Coastal Transport and Deposition

Question 1

What are the four processes of sediment transport?

Answer 1

• Saltation
• Solution
• Traction
• Suspension

Question 2

Saltation

Answer 2

Transport of sand-sized particles. Sediment bounces along, either due to the force of water or the wind

Question 3

Solution

Answer 3

Transports chemical compounds in solution. Dissolved material is carried in the water as a solution.

Question 4

Traction

Answer 4

Pebbles, cobbles, boulders. Sediment rolls along, pushed by waves and currents

Question 5

Suspension

Answer 5

Silt and clay particles. Sediment is carried in the water column

Question 6

Currents

Answer 6

Flows of seawater in a particular direction driven by winds or differences in water density, salinity or temperature.

Question 7

Longshore Drift

Answer 7

The net transport of sediment along the coastline that contributes to many depositional landforms.

Question 8

How does longshore drift work?

Answer 8

Wave crests approach the beach at an angle (rather than 90 degrees to the coast), the swash from the breaking waves and the resulting backwash follows different patterns up and down the beach in a zig zag pattern. The result is net sediment transport along the beach and a longshore flow of sediment.

Question 9

What causes the dominant direction of longshore drift?

Answer 9

The dominant prevailing wind

Question 10

When is sediment deposited along coastlines?

Answer 10

When the force transporting the sediment drops

Question 11

What are the key sources of sediment for depositional landforms on coasts?

Answer 11

• longshore drift

- sediment transported down the coast from river systems or offshore sources are also important

Question 12

How can deposition occur?

Answer 12

• Gravity settling

- flocculation

Question 13

Gravity settling

Answer 13

When the energy transporting water becomes too low to move sediment. Large sediment will be deposited first.

Question 14

Flocculation

Answer 14

A depositional process that is important for very small particles such as clay, which are so small that they remain suspended in water. Clay particles clump together through electrical or chemical attraction, and become large enough to sink.

Question 15

The main depositional landforms

Answer 15

• Spit
• Bayhead beach
• Tombolo
• Barrier beach/bar
• Hooked/recurved spit
• Cuspate foreland

Question 16

What is a spit?

Answer 16

A sand/shingle beach ridge extending beyond a turn in the coastline, greater than 30 degrees.

Question 17

How is a spit formed?

Answer 17

At the turn in the coastline, the longshore drift current spreads out and loses energy, leading to deposition. Length of the spit is determined by the existence of secondary currents causing erosion, either the flow of river or wave action which limits its length.

Question 18

Example of a spit

Answer 18

Spurn head, Holderness coast

Question 19

What is bayhead beach?

Answer 19

Beach formed in a bay

Question 20

How is a bayhead beach formed?

Answer 20

Waves break at 90 degrees to the shoreline, move sediment into a bay, where a beach forms. Through wave refraction, erosion is focused at headlands and bays become an area of depositon

Question 21

Example of a bayhead beach

Answer 21

Lulworth Cove, dorset

Question 22

What is a tombolo?

Answer 22

A sand or shingle bar which links the coastline to an offshore island.

Question 23

How are tombolos formed?

Answer 23

Tombolos form as a result of wave refraction around an offshore island which creates an area of calm water and deposition takes place between the island and coast. Opposing longshore current may play a role, and cause the landform to be similar to a spit.

Question 24

Example of a tombolo

Answer 24

St Ninian’s tombolo, Shetland

Question 25

what is a Barrier beach/bar?

Answer 25

A shingle/sand beach connecting 2 areas of land, with a shallow-water lagoon behind.

Question 26

How does a barrier beach/bar form?

Answer 26

Forms when a spit grows so long that it extends across a bay, closing it off.

Question 27

Example of a barrier beach/bar

Answer 27

Chisel Beach, Dorset

Question 28

What is a hooked/recurved spit?

Answer 28

A spit whose end is curved landward into a bay/inlet.

Question 29

How is a hooked/recurved spit formed?

Answer 29

Seaward end of spit naturally curves landward into shallower water. Hook can be made more pronounced by waves from a secondary direction to prevailing wind.

Question 30

Example of a hooked/recurved spit

Answer 30

Hurst castle spit, Hampshire

Question 31

What is a cuspate foreland?

Answer 31

A roughly triangular shaped feature extending out from a shoreline.

Question 32

How is a cuspate foreland formed?

Answer 32

Debates about formation but one theory is that they form from the growth of 2 spits in opposing directions.

Question 33

Example of a cuspate foreland

Answer 33

Dungeness, Kent.

Question 34

What role does vegetation play in depositional landforms?

Answer 34

Stabilises them. Plant succession as salt marshes and sand dunes binds loose sediment together and encourages further deposition.

Question 35

What is the sediment cell model?

Answer 35

the wider context of the coastal region/area. Long stretches of coastline operate as cells, 11 around the english and welsh coast. Sediment cell must be considered in order to ensure the success of erosion management projects.

Question 36

What is a source?

Answer 36

Places where sediment is generated, such as cliffs, eroding sand dunes, offshore bars and river systems.

Question 37

What is a transfer zone?

Answer 37

Places where sediment is moving along the shore through offshore currents and longshore drift. Beaches and parts of dunes perform this function.

Question 38

What is a sink?

Answer 38

Locations where the dominant process is deposition. Depositional landforms are creates, including spits and offshore bars

Question 39

What determines whether a place is a source or a sink?

Answer 39

Depends whether erosion or deposition is the most dominant process operating at the time

Question 40

How do negative feedback mechanisms restore the equilibrium in sediment cells?

Answer 40

- EG erosion causes cliff collapse, but debris at base of the cliff protects it from further attack - erosion of sand dunes leads to deposition offshore, which forms an offshore bar, which reduces wave energy, and this allows sand dunes time to recover.

Question 41

What effect does human intervention have on the sediment cell?

Answer 41

- coastal management and threats to sea level rise as a result of global warming - put the equilibrium at risk - positive feedback occurs, rising sea levels erodes spits and estuaries, removing material before it can be replenished.