Geography: Coasts

The Coast is a narrow zone where the land and the sea overlap, which vary and rapidly change.


Created by the action of the wind on the surface of the sea. Breaking waves are usefully divided into two types:

  • Constructive waves ~ Have a stronger swash then backwash, so that sediment is pushed up onto the beach, giving them their name as the backwash can entirely remove all of the sediment. They are characterised by longer wavelengths, lower height and wave frequency.
  • Destructive waves ~ Have stronger backwash than swash, meaning more sediment is pulled off the beach. They are associated with storm conditions, and have a steeper, shorter wavelength with more frequent waves.

Wave Refraction

As waves approach coastline, they leave deep water and are increasingly affected by frictional drag resulting from contact with the sea bed. This causes them to realign to become more parallel to the line in the coast. As coastline is irregular, some parts of the wave will be slowed by frictional contact (shallow water) and others will remain unimpeded (deeper water).This creates a concentration of wave energy on headlands and dissipation of energy in the bays.

Sediment Sources

Sources of sediment at a coast include:

  • Coastal Erosion
  • Biogenic Input (shells)
  • Sediment transported by rivers and wind
  • Marine deposits transported either along the coast by Longshore Drift or onshore tides and currents from offshore deposits.

Sediments maybe lost to Coastal System if blown inland, transported offshore or removed by human action.

Sediment Cells

Defined as a length of Coastline that is relatively self-contained in terms of the movement of sand and shingle. This is where a interruption to such movement should not have a significant effect on adjacent sediment sources.

Each major littoral cell is divided into a number of Sub-cells.


They are the regular rising and falling movements on the surface of the sea. They are caused by the effects of the gravitational pull of the moon and the sun on the oceans.

The pull creates an outward bulge in the oceans closest to the moon, and the other side of the Earth away from the moon. Creates effect of high tide, where drainage of water from intervening areas between these bulges are low tides.

The tide cycle is 12 hours and 25 minutes, so there are approximately 2 tides (high and low) each day. When the moon is between Sun and Earth, creates biggest bulge of water = Spring Tides (high tides at highest, low tides at lowest). When Earth, Moon and Sun form Right angles, gravitational pull interferes with one another and this is where neap tides occur (lowest high tides and highest low tides).

Costal Processes

Sub-aerial Weathering

Slopes = subject to change. Some movements are slow where as others are rapid. For these mass movements to occur, the underlying rocks must be weakened by processes of Sub-aerial weathering.

Rocks are vulnerable to weathering, the disintegration and decomposition of


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