Coastal landscapes
1. How can coastal landscapes be viewed as systems?
1.a Coastal landscapes as systems
A system is a set of interrelated objects comprising components (stores) and processes (links) that
are connected together to form a working unit or unified whole. Coastland landscape systems store
and transfer energy and material on time scales that can vary from a few days to millennia
(thousands of years).
The energy available to a coastland landscape system may be kinetic, potential or thermal. It is this
energy that enables work to be carried out by the natural, geomorphic processes that shape the
landscape. The material found in a coastland landscape system is predominantly the sediment found
on beaches, in estuaries and in the relatively shallow waters of the nearshore zone.
The components of open systems
Coastland landscape systems are recognised as being open systems. This means that energy and
matter can be transferred from neighbouring systems as an input. It can also be transferred to
neighbouring systems as an output.
In systems terms, a coastland landscape has:
• Inputs – including kinetic energy from wind and waves, thermal energy from the heat of the Sun
and potential energy from the position of material on slopes; material from marine deposition,
weathering and mass movement from cliffs
• Outputs – including marine and wind erosion from beaches and rock surfaces; evaporation
• Processes – which consists of stores, including beach and nearshore sediment accumulations;
and flows (transfers), such as the movement of sediment along a beach by longshore drift
System feedback in coastal landscapes
When a system’s inputs and outputs are equal, a state of equilibrium exists within it. In a coastal
landscape, this happens when the rate at which sediment is being added to a beach equals the rate
at which sediment is being removed from the beach; the beach will therefore remain the same size.
When this equilibrium is disturbed, the system undergoes self-regulation and changes its form in
order to restore the equilibrium. This is known as dynamic equilibrium, as the system produces its
own response to the disturbance. This is an example of negative feedback.
Case study: Archill Beach, Ireland
As a result of storms in 1984, Archill Beach’s equilibrium was disturbed and the beach was
completely washed away. The system then underwent negative feedback and changed its form in
order to restore the equilibrium; 33 years later in 2017 the beach reappeared (dynamic equilibrium).
In 2019, sand storms swept the sand away from Achill island, removing the beach away.
Sediment cells
• A sediment cell is a stretch of coastline and its associated nearshore area
, • They are generally regarded as closed systems, which suggest that no sediment is transferred
from one cell to another.
• It is unlikely that sediment cells are completely closed. With variations in wind direction and the
presence of tidal currents, it is inevitable that some sediment is transferred between
neighbouring cells.
• The boundaries of sediment cells are determined by the topography and shape of the coastline.
• Large physical features, such as Land’s End, act as huge natural barriers that prevent the
transfer of sediment to adjacent cells.
• There are 11 large sediment cells around the coast of England and Wales with many sub-cells
of a smaller scale existing within the major cells.
Explain the features of an open system (3) 3/3 Good lol
Explain how the flows of energy can shape 3/3 Review
cliffs (3)
Explain how flows of material can influence 2/3 Review
beach profiles (3)
Explain how sediment budgets can be 1/4 Review
disturbed by human activity (4)
Explain how sediment budgets can be restored 3/4 Review
by natural processes (4)
Explain how feedback mechanism’s influence 7/8 Review
coastal systems (8)
,1.b Coastal landscape systems are influenced by a range of physical factors
The development of coastal landscapes and their operations as systems are influenced by a range of
physical factors. These factors influence the way processes work, and consequently affect the
shaping of the landscape. They also vary in terms of their spatial (from place to place) and temporal
(over time) impacts. In any one location, or at any one time, some factors will have greater influence
than others. The factors themselves may also be interrelated i.e. one factory may influence another.
Winds
The source of energy for coastal erosion and sediment transport is wave action. This wave energy is
generated by the frictional drag of winds moving across the ocean surface. The higher the wind
speed and the longer the fetch, the larger the waves and the more energy they possess. Onshore
winds, blowing from the sea towards the land, are particularly effective at driving waves towards the
coast. If winds blow at an oblique angle towards the coast, the resultant waves will also approach
obliquely and generate longshore drift. Wind is a moving force and as such is able to carry out
erosion, transportation and deposition itself. These aeolian processes contribute to the shaping of
many coastal landscapes.
Waves
A wave possesses potential energy as a result of its position above the kinetic energy caused by the
motion of the water within the wave. Moving waves do not move the water forward, but rather the
waves impact a circular motion to the individual water molecules. The amount of energy in a wave in
deep water is approximated by the formula: P = H2 T where P is the power (energy) in kilowatts per
metre of wave front, H is wave height in metres and T is the time interval between wave crests in
seconds, known as wave period. The relationship between wave height and wave energy is
non-linear.
Wave anatomy:
All waves have this same basic anatomy, but wave behaviour is complex and influenced by many
factors, such as the shape and gradient of the seafloor and the irregularity of the coastline. Waves
formed in open oceans can travel huge distances from where they are generated. These swell waves
generally have a long wavelength with a wave period of up to 20 seconds. In contrast, a locally
generated storm wave typically has a short wavelength, greater height and a shorter wave period.
, Breaking waves:
• When waves move into shallow water, their behaviour changes markedly. The definition of
shallow water depends on the size of the wave, but it is typically at a depth of half the
wavelength.
• At a shallow depth the deepest circling water molecules come in contact with the seafloor.
Friction between the seafloor and the water profoundly changes the speed, direction and
shape of waves.
• Firstly, waves slow down as they drag across the bottom. The wavelength decreases, and
successive waves start to bunch up. The deepest part of the wave slows down more than the
top of the wave. The wave begins to steepen as the crest advances ahead of the base.
• Eventually, when water depth is less than 1.3 X wave height, the wave topples over and breaks
against the shore. It is only at this point that there is significant forward movement of water as
well as energy.
• After a wave has broken, water moves up the beach as swash, driven by the transfer of energy
that occurs when the wave breaks. The speed of this water movement will decrease the
further it travels due to friction and the uphill gradient of the beach.
• When it has no more available energy to move forward, the water is drawn back down the
beach as backwash. The energy for this movement comes from gravity and always occurs
perpendicular to the coastline, down the steepest slope angle.
Constructive vs Destructive waves:
Constructive Destructive
Usually quite low in height, have a long Usually have greater height, shorter
wavelength and a low frequency, typically wavelengths and a higher frequency,
around 6-8 per minute typically around 12-14 per minute.
They usually break by spilling forwards, They tend to break by plunging downwards
and the strong swash travels a long way up and so there is little forward transfer of
the gently sloping beach. Due to the long energy to move water up the steeply
wavelength, backwash returns to the sea sloping beach as swash. Friction from the
before the next wave breaks, and so the steep beach slows the swash and so it does
next swash movement is uninterrupted and not travel far before returning down the
thus retains its energy. beach as backwash. With a short
wavelength, the swash of the next wave is
often slowed by the frictional effects of
meeting the returning backwash of the
previous wave.
