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Isabella Mo

on 22 March 2015

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Transcript of Coasts

What is a coast?
A coast is where land meets sea. A river would not be a coast as it is not the sea.There can be many coastal features as well such as rainforests, cliffs, arches and many more.
This is an example of a coast
Coastal features
Caves are formed by hydraulic action when the waves crash against the weaker rock of the headland causing the rocks to crack slightly, then weathering happens so the rock shatters to form a cave. This happens over a long period of time and as more waves crash the cave expands and becomes larger.
An arch is natural rock curved with an opening beneath it.Arches are formed by the weathering of rocks, abrasion of flung stones and hydraulic action in a cave. The cave then becomes very big and starts to break and eventually turns into an arch.
Stack and stump
Stacks are formed when the arch crumbles and separates from the headland. Then the waves erode more and attrition forms a stack to a stump over a long period of time depending on size.
Sea defences
Groynes are a form of coastal protection.They are built at right angles to prevent longshore drift. These structures absorb energy of the sea on the shore. Reducing the impact of energy on the coast. There are four types of groynes, wooden groynes, steel groynes, rubble mound and sand filled bag groynes and groynes of concrete element.
Sea walls
The traditional 'hard' defence is the sea wall. In the past sea walls were vertical and deflected the energy of waves away from the coast. In doing so, however, they suffered a lot of expensive damage in a short period of time. Modern sea walls have a slope and a curved top which breaks up the energy of waves and prevents water going over the top of the wall in heavy storms. Sea walls are very expensive but last 20-30 years.
Rip rap
Rip rap is rock or other material used to armour shorelines against water or ice erosion. It is made from a variety of rock types, commonly granite, limestone or occasionally concrete rubble. Rip rap works by absorbing and deflecting the impact of the wave before the wave reaches the defended structure. The size and mass of the rip rap material absorbs the impact energy of waves, while the gaps between the rip rap traps slows the flow of water, lessening its ability to erode.
Gabions are free draining walls that are constructed by filling large galvanized steel baskets with rock. Gabion walls are in many applications the most cost effective structural walls available. Flexibility is an important benefit of any gabion structure. Since the baskets are constructed of galvanized mesh wire and filled with rock, the flexibility of a gabion structure allows it to withstand pressure without deforming, cracking or breaking as in the case of concrete and other materials. There are very few limits when it comes to the construction of a gabion wall.
Rock revetments may be used to control erosion by armouring the dune face. They dissipate the energy of storm waves and prevent further recession of the backshore if well designed and maintained. Revetments may be carefully engineered structures protecting long lengths of shoreline.
Here are some coastal videos!

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