Coastal environments revision notes

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Coastal environments
Coastlines are important to the human race. 50% of the world's population live on coastal plains
and in other locations with easy access to the sea. The coastline itself consists of a series of
different zones in which specific conditions prevail that depend on factors such as tides, wave
action and the depth of the sea.
Backshore = is the area between the high water mark and the landward limit of marine activity.
Changes normally take place here only during storm activity.
Foreshore = is the area lying between the HWM and the low water mark. It is the most important
zone for marine processes in times that are not influenced by storm activity.
Inshore= is the area between the LWM and the point where waves cease to have any influence on
the land beneath them
Offshore = is the area beyond the point where waves cease to impact upon the sea bed and in
which activity is limited to deposition of sediments
There are a number of factors that determine the shape, form and appearance of a coastline:
Wave size, frequency, type, energy produced and direction
Local sea currents
Longshore drift
Tides
Depth of water offshore
Type and amount of sediments offshore
Rock type and structure
Sub-aerial processes ­ run off, weathering and mass movement
Land-based agents of erosion ­ rivers and glaciers
Climate and weather
Fetch
Long term sea level change
Coastal ecosystemts
The presence of a coral
Human activity

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Coastlines are dynamic environments that are undergoing continual change. In the short term,
tides, waves and longshore drift change the shape, form and appearance of elements of a
coastline. Changes in sea level bring about long term change.
The shape of the British Isles has altered continually over the
last few thousand years. At the end of the Pleistocene
glaciations, Britain was joined to the rest of Europe.…read more

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The coastal system
Coasts are considered an example of an open system because inputs are received, and outputs are
transferred, across the boundary of the system.
INPUTS
Energy to drive the system. This is inputted in the form of waves, wind, currents and tides.
The input is irregularly boosted by storm surges and tidal waves. Spatial variations in
energy result from variations in the strength of the wind, the fetch and the number and
intensity of storms.…read more

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Waves
Waves are a medium through which energy is transferred. They are created by the wind blowing
across the surface of the sea. Frictional drag increases as the wind speed increases, making the
wave bigger.
Wave energy depends upon three things:
1. The strength of the wind.
2. The length of time the wind has blown for.
3. The fetch of the wind (the distance it blows over).
Term Description
Swash A body of foaming water rushing up to the beach.…read more

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The rush of water up the beach is known as
swash and any water running back down the beach into the sea is the backwash.…read more

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Constructive waves
Constructive waves have a short amplitude and a long wavelength often up to 100m. They have a
low frequency of around 6-8 waves per minute. As they approach the beach, the wave front
steepens only slowly, giving a gentle spill onto the beach surface. Constructive waves produce a
strong swash, which loses volume and energy as water percolates through the beach material
which tends to give a weak backwash.…read more

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Effects of waves & Wave refraction
Most beaches are subject to alternating action of constructive and destructive waves. Constructive
waves build up the beach and result in a steeper beach profile. This encourages waves to become
more destructive ( as these waves are associated with steeper profiles).
With time though, destructive waves move material back towards the sea, reducing the beach
angle and encouraging more constructive waves. So the pattern repeats itself.…read more

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Tides
Tides are the periodic rise and fall in the level of the sea.
Caused by the gravitational pull by the moon and sun. The moon has the greatest influence due to
its distance (pull is lower).
Oceans closest to the moon have an outward bulge. This causes high tide and low tide and this is
the draining of water from areas.
The moon orbits the earth every 28 days and high tides follow its path (approx 2 high and 2 low
tides per day).…read more

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Storm surges
These are occasions when meteorological conditions giving rise to strong winds can produce much
higher water levels than those at high tide. One area affected by this phenomenon is the Bay of
Bengal.
Bangladesh has the worst record in the late twentieth century for storm surges.
Serious events occurred in 1970, 1985 and 1991. During a storm surge high winds,
associated with cyclones forming to the south, push water northwards up the
increasingly narrow Bay of Bengal.…read more

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