DESTRUCTIVE WAVES
Destructive waves have three main features:
- They are high in proportion to their length.
- The backwash is much stronger than the swash so that rocks, pebbles and sand are carried back out to sea.
- They are frequent waves, braking at an average rate of between eleven and fifteen per minute.
CONSTRUCTIVE WAVES
Constructive waves have three main features:
- They are long in relation to their height.
- They break gently on the beach, so that the carrying the materials up the beach is stronger than the backwash carrying them away.
- They break gently with only between six and nine waves per minute.
EROSION
Erosion in this case is where strong waves hit cliffs and the cliff gets breaks down and the cliff retreats. There are four main processes by which the sea can erode the cliff and land, the four processes are:
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HYDRAULIC PRESSURE – is the sheer force of the waves, especially when they trap and compress air in cracks and holes in a cliff.
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CORRASION – results from a large waves hurling beach material against the cliff.
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ATTRITION – is when waves cause rocks and pebbles on the beach to bump into each other and to break down in size.
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CORROSION – is when certain types of the cliff are slowly dissolved by acids in the sea water.
RATE OF EROSION
The rate of erosion depends on the geology of the rocks. There are certain types of rock which are resistant or less resistant. Headlands and bays form along coasts which have resistant and less resistant rock. The resistant rock will be worn away less quickly because it’s harder leaving a headland which sticks out into the sea. The less resistant rock, erosion will take place more rapid and a bay will form.
LANDFORMS OF COASTAL EROSION
Land forms of erosion are the result of erosion. Destructive waves hitting a cliff will form a wave cut platform. The waves attack the foot of the cliff which breaks the cliff and forms a wave cut notch. As the notch gets bigger there will be nothing to support the cliff above the notch so it will collapse. As this process continues this will cause the cliff to slowly retreat and increase in height. The gently sloping land left at the foot of the retreating cliff is called a wave cut platform. Another land form of erosion is the cave, arches, stacks and stumps.
LONGSHORE DRIFT
When waves approach a beach they come in the angle depending on where the prevailing wind is coming from. The water that rushes up the beach after a breaks is called the swash. The swash, which picks up sand and shingle travels up the beach in the same direction of the breaking wave. When this water returns down the beach to the sea, it is called backwash. The result is that material is transported along the beach in a zig-zag movement. This movement of beach material is called longshore drift.
DEPOSITION
Deposition occurs in sheltered areas where the build up of sand or shingle is greater than its removal. The most widespread coastal deposition feature is the beach. Although rocky beaches are formed by erosion (wave cut platforms, sand and shingle beaches result from deposition
BEACH AND SPIT
A spit is an area of sand or shingle which either extends at a gentle angle out to sea or which grows across a river estuary. Many spits are characterised by a hooked, or curved end. Spits only develop in places where:
- longshore drift moves large amount of material along the beach.
- There is a sudden change in the direction of the coastline.
- The sea is relatively shallow and becomes progressively more sheltered.
GLOSSARY OF COASTS - KEY TERMS
COASTAL PROCESSES
EROSION – Waves hitting cliffs and resulting in a part of the cliff breaking off, being slowly eroded.
HYDRAULIC ACTION – is the process of coastal erosion caused by the force of the waves.
CORRASION – process of erosion by waves hurling beach material against a cliff.
CORROSION – process of erosion caused by certain acids in the sea slowly dissolving the cliff.
ATTRITION – process of erosion where pebbles collide with each and break down in size.
TRANSPORTATION – Beach material being transported by the waves further along the coast before being deposited.
TRACTION – boulders rolling along a river bed.
SOLUTION – a form of chemical weathering.
SALTATION – small particles ‘jumping’ above a river bed.
SUSPENSION – small particles of clay and silt carried along in the river.
LONGSHORE DRIFT – the current that transports beach material along a coast in a zig-zag movement.
DEPOSITION – depositing sand and minerals on the beach.
WAVE MORPHOLOGY
FETCH – the length of water over which the wind has blown, which affects the size and strength of waves.
WIND DURATION – amount of time which wind blows over the sea
WIND STRENGTH – how strong the wind blows over the sea.
CONSTRUCTIVE WAVE – gentle wave with strong swash and weak backwash which deposits material.
DESTRUCTIVE WAVE – high wave with strong backwash which breaks frequently, causing erosion.
COASTAL LANDFORMS
COAST – is where the land meets the sea.
CLIFF – is the rock face along the coast.
HEADLAND – where there is resistant rock such as chalk and erosion is slowed down.
BAY – where there is weaker rock such as clay that is easily eroded causing a bay to be formed.
JOINT – how the coastline joins.
CAVE – area that has been hollowed out by waves at the bottom of a cliff.
ARCH – a rocky opening through a headland.
STACK – piece of rock surrounded by the sea, now standing away from the coast.
STUMP – due to undercutting of the stack it eventually falls down which leaves a stump which is covered by the high tide.
WAVE-CUT PLATFORM – area of gently sloping or flat rocks exposed at low tide.
BEACH – is a natural landform
SPIT – long ridge of sand and shingle, attached to the land at one end but in the open at the other end.
COASTAL MANAGEMENT
RECURVED SEA WALLS – Used to repel the waves.
GROYNE – are used to prevent longshore drift, they keep in the sand.
GABION – absorbs the sea water.
ROCK ARMOUR - big rocks such as granite are imported from Norway to absorb and stop the waves.
REVETEMENT – facing of stone and sandbags for walls.
CLIFF STABALISATION – to secure the cliff and make it safe.
MANAGED RETREAT – the cliff is moved back for different reasons.
THOERY OF COASTS – HUMAN USE AND MANAGEMENT OF COASTS
Human activities largely affect the coast. Many old people decide to live near the coast and leave the busy cities, they choose to live here mainly because of the pleasant scenery and it’s not busy as it is in the city. The beaches are also tourist attractions and in the summer hundreds of people are at the beach of Barton. However, due to these activities humans can cause erosion by trampling. Before houses were built, rainwater runs over the surface, and spreads out along the edge of the cliff. Rain runs off the roof and tarmac of the house into storm drains. It is then emptied down the cliff and starts to erode a gully. Then the gully widens and the cliff becomes unstable. Eventually the cliff collapses. There are many ways coastal engineers can prevent the coast suffering from erosion. At Barton on sea they have a wooden groyne which has been destroyed. After the wooden groyne had been destroyed they imported large boulders from Norway. These boulders are much more effective than wooden groynes and they are much cheaper. Other coastal management techniques that can be used can be used are beach replenishment, sea walls or rock armour.
BARTON ON SEA
Barton on sea is a pleasant seaside area with wonderful views of the Solent and the Isle of Wight, surrounded by a pleasant residential area. This is why many old people decide to live there. It is in addition an area of particular scientific interest.
The history of Barton can be traced back some 35 million years, to a period when crocodile type creatures roamed the area. This is confirmed by evidence unearthed by the constant erosion of the cliff face and analysed by geological scientists. Barton is better known by geologists for its fossils. Due to the never-ending cliff erosion, it is not possible to walk along the Barton cliff-top towards highlife in the west, and although it may be possible to walk to high cliff along the beach, but is not recommended due to the continuing cliff collapse. The geology at Barton is sand and clay. Clay is soft rock and is easily eroded by waves, When it rains, water soaks down through the sand above the layer of clay. The bottom layer of sand becomes saturated and moves, causing landslides and slumping.
I have chosen Barton on sea to study coasts because it is under threat by the Atlantic ocean. The combining south-westerly prevailing winds and the distance that the wave travels will cause viscous destructive waves and will destroy Barton’s cliffs.
I am now going Barton to test my hypothesis and see if my predictions are correct, if Barton’s coastal management techniques are effective.