Coasts

  • Created by: barry
  • Created on: 09-05-18 23:21

Definitions

  • Open System-   transfers both matter and energy can cross its boundary 
  • Closed System- transfers energy, but not matter, across its boundary 
  • Positive Feedback- where a flow/transfer leads to increase or growth

1- Groynes and sea wall are constructed to protect from marine erosion. Supply of sediment is reduced.

2- Rate if erosion increases downdrift and depostional landfrom are threatend.

  • Negative Feedback- where a flow/transfer leads to decrease or decline

1- Constructive waves build up the beach as they have a more powerfull swash than bacwash, beach becomes steeper.

2- Steeper beaches encourages the formation of destructive waves and these remove material from the beaches  as thet have more powerful backwash.

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Mass Movement

  • Soil creep- when wet soil partcles increase in size and weight, and expand. Whrn soil dries it contracts vertically
  • Mudflow- rapid sudden movent which occurs after periods of heavy rain. Saturated soilt flows rapidly over impoermable surfaces.
  • Landslide- unsupported mass of rock on the cliff material collapses on to the beach
  • Rockfall- rapid free fall of rock from a steep cliff face becuase of gravity.
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Coastal Energy

Wind

  • Fetch is the length of water over which a given wind has blown
  • The strength of the wind can affect the type of wave
  • The duration of the wind affects the strength of the wave

Waves Constructive

  • Long wavelength
  • Low wave frquency 4-6
  • Strong swash and a weak backwash
  • This means they deposit more material on a beach than they remove build gentle beaches

Destructive

  • Short wavelength and steep
  • High wave frequency 10-12
  • Weak swash but powerful backwash
  • Remove material from a beach and produce a steep beach
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Coastal Energy 2

Tides

  • Tides are change in the water level of seas and oceancaused by gravatational flow of the sun and moon
  • Tides affect the position at which waves break on the beach

Currents

  • Is the general flow of water in one direction- it can be caused by wind or by variation on water temperture and salinity

High Energy Environments

  • Destructive waves are commonly found
  • Where the rate of erosion exceeds the rate of deposition

Low Energy Environments

  • Constructive waves are commonly found
  • Where the rate of deposition exceeds the rate of erosion
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Sediment Source

Rivers

Sediment that is transported in rivers accounts for the majority of coastal sediment. This sediment will be deposited in river mouth, estuaries where it will be transported by waves, tides and currents.

Cliff Erosion

This is extremely important locally in areas of relatively soft or unconsolidated rocks. For example, Holderness Coast 

LSD

Sediment is transported from one stretch of coastline (output) to another stretch of coastline (input)

Wind

Wind-blown sand can be deposited in coastal regions

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Sediment Cells

Sediment cell

  • Is a stretch of coastline, usually bordered by two headlands, where the movement of sediment is more or less contained. 
  • Are considered as a closed system as headlands acts a barriers and stop sediments from travelling further
  • Sometimes some material within the cell may be swept out to the sea to act as an output from the system, this may be a result of a severe storm event. 
  • Coastal protection can significantly disrupt the sediment cell and affect the sediment budget.
  • In the UK, there are 11 major cells  
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Sediment Budget

Sediment Budgets

  • A sediment budget is the balance between changes in the volume of sediment held within the system and the volume of sediment entering or leaving the system.

The budget can change because of the following factors:

•Input changes: volume of material being deposited into the coastal system and the impact that human intervention can have on that, e.g. damming a river. Coastal defenses can impact upon the inputs too with reduced cliff face erosion taking place. •Output changes: human intervention, such as removing large amounts of sand from an area for industrial or coastal protection use. Also, sea level rise can increase the likelihood of changing ocean currents and material being removed from sediment cells

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Weathering 1

Weathering- is the breakdown of rock in its (original place) at or close to the ground surface. 

Chemical Weathering

Involves a chemical reaction where salts may be dissolved

  • Carbonation- rainwater absorbs carbon dioxide from the air to form a weak carbonic acid. The reacts with the rocks, and easily dissolved
  • Oxidation- the reaction of rock minerals with oxygen, makes rocks more vulnerable
  • Solution- the dissolving of rock mineralsls, such as halite
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Weathering 2

Physical Weathering

  • Involves the break up of rocks without any chemical changes
  • Frost shattering occurs when water enters a crack or joint in the rocks when it rains and then freezes in cold weather 
  • Salt crystallisation when salt water evaporated, it leaves salt crystals behind. These grow overt time and break the rock
  • Wetting and Drying rocks expand when they are wet and contract when dry, this cause them to crack and break up

Biological Weathering

The breakdown of rocks by organic activity

  • Thin roots grown into small cracks on the cliff. These cracks widen as the roots grow, which breaks up the rock
  • Water running through decaying vegetation becomes acidic, which leads to increased chemical weathering
  • Birds and animals dig burrows into cliffs
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Erosion

Coastal erosion involves the breaking down and removal of material along a coastline by the movement of wind & water. It leads to the formation of many landforms and, combined with deposition, plays an important role in shaping the coastline.

Hydraulic Action- Air may become trapped in joints and cracks on a cliff face. When a wave breaks, the trapped air is compressed which weakens the cliff and causes erosion.

Corrasion- High energy waves carry pebbles, as the wave breaks at the foot of the cliff, material is thrown at the cliff face and wears it away by chipping fragments off

Abrasion- Bits of rock and sand in waves grind down cliff surfaces like sandpaper

Solution- Acids contained in sea water will dissolve some types of rock such as chalk or limestone

Attrition- Waves smash rocks and pebbles on the shore into each other, and they break and become smoother

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Erosional landforms

liffs and wave-cut platforms

  • Destructive waves erodes the cliff by corrosion or hydraulic action
  • The cliff continues to erode creating a notch
  • As the erosion continues the notch continues getting larger and becomes a cave
  • Eventually the top layer of the cliff fall as there is no support at the bottom
  • This creates a wave cut platform, which is only visible at a low tide

Caves, Arches and Stacks

  • Cracks in cliff starts to open up due to the process of  hydraulic action
  • The crack grows into a cave by processes hydraulic action and abrasion
  • The cave breaks through creating an arch a component
  • The arch collapses due to sub aerial erosional processes like freeze thaw which will weaken the arch roof.
  • The collapsed material will be transported by the energy of waves - this is a transfer of sediment
  • This leaves a (component) stack and continues to weathered by sub areal processes.
  • Marine ersoion attacks the base of stack till it collapses, any sediment transferd out the system is an output
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Transportation

Transportation is the movement of material or sediments in the sea and along the coast by waves

Traction- The rolling of sediment along the sea bed which is to heavy to be carried by the sea 

Saltation- Sediment “bounced” along the seabed, light enough to be picked up

Suspension- Smaller, lighter sediment picked up and carried with the flow of the water 

Solution- Chemicals dissolved in the water, transported and precipitated elsewhere. 

Longshore Drift- 

  • The prevailing wind causes waves to approach the coast at an angle. The swash carries the sand and pebbles up the beach at the same angle.The backwashcarries the material back down the beach at right angles
  • Sediments are carried along the coastline in a zig-zag motion and would eventually be deposited when the waves lose energy
  • Therefore longshore drift is moving material from the west to the east
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Deposition landforms 1

Deposition is when material that is being transported is dropped by waves. This happens when the forces responsible for transporting sediment in a coastal environment is weaken and can no longer support the sediment

Beaches- Beaches are made up of sediments that has been transported from elsewhere and deposited by the sea. Constructive waves help to build up beaches, as the swash tends to deposit sediments 

Spits- A spit is a long, narrow feature, made up of sand and shingle, that extends from the land into the sea. Sand or shingle is moved along the coast by longshore drift but the coastline changes direction because of a river estuary or a second prevailing wind. Sediment starts to build and a spit forms

Tombolo- Tombolo is a beach that has formed between a small island and the mainland. Deposition occurs where the waves lose their energy and a tombolo beings to build up 

Sand dunes- Is sediments blown onto beach inland. Large quantities of sediment deposited onshore by constructive waves 

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Sea level change

Eustatic Change- when the sea level itself rises or falls  

  • Global
  • In glacial periods, huge ice sheets form. This causes the sea levels to fall
  • As the temperature rises the ice sheets begin to melt and retreat. The water from the ice causes the sea levels to rise

Isostatic Change- when the land rises or falls, relative to the sea relative to the sea

  • Local
  • During glacial periods, the weight of ice sheets makes the land sink- isostatic subsidence
  • As the ice begins to melt at the end of the glacial periods, the reduced weight of the ice causes the land to readjust and rise- isostatic recovery 
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Emergent and Submergent landforms

Emergent Coastal Landforms

Raised Beaches- Are wave-cut platforms & beaches that are above the current sea level

Submergent Coastal Landforms

Rias-

  •  Drowned river valleys
  • As sea levels rise they flood the river valleys, only leaving the high land visible
  • The cross section of a ria is really similar to the a river in the lower course

Fjords- 

  • Drowned glacial valley
  • As sea levels rise, U-shaped valleys left by glaciers are submerged
  • Steep valley sides

Dalmatian Coasts-These form in areas of the world where valleys lie parallel to each other. When the valleys are flooded by the rise in sea level, the tops of the valleys remain above the surface of the sea and appear to be a series of islands that run parallel to the coastline

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Hard engineering

Groynes

  • Timber or rock structures built at the tight angles to the coast
  • They trap sediments being moved along the coast 

Advantages:

  • Builds up beaches
  • Not too expensive
  • Increases tourist potential and protects the land behind

Disadvantages:

  • Beaches further along the coast will be at risk because they interrupt the longshore drift
  • Unnatural and unattractive

Sea Walls

  • Stone or concrete walls at the foot of the cliff, or at the top of beach.
  • They usually have a curved face to reflect waves back to the sea

Advantages:

  • Effective prevention of erosion
  • Protects land behind 

Disadvantages:

  • They reflect wave energy rather than absorbing it
  • Unnatural
  • Expensive to build and maintain- £6,000/m

 

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Hard engineering

Groynes

  • Timber or rock structures built at the tight angles to the coast
  • They trap sediments being moved along the coast 

Advantages:

  • Builds up beaches
  • Not too expensive
  • Increases tourist potential and protects the land behind

Disadvantages:

  • Beaches further along the coast will be at risk because they interrupt the longshore drift
  • Unnatural and unattractive

 

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Hard engineering 2

Sea Walls

  • Stone or concrete walls at the foot of the cliff, or at the top of beach.
  • They usually have a curved face to reflect waves back to the sea

Advantages:

  • Effective prevention of erosion
  • Protects land behind 

Disadvantages:

  • They reflect wave energy rather than absorbing it
  • Unnatural
  • Expensive to build and maintain- £6,000/m

 

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Hard engineering 3

Rock Armour

  • Large rocks are placed at the foot of the cliff or at the top of beach
  • Forms a permeable barrier to the sea- breaking up waves but allowing water to pass through 

Advantages:

  • Relatively cheap and east to construct and maintain
  • Often used for recreation- fishing, sunbathing 

Disadvantages:

  • The rock can look out of place with the local geology
  • Can be dangerous for people clambering over them 

Revetments

  • Sloping wooden, concrete or rock structures placed at the foot of a cliff or the top of a beach.
  • They break up the waves’ energy. Relatively inexpensive to build- Up to 4,500 /m. Unnatural and Need high levels of maintenance

 

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Soft engineering

Beach Nourishment

The addition of sand or pebbles to an existing beach to make it higher or wider 

  • Relatively cheap and easy to maintain
  • Natural looking and blends with the beach
  • Increases tourist potential by creating a bigger beach 
  • Disadvantage- needs constant maintenance

Dune Stabilisation Marram grass can be planted to stabilise dunes. Areas can be fenced in to keep people of newly planted dunes

  • Maintains a natural coastal environment
  • Provides important wildlife habitats
  • Relatively cheap and sustainable 
  • Disadvantage- Time consuming to plant marram grass
  • Disadvantage- People may respond negatively to being kept off certain areas 
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Soft engineering 2

Marsh Creation

A form of managed retreat by allowing low-lying coastal areas to be flooded by the sea, he land then becomes a salt marsh

  • A form of managed retreat by allowing low-lying coastal areas to be flooded by the sea, he land then becomes a salt marsh
  • Disadvantage- agricultural land is lost
  • Disadvantage- farmers or landowners need to be compensated
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Sustainable Integrated Approaches

Shoreline Management Plans (SMP)

A Shoreline Management Plan is a policy that describes how your stretch of the shoreline is likely to be managed, to prevent flooding or erosion. Stretches of coast are divided into management units, and one management policy need to be agreed. There are four different types of management policies.

•No active intervention – There is no planned investment in defending 

•Hold the line – A idea to build and maintain artificial defenses, so the shoreline doesn’t move. 

•Managed Realignment – allowing the shoreline to move naturally, but managing the process to a certain direction and area. 

•Advance the Line - New defenses are built on the seaward side

An SMP aims to manage risk by employing a range of methods which reflect both national andlocal priorities, to: 

Reduce the threat of coastal flooding and erosion to people and their property. Benefit the environment, society and the economy as far as possible.

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Sustainable Integrated Approaches 2

Integrated Coastal Zone Management (ICZM)

The key aim of ICZM planning is to co-ordinate all the potential pressures and conflicts of interest at the coast and manage them fairly, responsibly and sustainably. Specifically:

  • Monitoring, information-gathering and recording of what is taking place at the coast
  • Identifying and involving all stakeholders (who may change with time)
  • Following sustainable strategies
  • Managing the natural and human systems responsibly
  • Considering changes to coastal systems and anticipating likely impacts
  • Adapting plans accordingly
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Sundarabarns

Location- The Sundarbans is a coastal zone which is part of the world’s largest delta that southern Bangladesh and India. Characteristics- The Sundarbans are a low lying coastal environment dominated by mangrove forests and swamps. A delta is a depositional river landform(C)located on the coast at the point where rivers transporting(P)large amounts of sediment meet the sea and deposit significant amounts of fine silt.  Risks- Natual threats- Coastal flooding, Tropical cyclones, Tigers.              Human threats- Over exploitation of resources, Destructive fishing techniques, Conflict over resources Opportunities- Goods from mangroves Construction materials (timber), Fishing materials (poles, floats), Fuel (charcoal, firewood), Food and drink (fish, fruit, honey, alcohol, cooking oil), Others (medicines, aquarium fish, paper, cattle fodder) Services- Protection from, floods, cyclones, coastal erosion and tsunamis.   

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Sundarabarns 2

Responses- 

Resilience this means that people and communities are able to withstand and recover from extreme physical events because mangrove forest enable people to recover easily as it it is a source of food, supplys and medcine.  Mitigation – this means that people and communities take action to reduce the impacts of extreme physical events such as a cyclone in the Sundarbans. Adaptation – this means that people and communities are able to change in some way to live with extreme physical events such as a cyclone in the Sundarbans- NGOs provide tempory cyclone shelters and new rice crops immune to flooding.

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Abbots Hall

Managed Retreat on the Essex Coast

The existing  sea wall at Abbotts Hall was in need of repair and ETW wanted to consider different ways of coastal defence which took into account the problems of the sea level rising. The scheme to have a managed retreat was introduced in 2002.

5 Counter walls were constructed at each end of Abbotts Hall to ensure that neighbours land was not flooded. 5 breaches were made and in 2002 the firdt big tide flooded 120 acres

Benefits of the coastal re-alignment at Abbotts Hall farm 

  • New wildlife habitats are created in the marshes
  • The marshes act as a natural sea defence. Waves are slowed as they cross the marshes in the same way as a large beach slows waves. They can also absorb flood water
  • As marshes can adapt to gradual changes in sea level this is a sustainable defence  
  • To replace the existing old sea walls would be very expensive and probably not sustainable in an area at risk from sea level rises.
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Abbots Hall 2

Drawbacks of the coastal re-alignment at Abbotts Hall farm

  • Agricultural land is lost and so less can be produced.
  • The plan was not initially popular with some local residents who were concerned that the marshes would not offer the same level of protection as improved sea walls
  • The eustatic rise and isostatic sinking has resulted in a 6mm rise per year in this area.
  • 40% of salt marshes have been lost to coastal squeeze over the last 25 years- habitats at risk
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Sheringham

Chararcter

Sheringham is located on the North Norfolk coast with a population of 7500. It is an important tourist resort for Norfolk and it has many hotels and cafes to cater for the industry which brings in a large proportion of its revenue for the local economy. The area has been protected because of the high land value and the busy tourist town environment which brings in revenue.

Hard engineering 

Sea wall-

  • Found at sea front 
  • 6m tall made from concrete
  • £5000 pm

Rock armour-

  • Protects sea wall and promenade 
  • sometimes needs maintaince 
  • £2000 pm
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Sheringham 2

Hard engineering:

Groynes-

  • igneous rocks from norway
  • £125,000 
  • needs maintanice
  • Starves other beacches and spits- potentially get eroded
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Feedback

  • Dynamic eqilibrium- the inputs and outputs are in balance
  • Negative feedback- the events damp down the effects of the intial change, promoting Dynamic equilibrium.

1- Constructive waves build up a beach as they have stronger swash, beache becomes more steeper 

2- Steeper beaches encourage the formation of destructive waves, these waves remove material from beach as the waves have a strong backwash.

  • Positive feedback- the events increase the effects of the intial change, promoting enviormentalinstability.

1- During a storm destructive waves erode the cliffs and remove materials from the beach as they have a stronger backwash (beach is smaller so more ersoion)

2- This material is deposited to form an offshore bar.

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