Coasts and rivers

• How are waves caused?

  Waves are caused by wind blowing over the sea
• What is the size/energy of a wave determined by?

  3 factors:

  • Wind speed /strength
  • How long wind has been blowing in one direction
  • Distance the wave has travelled (the fetch)
• What is wave height, length and frequency?

  Wave height is the distance between wave trough and peak.

  Wave length is the distance between 2 wave peaks.

  Wave frequency is the number of waves per minute.
• What is swash?


  When a wave breaks, water rushes up the beach.
• What is back wash?

  When the water goes back into the sea due to gravity.
• Constructive and destructive waves

  Constructive:

  • Wave height lower (less than 1m)
  • Wave length longer (over 100m?
  • Wave frequency lower (8 per min)
  • Stronger swash
  • Sediment is pushed up the beach

  Destructive:

  • Higher Wave height (over 1m)
  • Shorter Wave length (less than 100m)
  • Higher Wave frequency (14 waves per min
  • Stronger backwash
  • Sediment dragged out to the sea
• Types of erosion?


  . Hydraulic power - sheer force of water, trapped air is forced in holes and cracks causing rock to break

  . Abrasion - waves hurl rock fragments at cliff, makes it smooth

  . Attrition - rock fragments smash into each other becoming sand

  . Solution - sea water dissolves certain rocks e.g. chalk
• Weathering


  The break down of rock "in situ".

  2 types:

  • Mechanical
  • Chemical e.g. acid rain
• Mass movement 


  A large scale movement of the earth due to erosion and weathering.

  • Rockfalls - undercutting waves create a screen slope on the base of a cliff due to weaknesses called joints and faults.
  • Slumping - permeable rock over impermeable rock. Water soaks through. Saturated rock e.g. clay becomes unstable and collapses in rational movement
  • Sliding - whole sections of rock slide down, caused by rain
• Wave cut platforms 


  Caused by erosion of the cliff. Waves erode the cliff using hydraulic action and abrasion. This will produce a wave cut notch at the base of the cliff. Eventually cliff will become top heavy and collapse. Process is repeated
• Headlands and bays


  These are formed when the rock types are arranged at right angles to the coastline.

  The hard rock is resistant to erosion, these will stick out to sea forming a headland.

  The soft rock is susceptible to erosion, these areas will retreat forming bays.

  Then the headlands erode because they stick out more and deposition occurs on waves - heavens out coast.
• Sea wall

  . Made from concrete or rock and reflect the wave

  . Cost £5000 - £10000 per metre

  . Negatives are expensive to make and maintain
• Groynes 


  . Made from timber or rock and stop Sediment moving by longshore drift - widens beach

  . Costs £150000 per every 200m

  . Negative is starves beaches further along the coast
• Rock armour 


  . Piles of boulders at bottom of cliff that force waves to break by absorbing their energy

  . Costs £200,000 per 100m

  . Negative is that rocks are from other parts of the coast or abroad
• Gabions


  . Wine cages filled with rocks that are built up against the cliff to buffer against the sea

  . £50000 per 100m

  . Negative is only last 5-10 years
• Soft engineering of coasts

  • Beach nourishment and re-profiling
  • Dune regeneration
  • Managed retreat (do nothing)
• Long shore 


  The zig-zag movement of material. The beach will be wider at the end of the beach due to the Prevailing wind.

  Prevailing wind - most common wind direction
• What are spits?


  A long narrow finger of sand that juts put into the sea from the land.

  Longshore drift and deposition is responsible. Made from Sediment, shingle and grass. They can have curved ends because of change in wind direction. The coastline needs to have a sudden change in direction like a headland.

  Low pressure waves go behind the spit so Sediment is deposited creating a slow build up of sand - forming a Saltmarsh
• Bars 


  When a spit grows into a bar due to longshore drift. The water trapped is called a lagoon and may form a salt marsh. An example of a bar is Slapton Ley in Devon.
• How are dunes caused?

  Caused by wind blowing sand to the back of the beach. The sand gets trapped by an object e.g. driftwood. Plants such has Margam grass atart to grow. They stabilise the dunes by binding the sand together.
• What is plant succession?

  As the plants like marram grass die they add nutrients to the sand. The soil becomes more fertile, allowing larger plants to grow
• What do you find at the back of dunes?

  The climax community, this is the final outcome of plant succession. Normally this is mature woodland
• Case study - Mappleton on Holderness Coast


  . Fastest eroding coastline in Europe

  . Lost 4km of land since roman time

  . Lost 29 villages

  . 20cm sea level rise since 1900

  . Cliffs made of boulder clay - dumped there in ice age by glaciers

  . Slumping occurs from heavy rain

  . Sea level rising due to climate change means waves break directly on cliffs
• Mappleton case study


  . Groynes and rock armour built (granite from norway)

  . 50 properties/ 600 residents

  . Cliff slumping south of rock armour

  . 50 properties were saved

  . B1242 was protected

  . Now wide substantial beaches reducing erosion and good for tourism

  • The scheme cost £2 million in 1991
  • Council has max of £4 million for repairs annually