Topic 3: Coastal Landscapes and Change Flashcards
(229 cards)
1
Q
How can we classify coastlines?
A
- Geology: the type of rock influences the resulting type of coast, e.g. rocky cliffs or coastal plains.
- Energy levels: creates high or low energy coastlines .
- Balance: deposition and erosion have a balance which either leads to coastlines being built or eroded away.
- Sea level: changes in sea levels results in submergent or emergent coastlines.
2
Q
What are the types of rock?
A
- sedimentary
- igneous
- metamorphic
3
Q
Sedimentary rock:
A
Form from the build up, compacting, and hardening if sediments into layer over time by lithification.
- Older sedimentary rock can be very resistant.
- Younger sedimentary can be more easily eroded, e.g. clays
- the average rate of erosion of sedimentary rocks is 2 - 6cm per year.
4
Q
Metamorphic rock:
A
Highly resistant rock formed from the change in the structure of sedimentary and igneous rocks, caused by variations in heat and pressure. e .g. slate, marble and schist.
- the process of change is referred to as the rocks having been metamorphosed..
- marble is a np example of a M rock that has been formed from the changing structure of limestone caused by the re-crystallisation of calcite.
- M rocks are resistant to erosion
5
Q
Igneous rock:
A
Highly resistant rock produced by volcanic activity, e.g basalt and granite. Form from the crystallisation of magma.
- they here more resistant to erosion and weathering as they contain crystals which increase the strength of the rocks and reduce the number of lines of weaknesses that would be exploited by physical processes.
- they can either be intrusive (formed from magma inside the Earth) or extrusive (formed when magma escapes through vents on the Earth’s surface).
- average rate of erosion of igneous rocks is 0.1 - 0.5cm per year
6
Q
What is the littoral zone?
A
- the littoral zone is a series of sub-zones to represent the features of the wider coastline from sea to land.
- it includes four key sub-zones: offshore, foreshore, backshore and nearshore.
- this zine reaches dynamic equilibrium where there is a balance between inputs and outputs.
- short term factors: individual waves, daily tide and seasonal storms.
- long term factors: climate chnage and sea level changes.
7
Q
The littoral zone inputs and outputs
A
Sediment is the key input and output of the system and is determined by:
- inputs - the action is waves, currents and wind.
- outputs - washed out into the sea by erosion.
8
Q
Coastal system inputs:
A
- Marine: waves, tides, storm surges
- Atmospheric: weather/ climate, climate change, solar energy
- Land: rock type and structures, tectonic activity
- People: human activity, coastal management
9
Q
Coastal system processes:
A
- weathering
- mass movement
- erosion
- transport
- deposition
10
Q
Coastal system outputs:
A
- erosional landforms
- depositional landforms
- different types of coasts
11
Q
High energy coastlines:
A
Rocky coastlines are generally found in high-energy environments.
High energy coasts are characterised by:
- destructive waves
- long fetches
- high rates of erosion
- caves, arches, stacks and stumps
- cliffs and wave-cut platforms
12
Q
High energy coastlines in the UK:
A
- stretches if the Atlantic - facing coast, where the waves are powerful for much of the year (such as Cornwall or northern Scotland)
- the rate of erosion is higher than the rate of deposition
- erosional landforms, such as headlands, cliffs and wave-cut platforms tend to be found here
13
Q
Low energy coastlines:
A
Sandy coasts are generally found in low-energy environments.
Low energy coasts are characterised by:
- constructive waves
- shorter fetches
- higher rates if deposition
- spits and bars, beaches, sand dunes and salt marshes.
14
Q
Low- energy coastlines in the UK:
A
- stretches of the coast where the waves are less powerful, or where the coast is sheltered from large waves (such as Lincolnshire and Northumberland)
- the rate of deposition is higher than the rate of erosion
- landforms such as beaches, spits and coastal plains tend to be found here.
15
Q
Lithology definition:
A
Geological structures and characteristics
16
Q
Joints definition:
A
(Vertical cracks) - these are fractures caused either by contraction as sediments dry hit, or by earth movements during uplift.
17
Q
Dips definition:
A
Refer to the angle at which rock strate lie (horizontally, vertically p, dipping towards the sea, dipping inland)
- bedding planes that dip towards the sea create a gentler cliff profile, but these cliffs are vulnerable to mass movement processes, like rockfalls.
- bedding planes that dip towards land tend to create a steeper cliff profile, but these cliffs are more vulnerable to erosion processes, like hydraulic action and abrasion.
18
Q
Faults definition:
A
Formed when the stress or pressure to which a rock is subjected, exceeds its internal strength (causing it to fracture). The faults then slip or move along fault planes.
- rocks with the presence of more joints and faults, like sedimentary rocks, are more susceptible to the processes of erosion and weathering. This is because these processes exert forces on the weaknesses found in the layers of the rocks.
19
Q
Folding definition:
A
Formed by pressure during tectonic activity, which makes rock buckle and crumple (e.g. the Lulworth Crumple)
20
Q
Strata definition:
A
Layers of rock
21
Q
Concordant coastlines - what are they?
A
Concordant coastlines have alternating bands of hard (more resistant) and soft (less resistant) rock parallel to the coast.
A resistant rock is eventually eroded - allowing the sea to break through to the less resistant rocks behind. Erosion follows quickly.
E.g. this has led to a formation of a small bay or cove at Lulworth.
22
Q
Discordant coastlines:
A
- Discordant coastlines have alternating bands of hard and soft rock at 90 degrees to the coast.
- Erosional landforms are more common on discordant coastlines because erosion happens at different rates along their length.
- more resistant rock leads to headlands
- less resistant rock forms bays
23
Q
Discordant coast - Isle of Purbeck:
A
- Bagshot and Tertiary beds consist of unconsolidated clays which are less resistant and have formed a large bay at Studland.
- chalk is strong and resistant therefore has led to the Foreland headland.
- Wealden bed also consists of unconsolidated material and has led to the formation of Swanage Bay.
- Purbeck and Portland beds consist mainly of limestone . This is resistant and has led to headlands at Peveril point and Durlston Head.
24
Q
What are Dalmatian coasts?
A
- another type of concordant coastlines
- they have formed as a result of a rise in sea level. Valleys and ridges run parallel to each other and when the valleys flood because of a rise in sea level, the tops of the ridges remained above the surface if the sea - as a series of offshore islands that run parallel to the coast.
25
Examples of Dalmatian coasts:
- e.g. the Dalmatian coast, Croatia
- e.g. Lulworth Cove, south-west Dorset coastline. Here, the more-resistant rock (e.g. limestone) acts as a barrier to protect the less-resistant rock.
26
Haff coats:
- also consist of concordant features - long spits of sand and lagoons - aligned parallel to the coast.
- these are named after the Haffs, or lagoons of the southern shore of the Baltic Sea, which are enclosed by sand spits or dunes.
27
Bays and headlands:
On discordant coastlines, the retreating, less resistant rock and the exposed resistant rocks cause a change in the shape of the coastline. This leads to wave refraction.
This changes in the way in which waves approach the coastline can cause an increase in the rate of erosion on the headlands.
This leads to the formation of headland features like caves, arches, stumps and stacks.
Bays are formed when weaker rocks (e.g. shale and clays) are eroded.
28
How do headlands and bays affect incoming waves in different waves?
- Headlands: force the incoming waves to refract or bend - contracting their energy at the headlands. This increases the waves’ erosive power, which leads to a steeping of the cliffs and their eventual erosion into arches and stacks
- Bays: when waves enter a bay, their energy is dissipated and reduced. This leads to the disposition of sediment (sand or shingle) - forming a beach.
29
Why is vegetation important?
Supports the development of sandy coastlines and so plays an important role in the rate of coastal recession.
30
Sand dunes:
- Sand dunes need a continuous supply of sand, powerful winds to transport sand and obstacles to trap the sand, like plants.
- a typical sand dune transect goes from the mobile dunes nearest the sea (embryo, fore and yellow) to the fixed dunes nearest the backshore (grey dunes and dune slack)
31
Sand dunes - plants:
- Xerophytes, which can withstand periods of dry weather.
| - Halophytes, plants that can withstand high concentrations of salt from seawater.
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Vegetation succession in dunes:
- typical plants that colonise embryo and foredunes are sea rocket and sea crouch. These plants have deep roots and can tolerate high concentrations of salt.
- yellow dunes tend to be colonised by marram grass. These plants also have deep roots and are salt tolerant.
- heathers are commonly found in grey dunes because of the higher rates of humus.
33
What are the two types of waves?
- destructive
| - constructive
34
Factors affecting waves:
- fetch: distance the wave has travelled
- duration of the wind: how long the wind has been blowing for
- speed of the wind: how fast the wind is blowing.
35
Destructive waves:
- also referred to as winter waves
- responsible for erosional processes
- happen at a high frequency (10-15 waves per minute)
- steep and hug, with a circular motion so waves break at a greater height. This causes the wave to ‘plunge’ a shorter distance along the beach.
- destructive waves remove material from coasts because the swash is less powerful than the backwash.
36
Constructive waves:
- happen at a low frequency (6-9 waves per minute)
- long and low
- over time, constructive waves will form gently sloping beaches
- constructive waves deposit material on coasts as the backwash is less powerful than the swash.
- they move in an elliptical motion, with waves breaking with little height. This results in the ‘spilling’ and breaking out further along the beach.
37
Swash and backwash definitions:
Swash: the movement of the wave up the beach - constructs the beach
Backwash: the movement of the wave back down the beach - destructs the beach
38
Beach profiles - summer:
- steeper in summer, when constructive waves are more common than destructive.
- constrictive are less frequent, so wave energy dissipates and deposits over a wide area.
- swash deposits larger material at the top of the beach - creating a berm.
- as berm builds up the backwash becomes weaker and only had enough energy to move smaller material so beach material becomes smaller towards the shoreline.
39
Beach profile - winter:
- destructive waves occur at a higher frequency.
- berms are eroded by plunging waves and high-energy swash.
- strong backwash transports sediment offshore (depositing it as offshore bars)
- sometimes backwash exerts a current known as a rip, or undertow - dragging sediment back as the next wave arrives over the top.
40
Processes of erosion:
- abrasion
- corrosion
- attrition
- hydraulic power
41
What is erosion?
Erosion is the wearing away of rock.
Several erosional processes happen at coastlines, with their ability to alter the shape of coasts influenced by the wave type, the coastline shape and its lithology.
42
What is abrasion?
- where pieces of rock are picked up by waves and hit against the bed, beach or cliffs. This wears them away over time.
43
What is corrosion?
Corrosion happens when there is a chemical reaction between the seawater (which contains a weak acid) ans susceptible rocks like limestone.
44
What is attrition?
Attrition is where pieces of bedload (material carried in the water) are hit against one another. This causes them to break apart and become smaller and more rounded.
45
What is hydraulic power?
- Hydraulic power causes the breakdown of cliffs due to the force of the water being compressed until the cracks of the rock.
- the repeated action of the water forces in and out of the cracks in the rock leads to the breakdown if the surrounding cliff.
46
Wave-cut platforms and cliffs:
Over time, cliffs are eroded by destructive waves, resulting in the marination of wave-cut platforms.
47
Wave cut platforms and cliffs process:
- when waves break against the foot of a cliff, erosion is concentrated near the high-tide line. This creates a wave cut notch which undercuts the cliff.
- as the wave-cut hitch gets bigger the rock above becomes unstable and eventually the upper part collapses.
- the repeated action of erosional processes means that the notch migrates inland and the cliff retreats - leaving a shoreline or wave-cut platform.
- they usually have a gentle slop of less than 4 degrees and are only exposed during low tide.
- they rarely extend further than a few hundred metres as their width means a wave will break and disspaite its energy before hitting the cliff. This reduces the rate of erosion and prevents further growth of the platform.
48
Erosion of headlands:
1) corrosion and hydraulic action - destructive waves can erode weaknesses in headlands by the processes of corrosion and hydraulic action.
2) when the weaknesses in the rock widen, abrasion becomes more important.
3) formation of coastal landforms - over time, these erosional processes lead to the formation of coastal landforms such as caves, arches, stacks and stumps.
49
Coastal landforms caused by headland erosion
- caves
- arches
- stacks
- stumps
50
What are caves?
- erosion attacks lines of weaknesses in the headland
- when the crack widens into a small hollowed out area, a cave has formed.
- when joints and faults are eroded by hydraulic action and abrasion, creating caves
51
What are arches?
- when two caves are joined up or a single cave is eroded right the way through the headland, an arch is created.
- e.g. Durdle Door on the Dorset Coast.
- the gap is then further enlarged by erosion and weathering - becoming wider at the base.
52
What are stacks?
When the top of an arch collapses because of gravity, a column called a stack is left behind.
53
What is longshore drift (LSD)?
Longshore drift transports transport material along coastlines when waves approach the beach at angle.
54
Longshore drift process:
- Wind approaches the coast at an angle because of a prevailing wind direction.
- waves are controlled by the wind and so this angle will be the direction the swash moves up the beach.
- gravity is the only force that acts on the backwash, so it falls back to the sea at right angles to the coastline.
- because of the difference between the angle of the swash and the angle of the backwash, sediment repeatedly moves in the shape of a right-angled triangle.
- the net effect of the movement of sediment up and down the beach is a lateral shift - and the process is known as longshore drift.
- over time, sediment is carried along the beach.
- where the removal of sediment is greater than the supply of new sediment, the beach is eroded.
55
Types of despositional landforms:
- spits
- bars
- tombolo
- cuspate forelands
- beaches
- barrier beaches
56
What are spits?
- when the coast changes direction at an estuary, longshore drift continues to move sediment across the inlet.
- the river doesn’t let the spit completely join to the coast on the other side because the river has the energy to move the sediment.
- spits are the long fingers of sand sticking out from one side in a coastline that have been curved by secondary winds. They often have salt marshes behind them.
57
What are bars?
- A bar is formed when a spit grows across a bay.
- Lagoons often form behind bars.
- they are also known as sandbars snd are submerged (or partly exposed) ridges of sand or coarse sediment - created by waves offshore from the coast.
destructive waves erode sand from the beach with their strong backwash and deposit it offshore in bars.
- e.g. Moria Harlech, Wales
58
What are tombolos?
- tombolo: a beach (or ridge of sand and shingle) that has formed between a small island and the mainland.
- deposition occurs where waves lose their energy and the tombolo begins to build up.
- tombolos may be covered at high tides, e.g. at St Ninian’s in the Shetland Islands, and the Lindisfarne in Northumberland .
59
What are cuspate forelands?
- Cuspate forelands form when sediment is deposited across a bay caused by longshore drift transporting sediment in two directions.
- This leads to the formation of two spits which eventually meet and this then results in the trapping of sediment until eventually new land is formed.
- cuspate foreland - a triangular-shaped headland that extends out from the main coastline.
- occurs where a coast is exposed to LSD from opposite directions.
- sediment is deposited at the point where the two meet, which forms a natural triangular shape as it builds up.
- as vegetation begins to grow on the deposited sediment, it helps to stabilise the landform and protect it from storms that could erode it.
- cuspate forelands can be small - extending out from the coast for just a few metres or they can extend to up to 3 miles.
- e.g, Dungeness in Kent.
60
What are beaches?
- Beaches are made by constructive waves moving and depositing sand or shingle inland.
- Generally, a more gently sloping beach tends to be formed from sand, whereas a steeper sloping beach is formed from pebbles.
- beaches are commonly found in bays
- wave refraction creates a low-energy environment, which then leads to deposition.
- a beach could consist of either sand or shingle - depending on factors like the nature of the sediment and the power of waves.
- beaches can also be swash-aligned or drift-aligned.
- sediment may be graded asking a drift-aligned beach. Finer shingle particles are likely to be carried further by LSD and become increasingly rounded as they move.
61
What are barrier beaches?
- where a beach or spit extends across a bay to join two headlands, it forms a barrier beach or bar. For example, Loe Bar in Cornwall and Start Bay in Devon.
- barrier beaches and bard can also trap water behind them to form a lagoon, such as Slapton Ley, Devon.
- where a beach becomes separated from the mainland, it is referred to as a barrier island. They vary in scale and form - usually sand or shingle features - are common in areas with low tidal ranges, where the offshore coastline is gently sloping.
Large-scale barrier islands can be found along the Dutch coast, and in Nirth America along the south Texas coast.
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Deposition definition:
Waves lose their energy and sediment is deposited (dropped off)
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Methods of transportation:
- traction
- saltation
- suspension
- solution
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Traction:
- sediment rolls along, pushed by waves and currents
- the sound of rolling pebbles and shingles can often be heard clearly at the beach.
- e.g. pebbles, cobbles and boulders
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Saltation:
- sediment bounces along, either due to the force of water or wind.
- on a dry, windy days a layer of saltating sand is often seen 2-10cm along the beach surface.
- e.g. sand-sized particles
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Suspension:
- sediment is carried in the water column
- on soft-rock coasts such as Holderness, the sea is often muddy brown in colour due to suspended sediment.
- e.g. silt and clay particles.
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Solution:
- dissolved material is carried in the water as a solution.
- this type of sediment transport is of limited importance on coasts.
- e.g. chemical compounds in solution.
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What are sediment cells?
- sediment moves along the coast in sediment cells.
- within each cell, the sediment moves between the beach, cliffs and sea through the process of erosion, transport and deposition.
- any action that takes place in one place has an impact elsewhere in the cell.
- each cell operates between physical barriers that prevent the sediment from moving any further along the coast (e.g. major headlands or river estuaries.
- the coastline of England and Wales is divided up into 11 major sediment cells.
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The sediment cell as a system:
- sediment cells act as systems - with sources, transfers and sinks.
- larger sediment is not transferred between cells, but finer sediment in suspension out at sea (e.g. some of the finer boulder clay eroded from Holderness) can be be transferred.
- keywords: sediment budget, positive feedback, negative feedback, dynamic equilibrium.
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Sediment cells - sources:
- The sources are subaerial processes, erosional processes (breaking down cliffs) and sediments brought to the coastline by rivers.
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Sediment cells - transfers:
- Transfers are longshore drift, onshore and offshore winds and tides.
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Sediment cells - sinks:
The sinks are depositional landforms (spits, bars, beaches and sand dunes).
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Sediment cells - sediment budget definition:
- the amount of sediment available within a sediment cell.
- within each cell, depositional features build up which are in line (equilibrium) with the amount of sediment available.
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Sediment cells - positive feedback definition:
- if the sediment budget falls, waves continue to transport sediment (erosion may therefore increase in some areas, because the sea has surplus energy). One change has led to another.
- enhances and speeds up processes, promoting rapid change.
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Sediment cells - negative feedback definition:
- if the sediment budget increases, more deposition is likely.
- the sea corrects itself, because it can only carry so much - and any surplus is deposited.
- NF: the sea returns to a situation where it can handle the sediment supply.
- the regulation and reduction of a natural process.
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Sediment cells - dynamic equilibrium definition:
- where landforms and processes are in a state of balance.
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Weathering definition:
- the wearing away of rock in situ (where it is) by various processes.
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Types of weathering:
- mechanical: when rocks are broken down without their chemical composition being changed.
- chemical: when rocks are broken down because of their chemical composition being changed.
- biological: when rocks are broken down by living things.
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What are the processes of mechanical weathering?
- freeze-thaw
- salt crystallisation
- wetting and drying
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What is freeze-thaw (mechanical weathering)?
- dominant in cold climates, such as the UK.
- occurs when water enters crack or joints when it rains. Thus water then freezes in the cold weather.
- when the water freezes, it expands in volume by around 10%. This puts pressure on the rocks which causes the cracks to widen.
- this repeated action causes material (scree) to break off and collect at the bottom of the cliff face.
81
What is salt-crystallisation? (mechanical weathering)
- when salt water evaporates, it leaves salt crystals behind.
- these can grow over time and exert stresses in the rock (just like ice does) which causes it to break up.
- salt can also corrode rock, particularly if it contains traces of iron.
-
82
What is wetting and drying? (mechanical weathering)
- frequency cycles of wetting and drying are common on the coast.
- rocks are rich in clay (e.g. shale) expand when they get wet and contract as they dry. This can cause them to crack and break up.
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What are the processes of chemical weathering?
- carbonation
- hydrolysis
- oxidation
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What is carbonation? (chemical weathering)
- the slow dissolution of limestone due to rainfall (weak carbonic acid pH5-6) producing calcium bicarbonate in solution.
- this affects limestone and other carbonate rocks.
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What is hydrolysis? (chemical weathering)
- the breakdown of minerals to form new clay minerals, plus minerals in solution, due to the effect of water and dissolved CO2.
- igneous and metamorphic rocks containing feldspar and other silicate minerals.
86
What is oxidation? (chemical weathering)
- the addition of oxygen to minerals, especially iron compounds.
- this produces iron oxides and increases volume contributing to mechanical breakdown.
- Sandstones, silt stones and shales often contain iron compounds that can be oxidised.
87
What are the processes of biological weathering?
- plant roots
- rock boring
- animals
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Biological weathering - plant roots:
- tree and plant roots grow into small cracks and fissures in the rock faces with cause the rocks to break apart.
- this happens more as the plants grow.
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Biological weathering - rock boring:
- many species and molluscs bore into the rock face and may also secrète chemicals that dissolve rock.
- this can especially affect sedimentary rocks such as limestone in the inter-tidal zone.
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Biological weathering - animals:
- different birds (e.g. puffins) and animals (e.g. rabbits) dig burrows into cliffs and cause them to break.
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What is mass movement?
- Mass movement describes when rocks and loose material shift down slopes.
- This happens when gravity overcomes the force supporting the material.
- Mass movements can cause rapid coastal retreat and are common when the material is saturated.
- the downslope movement of materials under the force of gravity.
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Mass movement; flows - soil creep:
- soil creep is the slowest form of mass movement - ans is an almost continuous process.
- it is a very slow downhill movement if individual soil particles
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Mass movement; flows - earth flows and mudflows
- an increase in the amount of water (e.g. as a result of heavy rain) can reduce friction - causing earth and mud to flow over underlying bedrock.
- the difference between a slide and a dois is that in a slide the material remains intact (it moves ‘en masse’). In a flow, the material becomes jumbled up.
94
Mass movement;slides - rockfalls:
- rockfalls are more likely to occur when string, jointed and steep rock face/cliffs are exposed to mechanical weathering (such as freeze-thaw).
- rockfalls occur in slopes over 40 degrees.
- the material once broken away from the source, either bounces or falls vertically to form scree at the foot of the slope/cliff.
95
Mass movement; slides - rock/debris slides:
- rocks that are jointed, or have bedding planes roughly parallel to the slope or cliff surface, are susceptible to landslides.
- an increase in the amount of water can reduce friction - causing sliding.
- in a rock or landslide, slabs of rock/blocks can slide over underlying rocks along a slide or slip plane.
96
Mass movement; slumps:
- often occur in saturated conditions.
- the difference between sliding snd slumping is that there is a rotational movement in slumping.
- slumps occur on moderate to steep slopes.
- they are common where softer materials (e.g. clays or sands) overlie more-resistant it impermeable rock, such as limestone or granite.
- slumping causes rotational scars.
- repeated slumping creates a terraced cliff profile.
- Slumps happen slower than rockfalls.
- a combination of heavy rainfall and erosion processes cause the rotational movement of the cliff.
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Sea level changes:
- sea level is measured relative to land so the relative sea level can change if either the land or the sea falls or rises.
- the two types of sea level change are called:
eustatic change - when the sea level itself rises or falls
isostatic change - when the land rises or falls, relative to the sea
- threatens the lives of people who live near coasts.
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Factors contributing to sea level change:
- There are three key factors that have contributed towards sea level change over different time periods, plus climate change.
- these include; eustatic change, isostatic change and tectonic events.
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Sea level changes - tectonic events:
- Tectonic change causes land to either rise or sink at the boundaries where tectonic plates meet.
- A sudden change in the movement of a plate can lead to a rise or fall in the seabed, causing a change in sea level.
- Earthquakes out at sea can trigger a tsunami, causing devastating effects for people living along coastlines.
- past tectonic activity has had a direct impact on some coasts across the world, as well as on sea levels, due to the:
> the uplift of mountain ranges and coastal land at destructive and collision plate margins
> local tilting of land.
- the shape of the ocean basin can also be changed by tectonic events.
100
What is eustatic change?
- Eustatic change is the rising and falling of sea levels, influenced by ice ages.
- Water is stored in the form of ice when the world is experiencing an ice age, which causes the sea level to fall.
- As the world moves out of an ice age, the ice melts. This results in the sea level rising again.
101
What is isostatic change?
- Isostatic change refers to the level of the land, which is also influenced by ice ages.
- During an ice age, the weight of the ice forces the land to sink.
- When the ice age has finished, the melting of the ice causes the land to rebound back up, like a spring.
102
What is marine regression?
- where the sea level drops and produces an emergent coastline.
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What is marine transgression?
- where the coastline is flooded and produces a submergent coastline.
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Marine regression process:
Eustatic fall in sea level:
- during glacial times, when ice sheets form on land in high latitudes (far north and south), water evaporated from the sea us locked up on land as ice.
- global sea levels fall.
Isostatic fall in sea level:
- during the build up of ice sheets, the weight of the ice causes the Earth’s crust to sink (isostatic subsidence).
- as it melts it causes the earth to slowly rebound (called post-glacial adjustment or isostatic recovery).
- the land slowly lifts out of the sea.
105
Marine transgression process:
Eustatic rise in sea level:
- at the end of the glacial period, melting ice returns water to the sea causing sea levels to rise globally.
- thermal expansion (expansion of sea water due to temperature increase) causes sea levels to rise.
Isostatic rise in sea level:
- land can ‘sink’ at the coast due to the deposition if sediment (accretion).
- this can happen especially in large river deltas where the weight of sediment deposition causes delta subsidence.
106
What are emergent coastlines?
- these are coastlines that are formed where water level has fallen, or land has risen due to tectonic activity. This happens due to isostatic change (where the land rises due to something such as ice on top of it melting).
- these are quite often rocky coastlines with cliffs and platforms.
- the west coast of USA (e.g. California) is a good example due to its proximity to a plate margin.
107
What are submergent coastlines?
- submergent coastlines are those that have been flooded due to a rise in sea level at that location. This is known as eustatic sea level change.
- e.g. Dalmatian coast or Pacific coats (e.g. Croatia or southern Chile).
- they are a type of concordant coastline which have formed due to a rise in sea level.
108
Submergent coastline landforms:
Submergent coastlines cause the formation of rias, fjords and Dalmatian coasts.
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Emergent coastline landforms:
Emergent coastlines cause the formation of raised beaches and fossil cliffs caused by isostatic rebound.
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What are rias?
- sheltered winding inlets with irregular shorelines.
- they are one of the most distinctive features associated with rise in sea level.
- they form when valleys in a dissected upland area are flooded.
- rias are common in south-west England, where sea levels rise after the last Ice Age - drowning the lower parts of many rivers and their tributaries to form rias. The Kingsbridge estuary un Devin is one if these. It provides a natural harbour with the deepest water at its mouth.
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What are Dalmatian coasts?
- Dalmatian coasts are formed because of the arrangement of alternating rock types parallel to the coast.
- are similar to rias. In this case, the rivers flow almost parallel to the coast - rather than at right angles to it.
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What are fjords?
- formed when deep glacial troughs are flooded by a rise in sea level.
- they are long ans steep-sided, with a U-shaped cross-section and hanging valleys.
- unlike rias, fjords are much deeper inland than they are at the coast.
- the shallower entrance marks where the glacier left the valley.
- fjords can be found in Norway, New Zealand and Chile.
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What are raised beaches and fossil cliffs?
- A raised beach and fossil cliff are formed when, following an ice age, the land rebounds. This causes the original height of land to increase.
- This leaves behind a beach and fossil cliff higher than their original position.
- E.g. in Fife, Scotland.
- wave-cut notches and caves can be found behind the raised beach as evidence of past Marin erosion.
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What is global warming and its effect?
- Evidence from the IPCC (Intergovernmental Panel on Climate Change) indicates that the between 1983 and 2012, the Northern Hemisphere experienced the warmest 30-year period of the last 1,400 years.
- Changes in the world’s atmospheric temperatures are causing thermal expansion of the oceans, melting of glaciers and ice sheets.
- Global warming is largely because of anthropogenic greenhouse gas (GHG) emissions. The concentration of these gases has risen rapidly since industrialisation.
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What are the consequences of global warming?
- rising sea levels
| - increased frequency of storms.
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Are sea levels rising and why?
Data from the IPCC indicates from 1901 to 2010, average sea levels have increased by 0.19m.
Some of the contributing factors being linked to the melting of glaciers and ice sheets.
E.g. the Greenland and Antarctic ice sheets have been decreasing rapidly.
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What are the consequences of rising sea levels?
Higher sea levels could cause higher tides, and this would increase the frequency of coastal flooding.
Higher tides could also remove more material from beaches, leaving cliffs less protected.
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What are the consequences of increased frequency of storms?
- The strong winds caused by storms create high energy, destructive waves which have considerable erosional power.
- The increased energy of the sea will mean more material can be transported and for greater distances. This could leave some areas vulnerable to erosion if they are left without much protection.
- The frequency of storm surges will increase. When combined with sea level rise, these surges will reach further inland and cause more damage.
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Sea level change due to tectonic activity - Boxing Day tsunami example;
-
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What causes coastal recession?
Coastal recession is caused by a combination of physical factors (subaerial processes, waves, geology, chemical weathering, mass movement) and human factors (dredging, climate change and hard engineering).
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Subaerial processes:
- Weathering and mass movement processes combine to increase the rate of coastal recession.
- Long periods of rainfall weaken rock structure and in turn, leads to mass movement of material.
- This collapsed material is then eroded and transported away by wave action.
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What is dredging?
- used in the UK to remove sediment to deepen entrances to ports or to provide sediment for beach nourishment.
- deeper water caused by dredging may also allow waves to maintain their circular motion and energy closer to the shore, having a more destructive impact on the coast.
- increased human use of beaches (as a result of increased economic development)a amenas coastal areas are more likely to expand, exacerbating the cycle.
- Removal of the sediment causes the depth of the ocean to increase.
- This can cause an increase in the occurrence of destructive waves at the coast because they can maintain their energy further towards the shoreline.
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About dredging in California:
- Dredging along the coastline of California has had long-term implications on the supply of sediment to the Santa Barbara littoral cell.
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Climate change - factor of recession:
- increases storm activity, as a result of warmer atmospheric temperatures has caused bad erosion to many beaches, including Brisbane in Australia.
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Hard engineering -human factor of coastal recession:
- The construction of hard engineering structures at the coastline can disrupt sediment cells.
- This means that by disrupting one bit of coast, areas further along the coast may be starved of sediment supply, which can then result in the destruction of beaches.
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What are human influences in coastal recession?
- humans alter the natural processes within the sediment cell.
- for example, coastal defences build at one location can stop or limit the supply of sediment to another location in the sediment cell. E.g. groynes are built at Southwold to protect the town.
- when the supply is cut off, the beach gets narrower and is less able to absorb wave energy, so waves hit the backshore with more force, leading to more erosion. (Dunwich further south than Southwold receives less sediment as a result if the barrier at Southwold).
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Sustainability definition:
- making sure the needs if today (this generation) are met without compromising the needs of future generations.
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Sustainable coastal management definition:
- managing the people and their economic livelihoods, social and cultural wellbeing snd safety from coastal hazards, as well as minimising environmental impacts.
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Sustainable methods:
- managing natural resources (fish, farmland, water supplies) to ensure ling-term productivity.
- managing flood and erosion risk where possible, or relocating to safe areas.
- creating alternative livelihoods before existing ones are lost to the sea.
- adapting to rising sea levels by relocating, alternative building methods and water supplies.
- educating communities to understand why change is needed and how to adapt.
- monitoring coastal change and adapting to unexpected trends.
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What are the factors affecting the rate of coastal recession?
- wind direction
- tides
- weather systems
- seasons
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How does wind direction affect the rate of coastal recession?
- Wind direction controls the movement of waves, influencing the rate of coastal erosion.
- A dominant wind direction causes powerful destructive waves to attack the coastline.
+ E.g. the south-westerly wind directing waves across the Atlantic Ocean towards Land’s End in Cornwall.
- This happens because the waves have travelled a long distance, influenced by the dominant wind, which is linked to the fetch of a wave.
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How does tides affect the rate of coastal recession?
- Tides are linked to gravitational pull. When the pull is at its strongest, there are high tides. When the pull is at its weakest, there are low tides.
- During periods of high tide, the rate of coastal recession can increase because waves can reach further towards the shore.
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How do weather systems affect the rate of coastal recession?
- Weather systems are influenced by areas of high pressure, creating anticyclones, and areas of low pressure, creating depressions.
- Increased belts of high pressure reduce the rate of coastal recession because this leads to calmer weather.
- Belts of low pressure systems cause unsettled weather conditions.
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How do season affect the rate of coastal recession?
- During the winter season, the rate of coastal recession tends to be greater than during the summer season.
- This is because winter brings stormy weather, linked with higher tides and long wave fetch.
- The average rate of erosion increases at this time of the year.
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Why is coastal flooding a risk?
- Coastal flooding poses a risk to millions of people today because many continue to live near coastlines for recreation and employment purposes.
- Low-lying coasts are at risk of flooding from local factors and global rises in sea levels.
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Coastal flooding in the Maldives:
- In the Maldives, the removal of Mangroves is leading to an increased risk of flooding with increased wave height and less stable cliffs.
- This is because there's a lack of roots in the soil.
- Several factors, such as waste disposal and logging, have caused the soil to lack roots.
- The disturbance and removal of the Mangroves is leading to increased wave energy and height. This is because the trees would normally act as a barrier, helping to dissipate the wave’s energy before it reaches land.
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Coastal flooding in Bangladesh:
- In Bangladesh, storm surges threaten the lives of those living near the coast.
- The rate of coastal erosion is expected to increase in the future if storm surge events continue to rise.
- The risk associated with storm surges in the Bay of Bengal is because Bangladesh is so low-lying.
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Coastal flooding - impacts of climate change:
- Climate change is changing the frequency and intensity of low-pressure depressions and tropical storms.
- Rising global temperatures are causing our oceans to warm, triggering these low-pressure systems.
- This increases the risk of coastal flooding and creates unusual weather conditions.
- more storms: CC will not necessarily cause the frequency of hurricanes to increase, however having warmer and higher oceans are expected to make them more intense. North Atlantic - the long term average = 11 storms annually. Now this is 16 per year with 8 becoming hurricanes. This also correlated with with the rise in ocean-surface temperatures in the North Atlantic.
- more flooding: countries with low-lying coastlines already suffer from coastal flooding, but climate change is likely to increase the risk. IPCC - predicted hundreds of millions will be forced to abandon many coastal zones worldwide, due to rising sea levels and the increase of storm surges.
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What are storm surges?
- storm surges are changes in sea level causes by intense low-pressure systems and high wind speed.
- air pressure decreases causing the sea levels to rise. During tropical cyclone, the air pressure may be 100mb lower than usual, which raises the sea level by 1m.
- the forward motion of the storm towards the coastline pushes the storm surge water forward onto the land.
- the rise in sea level is intensified in areas where the coastline is funnel-shaped.
- during high tide and in low-lying areas (such as Bangladesh), the results csn be deadly.
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Low air pressure:
- ‘weight’ of the air pushing down is lower (when we have low pressure)
- so air below can rise
- rapid evaporation and condensation
- storms/hurricanes.
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Why is Bangladesh vulnerable ?
- population density: Bangladesh is the world!s most densely populated country, with 3,277 people per square mile.
- land height: 46% if the country’s population live less than 10 metres above sea level.
- location: Bangladesh lies in the floodplains of three major rivers (Ganges, Maghna, Brahmaputra). The three converge in Bangladesh and flow through to the Bay of Bengal.
- Himalayas: Bangladesh lies to the south of Nepal. As increased snow melt (due to global warming) flows into rivers, more water is flowing through Bangladesh.
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Vulnerability in Bangladesh - subsidence:
- isostatic readjustments is partly responsible, but the main reason is clearance and drainage of more than 50 large islands in the Ganges - Brahmaputra river delta.
- these islands used to grow rice to feed the population.
- in the 1960/70s, large embankments were built about these islands to protect them against tidal and storm surge inundations. Although human actions have prevented the natural deposition of sediment that is used to maintain the island’s height.
- now, the islands are fastly submerging and those living on them are at an increased risk of flooding if the embankments give way.
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Vulnerability in Bangladesh - removing vegetation:
- mangrove forests are found along the tropical and sub-tropical coasts of Africa, Australia, Asia and the Americas - but the largest remaining tract is found in a region of Bangladesh.
- essential to marine, freshwater and terrestrial biodiversity - because they stabilise coastlines against erosion, collect nutrient-rich sediments, and provide a nursery for coastal dish. They also provide protection and shelter against extreme weather events (e.g. storm surges, floods and tsunami) as they absorb and disperse tidal surges associated with these events.
- however, now, they are retreating by 200 metres a year. This is caused by erosion and rising sea levels. As well as human actions that deliberately remove the vegetation.
- half of all m’arrive forests gave been lost since the 20th century. 25% of this is due to the forest being converted into lucrative shrimp farms.
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Storm surge - UK impacts:
- 5/6th December 2013
- cost: £100 million worth of damage.
- several properties collapsed into the sea at Hemsby as a result of cliff erosion.
- 100s of thousands of property were protected by flood defences and the Thames Barrier was closed to protect London.
- due to plans in place, 2 people died.
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Storm surge - the Netherlands impacts:
-strong winds, together with a storm surge that was predicted to be up to 2 metres high in the Netherlands.
- however, in Germany, on Dutch border (East Frisian coast) it reached 3.74 metres above mean sea level.
- unlike in the 1953 storm surge, no one died.
- The Netherlands constructed a series of Delta Works in response to the 1953 storm surge.
- Delta Works consist of a series of dams and storm-surge barriers, designed to protect the country from flooding by the North Sea.
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Netherlands - Eastern Scheldt barrier:
- the largest of the Delta Works and one of the biggest construction projects in the world.
- it costs £2.5 billion Euros to build, and costs a further 17 million euros to operate.
- opened in 1986, and was closed against the storm surge on 5-6th December 2013.
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Storm surge - Bangladesh impacts:
- 15th November 2007
- the storm surge breached many coastal and river embankments - causing severe flooding in low-lying areas.
- high winds and floods damaged housing, roads, bridges and other infrastructure.
- sanitation infrastructure was destroyed, increasing the risk of disease.
- drinking water was contaminated by debris, and many freshwater sources were inundated with saltwater.
- over 10,000 deaths
- cost: just under £1 billion.
- didn’t have many, if any, defence systems
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Storm surge - Hurricane Sandy causes:
- October 2012
- started as a cluster of thunderstorms which left Western-Africa-Caribbean Sea.
- storm surge combined with a norista - causing further damage.
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Storm surge - Hurricane Sandy impacts:
- 2nd most costly hurricane on record - $71 billion (NYC - $18 billion)
- more than 18,000 flights were cancelled, leading to disruptions in business, tourism and trade.
- more than 8.5 million homes/businesses were left without power.
- 286 deaths in USA, Cuba and Haiti.
- power failure to many homes/infrastructure.
- 346,000 homes were damaged or destroyed.
- more than 70% of crops were destroyed in Haiti.
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Storm surge - hurricane Sandy management:
- people were temporarily relocated yo evacuation centres such as schools and community centres.
- schools/public transport closed to minimise damage.
- police evacuated hundreds of thousands of people in low-lying coastal areas most vulnerable to Hurricane Sandy.
- Caribbean - early curfews were put in place in place to protect residents/properties.
- stockpiled medical supplies.
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USA’s physical and economic vulnerability to the impact of climate change:
Physical: 25 million US residents live in areas vulnerable to coastal flooding.
Economic: coastal and ocean activities, such as marine transportation of goods, offshore energy drilling, resource extraction, etc. Integral to the UK economy. These activities generate 58% of the GDP ($9.86 billion - bigger than the UK and Japanese economy combined).
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What are the impacts of coastal recession and coastal flooding?
- loss in value of house prices due to the risk of coastal flooding.
- in the UK, property insurance doesn’t cover coastal erosion. For residents, this means; falling property values as erosion brings the coastline closer, an inability to sell their property because of the risk of erosion and the loss of their major asset and the coast of getting a new home.
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What are the wider impacts from erosion?
- increased costs to the owners of cliff top caravan parks who face the costs of relocation.
- loss of access as roads, paths and steps down to the beach are lost.
- loss of amenity value as the coastline is visually scarred by collapsing roads, abandoned properties and warning signs.
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Coastal recession and coastal flooding - Kiribati (LIC)
- rising tides - eroded the coast and contaminating water.
- 200m of land has disappeared - many do the population have moved inland.
- if temperature increases water expands. Thus happens when ice sheets from north/south melt snd cover the land.
- many, including the Vice President, have been trying to decrease the carbon levels on an international level. Although there is a lack of urgency from industrial companies.
- rising swamps - could have the same consequences as other cities.
- government have set up a ‘migration with dignity programme’. This allows people to move and be relocated to the capital or other safe areas. Although many have missed out on this.
- freshwater supply is vulnerable to contamination - this could last for up to two years.
- communities are trying to grow mangroves to help prevent coastal erosion and preserving islands so they can stay.
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Coastal recession and coastal flooding - China (NEE)
- dramatic coastal erosion over the last 50 years.
- 25% of farmland lost due to rising sea levels.
- 2m is lost annually, increases every year.
- 250 locals have needed to leave due to their land being covered.
- 15,000km of coastline. 70% of this is prime to erosion.
- 2.6mm rise in sea levels per year. Global average = 1.7mm.
- 10s of thousands of coastline could be lost - millions may need to be relocated.
- over the next 30 years it is predicted sea levels will rise by 8-10cm.
- sea levels are being built as defences go save/preserve land for future generations.
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Coastal recession and coastal flooding - The Netherlands (HIC)
- battling rising sea levels for years.
- many were forced to relocate due to severe flooding of water.
- deltawerken
- the Dutch are trying to build a new wide river to prevent many villages from flooding, creating an island. However, this was originally rejected due to the destruction of property to build the new river. Although many have come to terms as they have been given compensation.
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Consequences of coastal recession/flooding in Australia:
- rising sea levels in Australia are increasing the risk of coastal flooding.
- A $216 billion worth of key infrastructure, such as road and rail networks, residential housing, commercial properties and emergency service stations, are at risk in the future if sea levels continue to rise.
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Consequences of coastal recession/flooding in the Maldives:
- the Maldives, made up of over 1,000 islands, is one of the lowest lying countries in the world. The Maldives is at serious risk of being completely submerged because of coastal flooding.
- the islands rely on tourism as a key contributor to the local economy, but increased coastal flooding events threaten the physical features that cause many people to flock to the islands in search of paradise.
- coastal flooding also threatens housing and freshwater sources, which has forced many locals to migrate away from the annual flooding.
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What are the main approaches to management?
- hard engineering: this involves building structures along the coast (usually at the base of a cliff or in a beach). E.g. sea walls, groynes and revetments. These tend to be very expensive snd big attractive to the eye.
- soft engineering: this approach is designed to work with the natural processes in the coastal system in order to manage erosion. Soft engineering tend to look nicer and be more popular in public opinion.
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Management - what are costs?
- costs are predicted (design, cost, maintenance, etc) and compared with the benefits that would be produced (value if land saved, housing protected, savings in relocating people).
- costs and benefits are split into two categories.
+ tangible - where costs and benefits are known snd can be assigned monetary value (e.g. building costs).
+ intangible - where costs may be difficult to assess but are important (e.g. the visual impact of a revetment).
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What are the types of hard engineering?
- groynes
- sea walls
- rip-rap/rock armour
- revetments
- offshore breakwaters
- gabions
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What are groynes?
- they are commonly stone or wooden walls/fences on a beach at right angles to the coast, to slow down LSD movement.
- they may be open or closed, depending on how much beach sediment engineers wish to trap.
- they make a beach wider and higher so that waves expend their energy on it rather than the backshore.
- they stop material being transported long distances by LSD.
- they slow down waves reducing erosion and flooding.
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What are the advantages of groynes?
- maintain the size of the beach, which protects the coast at that point.
- enhance the beach for recreational amenity, assisting tourism.
- less expensive than sea walls.
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What are the disadvantages of groynes?
- expensive (about £1000 per linear) due to the difficulties in getting firm foundations in a beach.
- may be an obstacle to people moving freely along a beach, because they may be high, or create a large drop on the down drift side.
- are clearly not natural and may be considered unsightly.
- greatly reduced longshore drift transport may cause narrower beaches and increased erosion down drift.
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What are sea walls?
- these appear in different shapes parallel to the backshore.
- recurved sea walls use the shape of a wave to direct the water into the following wave to reduce wave energy. They refract the energy back towards the sea.
- stepped sea walls use the pointed edges to break up a wave as it hits the wall, so dissipating wave energy.
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What are the advantages of sea walls?
- made of long-lasting concrete and able to absorb wave energy.
- give people confidence and a sense of security.
- the tops can be used as promenades, providing access along the coast.
- prevent high water levels from moving inland.
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What are the disadvantages of sea walls?
- the most expensive of all coastal defences (about £5000 per linear).
- do not fit with the natural surroundings and may be considered unsightly.
- may make accessing a beach difficult due to their height.
- scouring by waves makes it necessary to have deep pilings at their base to prevent it being undercut.
- greatly reduce the supply of sediments, which may affect other coastal areas nearby.
- they can create a strong backwash that can undercut the wall.
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What is rip-rap?
- boulders (usually granite) or specifically designed concrete shapes (tetrahedrons).
- they are resistant to erosion and with a large surface area break up waves, so dissipating their energy.
- they may also be used to hold back mass movement on an unstable cliff.
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What are the advantages of rip-rap?
- long lasting and flexible in use.
- can be placed at susceptible points on the backshore, to protect the base of a sea wall or to be used as a breakwater or groyne.
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What are the disadvantages of rip-rap?
- cost about £50 per metre2.
- may look unsightly and, even if natural rock, may contrast with the local geology.
- can create access difficulties as they are dangerous to climb over.
- seawater may still move through it, so some weathering and erosion may still occur on the backshore.
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What are revetments?
- these are sloped walls, often made of wood, placed parallel to the backshore, but a short distance in front of it. (placed just offshore)
- they are able to take the force of breaking waves, so weakening their erosive strength and protecting the backshore.
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What are the advantages of revetments?
- absorb wave energy
- trap beach sediments behind them, reducing its removal by backwash or LSD.
- LSD able to continue.
- allow linear access along a beach.
- a cheaper alternative to sea walls.
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What are the disadvantages of revetments?
- cost about £1500 per linear m.
- reduce access up and down the width of a beach.
- look unsightly, especially if they stretch several km along a coast.
- may need constant maintenance as the wood is abraded by powerful waves.
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What are offshore breakwaters (reefs)?
- Rock boulders (usually granite) may be dropped and aligned in short lengths in shallow nearshore waters parallel to the shore.
- their purpose is to absorb wave energy and dissipate waves before they have the chance to damage the foreshore and backshore.
- being offshore, they allow LSD to continue behind them.
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What are the advantages of offshore breakwaters?
- have proved effective in protecting vulnerable sections of coast.
- can create sheltered water areas behind them for water sports, as well as keeping a beach in place for recreational and tourist use.
- can be used to protect the entrance to harbours, creating calmer waves for safe entry or exit.
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What are the disadvantages of offshore breakwaters?
- costly: between £1 million and £2 million.
- may look unsightly at low tide as the geology of the boulders does not match the local geology.
- may need other coastal engineering to complement them, such as sea walls in the gaps between the reefs.
- may create increased deposition on the landward slide, reducing LSD.
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What are gabions?
- these are pebbles in wire baskets, which then tied together can make a wall where the great surface area absorbs wave energy and breaks up waves.
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What are the advantages of gabions?
- very flexible in terms of placement on the backshore as an additional defence above a sea wall, or to help hold back mass movement on a cliff.
- relatively cheap and easy to maintain.
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What are the disadvantages of gabions?
- not very strong, so not suitable for high-energy locations.
- need frequent repair.
- may be considered unsightly.
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Hard engineering at Holderness:
- 85km long, only 9.2km are protected by hard-engineering structures (maintained by the East Riding of Yorkshire Council).
- an additional 2.15km are protected by other bodies and the rest of the coastline is unprotected.
- most consist of a mixture of 19th century structures, together with more-recent upgrades, extensions and alterations.
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Defences at Hornsea:
- concrete sea walls, groynes and rock armour.
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Impacts at Hornsea:
- the groynes trap sediment and maintain the beach at Hornsea, but Mappleton downdrift has been starved of sediment as a result.
- there, rapid wave attack has eroded the cliffs, so that by the 1990s, nearly 4 metres of cliff were being eroded each year.
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Defences at Mappleton:
- two rock groynes (costing £2 million) were built in 1991, with the aim of preventing the removal of the beach by LSD.
- rock armour was also used.
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Impacts at Mappleton:
- At Cowden, 3km south of Mappleton, the resultant sediment starvation caused increased erosion of the cliffs (from 2.5 - 3.8 metres a year between 1991 and 2007)
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Defences at Withernsea:
- a straight sea wall was built in 1874. However, over time, wave energy eroded (scoured) the base of the wall - causing it to collapse.
- in 1990s (following a cost-benefit analysis) the straight wall was replaced by a recurved sea wall - at a cost of £6.3 million (£5000 per metre).
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Impacts at Withernsea:
- waves are now noisier when they break against the wall, and the promenade is smaller.
- the views from sea-front hotels have also been restricted.
- some tourists at the base of the sea wall unattractive.
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What are the types of soft engineering?
- beach nourishment
- cliff regrading
- cliff drainage
- dune stabilisation
managed retreat (management approach rather than SE)
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What is beach nourishment?
- definition: the addition of sand and pebbles to an existing beach to make it higher or wider. The sediment is usually dredged from the nearby seabed.
- replaces beach sediments that may have been eroded or transported by LSD.
- a large beach will absorb wave energy and protect the backshore from erosion.
- involves moving materials to the upper sections of beaches from elsewhere.
- it slows down waves by widening beaches and so reduces the risk of erosion and flooding.
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What are the advantages of beach nourishment?
- uses natural sediments, so the beach looks natural.
- increases tourist potential by creating a bigger beach.
| - provides an amenity for recreation and so supports the local tourist industry.
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What are the disadvantages of beach nourishment?
- cost about £10 per metre2.
- does not last long, especially under winter storm conditions so may have to be repeated frequently.
- sediments may have been dredged offshore, so changing sediment cell balances and deepening the water, so that waves may approach the shore with more destructive energy.
- removing sand and shingle from the seabed can threaten certain organisms (e.g. corals).
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What is cliff regrading?
- the lithology of a cliff may be unstable and prone to sudden collapses, so to remove this uncertainty engineers calculate a stale slope angle based the rock characteristics.
- the cliff slope is then artificially cut back to the stable angle.
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What are the advantages of cliff regrading?
- creates a natural-looking slope.
- brings some certainty and confidence to the cliff edge and reduces risk of sudden loss of property.
- should remain stable if the base of the slope is protected from marine erosion.
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What are the disadvantages of cliff regrading?
- cost about £1 million.
- some land and property will be lost when the slope angle is changed.
- engineers may get their calculations wrong, or extreme natural conditions may overwhelm the changes.
- stabilisation measures such as cliff drainage and vegetation planting also needed.
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What is cliff drainage?
- where the cliff lithology consists of a permeable layer above an impermeable layer, it may be unstable after rainfall, due to pore pressure.
- to reduce this pressure and reduce mass movement , drains with gravel can be inserted into the cliff to drain water out quickly.
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What are the advantages of cliff drainage?
- looks natural one completed, as the engineering is not generally visible.
- reduces mass movement, bringing some confidence to those owning and and property near the cliff edge.
- provides a natural environment for plant and wildlife to continue to flourish.
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What are the disadvantages of cliff drainage?
- difficult to implement along the whole of a cliff without disturbing the cohesion of the rock layers.
- will not prevent mass movement; only reduces it to some extent.
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What is dune stabilisation?
- dunes can provide a natural barrier to sea-level rise and storm waves, but are fragile.
- monitoring their condition and repairing them with a geo-fabric or replanting of grasses (e.g. marram grass), together with infilling of slacks, will help keep them in place.
- dune stabilisation involves the creation or restoration of sand dunes to maintain their protective position. This can be achieved through nourishment or planting vegetation.
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What are the advantages of dune stabilisation?
- looks natural and is an effective barrier to higher sea levels and tides.
- provides a natural ecosystem and recreational area.
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What are the disadvantages of dune stabilisation?
- may need to be fenced off during works, which reduces the amenity value in the short term.
- powerful storms may ensure that this approach only works for a short while.
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What is managed retreat?
- where it is accepted that there is little that can be done to stop high sea levels changing the coast, areas can be set aside for the sea to flood or erode.
- e.g. former salt marshes that are now farmland may be allowed to flood again, or buffer zones next to eroding cliffs can be created so that no valuable property is lost.
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What are the advantages of managed retreat?
- allows natural processes to take place uninterrupted.
| - can extend current ecosystems.
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What are the disadvantages of managed retreat?
- needs agreement from land and property owners to create these areas.
- does not prevent land being lost, and may only be a medium-term solution - depending on the rate of sea-level rise.
- currently no compensation in the UK for land or property loss.
- possible lose of archaeological evidence.
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What is the ICZM?
- the Integrated Coastal Zone Management is a holistic approach to coastal management.
- the ICZM's work involves careful consideration of the most effective management approach for a stretch of coastline.
- it considers the social, economic and environmental implications.
- the concept of the ICZM was created by world leaders at the Earth Summit in 1992.
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What are the factors of consideration - ICZM?
- stakeholders consider the following factors when deciding the type of coastal management that should be adopted on a coastline:
+ the proposed risk to residential, commercial and industrial buildings.
+ the implication of coastal recession on the local economy.
+ the impact of coastal recession and flooding on the natural environment.
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what are the benefits on ICZM - according to leader’s opinions?
- it promotes the careful conservation of the natural environment.
- it encourages the efficient use of resources to reduce unnecessary costs.
- it tries to reduce the potential loss to the various stakeholders that rely on coastal regions for their livelihoods.
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About Odisha's coastal zone:
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ICZM project Odisha - players and stakeholders:
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ICZM - Holderness:
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What are stakeholders?
- people or groups whom have an interest in a management plan.
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What is a Shoreline Management Plan (SMP)?
- a plan that has been devised by key organisations to determine the most appropriate management strategies for a stretch of coastline.
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Who were the stakeholders involved in the Holderness SMP?
- National government agencies: Environment Agency and Natural England
- Local government: Lincolnshire County Council, North East Lincolnshire Council, East Lindsey District Council
- Stakeholders in the economy: The National Farmers Heritage
- Environmental stakeholders: English Heritage
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What are the four key management approaches?
- no active intervention
- advance the line
- strategic realignment
- hold the existing defences
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What is no action intervention?
- no management used along this coastline with physical processes allowed to work naturally
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What is advance the line?
- The construction of new engineering techniques to protect the coastline from further recession.
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What is strategic realignment?
- Physical processes allowed to work naturally, with monitoring and intervention only when necessary.
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What is hold the existing line?
- maintaining the existing defences to make sure they continue to be effective.
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What is a CBA?
- cost-benefit analysis
- a CBA is used to determine the economic value of a coastline to decide if the intervention is needed to protect the surrounding land.
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What is an EIA?
- environmental impact assessment.
| - is used to assess the short and long term implications of using management strategies on the environment.
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About Happisburgh:
- Happisburgh is on the North Norfolk coast.
- Failed management and lack of funding to maintain existing structures led to a failed attempt to protect the coastline from coastal recession.
- The village has a population of 1,400 people. Since 1998, a group of residents have been working to campaign for renewal of the failing defences.
- They are the CCAG (Coastal Concern Action Group).
- Powerful destructive waves from the North Sea have caused an average erosion rate of approximately 0.9m per year.
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Happisburgh coastal management - 1990:
- During the 90’s, the rate of erosion increased because of the failure of wooden defences
- The shoreline management plan changed to ‘no active intervention’ implemented.
- But after campaigns from CCAG, the shoreline management plan was changed to ‘managed realignment’.
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Happisburgh coastal management 2012 onwards:
- Following fundraising in 2012, rip-rap was placed on the beach to help dissipate the wave’s energy and protect people’s homes and businesses.
- Continued protection of the coastline through maintaining the existing structures or installing new engineering techniques is undecided at the moment.
+ The government believes the economic cost to install new defences is not cost-effective compared with the properties at risk.
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What are the landforms created by coastal erosion?
- headlands and bays
- cliffs
- stacks and stumps
- shoreline platforms
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What are headlands and bays?
- several headlands protrude out to sea in the background, with sandy bays between them.
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Tides definition:
- changes in the water level of seas and oceans - caused by the gravitational pull of the moon and, to a lesser extent, the sun.
- the UK coastline experiences two high and two low tides a day,
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What is the tidal range?
- the relative difference in height between high and low tides.
- a high tidal range creates relatively powerful tidal currents, as tides rise and fall.
- tidal currents can become particularly strong and fast in estuaries and narrow channels, and are important in transporting sediment.
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What are salt marshes?
- salt marshes are areas of flat, silty sediments that accumulate around estuaries or lagoons.
- they’re covered at high tide and exposed at low tide.
- they are common around the coast of Britain.
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Where do salt marshes develop?
- in sheltered areas where deposition occurs
- where salt and fresh water meet
- where there are no strong tides or currents to prevent sediment deposition and accumulation
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What is the cave, arch, stack, stump sequence? FC53
- the erosion of rocks, e.g. limestone and chalk, tends to exploit any lines of weakness (joints, faults and cracks).
- when joints and faults are eroded by hydraulic action and abrasion, this can then create caves. If the overlying Rick then collapses, a blowhole will develop a the cave opens up at ground level.
- if two caves in either side of a headland join together or a single cave is eroded an arch is formed. This gap is then further enlarged by erosion and weathering - becoming wider at the base.
- eventually the top of the arch will become unstable ans collapse - leaving an isolated oillar of rock (stack)
- the stack will be eroded by the sea and as it collapses and eroded further, it may only appear above the surface at low tide and is now known as a stump.
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Sea level change due to tectonic activity - Boxing Day tsunami:
