AS coasts revision

Coasts revision

• Contents
• The coastal system
• Coastal processes
• Landforms produced by coastal erosion
• Landforms produced by coastal deposition
• Sea level change
• Coastal flooding
• Coastal protection schemes
• Green= Key terms

Coastal systems

• Like rivers coasts also have systems.
• INPUTS- River sediment, sediment from cliffs that have been eroded or suffered landslides and sediment that has been transported by waves from offshore.
• PROCESSES- wave action, tidal movement, erosion, weathering, transportation and deposition
• OUTPUTS- Sediment washed out to sea or deposited further along the coast
• Coastal sediment cells also known as littoral cells are lengths of coastline that are pretty much entirely self-contained for the movement of sediment. Each one is a coastal system. So processes going on in one cell don't affect the movement of sediment in another cell.

Waves

• A wave is created by the wind blowing over the surface of the sea, this friction causes the water to move in a circular motion.
• The effect of a wave on shore depends on the height, this is affected by wind speed and fetch.
• As waves approach the shore they break. Friction with the sea bed slows the bottom of the waves and makes their motion more elliptical, the crest of the wave rises up and then collapses.
• Tides are the periodic rise and fall of the ocean surface, they are caused by the gravitation pull of the moon and the sun.
• 

Constructive waves

• Constructive waves:
• Have low frequency around 6-8 waves per minute
• low and long
• Elliptical cross profile
• Powerful swash
• Creates beaches
• 

Destructive waves

• Destructive waves are:
• High and steep
• Circular cross profile
• High frequency 10-14 waves per minute
• Powerful backwash
• Erodes beaches
• 

Sub aerial weathering

• This describes the coastal processes that are not linked to the action of the sea, it includes freeze thaw weathering and salt weathering
• .
• Throughflow and runoff caused by heavy rain can also make cliffs more unstable and increase the likelihood of mass movement.
• Mass movement is the movement of material downhill due to gravity. It includes, landslides, slumping and rockfalls.

Erosion and long shore drift

• The rate at which a stretch of coastline is eroded depends on several factors.
• The width of the beach- the distance between high and low tide marks. Beaches slow down waves, reducing their erosive powers.
• The breaking point of the waves- a wave that breaks at the foot of a cliff transfers most energy to the cliff and causes erosion. Waves that hit the cliff before they break will erode mush less
• The aspect- If the coastline faces the dominant wind and wave direction erosion will be faster
• The fetch- waves with a long fetch are higher and steeper with more energy
• Rock type- soft rocks like clay will erode quicker
• 
• Caption: Long shore drft

Coastal landforms

• Cliffs and wave cut platforms
• Cliffs retreat due to the action of waves and weathering.
• This causes a notch to form at the high water mark, this develops into a cave. Rock above the cave becomes unstable and so it collapses. Wave-cut platforms are flat surfaces when a cliff is eroded.
• Headlands and bays
• They form when there are bands of alternating hard rock at right angles to the shore. The soft rock is eroded quickly forming a bay. The harder rock is eroded less and sticks out as a headland.
• 

Coastal landforms

• Caves, blowholes, arches and stacks
• Weak areas in rock eg joints are eroded to form caves.
• Occassionally the roof of a cave is weakened along a major joint by hydraulic pressure and the roof collapses to form a blowhole. Caves on the opposite sides of a narrow headland may eventually form an arch. When an arch collapses it forms a stack.
• 

Coastal landforms

• Beaches
• They are formed when constructive waves deposit sediment on the shore. Shingle beaches are steep and narrow. They're made up of largeer particles which pile up at steep angles, sand beaches are wide and flat.
• Berms are ridges of sand and pebbles found at high tide marks. They're formed by deposition of coarse material at the limit of the swash.
• Runnels are grooves in the sand running parallel to the shore they are formed by backwash draining to the sea.
• Cusps are crescent shaped indentations that form on beaches of mixed sand and shingle they develop in areas where waves break parallel to the beach and where there's a large tidal range.
• 

Coastal landforms

• Spits tend to form where the coast suddenly changes direction.
• Longshore drift continues to deposit material across the river mouth leaving a bank of sand and shingle sticking out into the sea
• Occasional changes to the dominant wind and wave direction may lead to a spit having a recurved end
• Over time several recurved ends may be abandoned as the waves return to their original direction
• The area behind the spit is sheltered from the waves and often develops into mudflats and salt marshes.
• 

Coastal landforms

• Bars
• These are formed when a spit joins two headlands together. This can occur across a bay or across a river mouth. A lagoon forms behind the bar.
• Sand dunes
• These are formed when sand deposited by longshore drift is moved up the beach by the wind. Sand trapped behind driftwood or bems is colonised by plants. The vegetation stabilises the sand and encourages more sand to accumulate there forming embryo dunes. Over time the oldest dunes migrate inland as newer embryo dunes are formed.
• Salt marshes
• They form in areas of sheltered water. As silt and mud are deposited by the river or the tide mudflats develop. The mudflats are colonised by vegetation that can survive the high salt levels and long periods of submergence by the tide. The plants trap more mud and silt and gradually they create an area of marshland that remains exposed for longer between tides.

Case study

• The rate of erosion at Holderness is about 1.8m per year
• Main reasons for the erosion
• Soft rock-boulder clay eroded by corrasion.
• Narrow beaches slow the waves reducing erosive powers. Flamborough head stops sediment replenishing the beach, coastal defences may lead to narrower beaches.
• Powerful waves- long fetch and the coast face the dominant wind and wave direction
• Social- property prices have fallen around 30 villages have been lost since roman times.
• Economic- visitor numbers have dropped, caravan parks are at risk, £2 million spent at Mappleton
• The gas terminal is at risk, it accounts for 25% of Britain's gas supply, 80,000m2 of farmland is lost each year
• Environmental- somes sssi's are threatened this also may affect the lagoon at spurn head.

Sea level changes

• Eustatic
• This is caused by a change in the volume of water in the sea or a change in ocean basins
• The effects are global. And main causes are:
• Tectonic movements
• Changes in climate
• Sea level rise has a variety of impacts
• More frequent and severe coastal flooding
• submergence of low lying land
• changes in the coastline
• Isostatic
• This is caused by vertical movementsof the land relative to the sea. Any downward movement of the land causes sea level to rise locally while uplift of the land causes the sea level to fall
• The effects are local and the main causes are;
• Tectonic movements
• Compression/decompression
• subsidence

Submergence landforms

• Rias are formed where river valleys are partially submerged. They have a gentle long and cross profile, they are wide and deep at their mouth becoming narrower and shallower the further inland they are.
• Fjords are drowned glacial valleys, they are straight and narrow with steep sides, the have a shallow mouth caused by the threshold which is formed by deposition material from the glacier, they are very deep further inland,
• In areas where valleys lie parallel to the coast an increase in sea level can from a dalmation coastline
• 

Emergence landforms

• When sea level falls relative to the coast new coastline can emerge.
• Raised beaches can form when the fall in sea level exposes wave cut platforms and their beaches, over time beach sediment becomes vegetated and develops into soil.
• The cliffs above raised beaches are no longer eroded by the sea and slowly get covered by vegetation , they are called relict cliffs.
• 

Coastal flooding

• Physical causes of flooding
• Low pressure atmospheric systems reduce atmospheric pressure on the sea surface causing it to rise, this is caused a storm surge
• Strong offshore winds can force water to high levels
• Tidal currents and surges can be funnelled into a coastal bottleneck
• High rainfall may cause high river discharge
• Tsunamis

Coastal flooding

• Human causes of flooding
• Management of river systems- some management strategies trap sediment and so reduce the amount being deposited at the rivers mouth-this causes deltas and salt marshes to shrink providing less protection against high tides and storm surges.
• Building on coastal lowlands-especially sand dunes has restricted sediment supply to protective beaches and marshes
• Management of coastal systems- some strategies alter sediment movement reducing the amount of protective beach material further along the coast
• Reclamation of coastal lowlands- draining this land to reclaim it causes the land to shrink to become lower than sea level.

Coastal flooding case study

• Tsunami struck southern asia on 26th december 2004
• The tsunami devastated areas or Indonesia, shri lanka, thailand and india, the tsunami was caused by a magnitude 9 earthquake. The tsunami travelled across the bay of speeds up to 800km per hour the waves were up to 30m high and the epicentre of the earthquake was off the western coast of sumatra.
• Social factors;
• Deadliest tsunami ever recorded 230 000 people dead
• 1.7million made homeless
• Drinking water was polluted
• 400 000 lost their jobs in sri lanka
• Economic factors;
• cost between $8 and $15 billion
• Fishing is a large part of the economy boats, netsand other equipment were destroyed affecting the livelihood of fishermen.
• Salinisation of land has reduced soil fertility
• 25% of tourism was lost
• Envrionmental factors
• 8 million litres of oil was released
• mangrove forests wered etroyed
• High salt content of the floodwater destroyed many ecosystems

Coastal management

• Only some parts of the coast is managed this is due to the cost benefit analysis.
• There are four options for coastal management.
• Hold the line- maintain the existing coastal defences
• Advance the line- build new coastal defences further out to sea
• Do nothing-build no coastal defences at all and deal with erosion and flooding as it happens
• Retreat the line-Build no defences, move people away from the coastline
• 

soft engineering

• Beach nourishment-sand and shingle are added to beaches from elsewhere, creates wider beaches.
• Beach stabilisers-reducing the slope angle and planting vegetation, creates wider beaches
• Dune regeneration-sand dunes are created, provides a barrier between land and sea
• land use management-vegetation that bind the dunes can be trampled on wooden walkways can stop people from walking on them
• Creating marshland- planting vegetation, reduces speed of waves
• Coastal realignment- breaching an existent defence and allowing the sea to flood the land, plants will colonise the land and it will become a marshland
• Hard engineering is expensive and disrupts natural processes
• Sustainability
• Rising sea level means more coast al management will be needed to protect coastal settlements
• Shoreline management plan is a plan for how the coastline in one sediment cell should be managed
• The process of coming up with an integrated sustainable management plan is called integrated coastal zone management

coastal management

• Hard engineering along the Holderness coastline.
• Bridlington is protected by a 4.7km seawall and groynes.
• Mappleton is protected by groynes, revetment, this is to protect the village and coastal road.
• Withernsea is protected by groynes, a seawall and riprap
• Hornsea is protected by a sea wall, groynes and riprap. Gabions protect the caravan park.
• Easington gas terminal is protected by revetments.
• Spurn head is protected by groynes and rip rap.
• Problems
• groynes trap sediment increasing width of beach- protects the local area but increase erosion of cliffs downdrift
• Sediment produced from erosion is normally washed into the Humber-reduction in this increases risk of flooding.
• The protection of local areas forms bays
• possible schemes
• SMP recommends holding the line at some settlements and gas terminal and Do nothing along unpopulated areas
• Coastal realignment of businesses has been suggested
• A sea wall suggested to protect Easington gas terminal
• Offshore reefs.

Coastal management

• soft engineering along blackwater estuary
• Blackwater estuary is part of Essex coastline
• Coastal realignment implemented at Tollesbury fleet a sea wall was breached
• Beaches have been nourished
• A sea wall was lowered which led to the land being flooded.
• Marsh stabilisation has been carried out by planting stakes and brushwood on the water line
• These schemes are more sustainable
• They are more sustainable in long term dosent always need maintaining and some techniques are self-repairing
• Created more marshland which provides habitats for wildlife

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