Coastal Processes (CIE IGCSE Geography)

Coastal regions

• Where the land meets the sea is called the coast
• The coastline is the edge of the land marked through the high-water mark on a low-lying coast or the foot of steep sloped coasts
• The area between the lowest tide point and the highest point is known as the shore
• Tides are usually twice a day, but vary from coast to coast and with the time of the year
• The difference between low and high tide is known as the tidal range
• The tide controls high low and high the waves can work 
• It is the action of waves and currents that contribute to coastal features

Waves

• Waves are marine processes that erode, transport and deposit material
• Waves are formed by winds blowing over the surface of the sea 
• The size of a wave depends on:
  • The speed of the wind
  • The fetch (distance the wind travels)
  • The amount of time the wind blows (in the same direction)
• The greater the strength, time and fetch of the wind, the larger the wave
• As a wave approaches the coast and enters shallower water, friction from the seabed causes the wave to lean forward and eventually will crest and break onto the beach 
• The movement of water up the beach is called the swash, and the return movement is the backwash

• There are two types of waves:
  • Destructive waves erode the beach. They have a short wavelength, high-frequency rate and a steep wave gradient. Their backwash is stronger than their swash, which scours the beach, dragging material out to sea 
  • Constructive waves are beach builders. They have a long wavelength, low-frequency rate and a shallow wave gradient. The swash is stronger than its backwash, which carries material up onto the beach and deposits it there  

Comparison of Wave Type

Marine erosion

• Destructive waves are responsible for the majority of erosion that happens along a coast
• They cut into the coastline in four ways:
  • Hydraulic Action 
  • Attrition
  • Corrosion 
  • Abrasion 
• The effects of attrition are enhanced when the waves move sediment further and longer
  • A large, rough bolder is eventually eroded into round sand grains (quartz) the longer it stays in the water and the further it travels along the coast
• Rounded pebbles on a beach are known as shingle

• The sea transports sediment that it gets from erosion in the same way as a river does
• Material in the sea arrives from many sources:
  • Eroded from cliffs
  • Transported by longshore drift along the coastline
  • Brought inland from offshore by constructive waves
  • Carried to the coastline by a river
• Once in the water, the material is moved in different ways:
  • Traction 
  • Saltation
  • Suspension
  • Solution 

Longshore Drift

• It is the main process of transportation along the coast 
• Influenced by the prevailing wind, waves approach the beach at an angle
• As the waves break, the swash carries material up the beach at the same angle
• As the swash dies away, the backwash carries the material down the beach at right angles (90°) 
• The process repeats, transporting material along the beach in a zig-zag movement

Process of longshore drift

• On coasts where longshore drift in one direction, beach sediment is transported further down the coast
• If obstructed, sediment is prevented from moving and the area further along the coast is deprived of sediment
• This causes two issues:
  • Smaller beaches which are less attractive to tourists, causing a loss of income
  • Removes natural coastal protection 

• The movement of waves carries sand or shingle with them
  • Swash carries onto a beach
  • Backwash carries it away
• When a constructive wave carries sediment up the beach, the largest material is deposited along the upper reach of the swash
• As the backwash moves back down the beach, it loses water and therefore energy as it travels due to the porosity of the sand
• Consequently, the deposition of sediment gets progressively smaller, and the beach is therefore, sorted by wave deposition, with the smallest mud particles settling in the low-energy environment offshore
• If a destructive waveform due to a storm, then a large shingle is thrown above the usual high tide level to form a ridge at the top of the beach called a berm

Sediment Deposition