CGP The Coastal System

• Coastal system


  The area where the land meets the sea
• Coastal systems

  • They are natural systems
  • They have inputs, outputs, flows/transfers, and stores/components
• Inputs to coastal systems

  • Sediment
  • Energy from wind, waves, tides, and currents
• Outputs from coastal systems

  • Sediment washed out to sea
  • Sediment deposited farther along the coast
• Flows/transfers in coastal systems

  • Erosion
  • Weathering
  • Transportation
  • Deposition
• Stores/components in coastal systems

  • Beaches
  • Dunes
  • Spits
• Dynamic equilibrium


  Inputs and outputs are balanced in coastal systems
• Negative feedback

  A change in the system causes other changes that have the opposite effect
• Positive feedback


  A change in the system causes other changes that have a similar effect
• Sources of energy in coastal systems

  • Wind
  • Waves
  • Tides
  • Currents
• Winds in coastal systems

  • They are created by air moving from areas of high pressure to areas of low pressure
  • They can be very strong during events such as storms
• Prevailing winds


  • Winds that consistently blow from the same direction, causing higher-energy waves than winds that change direction frequently
• Waves in coastal systems

  • They are created by the wind blowing over the surface of the sea
  • Their effect on the shore depends on their height, which is affected by wind speed and fetch
• Wave breaking

  1. Friction with the sea bed slows the bottom of the waves and makes their motion more elliptical

  2. The crest of the wave rises up and then collapses

  3. Water washing up the beach is called the swash

  4. Water washing back towards the sea is called the backwash
• Constructive waves

  Low frequency (6-8 waves per minute), low and long, with a more elliptical cross profile. The powerful swash carries material up the beach and deposits it.
• Destructive waves

  High frequency (10-14 waves per minute), high and steep, with a more circular cross profile. The strong backwash removes material from the beach.
• Wave frequency


  How many waves pass a point in a particular time
• Tides


  The periodic rise and fall of the ocean surface, caused by the gravitational pull of the Moon and the Sun
• Tides


  • They affect the position at which waves break on the beach
  • The area of land between maximum high tide and minimum low tide is where most land is created and destroyed
• Currents

  The general flow of water in one direction, caused by wind or variations in water temperature and salinity
• Currents


  • They move material along the coast
• High-energy coasts


  Receive high inputs of energy in the form of large, powerful waves, often caused by strong wind, long fetches, and steeply shelving offshore zones. They tend to have sandy coasts and dynamic landforms like cliffs, caves, stacks, and arches. The rate of erosion is often higher than the rate of deposition.
• Low-energy coasts

  Receive low inputs of energy in the form of small, gentle waves, often caused by gentle winds, short fetches, and gently sloping offshore zones. They often have saltmarshes and tidal mudflats. The rate of deposition is often higher than the rate of erosion.
• Sources of sediment in coastal systems

  • Rivers carrying eroded sediment
  • Sea level rise flooding river valleys to form estuaries
  • Erosion of cliffs by waves, weathering, and landslides
  • Crushed shells of marine organisms
• Sediment budget


  The difference between the amount of sediment that enters the system and the amount that leaves. A positive budget means the coastline builds outwards, a negative budget means the coastline retreats.
• Sediment cells

  Lengths of coastline (often between two headlands) that are self-contained for the movement of sediment, meaning processes in one cell don't affect another.