• The main source of energy at the coast is the waves 
  • Waves are mainly generated by wind 
  • They can be caused by tectonic activity but this is much less regular 
• Wind occurs because of the rotation of the earth and differences in atmospheric pressure when different parcels of air are heated differently by the sun
• Various features of the wind will affect how much energy a wave has: fetch, duration and strength of the wind.  

Wave characteristics

• The tide and tidal range also have an important role in the energy of the waves at a coast
  • A high tidal range such as in the Bristol Channel, means that waves only reach a particular part of the cliff for a small amount of time, and less energy is focussed on that spot 
  • A low tidal range such as in the Mediterranean, means that waves will be concentrated on a small part of the cliff for longer, increasing the energy directed at that point 
• Other currents like rip currents also transfer energy at the coast
  • These are localised channels of powerful, fast-moving water that cut through the breaking waves
  • They have localised high energy
• High energy coastlines are those that face powerful waves for most of the year 
  • Erosion exceeds deposition at high-energy coastlines and the landforms reflect this such as headlands with arches and caves eroded into them and wave cut platforms
• Low energy environments are those where the waves are less powerful and the coast is more sheltered 
  • Deposition exceeds erosion at these coastlines creating beaches and spits

Waves are created due to friction between the wind and the surface of the sea

• There are two main types of wave, constructive and destructive

• The type of wave in an area can vary depending on time of year or coastal management
• Wave refraction changes the amount of energy reaching the shore on a small local scale
  • Wave energy concentrates at the headland and increases the rate of erosion

wave refraction

• There are a range of sources of sediments in the coastal zone 
• Most coastal sediment is brought to the shore by rivers
• Cliff erosion is also an important source of sediment at most coastlines
• Where coastlines are retreating by a few metres a year there is a large input of sediment to the coastal zone 
• Wind can also transport sediment to the shore and this can lead to the build up of sand dunes 
• In high latitude coastal areas glaciers break off into the sea and sediment that was trapped within the ice is deposited at the coastal zone 
• Sediment Cell are an important way of understanding the coastal system
• They can be considered a closed system as most sediment movement is contained within the cell 
• There are 11 sediment cells around the UK coastline 
• Sediment cells can be divided into sub cells where the inputs (sources), stores (sinks), transfers and outputs within the system can all be identified 

The sediment cells of England and Wales

• The sediment budget is the balance between the 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 
• However, human activity and natural changes like climate change can disturb the state of dynamic equilibrium.