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