Coasts, chapter 5
- Created by: RevisingNicole
- Created on: 18-05-17 19:31
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- Coastal change and conflict
- Flood risk
- Sea levels are constantly changing. twice a day due to the gravity of the moon, high tides cause raised sea levels.
- A few times every year there are exceptionally high tides, called spring tides. during spring tides flood risk rises
- If spring tides occur when there are large waves, the sea will be even higher
- Worse, if spring tides and waves combine with low air pressure, then a storm surge can form.
- Storm surges are caused by hurricanes and depressions, which are both low-pressure weather systems
- Global warming could make depressions and hurricanes more powerful. they might also become more frequent, meaning storm surges could happen more frequently.
- Storm surges are caused by hurricanes and depressions, which are both low-pressure weather systems
- A few times every year there are exceptionally high tides, called spring tides. during spring tides flood risk rises
- Sea levels are constantly changing. twice a day due to the gravity of the moon, high tides cause raised sea levels.
- Erosion and deposition
- with higher sea levels and possibly increased storms, the balance of erosion and deposition may change
- Beaches, spits, barrier islands and river deltas may erode faster, and in some cases become submerged
- Sea defences could become useless and the only choices will be to build new, higher sea defences or abandon some areas of the sea.
- STORM SANDY
- October 2012, New York and New Jersey, USA
- High winds and a 4m storm surge caused massive flooding, knocked out power for 5 million people, killed over 100 and caused around $50billion damage
- Managing the coast
- Managing the coast is expensive, some areas are managed, others aren't because...
- value of land doesn't justify cost
- Building defences causes erosion elsewhere along the coast
- Climate change is likely to rise sea levels anyway
- Takes into account...
- Needs for different groups of people
- economic costs and benefits of different strategies today and in the future
- Environment, land an sea
- The choices
- HOLD THE LINE: use sea defences to stop erosion and keep the coast where it is today, this is expensive
- ADVANCE THE LINE: use sea defences to move the coast further into the sea, very expensive
- STRATEGIC REALIGNMENT: gradually let coast erode. move people and businesses away from areas at risk. May involve compensation for lost homes
- DO NOTHING: take no action let nature take its course
- SMP (shoreline management plan) sets out how coast will be managed
- Soft engineering
- works with natural processes and tries to stop erosion by stabilising beaches, cliffs and reducing wave energy.
- Cheaper and less intrusive
- Planting vegetation: £20-£50 per sq m
- Beach nourishment: £500-£1000 per sq m
- Offshore breakwaters: £2000 per sq m
- Using smaller structures. sometimes built from natural materials to reduce energy in waves
- Hard engineering
- Using concrete and steel structures such as sea walls, to stop waves and there tracks
- Very costly, unnatural, ugly aethetic
- Managing the coast is expensive, some areas are managed, others aren't because...
- Why cliffs collapse
- MARINE PROCESSES: base of cliff eroded by hydraulic action and abrasion, making clff face steeper
- HUMAN ACTION: building on top of cliff adds a heavy load, pushes down on weak rock
- SUB-AERIAL PROCESSES
- weathering weakens rock.
- heavy rain saturates the permeable rock at the top of the cliff. rainwater may erode the cliff as it runs down it or emerges from the cliff at a pring face
- water flows through the permeable rock, adding weight to the cliff
- heavy rain saturates the permeable rock at the top of the cliff. rainwater may erode the cliff as it runs down it or emerges from the cliff at a pring face
- weathering weakens rock.
- Flood risk
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