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Coastal Systemand Processes
Refer to Pages 254 to 271 of theTextbook
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Learning Objectives
Describe the different agents of coastal processes
Explain the different coastal processes (erosion,deposition and transportation)
Describe and explain the formation of erosional
and depositional landforms
Illustrate the formation of these landforms withwell-labelled diagrams
Assess the effectiveness of the various coastalprotection measures (natural/soft engineeringmethods and artificial/hard engineering methods)
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What is a Coast? (p. 254)
The zone where the land meets and is shaped bythe sea.
A coast is dynamic, ever changing as it is alteredby the coastal processes of erosion, deposition andtransportation: a result of waves, tides and
currents.
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Agents of Coastal Processes:
Waves, Tides and Currents
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What are Waves?
Waves are agents of erosion, deposition and
transportation.
Waves: Generated by wind (small-scale).As wind blows over the surface of the ocean, wind
energy is transferred from the wind to the water,causing the water on the surface to rise and fall,
leading to the formation of waves.
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What are Waves?
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What are Waves?
Wave Energy: Energy produced by the movementof waves.
Three factors affecting wave energy:1. wind energy
2. duration of fetch3. fetch (definition: distance of sea over which
wind blows to generate waves)
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Factors that Determine the Size
and Energy of Waves
Factor Size and Energy of Waves
Wind Energy
The greater the difference in pressure
between 2 regions, the faster the windspeed, the greater the wind energy.
Duration ofWind
The longer the wind blows, the largerthe waves.
FetchThe greater the fetch, the more energythe waves have
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How do Waves Move?
Waves move in a series of circular loop-likemotions.
Waves slow down as they approach the coast dueto friction (the shallower waters and sea floor),
causing the waves to rise and bend forward,eventually collapsing into foaming water as itbreaks onto the beach.
Forward movement of waves up the shore: swash(carries material up the shore)
Flow back to the sea (due to gravity): backwash(carries material back away from the shore)
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Types of Waves
Two types: destructive and constructive
Destructive Waves:- Occur on steep sloping coasts, breaking violently
with high energy.
- Steep gradient causes waves to break and plungedirectly back down the coast.- Near vertical breaking of waves resulting in
weak swash (depositional) and strong backwash
(erosional).
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Types of WavesConstructive Waves:
- Occur on gentle sloping coasts during calmweather, breaking gently with little energy.
- Gentle gradient allows waves to surge a greaterdistance up the coast and carry sediments up the
beach, depositing them.- Strong swash (depositional) and weak backwash
(erosional).- Over time, the beach is built up by the deposited
sediments.
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Whatre the Differences?Constructive Waves Destructive Waves
Low wave height High wave height
Long wave length Short wave length
Wave frequency of between6 and 8 per minute
Wave frequency of 10 and14 per minute
Spilling breakers Plunging breakers
Swash more powerful thanbackwash
Backwash more powerfulthan swash
Occur on gentle slopes andsheltered coasts
Occur on steep slopes andopen coasts
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What are Tides?Daily alternate rising and falling sea level seen
along the coasts.
Caused primarily by the gravitational pull of theMoon and Sun.
Tides affect the part of the coast that can bereached by waves.
At high tide, waves attack, erode and transportaway a larger part of the coast than at low tide.
Areas located between low and high tides willhave more erosion than areas constantlysubmerged by sea water as it experiences
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What are Currents?
Large-scale and persistent movements of water inthe ocean, driven by prevailing winds.
E.g. Longshore currents- Flow parallel to the coast
- Formed by waves that approach the coast at anoblique angle
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Coastal
Processes:
Erosion,Transportation
and Deposition
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Coastal Transportation
Longshore drift:- When waves approach the beach at an angle, theswash (depositional) carries the materials up the
beach at an oblique angle while the backwash(erosional) carries the materials perpendicularly
down the beach because of the pull of gravity.- This results in a zigzag movement of materials
along the beach.- Capable of moving large amount of sediments
along the beach.
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Coastal Transportation
Longshore drift:
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Coastal Transportation
Factor affecting direction of longshore drift:wind direction.
For example: If the wind is moving from aSoutheast direction, the direction of the longshore
drift will be from East to West.
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Coastal ErosionProcesses of coastal erosion:
1. Hydraulic action
- Direct impact of waves against coast, exertinggreat pressure on the coast.
- Air in the cracks in the rocks along the coastsmay be compressed by the entry of water into the
cracks, exerting pressure, widening the cracksand causing it to break down.
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Coastal Erosion
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Coastal ErosionProcesses of coastal erosion:
2. Abrasion:
- Impact of materials carried by waves scrapingagainst the coast.
- Destructive waves are capable of lifting largepieces of rock from the sea bed and hurling them
against the coast.
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Coastal Erosion
Processes of coastal erosion:
3. Attrition
- Rocks break down into smaller pieces as they arecarried by waves and rubbed and hit against each
other.- Rounded edges of rocks over time.
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Coastal Erosion
Processes of coastal erosion:
4. Solution
- Soluble minerals in the rocks react chemicallywith the waves, resulting in the formation of a
chemical solution.- Rock is weakened and breaks down over time.
- E.g. limestone.
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3 Factors Affecting Coastal Erosion
1. Types of waves:- Destructive waves VS constructive waves
2. Structure and composition of coastal rocks- Lines of weaknesses
- Soft rock VS hard rock- Chemical composition of rocks
3. Position of the coast- Protected (natural or artificial) coasts VS open
coasts
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4 Factors Affecting Coastal
Deposition
1. Energy of waves:- Weak wave energy
2. Increase in load:- Insufficient energy to transport load
3. Gradient of slope:- On gentle slopes, wave energy is spread out andreduced due to friction with shore and
gravitational pull, resulting in constructive waves
4. Position of coast:- Protected coasts allow for calm coastal
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Landforms Created by Coastal
Processes (p. 259-265)
Erosional Landforms:1. Cliff and Wave-cut/Shore Platforms2. Headland and Bays
Depositional Landforms:1. Beaches2. Spits and Tombolos
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Erosional Landforms: Cliff and Wave-
cut/Shore Platforms (p. 260-1)
Cliff:- Steep rock surface, tilts forward or backwards.- Produced by the action of waves undercutting asteep rocky coast.
- Hydraulic action and abrasion causes lines ofweaknesses to form on the rocks surface, erodes
and enlarges it to form a notch.- Notch may be further eroded to form a cave.
- Overhanging cliff collapses over time.- Some materials may be washed out to sea while
others are picked up by the waves for furthererosion of the base of the cliff.
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Erosional Landforms: Cliff and Wave-
cut/Shore Platforms (p. 260-1)
Wave-cut/Shore Platform:- Formed after the cliff retreats inland.- Gently sloping platform at the base where the cliff used
to be.
- Usually submerged during high tide and undergoes
continuous erosion.- At low tide, sediments are deposited on the wave-cut/
shore platform because it lies exposed above the water
and its gentle slopes causes waves to lose their energy
due to friction.
Good examples of cliffs and wave-cut platforms can befound at Hunstanton (North Norfolk) and Flamborough
Head (Yorkshire)
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Erosional Landforms: Cliff and Wave-
cut/Shore Platforms (p. 260-1)
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Erosional Landforms: Cliff and Wave-
cut/Shore Platforms (p. 260-1)
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Erosional Landforms:
Headlands and Bays (p. 262-3)
Characterised by coasts with bands of alternatingresistance to erosion.
Results in an indented coast/uneven coastline
Less resistant soft rock is eroded more quickly(resulting in the formation of bays) than the moreresistant hard rock (resulting in the formation of
headlands which extends into the sea).
E.g. South coast of United Kingdom.
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Erosional Landforms:
Headlands and Bays (p. 262-3)
Gives rise to wave refraction (bending of waves anduneven wave energy).- Energy of waves concentrated on headlands due to waverefraction, resulting in erosion.- Other waves continue, unaffected and its energy spreads
out in the bays, resulting in deposition.
Wave refraction determines when and where erosion,transportation and deposition take place.
Indented/uneven coastline becomes more prominent overtime.
The Dorset coast has excellent examples of Headlands andBaysE.g. Swanage Bay and the Foreland (a headland)
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Erosional Landforms:
Headlands and Bays (p. 262-3)
Headlands can be further eroded to form caves,arches, stacks and stumps (not in syllabus).
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Erosional Landforms:
Headlands and Bays (p. 262-3)
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Erosional Landforms:
Headlands and Bays (p. 262-3)
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Depositional Landforms:
Beaches (p. 264)
An accumulation of sediments on the coast. Sand,broken coral pieces, small stones and blackvolcanic sand.
Different materials ---> Different gradient.
Coarser materials ---> SteeperFiner materials ---> Gentler
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Depositional Landforms:
Beaches (p. 264)
Size and composition of material on beach variesand changes over time according to changes inweather conditions, wind direction and ocean
currents.
- Waves and winds cause materials to be sorted bysize.* Finer materials are typically deposited near the
sea and coarser materials further inland if the
wind is strong and there are destructive waves.* Fine materials are deposited further up thecoast and coarser materials near the sea when the
weather conditions are calm and there are
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Depositional Landforms:
Beaches (p. 264)
Bondi Beach in Australia
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Depositional Landforms:
Spits and Tombolos (p. 264)
Created by longshore drift:- Longshore currents encounter a bay with shallowsheltered water, causing materials to be deposited in thedirection of longshore drift.
Spit: One end is connected to the mainland while the otherend projects out into the sea.Examples of apits:- Spurn Head - Holderness Coast- Orford Ness - Suffolk
Tombolo: When the spit is joined to a neighbouring island,forming a bridge.Example of tombolo: Chesil Beach (joining S Dorset Coastto Isle of Portland)
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Depositional Landforms:
Spits and Tombolos (p. 264)
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Depositional Landforms:
Spits and Tombolos (p. 264)
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Why Manage Coasts?
60% of the worlds population live near coasts.Tourism revenue.
Erosion and water pollution affects coasts and
settlements along it.
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2 Ways to Manage Coasts
(p. 266-271)
1. Hard engineering methods: Construction ofphysical structures.E.g. Seawalls, breakwaters, groynes and gabions.
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2 Ways to Manage Coasts
(p. 266-271)
2. Soft engineering methods:- Planning and management so that both coastalareas and property will not be damaged by
erosion.
- Aims to change individual behaviour or attitudestowards coastal protection by encouragingminimal human interference and allowing nature
to take its course.
- Added advantage of improving natural habitats.E.g. Beach nourishment, relocation of property,planting of mangroves, stabilising dunes and
growth of coral reefs.
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HEM 1: Seawalls (p. 266)
Made of concrete, rocks or wood: Absorbs theenergy of the waves and protects the coast againststrong waves.
Limitations:- May not protect the coast from erosion in thelong run.- Do not prevent the powerful backwash of waves
from eroding the base of the seawall. Undermines
the base of seawalls and leads to their collapse.- Must be carefully maintained.- Expensive.
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HEM 1: Seawalls (p. 266)
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HEM 1: Seawalls (p. 266)
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HEM 2: Breakwaters (p. 267)Made of granite.
Protects the coast and harbour by reducing theforce of high energy waves before they reach the
shore.
Can either be built with one end attached to thecoast or built away from the coast.
Create a zone of shallow water between itself andthe coast so that waves will break against it before
reaching the coast.
Sediments can then be deposited and built up inthis zone to form beaches.
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HEM 2: Breakwaters (p. 267)Limitation:
- Unable to provide complete protection as theystill leave areas of the coast unprotected (eroded
away due to lack of new supply of materials).
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HEM 3: Groynes (p. 267)
Low wall built at right angles to prevent materialsfrom being transported by the longshore drift andaccumulated on the side of the groyne facing the
longshore drift.
Limitations:
- Beach will not be replenished by materialscarried by the longshore drift on the other side of
the groyne, resulting in the erosion of the beachfurther down the coast.
- Eyesore
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HEM 3: Groynes (p. 267)
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HEM 3: Groynes (p. 267)
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HEM 4: Gabions (p. 268)Wire cages containing small rocks prevent
erosion.
Protect other coastal protection structures likeseawalls.
Limitations:- Easily destroyed by powerful waves duringstorms.
- Short life span of less than 15 years as compared
to others of 30 years.- Eyesore.
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HEM 4: Gabions (p. 268)
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SEM 1: Stabilising Coastal Dunes (p. 269)
Coastal dune: ridge of sand piled up by wind onthe coast.
Advantages of coastal dunes:- Barriers along the coast that protect humanproperty against coastal erosion and flooding.
- Provides habitat for animals.
Plant vegetation to trap and bind sand together toprevent it from being blown inland.
Limitation:- Limits the development of lucrative propertyand recreational establishments.
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SEM 1: Stabilising Coastal Dunes (p. 269)
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SEM 2: Planting Mangroves(p. 270)Propped and kneed roots of mangroves bind loose
soil and protects from erosion.
Success: Coastal areas of Bangladesh during 2004Indian Ocean Tsunami.
Limitation:- Characteristic of young mangroves as fragilerequires cooperation of local people in the area for
mangrove planting to be successful.
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SEM 3: Beach Nourishment (p. 270)
Add large amounts of sand to eroded beach.
Limitations:- Short-term effectiveness. 10 years.- Expensive and requires regular maintenance.
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SEM 4: Encouraging Growth of Coral Reefs (p. 271)
Coral reefs protect against coastal erosion byreducing speed of approaching waves (erosionpotential).
However, human activities have destroyed coralreefs and the polluted water prevents the growth
of coral reefs.
Success: Malaysia.
Limitations:- Short-term effectiveness. 10 years.
- Expensive and requires regular maintenance.
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SEM 5: Relocation of Property (p. 271)
Role of coastal planners in settlement planning.
Allow nature to reclaim beach in its own time.
E.g. Green line policy in parts of the East coast ofEngland where buildings are discouraged beyond
a certain line.
Limitation:- Opposed by people who have considerable
investments in the coastal areas.