Longshore Drift - Lecture notes PDF

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Longshore Drif  The transport of sand and pebbles along the coast is called longshore drift.  The prevailing wind (the direction the wind usually blows from) causes waves to approach the coast at an angle.  The swash carries the sand and pebbles up the beach at the same angle (usually 45°).  However, as the water runs back down the beach, the backwash carries the material back down at right angles (90°) as this is the steepest gradient.  If a pebble was placed in the water it would be carried along the coastline in a zig-zag motion and would eventually be deposited as the waves lose energy.  The general direction of longshore drift is decided by the prevailing wind. In the diagrams below the prevailing wind is approaching from the south-west. Therefore longshore drift is moving material from the west to the east.  Shortly after a defensive structure is put in place such as a groyne, a section of cliff immediately downdrift of the work begins to erode at an increased rate. This is because there is little or no sand due to the lack of longshore drift. A lack of sand prevents an increase friction to slow down the waves causing more destruction. This is known as Terminal Groyne Syndrome. The Effects of Terminal Groyne Syndrome on the UK Barton-on-sea is a coastal village located in Hampshire, South of England. The cliffs at Barton on Sea are subject to considerable erosion and a large part of the beach has been lost to coastal defences. The types of cliff collapse that occurred at Barton-on-sea were that of sliding and slumping Causes  The rocks that the cliffs consist of are made up of gravels, sands and clays. This means that they are easily eroded and have little strength to resist collapse.  The area of the coast has a south-westerly prevailing wind, this means that long shore drift will occur and pass the sand towards the hurst castle spit.  A large groyne has been built at Bournemouth, this means that any longshore drift that should bring a replenishment of sand, is being caught up at Bournemouth beach. This causes the destructive waves to have more effect on the cliff faces because there is less friction on the beach to slow the waves down.

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Effects The properties of people would have been endangered, destroyed or in the very least circumstances, damaged some beyond repair.  There will be a reduced tourism industry, as the beaches will not have as pleasant aesthetics in comparison to other beaches and the beaches that Barton-on-sea had prior to the cliff collapsing.  The resident's housing may have been destroyed and they may have had to move or relocate because of this....