S3 GE Slides 3 - Coasts GW3

Testing your memory and intelligence! : )
— Explain how waves can both erode and build
up a beach at different times.
— How do sediments get transported along the
beach?

Why the need for Coastal
Protection Measures?
Chapter 1: Coasts

Before After extensive Coastal Erosion
Spot the difference!

Management and Sustainability
Tsk tsk tsk! Look at
how terribly the beach
got eroded away!
Ya lor!
That’s why we need to
manage our coast if not we
won’t have any more pretty
beaches to go for holiday!

Wait!What do you
mean by managing
our coast?!!

Management of a coastal
area means controlling the
development and change in the
coastal zone according to agreed
principles and criteria.
57

Coastal zone
can change
one meh?
DUH!You can
implement policies to
restore sandy beaches
at certain places!
57

I know I know!
Textbook got say!
Can bring truckloads
of sand to restore
the sandy beach!
Not bad yo!
Somebody very
hardworking uh!
57

Simi
sustainable?!
But!Though coastal
areas can be managed,
it should be done in a
sustainable manner!
57

Ooh…so sustainable means
like today I can use, then my
children also can use, then
my grandchildren also can
use… aiyo! Say until so
cheem!
Well, sustainable means that
development should NOT
compromise the quality of
the environment for present
and future generations.
57

Textbook says we can
(i) limit damaging activities
(ii) protect coastal resources
(iii) restrict development
in areas prone to
natural hazards
Yup yup smarty pants!
Measures should be put in
place so that little or no
deterioration should occur
after restoration.
57

(i) Limiting damaging activities 58
Damaging activities
are activities that interrupt the
functioning of natural systems.
What are natural
systems?

(i) Limiting damaging activities 58
Highlight in your
textbook what are the
damaging activities that
are done to these
natural systems!
Natural systems are
for example
coral reefs and
mangroves

(iii) Restrict development in areas
prone to natural hazards
58
Natural hazards such as
tsunamis can be disastrous
to natural environments
and human activities L
Let’s look at some
‘before’ and‘after’
photos of some places
after the earthquake
inTohoku.

YouTube:
CLIFF COLLAPSE Dramatic coastal erosion in Cornwall

What are some coastal protection
measures?
Question:
Why do we need
different coastal
protection measures?
WHYYYYYYY?

What are some coastal protection
measures?
Because different
coastal locations have
different sets of
conditions,thus require
different measures!

Soft Engineering Hard Engineering
•  Involves protecting the
coast using natural
processes.
•  Used more often than soft
engineering
•  Does not involve the
construction of any
physical structures.
•  Involves the
construction of
physical structures to
protect coast against the
erosive power of waves.
Coastal protection measures
60

1.  Beach Nourishment
2.  Planting mangroves
3.  Stabilising dunes
4.  Encouraging coral reef
growth
1.  Seawalls
2.  Gabions
3.  Breakwaters
4.  Groynes
5.  Tetrapods
Coastal protection measures
60

— Split yourselves up into nine groups and each group will be
assigned to work on one coastal protection measure.
— With the aid of your textbook and creative minds, present
the coastal protection measure on the blankA4-sized paper
given to you in any creative way you can think of.
— It can be a mindmap, drawing/sketch,Whatsapp Chat
etc etc – I know you are definitely much more creative
than me.
— State: how does the measure work? How does it
look like (if applicable)?Where is it implemented?
Effectiveness/advantages?
Limitations/disadvantages?

Delegates, please be seated quietly
and we shall begin the
presentations! J

Dear delegates, the presentations
for today shall be in this sequence:
1.  Beach Nourishment
2.  Planting mangroves
Stabilising dunes
3.  Encouraging coral reef
growth
4.  Seawalls
5.  Gabions
6.  Breakwaters
7.  Groynes
8.  Tetrapods
9.  SpecialTask Force (East Coast Park, Singapore)

1. Beach nourishment (soft engineering)
How does it work?
— Adding large amounts of sand to a beach that has been
eroded (ie. a depleted beach).
— The sand may come
from another beach
or dredged from the
sea floor.
60

Effectiveness / advantages 
— Replenish sand that
has been eroded away.
— A coast can be
transformed into a
wide, sandy beach
that offers protection
to the immediate
inland areas.
60

Limitations / disadvantages 
— Effects of beach nourishment usually last for only about
10 years.
— Re-nourished beaches can be eroded again
unless other management strategies are put in place.
— Extremely high cost and time consuming:
— Piping in sand can be expensive.
— The cost of beach nourishment to renew 24 km of Miami
beach in USA in 2005 is US$64 million (S$105 million).
— Regular maintenance is required.
61

2. Planting mangroves (soft engineering)
How does it work?
— Mangroves have prop roots or kneed roots to anchor
the trees firmly in the muddy soil.
— Mangroves absorb wave
energy through their
dense roots system.
— Thus it helps to protect
the coast against erosion
by strong waves and winds.
61

Some examples:
— Studies have shown that coastal areas of Bangladesh with
mangroves suffered
less damage during
the 2004 Indian
OceanTsunami than
unprotected beaches.
61

— The mangroves protect the coast from strong waves and
wind by breaking the impact of the waves.
— Enhances natural beauty of the environment
— Mature mangroves require little monitoring.Able to break
down biodegradable waste and filter the water.
61

More examples:
— In Bang KhunThian, CentralThailand, 2012.

— Young mangroves are fragile, thus mangrove planting
exercises require the cooperation of the local people living in
the area.
— Does not offer immediate protection, need time for young
mangroves to grow and stabilize the soil in coastal areas.
— Local people need to be mindful not to let animals enter
and graze on the mangrove plantations.
— Thrives only in tropical climate.
61

3. Stabilizing dunes (soft engineering)
How does it work?
— A coastal dune is a ridge of sand piled up by wind on the
coast.
— Dunes form as a result of vegetation trapping and stabilizing
the sand.
— Coastal dunes act as
barriers along the
coast, protecting
human property
against coastal erosion
and flooding from waves. 61

Coastal dunes

How does it work?
— Sand dunes are common in countries where the coasts have
vegetation like spinifex and marram grass (eg. Omaha
Beach, New Zealand)
Marram grass
Spinifex

SpinifexMarram grass

— Vegetation trap and bind the sand together preventing sand
from being blown inland.
— The roots of grasses anchor the sand and thus stabilize
coastlines, preventing erosion.
61

— Matting is often put over the
dunes, and young grasses are
then planted into the sand
through the matting.
— Overtime, the grasses
become established and the
dunes become more stable.
The matting then rots away, adding nutrients to the sand.
61

— To prevent the vegetated dunes from being disturbed by
human traffic
(eg people stepping
on the dunes),
fences and access
paths need to be
built.
61

— Incurs costs for maintaining the fences and paths.
— Requires the cooperation of beach users.
— Cannot totally prevent erosion.
— For coastal dunes to be stabilised in the long run, human
activities such as property development and recreational
activities need to be minimised along these coasts.
61

4. Encouraging coral reef growth (soft engineering)
How does it work?
— Coral reefs are masses of rock-like
substances called corals growing
in the shallow seas.
— They protect beaches against
coastal erosion by weakening
wave energy.
— In some countries like Malaysia,
government has taken measures to
encourage growth of coral reefs in places like PulauTioman.

How does it work?
— Artificial reefs can be created by placing lasting materials
such as steel or concrete onto the sea floor.

How does it work?
— Corals, and other marine animals and vegetation, will start
to colonise these man-made materials and function as a
natural reef.

— Coral reefs help to reduce the speed of the waves, thus
reducing coastal erosion.
— Coral reefs are habitats for many types of marine life.
— As such, encouraging growth of coral reefs will also
encourage a wider biodiversity in the sea.
— Enhance the natural beauty of the waters in the area.

— It is not easy to encourage the growth of corals.
— Encouraging the growth of coral reefs requires a carefully
monitored environment:
— Ban fishing within certain protected areas.
— Ban the building of waste water treatment facilities near
coastal settlements.
— Requires constant effort to reduce water pollution.
— Coral reefs are very sensitive, they only thrive in tropical waters.
— Coral growth may be slow (20-30 yrs) à delayed effectiveness.

1. Seawalls (hard engineering)
How does it work?
— Usually made of concrete or stone built parallel to the coast.
— Constructed in front of cliff or along the coast to absorb
energy of the oncoming waves.
Sea wall

— Seawalls cause waves to be reflected back to the sea, thus
protecting the coast from
strong waves, especially
during a storm.

— Seawalls absorb only some wave energy, may not protect the
coast from erosion in the long run.
— Results in strong backwash which wears away the base of
the seawall.
— Energy from waves is redirected downwards to the base
of the seawall.
— Eventually the base of the seawalls is undermined,
leading to their collapse.

— Seawalls are costly to build and maintain as constant repairs
have to be made to prevent their collapse.
— In England, cost S$3million to build one kilometre
stretch of seawall.
— Prevents recreational activities due to lack of beach.

2. Gabions (hard engineering)
How does it work?
— Gabions are wire cages
containing small rocks,
used to form a wall to protect
the coast against erosion.

How does it work?
— These cages are built along a
shore or behind a beach.
— When waves approach, the
water enters the gaps between
the rocks.
— Thus, wave energy weakens,
preventing or reducing coastal
erosion.

Gabions at MOE Adventure Training Centre,
Changi Coast

— Breaks the impact of waves reaching the coast.
— Also used to protect other coastal protection structures,
such as seawalls.
— Less expensive than a seawall or breakwater.

— Ruin the natural beauty of the coast environment as the
wire cages are unsightly.
— Though expensive than a seawall or breakwater, their
regular maintenance is costly.
— Short life span of less than 15 years.
— Easily destroyed by powerful waves during storms.
— Wires rust easily / corroded by seawater.

3. Breakwaters (hard engineering)
How does it work?
— Usually made of granite.
— Built parallel to the coast
to break the force of
oncoming waves.
— Or can be built with one
end attached to the coast.

How does it work?
— Constructed offshore,
breakwaters create a
zone of calm water
behind them.
— A shallow zone of water
is created between itself
and the coast.

How does it work?
— Materials are the then
deposited and build up
in this zone of calm
water to form beaches.

Breakwater at East Coast Park, Singapore

— Breaks the impact of the waves before they reach the coast.
— The calm water zone can:
— Encourage deposition and build beaches.
— Be used as a sheltered harbour for boats.

— Unable to offer complete protection as it still leaves some
areas of the coast unprotected (ie coast is protected
unevenly).
— Expensive to construct a breakwater.
— In Singapore, breakwaters built along the beach at East
Coast Park, Siloso Beach in Sentosa.
o Cost of each breakwater is around S$1 million.

— Affects the natural beauty of the environment, does not
blend well with the natural environment
à aesthetically unappealing.
— Materials that have been deposited in the zone behind the
breakwater are protected.
— But those in the zones located away from the
breakwaters are subjected to wave action and possible
erosion.

4. Groynes (hard engineering)
How does it work?
— Groynes are low walls built at right angles to the
coast to prevent materials from being transported
away by the longshore drift.

Coasts4. Groynes (hard engineering)

— By absorbing or reducing the energy of the waves:
— Groynes prevent materials from being transported away
by longshore drift.
— Groynes enable transported materials to be
accumulated on the side of the groyne facing the
longshore drift.
— Depending on the direction of the prevailing waves, groynes
can help sustain and even extend beach areas.

— Beach on the other side of the groyne may not be
replenished by materials carried by the longshore drift.
— Unprotected part of the beach further down the coast may
be eroded away.
— Groynes are unsightly and expensive to build and maintain.
— Series of groynes spoil the beauty of the natural
environment.

5. Tetrapods (hard engineering)
How does it work?
— Tetrapods are four-
pronged concrete
structures that help to
dissipate wave energy.
— They are stacked
offshore in an interlocking
position.

Comparing with other hard engineering methods:
Tetrapods Breakwaters / seawalls
Allow water to pass around
them rather than hit against
them.
They are built to directly
oppose the force of
oncoming waves.
Thus, no powerful
backwash is generated,
which reduced the
possibility of tetrapods
being damaged by waves.
Thus, powerful backwash
of reflected waves
undermines the base of
the seawalls, leading to
their collapse.

— Tetrapods are pre-casted, meaning, they are cast into their
final shape before being positioned.
— Thus, they can be placed quickly while coasts are under
attack from waves, as compared to other structures
which may take time to build.

— They are aesthetically unappealing and expensive to build.
— They are also dangerous to swimmers, surfers and boaters.

Coastal Erosion at East Coast Park,
Singapore

Coasts
Below is a link which you can find out more on groynes:
http://www.geographysite.co.uk/pages/physical/coastal/
longshore.html
How the Crescent City was affected by tsunamis:
http://www.huffingtonpost.com/2011/07/22/cresent-city-
tsunami-aftermath-struggles_n_907514.html.
Coastal protection measures in Crescent City:
http://360panos.com/NorthCalif/RedwoodPark/CresentCity/
index.php/

S3 GE Slides 3 - Coasts GW3

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