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Coasts as a system (Inputs,outputs, energy, stores/components,…
Coasts as a system
Inputs,outputs, energy, stores/components, flows/transfers,positive/negative feedback,dynamic equilibrium
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Positive feedback
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Coastal management can inadvertently lead to an increase in erosion elsewhere along the coast. Groynes trap sediment, depriving areas further down-drift of beach replenishment and this can exacerbate erosion. Seawalls can have the same effect by transferring high energy waves elsewhere along the coast
Negative feedback
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When the rate of weathering and mass movement exceeds the rate of cliff-foot erosion a scree slope is formed. Over time, this apron of material extends up the cliff face protecting the cliff face for sub aerial processes. This leads to a reduction in the effectiveness of weathering and mass movement
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Waves
The formation of waves and their size and shape is a result of the exchange of energy wind blowing over the sea. The longer the wind blows for, and greater the distance it blows over, the larger the waves that result and the greater their energy
The extent to which the shape of a beach or coast can be altered depends largely on the action of waves upon it. Waves can be gentle and infrequent or larger, more frequent and more powerful
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Key Terms
Wave fetch- The distance of open water over which a wave had passed. Maximum fetch is the distance from one coastline to the next landmass, it often coincides with prevailing wind direction
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Wave Refraction
It is very rare for waves to approach a regular uniform coastline, as most have a variety of bays, beaches and headlans
Because of these features, the depth of water around the coast varies and as a wave approaches a coast its progress is modified due to friction from the seabed,halting the motion of waves.
As waves approach a coast they are refracted so that their energy is concentrated around the headlands but reduced around bays. Waves then tend to approach the coastline parallel to it, and their energy decreases as water depth increases
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Natural processes
Sub-arieal Weathering
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Chemical-
1) This involved the action of chemicals in weather conditions (acid rain) dissolving certain rock types over time. The decomposition is a result of chemical change
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Biological-
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For example - tree roots growing into and widening a crack in rocks or the action of burrowing animals physically enlarging joints in weak rocks
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Mass movement- This is the movement of large areas of material downslope under the force of gravity (Cliff Collapsing)
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Slides- A type of mass movement where large areas of coastal rock and soil slide downwards from the cliff
Slump-Very similar to a slide only it usually involves a smaller distance of movement that is on curved axis
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Soil creep-Very slow (1cm per year) movement of material due to raindrop impact, saturation and freeze-thaw expansion
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Sediment budgets-
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Sediment Gain-cliff erosion, river deposition, tidal deposition
Sediment loss- deposition in sediment sinks (stores) such as bars, spits, dunes or human dredging
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Upsetting the balance- storms, flooding, human engineering
Tides
Causes
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Moon pulls water towards it creating high tides and there is a compensatory bulge on the other side of the earth - results in " high tides and 2 low tides
Spring Tides
1) as the moon orbits the earth the tide follows it. Twice in a lunar month when the sun-moon and earth are in a straight line, the tide raising force is the strongest
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Neap tides
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This alignment gives the month tidal range, or neap high tide
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Currents
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Clockwise = northern hemisphere, Anit-clockwise = Southern hemisphere
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Sediment Cells
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What are sediment cells
movement of sand and shingle in the nearshore zone by longshore drift has been found to occur in discrete, functionally separate sediment cells
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