Coasts

• Sediment cell

  Section of a coast bordered by prominent headlands, movement of sediment is almost contained and there is dynamic equilibrium
• Coastal zones

  • Backshore
  • Foreshore
  • Inshore
  • Offshore
• Inputs

  • Marine inputs
  • Landward inputs
  • Atmospheric inputs
• Marine inputs

  • Longshore drift
  • Tides
  • Salt spray
  • Wave deposition
  • Sea level change
• Landward inputs

  • Mass movement
  • Cliff erosion
  • Sediment from rivers
  • Human activity
  • Coastal management
• Atmospheric inputs


  • Sun
  • Air pressure
  • Wind speed and direction
• Outputs

  • Sediment transfer
  • Evaporation
  • Rip tides
  • Ocean currents
  • Sand dune development
• Transfers / flows

  • Mass movement
  • Erosion (hydraulic action, abrasion, attrition, corrosion)
  • Transportation
  • Deposition
  • Longshore drift
  • Weathering
• Stores


  • Coastal landforms
• Energy


  • Wind
  • Waves
  • Tides
  • Currents
  • Gravity
• Positive feedback


  One change in the system amplifies the change and leads to further change
• Negative feedback


  Lessens a change that has happened, moving the system towards its original state
• Wind


  Movement of air from one area to another, always moves from high to low pressure, the greater the difference in pressure between places (pressure gradient), the stronger the wind
• Wind


  • Lower air pressure means lower temperatures, as warm air rises, and vice versa
• Strength of wind


  Differences in pressure are caused by variations in surface heating by the sun, larger pressure differences mean stronger winds, stronger winds mean stronger waves
• Duration of wind


  Longer periods of wind cause wave energy to build up
• Fetch


  The distance the wind blows over, a larger fetch means stronger waves
• Prevailing winds come from the southwest in the UK
• The southwest coast of the UK receives high wave energy as it travels across the Atlantic Ocean, meaning it has a large fetch</b>
• Wave terminology


  • Crest
  • Trough
  • Wave height / amplitude
  • Wavelength
  • Wave period
  • Wave frequency
  • Wave velocity
  • Swash
  • Backwash
• Wave formation


  1. Frictional drag between the air and the water creates small ripples

  2. Water particles orbit in a circular motion

  3. As the seabed becomes shallower near the coast, the orbit of particles becomes more elliptical as it is pushed forward by lower depths

  4. This increases wave height but decreases wave velocity and wavelength

  5. This causes water to back up behind the wave

  6. It breaks when it reaches a height:wavelength ratio of 1:7
• Constructive waves


  Weather systems in the open ocean, long wavelength, low frequency, low waves surge up beach, stronger swash than backwash
• Destructive waves


  Storms with strong winds near the coast, short wavelength, high frequency, high waves plunge on beach, weaker swash than backwash
• Constructive waves are more common in summer


  Destructive waves are more common in winter due to storms
• Constructive waves build up a beach, making it steeper


  This steeper gradient encourages waves to become more destructive, these destructive waves move sediment back to the sea with their strong backwash, reducing the steepness and again encouraging constructive waves
• Wave refraction


  The process of waves becoming increasingly parallel to a coastline with an irregular shape, when waves approach the shore at an angle, the bit closer to the shore is in shallower water and slows down due to more friction with the seabed, the bit of the wave in deeper water moves at a constant speed, so the wave refracts to make it more parallel to the coastline
• Areas with bays and headlands have more wave refraction, energy is focused on headlands leading to erosive features like stacks, bays are lower energy so depositional landforms like beaches are formed
• Tides


  Periodic rise and fall of the ocean surface, caused mainly by the gravitational pull of the moon but also the sun, more so moon as it is nearer, affect the position at which waves break, UK coastline has 2 high and 2 low tides per day, tidal range is the height difference between tides
• Spring tides


  When the Earth, sun and moon align, strongest gravitational pull, highest high tide and lowest low tide (biggest tidal range), occur twice a month when there is a full moon, areas closest and furthest from the sun/moon have highest tides, in between has the lowest
• Neap tides


  When the sun and moon are at a right angle to Earth, gravitational pull of the sun partially cancels out the moon's, low high tide and high low tide (small tidal range), also twice a month
• Tidal surges


  Strong winds produce higher water levels than usual, winds drive waves forward, pushing seawater towards the shore, intensified by spring high tides, happen in the North Sea
• Currents


  The general flow of water in one direction, in the surf zone (area where waves break) much of the energy is generates nearshore currents and sediment transport
• Longshore currents


  Driven by waves entering the surf zone with their crests at an angle to the shoreline, sediment carried by these is known as littoral drift, usually carry 10,000-100,000 cubic metres of sediment annually
• Flow and ebb currents

  Common in bays and estuaries, flood current picks up sediment on a rising tide and transports it inland, ebb current takes sediment back to sea on a falling tide
• Rip currents


  Strong, narrow currents near the shoreline moving away from it, plunging waves cause a buildup of water, backwash is forced underwater due to resistance from breaking waves, this forms an underwater current flowing quickly away from the shore, can reach 1m/second, faster than an Olympic swimmer, cause many deaths each year
• Upwelling


  Movement of cold water from deep to the surface of the ocean, denser cold water replaces warm surface water, creating nutrient-rich cold currents
• High and low energy coastlines

  • High energy: long fetch, erosion > deposition, destructive waves, large tidal range, strong currents, open and uninterrupted, high wave energy, steep offshore, more exposed to storms, erosional landforms

  Low energy: short fetch, deposition > erosion, constructive waves, small tidal range, gentle currents, closed and sheltered, low wave energy, gently sloping offshore, less frequent storms, depositional landforms
• Sediment sources


  • Rivers
  • Biogenic
  • Cliffs
  • Longshore drift
  • Wind
  • Glaciers
  • Offshore
  • Sea level rise
• Sediment cell


  An area of coastline separated from other areas by well-defined boundaries such as headlands, inputs and outputs are usually balanced, creating dynamic equilibrium
• Sediment transfers


  • Longshore drift
  • Saltation
  • Currents