systems and processes in coastal environments

• fetch - the distance the wind has travelled
• swash - the wave moving up the beach
• backwash - the wave moving out
• Constructive waves - adding sediment to the beach
• Destructive - removal of sediment from the beach
• prevailing winds - most dominant wind direction
• erosion - breaking down of material and the removal of it
• discordant coastline - perpendicular to the sea, mixture of hard and soft rock
• Concordant coastline - parallel to the sea and the same rock type
• long shore drift - movement of sediment along the coastline, by swash and backwash
• Coastal system

  • open system
  • a series of linked elements affecting the coastal zone through which energy and material circulate
  • dynamic interface where the land and the sea meet
• coast - part of the land near the sea; edge of the land
• coastline - regarded as an open system, with inputs, processes and outputs; interacts with the surroundings
• sand supply

  • sand is food for beaches and gives shorelines protection from waves
  • being starved of sand can cause increased rate of erosion
• waves:

  • the erosive action of a wave increased when the wave is high
  • the angle at which they strike and how much sand they are carrying can also influence the rate of erosion
• Factors affecting the coastline:

  • wave type
  • rock type
  • fetch
  • climate
  • agents of erosion
  • sea level change
  • sediment type
  • topography
• landform - a specific geomorphic feature on the surface of the earth, ranging from large scale features such as plains, plateaus and mountains to minor features such as hills, valleys and alluvial fans
• landscape - part of the earths surface that can be viewed at one time from one place. It consists of geographic features/landforms that are characteristics of a particular area
• inputs - human activity, sediment, relief, waves, tides, current, rocks, sediments and changes in sea level

  processes - erosion, long shore drift and deposition

  outputs - arches, stacks, beach, spits, salt marshes, cliffs, sand dunes and loss of wave energy
• inputs of energy at the coast:

  • wind
  • waves
  • tides
  • sediment
  • human activity
• wind

  • wind moves from high to low pressure
  • variations in atmospheric pressure is caused by differences in surface heating by the sun
  • the grater the pressure difference the stronger the wind
• roles of wind in coastal system:

  • prevailing wind
  • creation of waves
  • agent of erosion
• factors affecting wave energy:

  • strength of the wind
  • duration of the wind
  • fetch
  • prevailing wind
• UK prevailing winds

  • come from the south-west, the results from air moving from sub-tropical high pressure belt at 30 degree north to the sub-polar low pressure belt at 60 degree north.
  • wind blows across Atlantic ocean
• Wave formation:

  • waves are formed by wind moving over the ocean
  • as the wind drags over the surface, friction causes disturbance and causing waves
  • In open water, waves have orbital motion
  • as they approach the land this motion is interrupted by friction with the sea bed to become elliptical in shape
  • this reduces wave length and increases wave height
  • when the height to length ration reaches 1:7 the wave breaks
  • the breaking of a wave causes swash
  • when water has no energy left the water runs back down the beach under gravity as backwash
• Wave period - how long it takes two crests to pass a certain point
• wave frequency - the number of waves passing a certain point per minute
• constructive waves

  • causes deposition of material
  • decreased frequency
  • decreased height
  • increased wavelength
  • strong swash and weak backwash
  • created a berm
  • small, gentle waves
• destructive waves

  • removal of sediment
  • weak swash and strong backwash
  • high steep waves
  • base of cliff attacked
  • shorter wavelength
  • increased height
• Wave refraction

  • when waves approach an irregular shaped coastline, then waves are refracted
  • wave fronts can become distorted which can distort the spread of energy
  • as the wave nears the coastline it is slowed by friction in the shallower water off the headland causing waves to increase in height
• wave refraction

  • wave energy becomes concentrated on the headland, causing greater erosion. The low energy waves spill into the bay, resulting in beach deposition
  • the part of the wave crest in the deeper water approaches bay fast as not slowed by friction. waves bend around the headland and the orthogonal converge.
  • the low energy waves spill into the bay resulting in beach deposition, this caused a long shore drift movement
• swash aligned beach

  • waves break parallel to the shore. No long shore movement of sediment once the equilibrium form is established.
• drift aligned beach

  • sediment inputs are sufficient to meet the demand for long shore drift
  • beach progrades to become parallel to the line of maximum drift
• Tides - the periodic rise and fall of the level of the sea in response to the gravitational pull of the sun and moon
• tides:

  • moon pulls water towards it, creating a high tide
  • the draining of water from the intertwining areas between these bulges causes low tides
• spring tide - when the moon is between the earth and the sun, the combined gravitational pull creates the biggest bulge of water and highest tide. Tidal range = greatest
• neap tide - when the earth, moon and sun form a right angle, their gravitational pull interfere with one another and this is where the near tide occur, giving the lowest high tides and highest low tides. Tidal range = smallest
• tidal ranges determine the upper and lower limits of erosion and deposition and the amount of time each day hat the littoral zone is exposed and open to aerial weathering
• high energy coastlines:

  • tend to be rocky coastlines
  • tend to be stretches of the atlantic facing coast
  • the rate of erosion exceeds deposition
  • landforms: headlands, cliffs and wave-cut platforms
• low energy coastlines:

  • tend to be sandy coasts
  • stretches of the coast where the waves are less powerful
  • rate of deposition exceeds erosion
  • landforms; beaches, spits and coastal plains