3.1.3 Coastal Systems & Landscapes

Question 1

Inputs

Answer 1

Sediment can be brought into the system in various ways - energy inputs come from wind, waves, tides and currents.

Question 2

Outputs

Answer 2

Sediment can be washed out to sea, or deposited further along the coast.

Question 3

Flows/Transfers

Answer 3

Processes such as erosion, weathering, transportation and deposition can move sediment within a system.

Question 4

Stores/Components

Answer 4

Landforms such as beaches, dunes and spits are stores of sediment.

Question 5

Example of negative feedback

Answer 5

As a beach is eroded, the cliffs behind it are exposed to wave attack. Sediment eroded from the cliffs is deposited on the beach, causing it to grow in size again.

Question 6

Example of positive feedback

Answer 6

As a beach starts to form it slows down waves, which can cause more sediment to be deposited, increasing the size of the beach. The new equilibrium is reached when long-term growth of the beach stops.

Question 7

Wind

Answer 7

• Winds are created by air moving from areas of high pressure to areas of low pressure. During events such as storms, the pressure gradient is high and winds can be very strong.
• Strong winds can generate powerful waves. In some areas, wind consistently blows from the same direction (prevailing wind) - this causes higher energy waves than winds that change direction frequently.

Question 8

Waves

Answer 8

• Waves are created by the wind blowing over the surface of the sea. The friction between the wind and surface of the sea gives the water a circular motion.
• The effect of a wave on the shore depends on its height. Wave height is affected by the wind speed and the fetch of the wave. A high wind speed and long fetch create higher and more powerful waves.
• As waves approach the shore they break. Friction with the sea bed slows the bottom of the waves and makes their motion more elliptical. The crest of the wave rises up, then collapses.
• Water washing up the beach is swash and water washing back towards the sea is backwash.

Question 9

Constructive waves

Answer 9

• Constructive waves have low frequency (6-8 waves per minute)
• They’re low and long, which gives them a more elliptical cross profile.
• The powerful swash carries material up the beach and deposits it.

Question 10

Destructive waves

Answer 10

• Destructive waves are high and steep, with a more circular cross profile.
• They have a high frequency of 10-14 waves per minute.
• The strong backwash removes material from the beach.

Question 11

Tides

Answer 11

• Tides are the periodic rise and fall of the ocean surface, caused by the gravitational pull of the moon and sun.
• Tides affect the position at which waves break on the beach (at high tide they break higher up the shore). The area of land between maximum high tide and minimum low tide is where most landforms are created and destroyed.

Question 12

Currents

Answer 12

• A current is the general flow of water in one direction - it can be caused by wind or variations in water temperature and salinity.
• Currents move material along the coast.

Question 13

Low energy coasts

Answer 13

Low energy coasts receive low inputs of energy in the form of small, gentle waves. These can be caused by gentle winds, short fetches and gently sloping offshore zones. Some coastlines are low energy because there is a reef or island offshore, which protects the coast from the full power of waves. Low energy coastlines often have salt marshes and tidal mudflats. The rate of deposition exceeds the rate of erosion.

Question 14

Sediment sources

Answer 14

• Rivers carry eroded sediment into the coastal system from inland.
• Sea level rise can flood river valleys, forming estuaries. Sediment in the estuary becomes part of the coastal system.
• Sediment is eroded from cliffs by waves, weathering and landslides.
• Sediment can be formed from the crushed shells of marine organisms.
• Waves, tides and currents can transport sediment into the coastal zone from offshore deposits (e.g. sandbanks)

Question 15

Sediment budget

Answer 15

The difference between the amount of sediment that enters the system and the amount that leaves. If more enerts than leaves, it’s a positive sediment budget and overall the coastline builds outwards. If more leaves than enters, it’s a negative sediment budget and overall the coastline retreats.

Question 15

Sediment cells

Answer 15

• The coast is divided into sediment cells (aka littoral cells)
• These are lengths of coastline (often between two headlands) that are pretty much entirely self contained for the movement of sediment. This means that processes going on in one cell don’t affect the movement of sediment in another cell - each cell is a closed coastal system.

Question 16

Weathering

Answer 16

Weathering is the breakdown of rock in situ at or near the surface of the Earth. Weathering attacks the backshore and foreshore parts of the littoral zone and creates rock fragments that form sediment. There are 3 types of weathering: biological, chemical and mechanical.

Question 17

Erosion

Answer 17

Erosion refers to the wearing away of the land surface and removal of materials by river and seawater, ice and wind. The types of erosion are: corrasion (abrasion), hydraulic action, cavitation, wave quarrying, solution (corrosion) and attrition.

Question 18

Transportation

Answer 18

The process of transporting eroded material through the energy provided by waves, tides and currents. There are 4 main processes: solution, suspension, saltation and traction.

Question 19

Deposition

Answer 19

Deposition is when material being transported is dropped on the coast - there are two types: marine deposition and aeolian deposition. Both marine and aeolian deposition happen when the sediment load exceeds the ability of the water or wind to carry it. This can be because sediment load increases (e.g. if there is a landslide), or because wind/water flow slows down (so it has less energy). Wind and water slow down for similar reasons:
- Friction increases: if waves enter shallow water or wind reaches land, friction between the water/wind and ground surface increases, which slows down water or wind.
- Flow becomes turbulent: if water or wind encounters an obstacle (e.g. a current moving in the opposite direction, or an area of vegetation) flow becomes rougher and overall speed decreases.
If the wind drops, wave height, speed and energy will decrease as well.

Question 20

Estuarine mudflats & saltmarshes

Answer 20

• Mudflats and saltmarshes form in sheltered, low energy environments, e.g. river estuaries or behind spits.
• As silt and mud are deposited by the river or the tide, mudflats develop.
• The mudflats are colonised by vegetation that can survive the high salt levels and long periods of submergence by the tide.
• The plants trap more mud and silt, and gradually, they build upwards to create an area of salmarsh that remains exposed for longer and longer between tides.
• Erosion by tidal currents or streams forms channels in the surface of mudflats and saltmarshes. These may be permanently flooded or dry at low tide.

Question 21

Fjords - submergent coastline

Answer 21

Fjords are drowned glacial valleys. They’re relatively straight and narrow, with very steep sides. They have a shallow mouth caused by a raised bit of ground (called the threshold) formed by deposition of material by the glacier. They’re very deep further inland, e.g. Sognefjorden in Norway is over 1000m deep in places.

Question 22

Recent and predicted climatic change and potential impact on coasts

Answer 22

1) Storms are likely to become more frequent and intense due to changes in ocean circulation and wind patterns. This would cause damage to coastal ecosystems and settlements.
2) Sea level rise will have major impacts on coastal areas:
- More frequent and more severe coastal flooding
- Submergence of low-lying islands
- Changes in the coastline
- Contamination of water sources and farmland
3) Sea level rise and increased storminess will increase coastal erosion, putting ecosystems, homes and businesses at risk.

Question 23

Hard engineering

Answer 23

This is the traditional management process for erosion/flooding, encasing the coastline in concrete, stone and steel. The aim is to directly stop physical processes altogether (such as erosion or mass movement) or alter them to protect the coast (such as encouraging deposition to build larger beaches).
Techniques include: Sea walls, revetments, gabions, rip rap and groynes.

Question 24

Hard engineering advantages and disadvantages

Answer 24

Adv:

• It’s obvious to at-risk people that something is being done to protect them, its reassuring
• A ‘one-off’ solution that could protect a coastline for decades

Disadv:

• Ongoing maintenance costs
• Visually unattractive and the needs of a coastal ecosystem are usually overlooked
• Defences built in one place frequently have adverse consequences further along the coast

Question 25

Soft engineering

Answer 25

Soft engineering approaches attempt to work with physical systems and processes to protect coasts and manage changes in sea level. Techniques include: beach nourishment, beach stabilization, dune regeneration, land use management, creating marshland and coastal realignment