Coastal Processes - Transportation
The transportation of sediment; sand and shingle is constant due to the action of waves. The majority of movement along the coastline is due to the process of longshore drift.
Waves wash up the beach known as the swash, loose energy and then retreat back down the beach known as the backwash. It may appear that waves break at a right angle, but in most cases it is at an oblique angle in the direction in which the wind is blowing, known as praviling wind. There are however exceptions where this isnt true. Beaches where waves approach the beach at a right angle are rather rare, and are called swash aligned beaches. Where this is true, there is very little if any transportation of material in the form of longshore drift.
When a wave becomes top heavy it breaks on the shoreline , the swash is washed up the beach at the same angle the wave breaks. The retreating backwash runs down the beach carrying material from the beach with it. The backwash, as shown in the diagram, runs straight down at a right angle under the influence of gravity.
Material is therefore transported slowly across the beach in a zig-zag formation.
Groynes are a form of coastal defence in which more information can be found at Coastal defences. Groynes are commonly used on beaches to prevent the loss of sand and sediment by trapping it and preventing the depletion of sand and material from sections of the beach.
You should be able to determine the direction of longshore drift by carrying out a test as part of yor filedwork study on coastal erosion. By measuring the distance between the sand and the top of the groyne on both sides and repeating this method on at least 6 other groynes, you should record your results and see a pattern. You should be able to see that overall either left or right or the groyne contains a larger build up of sand. This would therefore be the direction the sea is transporting material (Direction of longshore drift)
On the East coast for example the Holderness Coastline the dominant prevailing winds are from the NorthEast so the dominant direction of longshore drift moves in a southerly direction:
On the South coatline the direction of prevailing winds is from the southwest so the dominant direction of longshore drift is Eastily.
Quiz
Animation of Longshore drift
Click on the animation below to view the process of longshore drift.
Direction of Longshore drift on the East Coast
Direction of Longshore drift on the East Coast - Longshore drift moves southerly due to the North Westerly Prevailing Winds.
Click the square and drag to view the map in Satellite view
Longshore drift creates landforms when the material is deposited known as: spits, bars and Tombolas. Click here to learn about Landforms and Depostion.