2B.5B: Depositional Landforms

• Deposition

  • Deposition occurs when waves no longer have sufficient energy to continue to transport material
  • This loss of energy might be due to:
  • the wind dropping, removing an energy source
  • resistance by obstruction, e.g. a groyne or headland
  • dissipation of energy through refraction
  • friction from extended transport across shallow angled nearshore and foreshore zone
• The two main ways in which deposition occurs

  1. Gravity settling occurs when the energy of transporting water becomes too low to move sediment. Large sediment will be deposited first, followed by smaller sediment (pebbles -> sand -> silt)
  2. Flocculuation is a depositional process that is important for very small particles, such as clay, which are so small that they will remain suspended in water. Clay particles clump together through electrical or chemical attraction, and become large enough to sink. 
• Beaches

  • ​Beaches are accumulations of sand and/or shingle found in the foreshore and backshore zones. 
  • They're produced by material deposited by constructive waves
  • The swash has the strength to carry material up the beach, but the backwash only has enough energy to transport some of the material back down the beach, leaving the remainder deposited
• Swash-aligned beach

  Oriented parallel to the shoreline. Fairly closed sediment system as limited transfer into or out of the beach.
• Drift-aligned beach

  Oriented obliquely to the shore. More open system as sediment enters at one end, passes along the length by longshore drift and then leaves the beach.
• Bayhead beach

  Bayhead beaches are curved beaches found at the back of a bay.

  • They’re common on swash-aligned coastlines where wave refraction disperses wave energy around the bay perimeter.

  Waves break at 90° to the shoreline and move sediment into a bay, where a beach forms. Through wave refraction, erosion is concentrated at headlands and the bay is an area of deposition. 
• Spits

  • Linear ridges of sand or shingle beach stretching into the sea beyond a turn in the coastline (usually greater than 30') but connected to the land at one end
• How do spits form?

  • They form on drift-aligned coastlines, where the coastline changes direction, usually by more than 30', e.g. at a bay or a river mouth
  • At the turn, LSD continues in the original direction, but its energy is lost as the wave refracts and the current spreads, leading to deposition on the sea bed. 
  • Over time, sufficient sediment is deposited to break the surface, extending the beach into the sea as a spit
  • The process continues until equilibrium is reached at the distal end (seaward) of the spit, between deposition and erosion by waves or the existing river current. 
• ​Hooked/Recurved spits

  • A spit whose end is curved landwards, into a bay or inlet.
  • A hook or a recurve may form at the end of the spit. 
  • This is because wave refraction round the distal end transports and deposits sediment for a short distance in the landward direction. 
  • Alternatively, it could be because the wind and wave front are frequently at an opposing angle to the prevailing wind, generating short periods of longshore drift in the landward direction. (These last two can make it more pronounced)
  • Or, a strong incoming tidal current can also create a recurved spit.
• Double spits

  • Two spits extend in opposite directions
  • They form where LSD is operating in different directions on opposite sides of the bay
  • e.g. Poole Harbour
  • They can also form when:
  • Rising sea levels drive ridges of material onshore from the offshore zone
  • Barrier beach driven across a bay forms a bar but a strong exiting river current may breach the bar to form a double spit
• Tombolos

  Tombolos are linear ridges of sand and shingle connecting an offshore island to the coastline of the mainland.

  E.g. Chesil Beach, Dorset Two ways they can form are:

  • Drift aligned coastlines - when LSD builds a spit out from land until it contacts with an offshore island. 
  • Swash aligned coastlines - when there is wave refraction around both sides of the island. 

  1. This causes a collision of wave fronts on the landward side, cancelling each other out and producing a zone of still, calm water where deposition occurs
• Cuspate Forelands

  • Low lying triangular shaped headlands of deposited sediment
  • Two streams of LSD come from different directions
  • Formation (debated):
  • LSD currents from opposing directions converge at a boundary of 2 sediment cells
  • When sediment is deposited out into the sea by both currents creating a triangular shaped area of deposited material
  • They can extend from a few metres to several kilometres. 
  • An example is at Dungeness in Kent
• Bars / Barrier Beaches

  • Linear ridges of sand/shingle extending across a bay and are connected to land on both sides.
  • It traps a body of seawater behind it, forming a lagoon. 
  • They can form in two ways:

  1. On drift-aligned coastlines, when longshore drift extends a spit across the entire width of the bay. 
  2. When rising sea levels cause constructive waves to drive a ridge of sediment onshore to coastlines with a gently sloping shallow sea bed. (barrier beach)
  3. E.g. there's a 9 km barrier beach that extends across Start Bay, Devon, trapping Slapton Ley lagoon behind it
• Offshore bars


  • Offshore bars are ridges of sand or shingle running parallel to the coast in an offshore zone.
  • They form from sediment eroded by destructive waves and carried seawards by backwash.
  • The sediment is deposited at the boundary of the offshore and nearshore zone, where the orbit of water particles ceases to reach the seabed, halting the transport offshore.
  • They can sometimes be exposed by neap tide.
  • They are used:
  • to construct wind farms
  • e.g. Scroby Sands, Norfolk
  • as a source of sand for beach nourishment
  • for shingle dredging for construction material