Coastal Systems (AQA A Level Geography)

Coastal Sources of Energy

• 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.  

• 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 and Wave Refraction

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

Coastal Sediments

• 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 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.