This document discusses coastal erosion, its causes, impacts, and various mitigation approaches. It identifies key physical parameters that contribute to coastal erosion like waves, tides, and vegetation. Approaches to mitigate erosion include hard engineering methods like seawalls, breakwaters, and groynes, as well as soft engineering methods like beach nourishment, relocating structures, planting mangroves, and growing coral reefs. Hard structures provide direct protection but can have negative environmental impacts. Soft methods aim to work with natural coastal processes but have challenges with feasibility and cost. Overall management requires consideration of engineering and environmental factors.
2. Introduction
โข Shorelines are dynamic landforms. With every
passing wave, and each changing tide, the
profile of the shoreline changes.
โข Large scale development of coastal areas will
bring about problems if development is not
properly planned and managed.
โข Proper coastal management and protection are
needed to preserve quality of coastal
environment.
5. IMPACTS OF COASTAL
EROSION
โข danger to life in the case of sudden onset landslide
events
โข destruction of buildings
โข destruction of infrastructure -water, sewage and
gas pipes,roads
โข loss of land, resulting in coastal cliffs or shorelines
retreating closer to other buildings
โข land instability at neighbouring slopes and
properties
โข loss of beach amenity due to cliff collapse or sea
wall construction
7. Types of Approach
โข Hard engineering
- Refers to the construction of physical
structures to defend against the
erosive power of waves.
- Also known as the structural approach.
8. Types of Approach
โข Soft Engineering
- Focuses on planning and management so
that both coastal areas and properties
will not be damaged by erosion.
- Also aims to change individual behaviour
or attitude towards coastal protection
by encouraging minimal human
interference and allowing nature to take
its course.
- Also known as the non-structural
approach.
9. Hard Engineering Measures
โข Seawalls (+)
- Seawalls absorb the energy of waves
before they can erode away loose
materials.
- most common form of shore protection
structure
- Seawalls can be made of concrete, rocks
or wood.
- They are effective in protecting cliffs
from erosion.
10. Hard Engineering Measures
โข Seawalls (-)
- They can only absorb the energy of
oncoming waves. They do not prevent the
powerful backwash of refracted waves
from washing away the beach materials
beneath the walls.
- Base of seawalls will be undermined
(weakened) and leads to their collapse
11. Hard Engineering Measures
- On a high-energy site-stone riprap
should be placed in front of the wall
to protect the toe of the wall from
erosion.
- Seawalls are costly to build and
maintain as constant repairs have to
be made to prevent their collapse
12.
13.
14. Hard Engineering Measures
โข Breakwaters (+)
โข Breakwaters
- Protect coast and harbour by reducing
force of high energy waves before they
reach the shore.
- They can either be built with one end
attached to the coast or built away from
coast.
15. Hard Engineering Measures
โข Breakwaters (-)
- Materials deposited in the zones behind
the breakwater are protected while
those in the zones located away from the
breakwater are not.
- Zones will not receive any new supply and
thus be eroded away.
19. Hard Engineering Measures
โข Groynes
- Built at right angles to the shore to
prevent longshore drift.
- These structures absorb or reduce the
energy of the waves and cause materials
to be deposited on the side of the groyne
facing the longshore drift.
20.
21. Hard Engineering Measures
โข Groynes (-)
- Erosion can still take place on the part of
the coast that is not protected by
groynes.
22.
23. Hard Engineering Measures
โข Gabions
- Gabions are wire cages usually filled with
crushed rocks, and then piled up along
the shore to prevent or reduce coastal
erosion by weakening wave energy.
24. Hard Engineering Measures
โข Gabions (-)
- This method offers only short-term
protection (about five to ten years).
- Wire cages need regular maintenance as
they are easily corroded by sea water.
- Affected by excessive trampling and
vandalism.
27. Hard Engineering Measures
โข Revetment
- The most effective type of shore
protection
- Beach material builds up behind them
- Need replacing more frequently than
other structures
28.
29.
30. Hard Engineering Measures
โข Bulkheads
- Used when deep water must be
maintained up to the shoreline for
boating or shipping
- Constructed-either steel sheet piles or
treated timbers
- These types of structures have very
little resistance to wave action
31.
32.
33. Soft Engineering Measures
โข Beach nourishment
- Refers to constant replenishment of
large quantities of sand to the beach
system.
- Beach is therefore extended seawards,
leading to improvement of both beach
quality and storm protection.
34.
35. Soft Engineering Measures
โข Beach nourishment (-)
- Very expensive and impractical to
constantly transport large quantities of
sand to fill up beach.
- Imported sand that can be continuously
eroded and transported away could have
serious consequences on wildlife living
within coastal environment.
36. Soft Engineering Measures
โข Beach nourishment (-)
- E.g. Coral reefs at Waikiki Beach of
Hawaii are destroyed as imported sand
gets washed out to sea and covers the
corals.
- Corals are deprived of sunlight they need
to survive
37. Soft Engineering Measures
โข Beach nourishment (-)
- E.g. Singapore โ Large scale land
reclamation along coast has led to muddy
and polluted water and has destroyed
coral reefs.
38. Soft Engineering Measures
โข Relocation of Property
- Coastal planners protect man-made
structures (e.g. buildings) by relocating
them and letting nature reclaim the
beach in its own time.
- No building of new properties of
structures would be allowed in coastal
areas that are vulnerable to coastal
erosion.
39. Soft Engineering Measures
โข Relocation of Property
- E.g. England โ โGreen Lineโ policy which
discourages any building beyond a given
line. Any properties built beyond the
given line will not be defended or
protected should they be threatened by
coastal erosion.
40. Soft Engineering Measures
โข Relocation of Property (-)
- Opposition by people with considerable
investments in coastal areas.
- This approach will be important in future
coastal management due to rising sea
level as a result of global warming.
41. Soft Engineering Measures
โข Planting of Mangroves
- Mangroves have long and curved roots
that prop up from soil. It traps
sediments and reduce coastal erosion.
- Mangoves can secure and trap enough
sediments to form small islands โ extend
coastal land seawards.
42.
43. Soft Engineering Measures
โข Planting of Mangroves (-)
- Not all coastal regions can support
mangroves, especially in coastal regions
with destructive waves.
- As sediments build up along coast after
planting mangroves, depth of coast may
become shallower and thus affect port
activities โ (E.g. Pose a problem for
countries like Singapore that depends
heavily on maritime trade.)
44. Soft Engineering Measures
โข Growth of coral reefs
- Coral reefs weaken wave energy.
- Artificial reefs can be created along coast
by placing environmentally friendly and
durable materials such as steel or
concrete on sea floor.
47. REFERENCES
โข by Jim DeStefano & John Roberge, 2004 August
STRUCTURE magazine.
โข Concrete Shore Protection, Portland Cement Association, 33
West Grand Avenue, Chicago, Illinois,1955.
โขDesigning for Bank Erosion Control with Vegetation, Knuston,
P. L., Reprint 78-2, U. S. Army Coastal Engineering Research
Center, February 1978, (NTIS #AO51 571).
โขDesigning Retaining Walls, Bulkheads and Seawalls of
Treated Timber, American Wood Preservers Institute
