Geography Reference
In-Depth Information
COASTS
Coastal areas are also subject to water pollution, much of which is
derived from polluted river waters entering the coastal environ-
ment as well as pollution from ships, oil spills and some industrial
effluent that is discharged into the sea. Coastal environments are
important since 40 per cent of the world's population live within
100 kilometres of the coast and it is even thought that 75 per cent
of the world's population could be living within 60 kilometres of
the coast by 2025. Coastal environments support fisheries, large
ecosystems, leisure activity and even power generation and act as
an important buffer during storm events. As discussed in Chapter
2, sea level rise is a major threat to the coastal community. Sea
levels are currently rising at 3 millimetres per year with a predicted
rise of 18 to 59 centimetres by 2100 leading to increased flooding
and erosion of land. It is therefore important to understand the
physical geography of coastal regions so that we may better antici-
pate and adapt to changes in the future.
Waves
Waves are the most important feature of coastal environments as
they drive many sediment transport processes and therefore the
inputs and outputs of sediment from an area. The inputs and
outputs of sediment in turn help shape the landforms of the coastal
environment. Waves are generated by wind. Stronger wind results
in larger waves. Waves can travel vast distances across the oceans
and so wind conditions a considerable distance from the coast can
influence coastal waves. Waves can be measured for their height
H
(height between top and bottom of the wave surface), length
L
(distance between successive wave peaks (crests)) and period (i.e.
time between two wave peaks or troughs passing by a point).
Wave behaviour depends on the depth of water in the ocean.
Where the water depth is more than twice the wave length then as
waves travel across the water surface, the water beneath moves in
circles; forward under the crest of the wave and backward under
the trough. The diameter of the circles of water decreases with
depth until in deep water the wave motion is no longer detectable.
In water which has a more intermediate depth, where the depth is
