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Sediment transportation + deposition - Coggle Diagram
Sediment transportation + deposition
Processes
Traction
Large boulders and pebbles are rolled along the seabed
Saltation
Smaller lighter materials bounce along the seabed. The wind can also saltate sediment on the beach.
Suspension
Fine material is suspended in a body of water or air
Solution
Material dissolved in water
Influences
Currents
Determine where and how far sediment is transported.
Continuous current:
global thermohaline current
Short-term current:
Rip currents are linked to strong winds or dominating prevailing wind direction. They are sporadic
Tides
Changes in the water level due to the gravitational pull of the moon.
High tidal range can cause strong currents moving more sediment- affects low-lying estuarine coastlines
Longshore Drift
When waves approach the coast at an angle transporting sediment in the direction of the waves. A dominant wind direction influences the direction of longshore drift making it more likely to travel in one direction than another.
Angle of wave attack
When wind is blowing onshore wave swash travels at 90' to the coast and so does the backwash so there is
no net lateral movement
Depositional landforms
Spits
drift-aligned coasts
Formation
Coast changes direction dramatically
Longshore drift transports sediment towards the dramatic change
Sediment starts to be deposited as wave energy dissipates growing the beach seawards
Low energy environment behind spit forms allowing for more sediment to be deposited
Vegetation stabilises the spit and allows for more sediment to be deposited.
As the spit grows the prevailing wind may cause it to curve landwards this is now a recurved spit.
Eg. Spurn Head Holderness Coast
Secondary currents, fluvial processes and wave action determine the length of the spit
Double spits
Formed when longshore drift is going in opposite directions across a bay. The spits start growing towards each other.
Bars breached by strong currents an also form double spits.
Beaches
swash-aligned coast
Formation
1. Waves are refracted by a headland creating low-energy waves.
Deposition occurs in the bay and a beach forms
Eg. Lulworth Cove Dorset
Barrier Beaches (bars)
drift-aligned coast sand/shingle beach which connects 2 areas of land with a shallow water lagoon behind
Formation
A beach or spit is extended over a bay by the processes of longshore-drift and deposition
Water is trapped behind forming a lagoon.
Eg. Chesil Beach Dorset
Offshore Bars
ridges of sand or shingle running parallel to the coast in the offshore zone
Formation
Sediment eroded by destructive waves is carried out to sea.
2.Sediment is deposited at the boundary between the near and offshore because orbit of water particles changes to stop further transport.
Tombolos
Sand/ shingle bar that connects an offshore island to the coast.
Formation swash-aligned
Low-energy environment behind the island allows for deposition
Eg. St Ninians Shetland
Formation drift-aligned
Opposing longshore currents build a spit out from the coast until it connects with the island
Cuspate Foreland
triangular shaped headland that extends out from the mainland coastline.
Formation
Debate about it. Opposing longshore drift currents converge at the edge of a sediment cell extending two spits seaward
Eg. Dungeness Kent
Plant succession stabilises all depositional landforms
Conditions for deposition
Low energy environment, shallow water, sheltered location
Deposition occurs through:
Gravity settling
Energy of transporting becomes too low so it drops the sediment.
Flocculation
Small clay particles suspended in water clump together until they are too big so are deposited
Swash-aligned coasts:
Waves approach parallel to the coast, limited longshore movement of sediment
Drift-aligned coasts:
Waves break at an angle to the coast so there is consistent longshore drift
