Detailed revision notes for the Coasts Topic of the AQA A-Level Geography Syllabus.
The notes include case studies, necessary information and essay plan arguments.
The format of the notes is as follows;
3.1.3.1 Coasts as natural systems 2
The Coastal System 2
Sediment cells 2
3.1.3.2 - ...
- The coast can be considered an open system as it receives inputs from outside the system and
transfers outputs away from the coast into other systems - these could be terrestrial,
atmospheric or oceanic and include the rock, water and carbon cycles
- Whilst they are open systems, they must be considered closed systems when talking about
scienti c research and coastline management planning.
Sediment cells
Coasts are split into sections called sediment cells and are often bordered by prominent
headlands. Within these sections, the movement of sediment is almost contained and the ows of
sediment act in dynamic equilibrium.
Within each sediment cell, there are smaller subcells - often which are used when planning
coastal management projects.
Dynamic equilibrium - The maintenance of a balance in a natural system, despite it being in a
constant state of change. The system counteracts any changes imposed on the system in order
to keep this balance, which is achieved by inputs and outputs constantly changing to maintain the
balance. Dynamic equilibrium may be upset in the long term by human interventions - or in the
short term by natural variations.
Inputs Outputs
• Marine - waves, tides, salt spray • Ocean currents
• Atmosphere - Sun, air pressure, wind speed • Rip tides
and direction • Sediment transfer
• Humans - pollution, recreation, settlement, • Evaporation
defences, sea level change • Dissipation of wave energy
Stores Transfers/ Flows
• Beaches, sand dunes, spits, bars and • Wind-blown sand
tombolos, headlands and bayys, nearshore • Mass-movement processes
sediment, cli s, wave cut notches and • Long shore drift
platforms, caves-arch-stacks-stumps, salt • Weathering
marshes, tidal ats, o shore bands and bars • Erosion - hydraulic action, corrosion, attrition,
abrasion
• Transportation - Bedload, suspension, traction,
solution
• Deposition - gravity settling, occulation
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,3.1.3.2 - Systems and natural processes
Sources of energy
Wind:
• Wind is a vital input to the coastal system as it is a primary source of energy for other
processes, but is also an important agent for erosion and transport itself.
• Features include;
- Spatial variations in energy result from variations in the strength and duration of wind. Where
wind speeds are persistently high and uninterrupted, wave energy is likely to be higher. Most
coastlines have prevailing wind that is the wind will generally reach the coast from one
direction - it is important as it is one factor that controls the direction the waves approach the
coastline, and also the direction of transport of sediment along the coast.
- Fetch refers to the distance of open water over which a wind blows uninterrupted by major
land obstacles. The length of fetch helps to determine the magnitude and energy of the
waves reaching the coast.
- Wind plays a vital role in wave formation, waves are created by the transfer of energy from
wind blowing over the sea surface - referred to as frictional drag. The energy acquired by
waves depends on the length of time it is blowing and the length of fetch.
- Wind cars as an agent of erosion as it can pick up sediment from the coast and use it to
erode other features. The most common type of wind erosion is abrasion where wind uses
the material it carries to wear away the landscape.
Waves:
After being created and driven by the wind, waves are a primary agent in shaping the coast.
- Wave height - the height distance between the wave crest and the wave trough
- Wavelength and amplitude - the distance between successive crests
- Wave frequency - the time for one wave to travel the distance of one wavelength, or the time
between one crest and the following crest passing a set point.
As waves approach shallow water, friction with the seabed increases and the base of the wave
begins to slow down. This increases the height and steepness of the wave until the crest plunges
forward and the wave breaks onto shore. This occurs when the wave steepness (height and
wavelength) exceeds the 1:7 ratio.
The rush of water up the beach = swash
The water running back down the beach = backwash
Constructive waves (low energy coastlines):
Waves with a low wave height, a long wavelength and low frequency 6-8per/min. Their swash
tends to be more powerful than backwash and as a consequence beach material is built up.
Formed by weather systems that operate in the open ocean.
Due to the very weak backwash, the waves have insu cient force to pull sediment o the beach
to impede swash from the next incoming wave - as a consequence, material is slowly but
constantly moved up the beach leading to the formation of ridges (berms)
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,Destructive waves (high energy coastlines):
Waves with a high wave height with a steep form and high frequency (10-14 per/min). Their
backwash is generally more powerful than their swash so more sediment is removed than added.
They are formed by localised storm exerts with stronger winds operating closer to the coast.
Destructive waves are typically associated with steeper beach pro les - the force of each wave
may project some shingle well towards the rear of the beach where it forms a larger ridge called a
storm beach.
Most beaches are subject to alternating cycles of destructive and constructive waves.
Constructive waves built up the beach pro le which encourages waves to become mire
destructive. With time, destructive waves move material back towards the sea, reducing the
beach angle and encouraging more constructive waves. —> example of negative feedback that
should maintain the state of dynamic equilibrium.
• In summer: constructive waves dominate, in winter: destructive waves dominate
• Constructive waves will become more destructive if a storm begins
• Climate change may increase storm frequency in the UK
• Coastal management may a ect the type of waves that occur
Wave refraction
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 into the bays leading to the formation of features associated with lower energy
environments such as beaches.
The topography of the coastline is a crucial factor in determining the wave e ect. Wave refraction
can only occur on non-concordant coastlines (when di erent rock types make up the coastline).
- As each wave approaches the coast, it tends to drag in the shallow water which meets the
headland.
- This increases the wave height and wave steepness and shortens the wavelength. The part of
the wave in the deep water moves forward faster causing the wave to bend - the overall e ect
is that the energy becomes concentrated on the headland, causing greater erosion.
- The low energy waves spill into the bay = beach deposition.
- As the waves pile against the headland there may be a slight local rise in sea level that results
in a longshore current from the headland, moving some of the eroded material towards the
bay = build up of beaches.
Negative feedback = due two di erent rock strengths, erosion leads to the formation of headlands
where resistant rocks exist and bays are where soft rocks are dominant. This increases the forces
of erosion on headlands and reduced in the bays meaning headlands are eventually worn away =
increasing erosion within the bays. This leads to dynamic equilibrium.
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, Currents
Current = permanent or seasonal movement of surface water in the seas and oceans. They often
lead to an output of sediment as well as providing an energy source for the coastal system.
There are 3 currents covered here;
1. Longshore currents (sometimes known as littoral drift): occur as most waves do not hit the
coastline ‘head on’ but approach the shoreline at an angle. This generates a ow of water
(current) running parallel to the shoreline. This not only moves water along the surf zone but
also transports sediment parallel to the shoreline.
2. Rip currents: Strong currents moving away from the shoreline. They develop when seawater
is piled up along the coastline by incoming waves. Initially the current may run parallel to the
coast before owing out through the breaker zone - possibly at a headland of where the coast
changes direction. They are powerful underwater currents that occur in areas close to the
shoreline on some beaches where plunging waves cause a buildup of water at the top of the
beach - the backwash is forced under the surface due to the resistance from breaking waves.
e.g. Backpackers rip on Bondi Beach Australia.
3. Upwelling: the movement of cold water from deep in the ocean towards the surface. The
more dense cold water replaces the warmer surface water and creates nutrient-rich cold water
currents. These form the pattern of the global ocean circulation currents - thermohaline
circulation.
Tides
The periodic rise and fall in the level of the sea caused by the gravitational pull of the sun and
moon - although the moon has the greatest in uence because it is nearer.
The moon pulls water towards it creating a high
tide - on the other side of the earth is a
compensatory bulge. It is between these two
bulges that the tide is at its lowest. As the moon
orbits, the high tides follow it. Twice in a lunar
month - when the sun, moon and earth are in a
straight line, the tide raising force is the strongest.
This = spring tide - the highest monthly tidal range.
Twice a month, the moon and sun are positioned at
90° to each other in relation to the earth. This
alignment gives the lowest monthly tidal range -
neap tides. At this time the high and low tides are
between 10-30% lower than average.
The regular pattern of tides is modi ed in individual locations due to the morphology of the
seabed, the proximity of land masses and the impact of the coriolos e ect.
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