Energy sources in the coastal system

Question 1

What is a system?

Answer 1

A set of interrelated components working together, consisting of inputs, outputs, flows and stores

Question 2

What is negative feedback (dynamic equilibrium) within the coastal system and give an example

Answer 2

When there is a balance between inputs and outputs meaning there is relative stability within the coastal system - when a change occurs it is counteracted. eg. constructive waves build up sediment on a beach making it steeper. This encourages destructive plunging waves which remove material and redistribute it back to the sea. This in turn encourages constructive waves which build the beach back up and the cycle continues.

Question 3

What is positive feedback within the coastal system and give an example

Answer 3

When a change within the coastal system continues to amplify feedback so there is a greater change from the original e.g. when salt water and fresh water within an estuary meet, the velocity of the water drops due to friction causing deposition of sediment. This deposited material will further slow the velocity in turn encourages further deposition until eventually it will build up to form a spit across the estuary.

Question 4

How is wind created and how does it lead to the formation of waves?

Answer 4

At the equator the suns rays are more concentrated which heats the air causing it to become less dense and rise. As the air rises it becomes more dense and sinks back down creating a current. This movement of air from a high to low pressure is wind.

Waves are formed when the wind blows over the sea. This causes friction with the surface of the water which results in the formation of small ripples which develop into waves

Question 5

What are the factors affecting wave energy and why?

Answer 5

• strength of the wind: determined by the pressure gradient - the high pressure generates low wave energy and low pressure generates stronger winds therefore high wave energy
• direction of the wind: winds consistently blown from the same direction (prevailing winds) generate higher wave energy than conditions where wind direction is constantly shifting
• fetch: the distance over which the wind blows - the longer the fetch, the more powerful the waves
• storm surges: causes sea surfaces to rise which creates a pressure wave that encounters the coast as a storm surge of higher water

Question 6

What happens as a wave approaches the coast?

Answer 6

As the water starts to get shallower, the seabed interrupts the circular motion of the waves (due to friction) making them more elliptical. This causes the crest of the wave to rise upwards and eventually breaks onto the beach and rushes up as swash

Question 7

What are tides and how are they caused?

Answer 7

The cyclic rising and falling of the Earth’s ocean surfaces caused by the tidal force of the moon and the sun acting on the Earth. They are caused by the gravitational pull of the moon which causes the earths oceans to bulge on the sides of the earth closest to and furthest away from the moon. As the earth rotates daily it will pass the 2 bulges twice which causes high and low tides.

Question 8

What is the difference between spring and neap tides?

Answer 8

Spring tides occur during the full and new moon when the sun and moon are in alignment and their gravitational forces combine together. This results in a larger bulge with higher high tides and lower low tides - higher tidal range

Neap tides occur when the sun and moon are at right angles to each other to there is a weaker gravitational pull meaning the spread of water over the earths surface is more even. This results in a higher low tide and a lower high tide - lower tidal range

Question 9

What are sediment cells?

Answer 9

• Coasts can be split into sections called ​sediment cells​ ​which are often bordered by ​prominent headlands​. Within these sections, the ​movement of sediment is almost contained​ and the flows of sediment act in ​dynamic equilibrium​.
• There are 11 sediment cells in the UK
• Cells consist of: stores eg. beaches or spits, transfers eg. LSD or aeolian processes

Question 10

What are the main sediment sources into the coastal system?

Answer 10

• Rivers
• Cliff erosion
• Wind
• Glaciers
• LSD

Question 11

What are sediment budgets?

Answer 11

Sediment budgets use ​data of inputs, outputs, stores and transfers to assess the ​gains and losses of sediment within a sediment cell​.
In principle a system will operate in a state of dynamic equilibrium where input and outputs of sediment are equal. However, ​human actions and natural variation​ ​in the system can disrupt the state of equilibrium

Question 12

What are rip currents?

Answer 12

Rip currents are powerful underwater currents occurring in areas close to the shoreline on some beaches when ​plunging waves cause a buildup of water at the top of the beach. The backwash is forced under the surface due to ​resistance from breaking waves​, forming an underwater current. Rip currents are an ​energy source in a coastal environment and can lead to ​outputs of sediment​ from the beach area.

Question 13

What is wave refraction and how is it an example of negative feedback?

Answer 13

Wave refraction is the process by which waves turn and lose energy around a headland on uneven coastlines. The ​wave energy is focussed on the headlands​, creating ​erosive features in these areas. The energy is ​dissipated in bays leading to the formation of features associated with ​lower energy environments​ such as beaches.

Due to the different rock strengths, erosion leads to the formation of ​headlands where resistant rock exists and ​bays where unconsolidated rocks and clays are dominant​. This then increases the forces of erosion on the headlands and ​reduced erosion in the bays as wave refraction dissipates wave energy and a beach protects the coastline behind. Eventually the
headlands are worn away​, which then again ​increases erosion within the bays​

Question 14

What is the difference between constructive and destructive waves?

Answer 14

Constructive:

• low wave height, low frequency, strong swash and weak backwash
• build up beaches resulting in a steeper profile
• features like berms, ridges and runnels

Destructive:

• high wave height, high frequency, weak swash and strong backwash
• high energy leading to erosion, sediment is washed out to sea
• features like storm ridges and offshore bars when material is washed offshore by destructive waves

Question 15

What is the difference between high and low energy coastlines?

Answer 15

Low energy:

• rate of deposition often exceeds rate of erosion, leading to the creation of landforms such as spits and beaches eg. Baltic Sea

High energy:

• strong, steady prevailing winds create high energy waves
• erosion rate is often greater than deposition rate
• landforms including headlands, cliffs and wave cut platforms
• eg. Cornish Coast - South West England

Question 16

Outline the role of waves in affecting coastal energy

Answer 16

• waves are undulations on the surface of the sea driven by the wind
• high, steep, high frequency destructive waves will have high energy and are likely to erode the coastline
• they have a powerful backwash which pulls sediment away from the beach

Question 17

Outline the role of tides in affecting coastal energy

Answer 17

• Consistent energy input, with 2 high tides and 2 low tides each day
• smaller tidal range = the more consistently a part of the coastline is subject to wave erosion
• can generate strong currents which influence the direction and scale of sediment movement
• long tidal range = inter-tidal zone is more subject to erosional and depositional processes

Question 18

Outline the role of currents in affecting coastal energy

Answer 18

• permanent or seasonal movement of water in the oceans
• longshore currents generated when waves approach at an angle which transports sediment parallel to the coastline
• rip currents move away and transport material seaward
• ocean currents can transport sediment thousands of miles and upwelling can bring material to the surface

Question 19

What are currents and how are they caused?

Answer 19

A flow of water in one direction. They can be caused by tides, temperature or salinity differences in water and wind. They can be at a local or global scale.

Question 20

How are currents formed?

Answer 20

Tides: - tides create a current in oceans which is strongest near the shore, and in bays and estuaries along the coast “tidal currents”. Tidal currents often occur between high and low tide and in estuaries

Wind: - winds drive currents that are at or near the oceans surface. This can be at a local or global scale

Thermohalide circulation: - driven by density differences in water due to temperature and salinity variations. They drive warm water from the equator and cold water from the poles around the earth

Question 21

What is tidal range and why is it important?

Answer 21

The height difference between the highest high tide and the lowest low tide. When tidal range is low, it restricts wave action to a narrow width. When tidal range is high, there is a wide zone of wave attack which results in erosional landscapes

Question 22

What is the significance of tides?

Answer 22

• generate ocean currents that influence the direction and scale of coastal sediment movement
• when combined with low pressure, high storm surges are generated which leads to coastal flooding
• can be used to generate renewable energy eg. Swansea Bay

Question 23

What are the types of currents?

Answer 23

• Longshore currents - current approaches shoreline at an angle which transfers sediment parallel to the shoreline
• Rip currents - currents moving away from the shoreline when seawater is piled up along the coastline by incoming waves
• Upwelling - movement of cold water from deep in the ocean towards the surface

Question 24

What is the thermohalide circulation?

Answer 24

Process driven by temperature and salinity variations in water. Caused by a combination of thermohalide currents and wind driven currents on the surface. Cold, salty water is dense and sinks to the bottom while warm water is less dense and remains on the surface.

Begins in the Norwegian Sea where warm water from the Gulf Stream heats the atmosphere in cold latitudes. This loss of heat to the atmosphere makes water cooler and denser, causing it to sink. As warm water is transported north it sinks and moves south which creates a conveyor belt

Question 25

What are the sources of sediment?

Answer 25

• rivers
• cliff erosion
• longshore drift
• wind
• glaciers
• offshore

Question 26

What leads to positive/negative sediment budgets?

Answer 26

When more material is added to the cell than is removed causing a net accretion, this leads to a positive budget which is a surplus of sediment leading to the shoreline building towards the sea

When more material is removed from the cell than is added, it leads to a negative budget causing a deficit in sediment supply, leading to the retreatment of the shoreline landwards