2. The coast
• The coast is a zone where the land meets the
sea.
• The coastline is the mean high watermark on a
lowland coast.
• The sea rises to high tide (high water mark)
and falls to low tide (low water mark)
• The area between the lowest tide and the
highest point reached by the storm waves is
known as the shore
5. Coasts
• What you will learn:
– How to describe and explain coastal processes
– How to describe the formation of landforms as a
result of these processes
– Describe coral reefs and mangrove swamps
– Describe coastal hazards
– Explain how to manage coasts
6. Coastal Processes
• What is the main agent of coastal processes?
• Can you come up with the three factors that
affect this agent?
– Duration of wind blowing across the sea
– Strength of wind
– Fetch
7. Waves
• Waves are formed because of friction
between the wind and the sea.
• When waves near the coast, the bottom of the
wave is slowed by friction with the sea bed.
• Because the top of the wave is experiencing
less friction, it moves faster and eventually
topples over the bottom of the wave and
breaks.
8. The size of the wave is effected by
three factors:
• Duration of wind
• Strength of wind
• Fetch (the distance that a wave travels)
13. Fetch
• Fetch is an important factor in the formation,
size and power of waves. Fetch is just the
maximum length of open water over which
the wind can blow.
(The fetch, also called the fetch length, is the
length of water over which a given wind has
blown)
14. Characteristics of Waves
• What is in a wave?
– Wave crest
– Wave front
– Wave trough
– Wave length
– Wave height
– Wave frequency
– Wave speed
15. Wave Terminology
• Crest: The top of the wave.
• Trough: The low area in between two waves.
• Wavelength: The distance between two crests or
two troughs.
• Wave height: The distance between the crest and
the trough.
16. • Wave Frequency: The number of waves per
minute.
• Velocity: The speed that a wave is traveling. It
is influenced by the wind, fetch and depth of
water.
• Swash: The movement of water and load up
the beach.
• Backwash: The movement of water and load
back down the beach.
17. Characteristics of Waves
• What happens when a wave meets the shore?
– Breaker
– Swash
– Backwash
• What are the factors that can affect the
strength of these parts of a wave?
• What happens to the wave when the strength
of these parts of a wave change?
21. Characteristics of Waves
Destructive Constructive
Swash strength < Backwash strength Swash strength > Backwash strength
Steep wave front Gentle wave front
Plunging breakers Spilling breakers
Short wave length Long wave length
High wave frequency Low wave frequency
28. Waves can be destructive or
constructive.
• When a wave breaks, water is washed up the
beach - this is called the swash.
• Then the water runs back down the beach -
this is called the backwash.
• With a constructive wave, the swash is
stronger than the backwash. With a
destructive wave, the backwash is stronger
than the swash.
29. Destructive waves: features
• Destructive waves are created in storm conditions.
• They are created from big, strong waves when the
wind is powerful and has been blowing for a long time.
• They occur when wave energy is high and the wave has
travelled over a long fetch.
• They tend to erode the coast.
• They have a stronger backwash than swash.
• They have a short wave length and are high and steep.
30. Constructive waves: features
• They are created in calm weather and are less
powerful than destructive waves.
• They break on the shore and deposit material,
building up beaches.
• They have a swash that is stronger than the
backwash.
• They have a long wavelength, and are low in
height.
31. Coastal Erosion (types of erosion)
• Hydraulic Pressure: This is when sea water and air
get trapped in cracks. The increasing pressure of
the water and air cause the rocks to crack.
• Corrasion (abrasion): Rocks been thrown into the
cliffs by waves and breaking off bits of the cliff.
• Corrosion (solution): The slight acidity of sea
water causing bits of the cliff to dissolve.
32. Coastal erosion
• Attrition: Rocks, sand and stones being thrown
into each other by the sea current and waves.
• Wave Pounding: This is the immense power of
waves crashing into cliffs that causing them to
weaken.
• Sub aerial weathering: This is the top of cliffs
being attacked by the weather, making the cliffs
weaker and less stable. Wind, rain, the heat and
the cold can all cause the cliffs to be weathered.
33. Activity: (HW)
• 1. Draw a sketch and explain
• (i) constructive waves
• (ii) destructive waves
• 2. Name and explain different types of coastal
erosion.
34.
35.
36. Coastal transport
• There are four ways that waves and tidal
currents transport sediment. These can then
contribute to the movement of sediment by
longshore drift.
37. Solution
• Minerals are dissolved in sea water and
carried in solution. The load is not visible.
Load can come from cliffs made from chalk or
limestone, and calcium carbonate is carried
along in solution.
38. Suspension
• Small particles are carried in water, eg silts
and clays, which can make the water look
cloudy. Currents pick up large amounts of
sediment in suspension during a storm, when
strong winds generate high energy waves.
39. Saltation
• Load is bounced along the sea bed, eg small
pieces of shingle or large sand grains. Currents
cannot keep the larger and heavier sediment
afloat for long periods.
42. Wave refraction
• Friction with the sea bed as waves approach
the shore causes the wave front to become
distorted or refracted as velocity is reduced.
The image below shows how the refracted
wave becomes increasingly parallel to the
shoreline.
46. Coastal Transportation Processes
• The movement of materials along a coast is
called longshore drift.
– Waves approach coast at an angle
– Swash pushes sediment up the coast at an angle
– Backwash pulls sediment back into the sea in a
direction perpendicular to the coast
– Process repeats and causes longshore drift
– The direction of the movement of material is
called the longshore current
48. Coastal Transportation
(longshore drift)
• Longshore Drift: This is the process of waves moving (transporting)
material (load) along a coastline.
• Swash: The waves breaking and traveling up the beach carrying load.
Waves will break and the swash will travel in the direction of the wind.
• Backwash: The waves returning to the sea with load. Waves will take the
shortest possible route back to the sea (gravity).
• Longshore drift only happens when the waves hit the beach at an angle. It
is the process of the swash transporting material up the beach at an angle
and the backwash returning directly under the force of gravity that causes
material to be transported along the beach.
49. Coastal Transportation
(longshore drift)
• Prevailing (or dominant) Wind: This is the direction that the wind
normally hits a coastline.
• Groynes: Groynes are wooden or concrete fences (walls) placed out
into the sea to stop longshore drift happening.
• Sea currents: Currents are the movement of water caused by
differences in temperature, changes in wind or tides. Currents can
be extremely strong and can transport large amount of material.
• Saltation: The wind can also transport sand and even small stones
across a beach. The process of the wind bouncing sand and small
stones across a beach is known as saltation.
50. Formation of Headlands and bays
• Headlands are formed when the sea attacks a
section of coast with alternating bands of hard
and soft rock.
• The bands of soft rock, such as sand and clay,
erode more quickly than those of more resistant
rock, such as chalk.
• This leaves a section of land jutting out into the
sea called a headland.
• The areas where the soft rock has eroded away,
next to the headland, are called bays.
51.
52. Erosional landforms: formation of
caves, arches, stacks and a stumps.
• When the waves hit a headland, it creates
cracks and cracks into caves. When caves
reach both sides of the headland, an arch is
formed.
• A collapse of the arch (roof) forms a stack and
when a stack is eroded, a stump is formed.
53. Formation of wave cut platforms
• At high tide the power of the sea attacks and erodes
the bottom of the cliff. Over time this erosion creates a
wave cut notch (basically an eroded hole at the bottom
of the cliff).
• As the wave cut notch gets bigger, the weight of rock
above the notch gets greater.
• Eventually the cliff can not support its own weight and
it collapses. As the process continues the cliff starts to
move backwards (retreat)and a wave cut platform (an
expanse of bare rock) is created. Wave cut platforms
are only visible at low tide.
58. Caves, Arches, Stacks and Stumps
• Hydraulic pressure will be the main type of erosion.
Overtime hydraulic pressure may turn the crack into a
cave.
• Slowly the cave will get bigger and cut all the way through
the headland, making an arch.
• As the arch gets bigger the weight of the arch roof gets too
great and it collapses, leaving a stack.
• The stack is then eroded by the sea and weathered from
the air leaving a stump.
• Blowhole: Sometimes the sea may erode through to the
top of the headland (following a large crack). If this
happens a blowhole is created.
60. Bays and Headlands
• Bay: An indented area of land normally found
between two headlands. Bays are usually
more sheltered so there is less erosive power,
meaning you often find beaches in bays.
• Headland: A piece of land that sticks out into
the sea. Waves refract around headlands so
they experience a lot of erosion forming
features like arches and stack
61.
62. Depositional Landforms
• Spits, bars and tombolos are all made by a
combination of longshore drift and deposition.
They are collectively known as depositional
landforms.
• Spits: A spit is a long thin stretch of sand
connected to the mainland but stretching out
into the sea. Spits are formed in areas of calmer
water where the sea has less energy. They are
normally found near the mouths of rivers where
the coastline changes direction creating some
protection.
65. • Salt marsh: A low energy, intertidal ecosystem
that develops behind a spit. The salt marsh will
have some salt resistant vegetation.
• Tombolo: A spit that joins the mainland with an
island.
• Mainland: The main land mass of an area
• Bar: A spit that connects two headlands or runs
across the face of a small cove (bay).
• Lagoon: The salt water lake that develops behind
the bar. Overtime the lagoon will become smaller
as deposition takes place.
71. Beaches and Sand Dunes
• Beach: The beach is the accumulation of sand
between the lowest spring tides and the highest
spring tides.
• Beaches can be made out of sand, shingle and/or
pebbles.
• Beaches receive their material from longshore
drift, constructive waves, cliff erosion and river
discharge.
• Beaches cane be divided into backshore, offshore
and foreshore.
72. • The backshore is the area above the normal high tide level,
• The foreshore is the area in between normal high and low tide
and
• Offshore is the area below the normal low tide.
73.
74. Berm and sand dunes
• Berm: The berm is a ridge (long thin hill) that
forms at the top of the beach. It is the highest
section of the beach and is basically sand
accumulated on the strand line (twigs, litter,
seaweed, etc. deposited at high tide).
• Sand Dunes are very dynamic, which means they
are constantly changing. Sand dunes are found
behind berms and are basically an extension of
the beach. They are formed by dry sand being
blown up the beach.
75.
76. Water table
• Water table: The line between saturated and
unsaturated ground.
77. The importance of coasts and why we need
to protect it.
• Coasts are vulnerable locations that need protecting.
• They need protecting because of the economic value
they bring to areas e.g. fishing, tourism and transport.
• Coastal erosion is mainly caused by hydraulic pressure,
corrosion, corrasion and wave pounding.
• Sub-aerial erosion can also play an important role.
• If coastal erosion is allowed to happen, coastal roads,
ports, holiday resorts, farmland and even whole
villages may be lost.
78.
79.
80. What can be done to manage the
impacts of coastal erosion?
• Hard Engineering: This building a physical
structure, usually out of wood or concrete to
protect the coast. Hard engineering is usually
more effective, but it can be very expensive
and ugly to look at.
81. • Rip-rap: Rip-rap is basically giant boulders
placed at the foot (bottom) of cliffs.
82. • Gabion: Gabion also uses large boulders, but
this time the boulders are placed in cages.
83. • Groynes: Groynes are designed to stop
longshore drift transporting away beach
material.
84. Sea walls
• Sea wall: Sea walls are made out of concrete
are aimed to absorb the waves energy.
85. Breakwater
• Breakwater: Breakwaters are built out into the
sea. They are a coat’s first line of defense.
Instead of breaking on the coast, waves, break
on the breakwater.
•
86. Soft engineering
• Soft engineering is working with nature (no
concrete or artificial structures).
• The advantage with soft engineering is that it
does not ruin the look of the coastline and it
can be cheaper.
• However, most forms of soft engineering can
not withstand strong storms or hurricanes.
87. Dune Stabalisation
• Dune Stabalisation: Dune stabalisation is
planting vegetation on the berm of the beach
or on the dunes.
89. Cliff Regrading
• Cliff Regrading: This means make cliffs less
steep. Cliffs often become unstable because of
undercutting. By reducing the angle you
should reduce the undercutting and the risk of
the cliff collapsing.
90. Case study: coastal management in
Holderness, NE England, UK
• The Holderness coast is in the north east of
England. This is one of the most vulnerable
coastlines in the world and it retreats at a rate
of one to two metres every year.
91. The problem is caused by:
• Strong prevailing winds creating longshore
drift that moves material south along the
coastline.
• The cliffs are made of a soft boulder clay. It
will therefore erode quickly, especially when
saturated.
93. The village of Mappleton
• The village of Mappleton, perched on a cliff
top on the Holderness coast. Due to the
erosion of the cliffs, the village is under threat.
94. Coastal management at Mappleton
• In 1991, the decision was taken to protect
Mappleton. A coastal management scheme
costing £2 million was introduced involving
two types of hard engineering - placing rock
armour along the base of the cliff and building
two rock groynes.
95. • Mappleton and the cliffs are no longer at great
risk from erosion.
• The rock groynes have stopped beach material
being moved south from Mappleton along the
coast.
• However, this has increased erosion south of
Mappleton.
• Benefits in one area might have a negative
effect on another.
97. Coral reefs
• Coral reefs are landforms created beneath the sea.
• Coral reef is a line of coral polyp found in warm shallow seas. Polyp
are tiny carnivorous (meat eating) animals
• Polyps cannot move from their limestone homes. They mostly feed
at night.
• A polyp reproduces by dividing its own body to form two polyps,
• Each polyp builds a case of limestone around itself, using calcium
from the water. It is like a house, with a floor and walls.
• This remains after it has died and forms a foundation for another
polyp to build a house on, putting a floor on the roof of the old one.
When these limestone formations increase, they are called a coral
reefs.
99. Corals need three factors for growth:
• Warm water
• Clear shallow saltwater, not deeper than 50
meters
• Plenty of sunlight for photosynthesis.
Reefs are established when a large continuous mass
of coral builds upwards and outwards from a rock
base.
Coals can grow in temperate regions but they are
usually found in tropical and sub-tropical waters.
100. Fringing Reef
• Fringing Reef: Fringing reefs circle or fringe the
coastline or islands. They are often protected
by barrier reefs further out to sea, so the
plants and animals that live in fringing reefs
are suited to low wave energy environments.
101. Barrier Reef
• Barrier Reef: These occur further from the sea
and are commonly separated from the
mainland or island by a deep lagoon. Barrier
reefs are normally older and wider than
fringing reefs. The Great Barrier reef in Eastern
Australia is a barrier reef and stretches for
1600km.
102. Atoll
• Atoll: They rise from submerged volcanoes.
They are similar to barrier reefs in terms of
biodiversity and form. However, they are
confined to submerged oceanic islands, unlike
barrier islands which can follow continental
coastlines e.g. Great Barrier Reef.
103. Benefits of coral reefs
• They support 25% of marine species
• They protect coastlines from erosion
• They form as a natural barrier against tropical
storms and even tsunamis (they can absorb
energy).
• They contribute material to the formation of
beaches and islands (eroded coral reef)
104. • They are source of raw material (coral for
jewelry and ornaments)
• Many species are being found to contain
compounds useful in medicine.
• They benefit the tourism industry because
many people like to dive and snorkel over
coral reefs
105. HOW CORAL REEFS ARE BEING
DAMAGED
• Rising sea levels - many coral reefs will not
receive enough sunlight to survive.
• Coral reefs are extremely sensitive to changes
in temperature and can bleach (die and turn
white) even with only small increases.
• Fishing techniques like dynamite, cyanide and
trawling and overfishing can damage corals
106. • The increased sediment reduces visibility and
means less sunlight reaches the coral.
• Pollution. The growth of urban settlements
and tourist developments, as well as increased
coastal traffic can also cause pollution to reefs.
• Tourism. Tourism can damage reefs in many
ways. Boating and diving are examples.
107. Saving corals
• Restrict fishing tourism and diving in coral
zones
• Sewage outlets can be moved downstream of
coral reefs
• Banning the dropping of anchors on coral reef.
• Reduce the use of fertilisers near coral reefs
• Educating people about why coral reefs are
important and how we can protect them
108. Coral ecosystem under threat!
• Coral reefs are home to more than 3000
different species of plants and animals. These
reefs are big tourist attractions.
• Tourism brings income to people living in
those areas.
• But it can damage the corals.
• Other human activities like farming, fishing
and water pollution can affect the survival of
corals.
110. Mangroves
• A mangrove is a shrub or small tree that grows
in coastal saline (salty) water around the
tropics and subtropics
• Mangroves are salt tolerant trees and are
adapted to life in harsh coastal conditions.
• They can survive in salt water , low oxygen
and withstand waves.
• Normal plants will die within hours in theses
conditions.
111. Importance of mangroves
• Mangroves are important habitat for many
species of plants, animals and birds.
• Humans are greatly benefitted from
mangroves (fish, wood, food).
• They protect the coastline from erosion (serve
as natural breakwaters) , provides firewood
and food.
• They are very important to coastal ecology.
112. Mangroves are under threat!
• They are cut down for salt pans, aquaculture
ponds, housing developments, roads, port
facilities, hotels, golf courses, and farms.
• And they die from a thousand indirect cuts: oil
spills, chemical pollution, sediment overload,
and disruption of their sensitive water and
salinity balance.
• Increasing population and economic
development are threatening the mangroves.
114. • Located in the delta region of Padma, Meghna
and Brahmaputra river basins of India and
Bangladesh.
• The Sundarbans is the worlds largest coastal
mangrove forest, with an area of approximately
10,000 sq km;.
• The Sundarbans are a network of marine
streams, mud shores and mangrove forests.
• The region is known to contain numerous species
of animals, birds and reptiles, including Royal
Bengal Tiger, Chital Deer, Crocodile and Snakes .
