Geography

• What does the size and energy of a wave depend on?

  The fetch, the strength of the wind, how long the wind has been blowing for.
• What does the fetch mean?

  How far the wave has traveled
• How many types of waves are there?

  2
• What is swash?

  The water flowing towards a beach when the wave breaks.
• What is backwash?


  The movement of water down the beach
• material from the coast is moved along the coastline by the sea and deposited when there is energy loss
• What leads to deposition?

  • Waves starting to slow down and lose energy
  • Shallow water
  • Sheltered areas eg bays
  • Little or no wind
• What is deposition?

  When the sea loses energy, it drops the material it has been carrying
• What is longshore drift?

  The movement of material along a coastline due to the angled approach of waves
• what is hydraulic action?

  This is the sheer power of the waves as they smash against the cliff. Air becomes trapped in the cracks in the rock and causes the rock to break apart
• What is abrasion?

  When pebbles grind along a rock platform, much like sandpaper. Overtime the rock becomes smooth
• What is attrition?

  this is when rocks that the sea is carrying knock against each other. They break apart to become smaller and more rounded
• Formation of caves, arches, stacks and stumps


  1. Cracks form in headland

  2. Waves erode and crack to form cave

  3. Cave becomes larger and breaks through headland to form arch

  4. Arch base becomes wider until roof collapses to form stack

  5. Stack undercut at base until it collapses to form stump
• Processes that break down and remove material from the coast

  • Erosion
  • Mass movement
  • Weathering
• Weathering


  The process that breaks down exposed rocks along the coastline
• Chemical weathering


  Rainwater and seawater can be a weak acid. If a coastline is made up of rocks such as limestone or chalk, over time they can become dissolved by the acid in the water.
• Mechanical weathering 


  A process that causes rocks to crumble. Breaking down of rocks where they are located, caused by rainwater, temperature extremes and biological processes
• Mass movement


  The downhill movement of sediment that moves because of gravity.
• Rock fall

  Bits of rock fall off the cliff face, usually due to freeze-thaw weathering.

  
• Rational slip


  Saturated soil slumps down a curved surface.

  
• Headlands and bays

  A bay is an inlet of the sea where the land curves inwards, usually with a beach. Hard rock is more resistant, soft rock is eroded inwards, the hard rock sticks out into the sea, forming a headland.

  
• Wave-cut platform


  A wide gently-sloping surface found at the foot of a cliff.
• Wave-cut platform 


  1. The sea attacks the base of the cliff between the high and low water mark.
  2. A wave-cut notch is formed by erosional processes such as abrasion and hydraulic action - this is a dent in the cliff usually at the level of high tide.
  3. As the notch increases in size, the cliff becomes unstable and collapses, leading to the retreat of the cliff face.
  4. The backwash carries away the eroded material, leaving a wave-cut platform.
  5. The process repeats. The cliff continues to retreat.

  
• Caves, arches, stacks and stumps

  Commonly found on a headland

  1. Cracks are widened in the headland through the erosional processes of hydraulic action and abrasion.
  2. As the waves continue to grind away at the crack, it begins to open up to form a cave.
  3. The cave becomes larger and eventually breaks through the headland to form an arch.
  4. The base of the arch continually becomes wider through further erosion, until its roof becomes too heavy and collapses into the sea. This leaves a stack (an isolated column of rock).
  5. The stack is undercut at the base until it collapses to form a stump.

  
• Coastal realignment 


  Is the overall term given to creating an engineered new position of a coastline. This involves moving the coastal boundaries inland, which is a process called manageable retreat.
• Medmerry managed retreat

  • In the past it was protected by a low sea wall
  • previously existing defence, a 3km shingle bank was subject to regular breach (£5million damage was caused in 2008)
  • building a new sea wall was too expensive
  • land is of relatively low value so the sea walk was allowed to be breached in 2013 and flood some of the farmland
  • cost £28million
• Medmerry managed retreat

  Positive effects:

  • created a large natural salt marsh that acts as a natural buffer to the sea and has established a valuable wildlife habitat
  • helps to protect surrounding farmland and caravan parks from flooding
  • encourages visitors to the are boosting the local economy through green tourism

  Negative effects:

  • Residents doubted the scheme would work and thought it would damage the local economy
  • £28 million was expensive in comparison to the sea wall that cost £0.28million a year to maintain
• Hard engineering


  The use of man-made structures to control the coast
• Sea walls


  Concrete walls placed at the foot of a cliff to prevent erosion, curved to reflect energy back into the sea
• Advantages of sea walls

  • Effective at protecting the base of the cliff
  • Usually have promenades for walking
• Disadvantages of sea walls

  • Waves can still break down and erode the wall
  • Expensive - approximately £2,000 per metre
• Rock armour


  Large boulders placed at the foot of a cliff to break waves and absorb their energy
• Advantages of rock armour

  • Cheaper than a sea wall and easy to maintain
  • Can be used for fishing
• Disadvantages of rock armour

  • Looks different to local geology as rock is imported
  • Expensive to transport
• Gabions


  Rocks held in mesh cages and placed in areas affected by erosion
• Advantages of gabions


  • Cheap - approximately £100 per metre
  • Absorbs wave energy
• Disadvantages of gabions


  • Not very strong
  • Looks unnatural
• Groynes


  Wooden or rock structures built out at right angles into the sea
• Advantages of groynes


  • Builds a beach which encourages tourism
  • Trap sediment being carried by longshore drift
• Disadvantages of groynes


  • Trap sediment, starving beaches further down the coastline and increasing erosion
  • Look unattractive