Factors Influencing Coastal Processes
In this essay I aim to describe and explain factors affecting coastal
processes. I will focus and explore how waves, tides, winds and mass
movement processes can change the form of the coasts within our
lifetime. The three key questions I will focus on are:
* What are the energy and sediment inputs into the coastal system?
* What are the processes that erode coasts?
* How is sediment transported and deposited?
I will conclude by describing and explaining factors influencing
coastal processes and how they make up the South Dorset coast.
The littoral zone is a narrow zone between high and low water ...view middle of the document...
Fig 3. Fistral Beach, Newquay, Cornwall UK
Tides ebb and flood in response to the gravitational attraction of the
moon and sun; exceptional high and low tides occur each month when the
sun and moon are aligned. Tides help determine where the waves break
-- low on the beach at low tide, high on the beach at high tide --
and, therefore, where sand is deposited and removed. Rip tides, or
undertow, occur along most beaches and can move significant amounts of
sand offshore. Where the waves hit the shore at an angle, they set up
longshore currents that can move vast quantities of sand and silt.
(Fig 4. Tidal currents)
Coastal environments are always changing as a result of the action of
the waves. Waves are formed by the wind blowing across the surface of
the water. The power of the wave increases as the strength of the wind
and the distance over which the wave has built up (known as fetch)
When waves break, water runs up a beach, forming the swash and back
toe beach as the backwash.
Constructive waves are lower waves with a strong swash and weaker
backwash that build up beaches. Destructive waves have a stronger
backwash and erode material from the coast. There are four main ways
in which waves cause erosion:
1. Abrasion/Corrasion occurs when the waves throw sand, shingle and
pebbles against cliffs, grinding and breaking away the rock surface.
2. Corrosion happens when the acids in seawater dissolve rocks.
3. Hydraulic action results in the breakdown of rocks when waves
breaking against the cliffs trap air in cracks causing pressure to
build up. When the waves retreat the pressure is released breaking off
fragments of rock.
4. Attrition occurs when pebbles and stones carried by the waves are
broken up into smaller fragments as they are thrown against each
These processes are quite simple but the patterns of erosion are
complex as they are influenced by these four factors:
1. Rock type- its resistance to wave action and sub aerial processes
and its solubility
2. Rock structure- the division between joints, bedding planes and
3. Beach character- the size of the beach varies within seasons, it
may shrink if there is a reduction in erosion and sediment supply. The
wider the beach, the more protective it is from erosion.
4. Fetch/Currents- the fetch of dominant and prevailing winds and the
influence of tidal and long shore currents.
The development of a dune begins with weathering of parent rock.