1.1.6

• -Traction is when larger calibre sediment rolls and slides along the seabed, but only when high energy conditions exist (you can hear pebbles being moved on a shingle beach). The size of the material is approx 4mm-64mm.
• Saltation is a skipping motion of sand grains along the seabed in an arc-shaped trajectory. This can move vast quantities of sand, even though one skip is relatively short distance. The calibre of the sediment is approx. 0.5-4mm (granules and coarse sand).
• flocculation

  Clay particles possess a negative charge that causes the individual particles to stay apart in freshwater, 

  but as the clay enters the estuary, the positive sodium ions in the saline water overcome the repelling negative forces of the clay particles. 

  They then bind together to form flocs.
• There is also organic flocculation. This is when invertebrates such as shrimps ingest clay particles, and then excrete pellets that are essentially clay flocs. These are large enough to settle out and be deposited.
• longshore drift

  • The wave approaches at an oblique angle. 
  • Sediment is entrained up the beach through swash. 
  • The wave eventually runs out of energy because of friction and the gradient of the beach profile. 
  • Larger sediment will be deposited at the point where the swash ceases. 
  • Smaller particles may continue to move with the water that returns to the sea as backwash. 

  This return is perpendicular to the beach.
• Deposition is when material being transported is dropped on the coast:

  • marine deposition is when sediment carried in seawater, i.e. waves drop the sediment

  aeolian deposition is when sediment carried by the wind is dropped
• Deposition happens when the sediment load exceeds the ability of the water/ wind to carry it. 

  This can be because the sediment load increases (e.g. if there is a rockfall onto the beach) 

  or the water flow/ wind speed slows down.
• Wind and water slow down for similar reasons:

  1. Friction increases - if waves enter shallow water or wind reaches land, friction between the wind/water and the ground surface increases, which slows down the wind and the water
  2. Flow becomes turbulent- if water/ wind encounters an obstacle, e.g. driftwood on the beach, then the flow becomes rougher and overall speed decreases

  If the energy input drops e.g. wind speed then size of the waves will decrease
• A spit is a long, narrow feature, made of sand or shingle, that extends from the land into the sea (or part way across an estuary). 

  Where the spit joins the land is known as the proximal end

  The end projecting out from the coast is the distal end. 

  They are found in locations that have;

  -a ready supply of sediment (sand and shingle)

  -the coast has an abrupt change in direction (estuary or bay)
• spit

  Sand and shingle is moved along the coastline by longshore drift, but if the coastline suddenly changes direction (e.g. because of a river estuary), sediment begins to build up across the estuary mouth and a spit will form. 

  The outward flow of the river will prevent the spit from extending right across the estuary mouth. The end of the spit will also begin to curve round, as wave refraction carries material round into the more sheltered water behind the spit. This is known as a recurved spit. Spits with several recurves along their length can be termed compound spits.