Notes on Coastal Studies

1. What is a coastal environment?
A coast is the area where the sea or ocean meets the land.

What factors lead to the differences and dynamism of coastal environments?
      Geology (rock composition)
      Human activities (e.g. trading, fishing, recreation)
      Types of ecosystems (e.g. mangroves and coral reefs)

·         It is the main shaping force of coastal environments
·         Waves form when wind blows across the surface of seas and oceans
·         Energy from the wind is transferred to the water and it is this wind that helps shape coasts when the waves hit land

  • They are large-scale and persistent movements of water in seas and oceans, driven by prevailing winds (generally blow in one direction)
  • Ocean currents play a very important role in distributing sediments and regulating temperatures
  • Currents (e.g. longshore currents) carry large amounts of energy and shape coasts through the processes of coastal erosion, sediment transport and sediment deposition
  • Ocean currents carry cool water away from the North and South poles towards the Equator and warm water from the Equator towards the Poles
  • In this way, ocean currents help create milder climates in coastal areas

  • Refer to the daily alternate rising and falling of the sea level seen along the coasts
  • They are caused primarily by the gravitational pull of the Moon and the Sun on the earth
  • Low tides are experienced between the high tides and takes about 6 hours for tides to change
  • Each coastal area receives two high tides and two low tides daily and the difference in water level between low and high tides is called the tidal range
  • Tidal action has a significant impact on the coast
  • For example at high tides, waves erode and transport more sediments away from the larger parts of the coasts than at other times
  • Areas located between low and high tides will have more weathering and erosion than areas constantly submerged by sea water
·         Coastal environments are affected by their geology, which is the arrangement and composition of rock found in the area
·         Rocks may be arranged in layers, such as in alternate layers of hard and soft rocks
·         More resistant rocks such as granite and basalt will erode slower than less resistant rocks such as limestone and shale
·         But granite and basalt are still vulnerable to erosion when the joints of these rocks are attacked by waves, thus erosion weakens the rocks
·         Coastal processes that operate on coasts consisting of different types of rock result in coasts with different coastlines

Human activities
·         People change coastal environments by living, trading, fishing and engaging in recreational activities in these environments
·         For example, people alter coastlines when they build marinas and port facilities
·         People also cause pollution in these environments by dumping waste

Types of ecosystems
·         Communities of plants and animals interact with each other as well as the environment and ecosystems in coastal environments include mangroves and coral reefs
·         They affect the rate of change of coastal environments by reducing the impacts of waves on coasts
·         For example, coral reefs provide natural barriers that help slow down the speed and impacts of waves on the coastline
·         Another example is mangroves with aerial roots, help to trap sediments and reduce coastal erosion
·         Over time, the trapped sediments can form small islands and extend the coastline further seawards

2. Explain how waves are generated and the factor influencing wave energy.

Waves are generated when there is a transfer of energy from wind to water surface

Wave Energy
  • It is the energy produced by the movement of waves
  • Wind energy depends the fetch, the wind speed and the wind duration

Size and energy of waves
The distance of the sea over which wind blows to generate waves
The greater the fetch, the more energy the waves have
Wind speed
The speed of air movement
The faster the wind speed, the greater the waves energy
Duration of wind
The length of time which the wind blows continuously
The longer the wind blows, the larger the waves

3. Explain the processes which occur when waves breaks.

The forward movement of waves up the shore is called swash (loses energy due to gravity)
The flow back to the sea (due to gravity) is called backwash
The swash carries sediments up the shore while the backwash carries the sediments back towards the sea.

5. Describe the different types of waves and their associated coastal environment.

Constructive waves
Destructive waves
  • Occur in calm weather on gentle-sloping coasts
  • These waves break gently with little energy
  • They have a strong swash but a weak backwash
  • The gentle gradient allows the waves to surge a greater distance up the coast and carry sediment up the beach
  • More materials are therefore brought up and deposited on the coast than are removed
  • Overtime, the coast is built up by the deposited sediment
  • Occur on steeply-sloping coasts
  • These break violently with high energy
  • They have a weak swash but a strong backwash
  • The steep gradient causes the waves to break and plunge directly down the coast
  • The near-vertical breaking of the waves result in a weak swash, which does not get to travel far up the coast to deposit materials
  • However it generates a strong backwash which can move a considerable amount of sediment towards the sea
  • Destructive waves erode the coast and transport coastal rocks and beach materials away from the coast

6. Explain wave refraction and the processes which occur when waves break.
·         The process by which waves change direction when they approach a coast
·         Waves converge on headlands and diverge on bays
·         When waves converge – increased wave height and greater erosive energy
·         When waves diverge – decreased wave height and lower erosive energy
·         Uneven impact on shoreline

Fig. 4: Action of wave refraction on headland and bay

At the headland – waves approach a headland and bend towards it. More erosion will occur at the headland where wave energy is concentrated.

At the bay - waves diverge when they reach the adjacent bays. More deposition will occur in bays where wave energy is spread out.

7. Why do coastal landforms and features vary from place to place?

Coastal Processes
A.        Coastal Erosion
B.        Coastal Transportation (Sediment transport)
C.        Coastal Deposition (Sediment deposition)

A)        Coastal Erosion
Factors affecting coastal erosion
Types of waves
Structure and composition of coastal rocks
Position of the coast
·      Destructive waves have more energy therefore more materials are eroded than deposited
·       Coastal rocks with cracks and joints will be eroded and broken down more quickly when attack by waves
·       A coast that consists of soft rocks such as shale and clay will be eroded much faster
·       Coastal rock with soluble minerals can chemically react with water to form new chemicals, which may gradually weakened and broken down under the constant attack of sea water
·      Coasts that are protected or sheltered from prevailing winds and wave action by natural or man-made structures will experience less erosion than coasts that are open and unprotected

Processes of Coastal Erosion
Type of coastal erosional processes
Hydraulic action
·      It is the direct impact of the waves against the coast
·      The sheer force of breaking waves pounding against a sea cliff exerts great pressure on the cliff face
·      Air in the cracks may be compressed by the water entering the cracks and the pressure exerted can widen the cracks
·      Over time, this constant compression and outward push of the air may cause the cracks to be enlarged
·      Eventually, it will cause the breakdown of the rocks

·      Refers to the impact of materials carried by the waves scraping/ hurling against the coast
·      Destructive waves are capable of lifting up large pieces of rocks from the sea bed and hurling them against the coast
·      This powerful impact of the rocks being thrown against the coast may eventually erode and change the coast
  • When waves react chemically with soluble minerals contained in the rocks and dissolved them, a chemical solution is formed
  • Limestone is susceptible to this process by the action of carbonic acid
  • When rocks carried by the waves rub or hit against each other, they break down into smaller pieces
  • Overtime, the rocks become more rounded too

B)        Coastal Transportation
  • One way of transporting sediments along the coast is by beach drift and longshore drift
  • When waves approach the coast at an angle, the swash carries the materials in the water up the beach at an oblique angle, while the backwash carries the materials perpendicularly down the beach due to the pull of gravity
  • This results in a zigzag movement of the materials along the beach
  • This process is known as beach drift

·         When the waves approach the coast at an angle, they generate longshore currents in the nearshore zone and move sediments along the shore
·         Longshore currents are ocean currents that flow parallel to the coast
·         The combined effect of sediment movement by longshore currents and beach drift is known as the longshore drift

  • The direction of the longshore drift is affected by the direction of the wind
  • For example, if the wind is blowing from a southeast direction, the direction of the longshore drift will be from east to west
  • This is a powerful process that is capable of moving very large amounts of beach sediments along the direction of movement

C)        Coastal Deposition

Sediments are transported away and deposited elsewhere. When wave energy decreases, the waves are unable to carry these sediments. Marge sediments are deposited first, followed by the smaller sediments. Deposited sediments vary in types and size, resulting in a variety of beaches.

Deposition of sediment along the coast is dependent on the following factors:

Supply of sediments
Gradient of slope
Position of the coast
  • Most sediment is transported down to the coast by rivers. Some sediment come from the coastal erosion, and some is deposited onto the coast by the waves
  • When the wave energy is weak and the waves cannot carry their load of sediments, deposition takes place
  • On gentle slopes, the wave energy is spread out and reduced because of friction with the shore as well as because of gravitational pull
  • Therefore the constructive waves deposit materials rather than erode the materials
  • Coasts that are sheltered by barriers have calm conditions that allow deposition to take place which may develop feature like beach
  • Sandy beaches are common in protected bays
  • Headlands which are extensions of bedrock jutting out into the sea, are also common features

In what ways do coastal landforms and features vary from place to place?

Different coastal landforms such as sandy beaches, rocky beaches or steep cliffs may be found along coasts. These are largely the result of erosional and depositional processes.

Erosional Landforms
Depositional Landforms
  • Cliffs and Wave-cut Platforms
  • Headlands and Bays
  • Beaches
  • Spits and Tombolos

Formation of Cliffs and Wave-cut Platforms
  • A cliff refers to a steep rock face
  • Can either tilt forward or backwards
  • They are produced by the action of waves undercutting a steep rocky coast
  • Hydraulic action and abrasion may erode a crack on the rock surface
  • Eventually, the crack may be enlarged to produce a notch
  • This notch may be further deepened inwards to produce a sea cave
  • Further undercutting by the waves will eventually cause the roof of the sea cave to collapse
  • As the process continues, an overhanging cliff is formed
  • The overhanging cliff will collapse and the materials will be deposited at the foot of the cliff
  • Some of these materials may be picked up by the crashing waves and thrown against the base of the cliff, thus causing further erosion
  • As the erosional process continues, the cliff may retreat further inland
  • Over time, a gently-sloping platform appears at the base of the cliff and this platform is called the wave-cut platform, which is usually submerged during the high tides
  • The wave-cut platform is also known as the shore platform
Headlands and Bays

  Some coastlines have alternate strips/ bands of resistant hard rock and less resistant soft rock arranged at right angles to the coast
  • The less resistant soft rocks will be eroded faster than the more resistant hard rocks
  • When the less resistant soft rocks are eroded away, bays are formed
  • The remaining more resistant hard rocks extending into the sea are known as headlands
  • The result is the formation of indented coasts with headlands and bays
  • For example, East coast of Johor, Malaysia and South coast of United Kingdom

  • Headlands and bays give rise to wave refraction
  • Waves usually approach the shore at an angle
  • However, as waves approach an indented shore with headlands and bays, the waves are refracted or bent
  • Consequently, they move almost parallel to the shore
  • The refraction is caused by the uneven depth of the sea-floor

  • As the waves bend, their energy is distributed unevenly along the shoreline
  • The waves nearer to the shore touches the sea floor first and slows down due to friction with the bottom of the sea
  • Meanwhile the waves at the back continue to move towards the shore at full speed
  • As a result of wave refraction, waves approach the shallow sea in front of the headlands first before they reach the adjacent bays
  • As wave energy tends to concentrate and strike at the headlands rather than the bays, erosion takes place at the protruding headlands
  • Along the bays, waves are diverged and their energy spread out and weaken
  • Deposition of sediment thus takes place along the bays and over time, sandy beaches are formed
  • Waves refraction, therefore, determines when and where erosion, transportation and deposition take place
  • It causes erosion at the headlands and deposition along the bays
  • Over time, the indented coast will become more and more prominent

Caves, arches and stacks
·         Within headlands, some rocks may be less resistant to erosion than other rocks. These parts of the headlands will be eroded more quickly, especially by hydraulic action and abrasion. Waves attack lines of weaknesses (joints and faults) at the base of the headland and undercut it. The continuous action of waves forms a cave (e.g. a cave in Hanauma Bay, USA) at the area that is hollowed by the wave action.
·         Caves may develop on each side of the headland. Erosion may eventually join caves together, leaving a bridge of rock known as an arch (e.g. an arch in Port Campbell, Australia) above the opening.
·         After a period of time, the roof of the arch may collapse to form a stack (a stack in ‘James Bond Island’, Thailand). A stack is a pillar of rock in the sea left behind after an arch collapses.

Beaches (depositional coasts)
  • It the most common depositional feature found along a coast
  • The size and composition of the materials on the beach vary greatly and may change over time according to changes in weather conditions, wind direction, wave energy and ocean currents
  • Usually the waves and winds will cause the materials on the beach to be sorted by size
  • The slope of the beach is determined by grain size. Finer grain sizes tend to result in beaches with a gentle gradient
  • On the other hand, materials of coarser grains form beaches with a steeper gradient
  • Generally, the finer materials are deposited nearer the sea and coarser materials further inland if the wind is strong and there is destructive waves
  • During calm conditions with constructive waves, fine materials are deposited further up the coast and the coarser materials are deposited nearer the sea 

Spits and Tombolos
  • It is formed by longshore drift
  • Along some coasts where the direction of the coastline changes abruptly, longshore drift continues to transport the materials in the original direction for some distance
  • The materials are deposited in the sea where they accumulate over time
  • Eventually, the accumulated materials will appear above the surface of the water, forming a spit
  • A hook or curve may develop at one end of the spit, most likely due to wave refraction concentrating at that point
  • A spit has one end connected to a mainland while the other end projects out into the sea
  • When a spit is formed, it may continue to expand until it joins the island to the mainland
  • In this case, a new landform called a tombolo (e.g. a tombolo found in the Gulf of Thailand) is formed
  • A tombolo may also join two islands
The Coral Triangle spans an area of 6 million square kilometres. It consists of countries such as Indonesia, Malaysia, the Philippines, Papua New Guinea, Timor Leste and the Solomon Islands. 76 per cent of the world’s coral species, 6 out of 7 of the world’s marine turtle species, and at least 2,228 reef fish species live in this area.

The Coral Triangle region is unique not only because of its wildlife and marine and coastal ecosystems, but also for the benefits the local communities and governments can gain from the area.
Consider this:
      120 million people are directly sustained by the marine and coastal resources of the Coral Triangle
      US$2.4 billion is the amount that fisheries in Southeast Asia make from making use of the coral reef ecosystem
      US$12 billion is the size of the Coral Triangle nature-based tourism industry

How do people use coastal areas?

Humanities activities in the coastal areas
Fisheries and aquaculture
Fisheries are areas where fish are bred and raised to meet the growing demand for fish.

These fisheries include farming fish in cages or ponds close to coasts in rivers or converted wetlands, which is known as aquaculture.

Ca Mau, Vietnam
Areas cleared from coastal mangroves which are waterlogged are favourable for shrimp production. The remaining mangroves protect the area from storms and coastal flooding.
Mud and concrete ponds have been constructed to hold the shrimps production. Production of shrimp farms reached a record high of US$800 million in 2010.
Clearing of mangroves has left the coastline more vulnerable to erosion from storms and pollution pond waste. Thus organic shrimp farming was introduced to help prevent clearing of mangroves and maintaining a balanced ecosystem.

Housing and transportation
There are some people who live on stilt houses, connected by walkways.

Boats are also there to facilitate movement, and are a common mode of transportation.

Kukup, Malaysia
It is a place with stilt house communities. Floating fish farms are a common sight. Fresh fish and other marine products such as salted fish and dried prawns are sold at these farms.
Boats are used by local fishermen to facilitate their fishing activities. Visitors can also use the ferry services to go to Kukup.
Over the years, Kukup has become an attractive tourist destination, with its economy largely driven by the income earned from local and foreign tourists.

Tourism and recreation
People usually associate coasts with tourism and recreation. Tourism at coastal areas makes up the most important component of international tourism.

Sentosa, Singapore
Many developments in Sentosa have capitalized on the coast. One such development is ONE015 Marina Club which has world-class marina facilities.
Its marina is in a harbor with wharfs offering maintenance services for boats and yachts. It also has recreational boating facilities.
Resort World Sentosa has also maxmised the use of its waterfront by building its hotels, museum and marine life park on the coast.
With these attractions, it is not surprising that the island had 19 million visitors in 2011, a 600% increase from 2003.

Why are coral reef and mangrove ecosystems distinctive and valuable?

Coral reefs
These reefs consist of colonies containing billions of tiny coral animals called polyps

Polyps secrete calcium carbonate around themselves as protection

Polyps leave empty outer limestone skeletons when they die

Provide microscopic algae with nutrients and CO2, while the algae provide the polyps with sugars and oxygen, which are products of photosynthesis

Algae lives in the coral tissue and they have a symbiotic relationship (live together and benefit each other)
Salt-tolerant tropical or sub-tropical plants which grow in conditions that most plants are unable to

Grow in tidal mud on sheltered coasts  

Habitat to many plants and animals

Widely distributed but are mostly found between the Tropic of Cancer in the northern hemisphere and the Tropic of Capricorn in the southern hemisphere
Region of Southeast Asia has the largest area and the highest biodiversity of coral reefs in the world
e.g. Great Barrier Reef in Australia, reefs around Philippines and Indonesia.

Found along coasts of countries located between Tropic of Cancer and Tropic of Capricorn

Most abundant on tropical coastlines such as the Malay Peninsula, Borneo, northern Australia

Environmental conditions affecting their growth
Strong waves increases the likelihood of food and oxygen supplies and prevents sediments from suffocating living corals
Storm waves can destroy corals
Sediments suffocate corals

Average seawater salinity
Lower salinity levels inhibit coral growth e.g. at the river mouth            
Clear saline water (between 10m and 60m deep) allows sunlight to penetrate, triggering algae photosynthesis
High turbidity restricts sunlight penetration so algae cannot photosynthesize efficiently

Sea temperature must be ideal (not lower than 170C to 180C)

Mangroves are a type of halophyte

Special aerial roots to enable them to take in oxygen in waterlogged conditions

Prop roots to anchor the trees firmly in the soft and muddy ground. The roots ensure that the trees will not be uprooted or swept away by strong waves
Some mangrove fruits are javelin-shaped so that they can pierce the soft mud to germinate and grow into sapling immediately

Some fruits are buoyant, allowing them to float away and germinate in other coastal areas

Some species have developed ways to secrete excess salt, through the underside of their leaves

Many mangroves show patterns of horizontal zonation, where the structure and dominant species in each zone varies due to environmental conditions

Provide food and habitat to many species of marine fish species. For example the parrot fish graze on the living coral polyps

Ability to absorb wave energy generated in the open seas, thus, protecting land mass from coastal erosion
Tropical cyclones can damage coral reefs and then the coasts become more prone to erosion

Dense network of roots help to build up sediment that can protect coastal areas from erosion by tides, storm waves and tsunamis

Breeding ground and habitat for a range of marine creatures. For example, Barnacles, oysters and sponges anchor on the hard surfaces of the aerial roots.

Development of coastal areas on a large scale is putting pressure on coral reef ecosystems
About 75% of the world’s reefs are threatened
But 95% of Southeast Asia’s coral reefs are threatened  
Since 1980, the world has lost around 3.6 million hectares of mangroves, equivalent to a 20% loss of total mangrove area.  

Pressures on coral reef ecosystems
Over-collection of corals
Overfishing in reefs and surrounding waters.
Depletion of fish disrupts the delicate balance of the ecosystem’s food chain; predators of these fish have less to feed on while their prey id able to increase in numbers.
Fishing methods
Dynamite blasting and the use of cyanide to stun fish.
Coral reef habitat is destroyed.
Selective depletion of fish population disrupts the ecosystem’s food chain. For example, parrotfish eat algae that may inhibit coral growth.
Belize Bonaire, the Netherlands
Recreational use of coast
Tourism activities such as building of facilities, trampling and anchoring of boats.
Waste may be discharged into water and stress corals; boat anchor may damage corals.
Sri Lanka
Coastal development
Reclamation and extension of land areas by dumping rock and sand onto reefs.
Coral reefs are suffocated by sediments and are destroyed.
Expansion of coastal resorts and urban housing increases likelihood of more waste being deposited into the sea.
Coral reefs are suffocated by sediments and are destroyed.
Florida, USA
Climate change
Rapid changes in sea temperatures and sea levels may be faster than the ability of the reefs and their associated life forms to adjust.
Coral bleaching occurs when higher sea temperatures result in the loss of algae; this cause the coral to turn white or be bleached.

Pressures on mangrove ecosystems
Demand for fuel wood and charcoal
Mangroves are cleared for fuel and charcoal, particularly in regions with low technology and low income economies.
Fish breeding grounds are reduced. Also coasts become more open to storm waves.
Need for more farming areas
Thousands of hectares of mangroves are converted into paddy fields and shrimp farms.
Mangroves are cleared and coasts become more vulnerable.
Coastal Development
Land if reclaimed for housing, industry and recreational uses.
Mangroves largely disappear from the environment. Moreover, coastal waters are polluted as a result of human activities.
Caribbean islands
Rising sea level
Rising sea levels, together with extreme storm activity, are likely to occur in future if climate accelerates.
Mangroves will have trouble colonizing areas further inland despite sea level rise as they will be in competition with human activities such as farming and construction of sea defences.
Gulf of Thailand

How can we manage coastal areas in a sustainable manner?

How can coastal areas be managed?

Management of coastal area means controlling the development and change in the coastal zone according to agreed principles and criteria. This involves implementing policies such as restoring sandy beaches at certain places. To enforce this policy, a strategy or a series of strategies are needed

Coastal areas should be managed in a sustainable manner, which means development that should not compromise the quality of the environment for the present and future generations.

To manage coastal areas, we can:
·         Limit damaging activities
·         Protect coastal resources
·         Restrict development in areas prone to natural hazards

1)         Limit damaging activities
·         Many national and local government bodies try to limit these activities
·         This is done through management that aligns the needs and demands of people together with the nature of the coastal environment
·         For example, sand dunes which are deposits of windblown sand from the foreshore zone stabilized by plants, were often trampled on by people visiting the beach in Port Philip
·         Dune vegetation was being destroyed and the sand dunes were left exposed to wind erosion
·         Houses behind the dunes were in danger of being partly buried by the large volume of sand blown by the wind
·         To allow the dunes to recover, authorities fenced off the dunes and built access paths to the beach
·         This decision allowed the coastal environment to recover
·         However, the fences make the beach look less attractive and do not allow visitors and residents access to all parts of the beach

2)         Protect coastal resources
·         Areas close to the coastlines where around 90% of all marine fish are caught are vulnerable to overfishing
·         This occurs especially in the coral reefs areas of Southeast Asia where destructive fishing methods of blasting and poison fishing are used
·         For example, Wakatobi National Park in Indonesia and Goat Island Marine Reserve in New Zealand, zones have been marked off to prevent commercial fishing
·         This is done through local management or establishment of a marine reserve
·         Marine reserves protect marine ecosystems which allows fish and endangered species to breed and thrive
·         The Goat Island Marine Reserve is now a tourist attraction because of its plentiful fish; there are up to 14 times more snappers within the reserve than outside it
·         This demonstrates the positive management impact of protecting coastal resources
·         However, the establishment of marine reserves is often strongly opposed by local fishermen because they see their access to a valuable resource and food, being denied
·         The potential long-term benefits of a marine reserve may not be significant to locals who can no longer in an area that has supported them for a long time

3)         Restrict development in areas prone to natural hazards
·         Tsunamis can be disastrous to natural environment and human activities
·         For example the powerful earthquakes in Tohoku in March 2011 resulted in a tsunami of powerful sea waves that swamped large areas of coastal Japan
·         The tsunami caused the death of 20,000 people, the destruction of coastal towns and failure of nuclear power stations
·         The cost of rebuilding has been conservatively estimated at US$300 billion
·         Despite the occurrence of natural hazards, people are still attracted to the coasts because many of the coasts provide natural resources such as food and building materials
·         Coasts also provide a substantial range of build services such as docks, ports, housing and recreational facilities
·         However, residents and investors of these areas may have to spend more in construction and maintenance and will also need to be prepared for emergencies
·         Many national governments and local authorities have developed management policies to deal with the threat of natural hazards in coastal areas
·         They research on how severe or widespread the problem is, plan for it, then make and enforce laws
·         The law and policies usually involves a combination of the following strategies

Retreat or relocation of built structures away from areas prone to natural hazards
In USA, the Federal Emergency Management Agency (FEMA) steers development away from areas prone to flooding or coastal erosion.
Avoidance, which includes regulating development
Indonesian laws restrict new farms and residences from being established on low-lying coastal areas.

Defence, such as nourishing beaches, building seawalls and replanting coastal vegetation
Beaches in the Netherlands are closely monitored and undergo beach nourishment when long-term erosion is identified.

What are the coastal protection measures?

Measures to protect coasts can be divided into:
Hard Engineering
Soft Engineering
  • Involves the construction of physical structures to defend against the erosive power of waves
  • Also known as the structural approach
  • Involves protecting the coast using natural processes
  • Does not involve the construction of any physical structures
  • Also known as the non-structural approach
  • Seawalls
  • Breakwaters
  • Groynes
  • Gabions
  • Tetrapods
  • Beach nourishment
  • Encouraging the growth of coral reefs
  • Planting vegetation and stabilizing dunes

Hard Engineering Measures

  • Constructed to protect coastlines against waves attack
  • Made of concrete or stone and are built parallel to the coast
  • Absorb the energy of waves before they can erode away loose materials
  • Especially effective in protecting cliffs from erosion
  • Costly to build and maintain as constant repairs have to be made to prevent their collapse
  • Can absorb only some wave energy and reflect incoming waves
  • But do not prevent the powerful backwash of refracted waves from washing away the beach materials at the foot of and beneath the seawalls
  • This erosion by waves eventually undermines the base of the seawalls and leads to their collapse
  • For example, a seawall along the coast of Drakes Island in England collapsed due to erosion occurring at its base

  • Built either parallel to the coast or with one end attached to the coast
  • Help to protect the coast by reducing the force of the high energy oncoming waves
  • When constructed offshore, breakwaters can create a zone of calm water behind them
  • Materials are then deposited and build up in this zone of calm water to form beaches
  • This calm water zone is often used as a sheltered harbour for boats

  • Aesthetically unappealing and are costly to build
  • Protect the coast unevenly
  • Only protect materials deposited in the zone behind the breakwater
  • Those materials in the zones located away from the breakwater are not protected and subjected to wave action and possible erosion
  • For example, breakwaters built in Portland Harbour, England, resulted in erosion and flooding problems, which affected properties, beaches and communication infrastructure

  • Low walls constructed at right angles to the shore to retain sediments that might otherwise be removed due to longshore drift
  • Absorb or reduce the energy of the waves and cause materials to be deposited on the updrift side of the groyne facing the longshore drift
  • Tips of groynes are sometimes angled about 5 to 10 degrees , depending on the direction of the prevailing waves to prevent or reduce the erosion of beach materials on the downdrift side of the groyne
  • Unsightly and expensive to build and maintain
  • No new materials are carried and deposited on the downdrift side which is not protected by the groyne
  • Longshore drift will gradually erode away the unprotected part of the beach
  • For example, large amount of sediments were eroded on the downdrift side of a groyne built along Sandy Hook in New Jersey, USA
  • Wire cages usually filled with crushed rocks

  • Built along a shore or behind a beach to prevent or reduce coastal erosion by weakening wave energy
  • Absorb wave energy better than seawalls because the gaps in between the rocks allow the water to filter through
  • Prove to be successful defences against high energy waves
  • Unsightly
  • Costly as they need regular maintenance
  • Easily corroded by sea water and damaged by excessive trampling or vandalism
  • For example, gabions were installed when the East Coast park in Singapore was first reclaimed but were subsequently removed as they were vandalised
  • Four-pronged concrete structures that help dissipate waves energy
  • Stacked offshore in an interlocking position
  • Allow water to pass around them, dissipating waves energy rather than hit against them
  • No backwash is generated, which reduces the possibility of tetrapods being damaged by waves
  • They can be placed quickly compared to other structures which may take time to build while the coasts are still under attack from waves
  • For example, Crescent City, a town on the coast of northern California, has used tetrapods for many years to defend against coastal erosion and to reduce the impacts of tsunamis, which occurred 31 times between 1933 and 2008
  • Aesthetically unappealing and expensive to build
  • Dangerous to swimmers, surfers and boaters

Soft Engineering Measures
Beach nourishment
  • Slows down the erosion of beaches
  • Involves using sand from external source to replenish of large quantities of sand on a depleted beach
  • Sand may come from another beach or be dredged from the sea floor

  • Can successfully change a coast into a wide, sandy beach that offers protection to the immediate inland area
  • For example, in Sentosa, Singapore, beach materials of fine sand was brought in to replenish Siloso, Palawan and Tanjong beaches and as a result, the beaches became aesthetically pleasing
  • Another example is the beach nourishment restored in the depleted beach at the coast of Cape May Point in New Jersey, USA
  • Trucking or piping in sand can be very expensive and time consuming
  • Beach nourishment projects have developed problems such as endangering wild life
  • For example, coral reefs at Wakiki Beach have been destroyed as sand used for beach nourishment was washed out to the sea and suffocated the corals
  • Re-nourished beaches can also be eroded unless other management strategies are put in place
Planting vegetation
  • Involves the planting of mangroves along the coastal area to help stabilize coastlines
  • Mangrove roots can help to trap sediments and reduce coastal erosion
  • Mangroves are able to absorb wave energy through their dense root system
  • Mangroves take a number of years to be established before they can resist natural elements such as storms and human elements such as trampling or even vandalism
Stabilizing dunes
  • Involves stabilizing sand dunes by planting grasses

  • The roots of grasses anchor the sand and prevent erosion
  • Matting is often put over the dunes and young grasses are then planted into the sand through the matting
  • Over time, the grasses become established and the dunes become more stable, then the matting rots away, adding nutrients to the sand
  • Fences and access paths need to be built to prevent the vegetated dunes from being disturbed by human traffic
  • For example, fences and access path are built at the coast along Triton Place, Western Australia
  • High cost incurred in maintaining the fences and paths
  • Taller fences need to be built as the sand accumulates
Encouraging coral reefs growth
  • Involves the growing of coral reefs near the shore
  • Artificial reefs can be created along the coast by placing environmentally friendly and durable materials such as steel or concrete onto the sea floor
  • Can help weaken wave energy
  • Serve as a breeding ground and nursery for fish
  • For example, in Maldives, a low-lying archipelago in the Indian Ocean has been operating a coral-growing programme and has received international recognition
  • Coral reefs may be destroyed and the waves may move towards the shore at full force and wash away beaches
  • Coral growth may be slow, taking perhaps 20 to 30 years before results appear

Read Users' Comments (3)

3 Response to "Notes on Coastal Studies"

  1. Xinying, on September 21, 2011 at 3:19 PM said:


  2. Rianize Cyanis, on October 7, 2013 at 1:16 PM said:

    THANKS THANKS THANKS!!!!!I would thank you from the bottom of my heart, but for you my heart has no bottom.Serious. LOL, i know it sounds corny but who cares! im so thankful!

  3. Luqman Msangi, on March 23, 2015 at 4:56 AM said:

    thanks for the notes
    really helped me