Coastal Transportation

The main principles of coastal transportation and a few resultant depositional landforms.

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  • Created by: Laura
  • Created on: 12-12-11 17:48

Coastal transportation

Sediment is moved either up or down the beach by swash/backwash 

or along by long shore drift.

It has been found that the movement of sediment close to the coast around the UK occurs in 'cells'.

The result is that the movement of sediment in one cell does not impact on beaches in another.


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Longshore drift

The process whereby material is moved along a stretch of coastline.

Waves approach the shore at an angle (usually in line with prevailing wind direction) and swash moves material up the beach in this direction.

Backwash pulls material straight down the beach.

The result is that material is transported in a zig-zag fashion.

It is important to remember that longshore drift can act on a beach in more than one direction, depending on the approach of waves and wind direction.

For example, Newquay in Cornwall has a southwesterly prevailing wind direction and wave approach, but can recieve them from other directions.

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Coastal deposition

Where sand/shingle is deposited on a beach rather than removed - inputs are greater than outputs

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Spits

Narrow, long stretches of sand/shingle that extend out to sea, or partway across a river estuary. One end is more protected than the other, and mud flats/salt marshes may develop in sheltered areas behind them. One of the most famous examples is Chesil Beach in Dorset.

Sandy spits form as a result of dominant constructive swell waves.

Shingle spits are a result of dominant destructive waves.

Why do spits develop hooked ends?  Two explanations are offered:

  1. A change from the prevailing wind direction, coinciding with the direction of second most dominant fetch and wave direction.
  2. Wave refraction occurs at the end of the spit which carries some material into more sheltered areas.
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Spits (http://www.s-cool.co.uk/a-level/assets/learn_its/alevel/geography/coastal-processes/coastal-deposition/2007-10-22_144058.gif)

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Tombolos and Bars

Tombolos

This is where a spit or bar connects the mainland to an island.

Bars

Such features are uncommon in the UK, but are the most common feature of coastal deposition in the world, shown by their presence on the Eastern Seaboard of the USA from New Jersey south to Florida. They are a number of sandy beaches that are totally separate to the main land, but run parallel to it, meaning that lagoons may develop behind them.

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Tombolos (http://www.s-cool.co.uk/a-level/assets/learn_its/alevel/geography/coastal-processes/coastal-deposition/2007-10-22_144113.gif)

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