The Coastal System

The coast is the part of the land near the sea, around the edge of a piece of land. The coastline is regarded as an open system with inputs, processes and outputs, and it interacts with the surroundings.

Inputs include energy from waves/wind/tides/sea currents, sediment, geology of coastline, sea level change.

Erosional processes


Components including erosional landforms and landscapes

Wind and water transport



Components including depositional landforms and landscapes

Wind and water transport



Outputs include dissipation of wave energy, accumulation of sediment above tidal limit, sediment removed beyond local sediment cells


Coasts can be studied in different ways dependent on classification:

  • Erosional or depositional
  • Sediment type – clastic like shingle or sand, or muddy
  • Submergent or emergent linked to sea level change
  • Tectonic setting
  • Process-based – wave dominated, tide dominated and wind dominated – agents of erosion
    • Wave dominated landform development – wave-cut platforms, cliffs, beaches, spits/tombolos, deltas
    • Tide dominated landform development – mudflats, sandflats, salt marshes, mangroves, deltas
    • Wind dominated landform development – sand dunes




Activity of coastline:

  • Coastal systems vary in response to wave intensity and tidal currents primarily
  • Breaking waves, and resultant currents, provide most of the systematic energy
  • Several additional factors also influence coastal processes and landforms
    • Original geology of the coastline
    • Relative ‘erodibility’ of regional bedrock
    • Sea level variations (global and local tectonic or glacio-eustatic changes – melting of ice during interglacial periods, and build-up of ice in glacial periods)
  • Systems are typically characterised as erosional or depositional
  • Erosional or depositional nature of any coastline varies with systematic energy


A landscape is an area as a whole on a relatively great scale – it refers to all visible features on the area of land and is often considered in terms of aesthetic appeal.

A landform is a specific natural feature within a landscape.

Feedback is a characteristic of all coastal systems. The assemblage of erosional and depositional landforms is constantly changing. A coastal system tends towards dynamic equilibrium, as it is driven by input of energy, processes operating in the environments, and the outputs in shape of coastal landforms in many cases.

Coastal systems positive feedback:

  • Cliffs are eroded through processes like abrasion
  • This causes more weaknesses in rock so more sediment becomes loose into the ocean
  • There is then more sediment in the sea to be thrown and attack cliffs
  • More abrasion occurs

Coastal systems negative feedback:

  • Sediment eroded from beach during a storm
  • Sediment is deposited offshore forming an offshore bar
  • Waves are now forced to break before reaching the beach, meaning their energy is dissipated and further erosion is reduced when they reach the beach
  • When the storm calms, normal wave conditions rework sediments from offshore bar back to the beach
  • The beach is in dynamic equilibrium