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Coastal management
Hard Engineering Methods
• Constructing physical structures
• Also called structural approach
• 4 structures
Seawalls
Seawalls
Sloping / Vertical retaining wall built on and parallel to coast – made of concrete or hard rock to withstand waves breaking on it
BUILDING SEAWALL & ITS EFFECT
Absorbs energy of waves and reflects waves
BUILDING SEAWALL & ITS EFFECT
Powerful backwash of reflected waves increases
erosion at bottom of seawall – may collapse and need
regular repair
Seawalls
Seawalls
Seawalls in Singapore
Sea Wall (page8,Q2d)
• The sea wall is a retaining wall built on and parallel to coast
• It is made of concrete and rocks and can be sloping or vertical
• It absorbs the energy of waves and reflects the waves from the coast to reduce the effects of strong waves. This will cut down erosion
Problems with Sea Walls
• But it has a problem.• It does not reduce the energy of waves. It
only reflects it to the area beneath and in front of the wall. This will cause the beach material at this area to be eroded and removed
• The bottom of the wall is undercut, and will weaken and collapse. The wall will need to be repaired and replaced.
Breakwaters
Breakwaters
Breakwaters
What’s the difference
between the seawall and breakwater
BUILDING BREAKWATER & ITS EFFECTS
Concrete / rock structure built parallel to coast some distance away
BUILDING BREAKWATER & ITS EFFECTS
Concrete / rock structure built with one end attached to the coast
Breakwaters• Break the force of the
waves some distance from the coast
• Reduce erosion along the coast
• Calm waters behind the breakwater caused deposition and formation of beach
• Erosion in areas not protected by the breakwater
A Breakwater in Singapore
Concrete used in Breakwaters
Breakwaters
Breakwaters
• Breakwaters are made of rocks and concrete• The most common type of breakwater is built
parallel to and some distance from the coast• Breakwaters break the force of waves some
distance away from the coast. When waves hit the breakwaters, they will lose their energy and there will be less erosion.
• The strength of the waves behind the breakwater is reduced so deposition takes place and a beach is formed behind the breakwaters.
Problems with Breakwaters
• The problem with breakwaters is erosion will take place on the part of the coast that is not protected by the breakwater.
• (CONCLUSION – Need to give conclusion because this is level marking question) Therefore I conclude that all the methods help to reduce erosion. However, they are not totally effective because all of them have some problems.
Groynes
BUILDING GROYNE & ITS EFFECTS
Perpendicular structure to stop sediment carried
by longshore drift
Sediment deposited on side of groyne facing longshore drift – builds up beach
BUILDING GROYNE & ITS EFFECTS
Erosion and no supply of sediments behind groyne
Coastal Protection
Coastal Protection
Groynes
Waves splashing against a groyne
Too many groynes
Groynes can be any type of structure
Groynes
• Built at right angles to the sea – trap sediments on the side facing the longshore drift – stops the removal of sediments by longshore drift – build up a beach
• Protects existing beaches behind the groyne from erosion
• Protects cliff behind groyne from wave erosion
Problem with Groynes
• Beach on the other side may disappear because there is no new addition of sediments. Also existing sediments removed by erosion
• The solution is to build more groynes along the coast – but this makes it very unattractive
Gabions
What are Gabions
Wire cages filled with crushed rocks and piled up along the shore to weaken the wave and reduce erosion
1: Original bank profile2: Gabion structure3: Berm of cylindrical gabions4: Erosion profile
Gabions
Gabions
Damaged Gabions
Disadvantage – ugly, danger to people stepping on it, easily corroded and damaged, need regular maintenance,
Two protective measures
Gabions
• Gabions are wire cages filled with crushed rocks and piled along the shore
• They help to weaken wave energy and will reduce or prevent erosion
Problems with Gabions
• The problems is they do not last very long because they get rusty very fast. Also, they are easily damaged because people keep stepping on it.
• They have to be maintained regularly as the wires can be a danger for people walking along the beach.
• Furthermore, they look quite ugly
Name the Hard-Engineering Method
Name the Hard-Engineering Method
Name the Hard-Engineering Method
Name the Hard-Engineering Method
Soft Engineering Approach
• Does not involve building physical structures – no need for regular maintenance – so easier and cheaper to carry out
• Also called non-structural approach
• Involves proper planning, management and use of the coast
Coastal Dunes
Coastal Dunes
Stabilising Coastal Dunes
Dunes protect coast from sea but they are easily removed by wind
Stabilising Coastal Dunes
Vegetation planted to hold the sand dunes together
Stabilising Coastal Dunes
Stablising Coastal Dunes
Plant acacia plant or marram grass – hardy, long underground roods, grows well in salty and porous sand
Grass planted to stablise Coastal Dunes
Grass planted to stabiliseCoastal Dunes
Coastal Vegetation (Great Ocean Road, Melbourne)
Planting Vegetation like Mangrove
Roots trap sediments and reduce erosion
Mangrove Coast
Mangrove Forest Close-up
Mangrove trees along the beach
Coral Reefs
Offshore Coral Reefs
Coral reefs weaken wave energy before reaching the coast
Coral Reefs off the Coast
Coral Reefs
Creating Artificial Reefs
Creating Artificial Reefs
Creating Artificial Reefs
Use environmentally friendly and durable materials like steel and concrete on sea floor
Moulds for making artificial reefs
Hard vs Soft Engineering MethodsHard Engineering Methods• Some physical structure has to
be built. Requires money, manpower and technology. (eg seawall, groyne, gabion and breakwater)
• The physical structure does not last very long and needs to be regularly maintained (eg the wire cages or gabions will rust and must be changes regularly)
• Protects only one part of the coast, but it creates new problems elsewhere along the coast (eg breakwaters only protect the coast behind it)
• May cause harm to humans (eg gabion are steel cages that have sharp edges…)
Soft Engineering Methods• Does not involve building any
physical structure. Only involves the proper planning, management and use of the coast as well as encouraging minimal human interference along the coast. So saves a lot of money. (eg stabilising dunes)
• As it involves educating people on how to use the coast, it is more long term
• It is environmentally friendly and beautifies the environment (eg mangrove trees are protected so that their roots will trap the sand)
• Level Marking
• Eg Do you agree that gabions are the only measures used to protect the coast from erosion?
Explain gabions
3 others – hard and/or soft methods
• Assess the effectiveness of hard engineering methods to protect the coast. (8 – Level Marking)
Intro- Hard engineering methods are effective only to a certain extent because it has advantages as well as problems.
Para 1- Eg Describe what seawalls are, how it helps and its problems.
Do the same for 3 other methodsConclusion- Therefore all the methods have
advantages and problems and are not totally effective.
Video on Coastal Erosion• http://www.youtube.com/watch?v=zUh3WeilFN4 • Pay attention to what the video says about Coastal
Erosion.
What factors are identified in the video?
[Deposition]
(1) Strength of waves
[4 Processes of Coastal Erosion]
Factors:
1. Geology – type of rock present
Video on Coastal Management
• http://www.youtube.com/watch?v=HiNGGwRfdMU