coasts 3

Question 1

what are the coastal protection measures?

Answer 1

SOFT

• —> Beach nourishment
• —> Planting vegetations & stablising dunes
• —> Encouraging coral growth

HARD

• —> Seawalls
• —> Gabions
• —> Breakwaters
• —> Groynes

Question 2

Beach nourishment

Answer 2

WHAT

• —> involves the sand from an external source to replenish the sand on a depleted beach
• —> sand from another beach

WHERE

• —> Sentosa, Singapore
• —> beach material brought in to replenish Siloso
• —> aesthetically pleasing

+

• —> change coasts to wide sandy beach
• —> offers immediate protection

-

• —> trucking/piping is expensive & time-consuming
• —> destroy corals
• —> corals at Waikiki Beach suffocated by sand washed out
• —> eroded again

Question 3

Planting vegetation & stabilizing dunes

Answer 3

• —> planting mangroves
• —> planting grasses on sand dunes
• —> fences built in vegetated dunes to prevent human trampling

+

• —> mangroves stabilize coastlines
• —> mangroves absorb wave energy through roots
• —> grasses stabilize sand dunes
• —> roots anchor sand & prevent erosion

-

• —> vegetation take a number of years to be established
• —> costly to maintain fences

Question 4

Encouraging coral reef growth

Answer 4

WHAT

• —> Artificial reefs can be created by placing lasting materials like steel/concrete onto seafloor
• —> Corals colonize these materials
• —> corals help weaken wave energy
• —> breeding ground for animals

WHERE

• —> The Maldives, Indian Ocean
• —> place steel rods
• —> structure charged with low-voltage solar-generated electricity to speed up coral growth
• —> Island now sustains a large variety of corals

-

• —> dangers of siltation
• —> slow growth of corals, 20-30 years

Question 5

Seawalls

Answer 5

WHAT

• —> made of concrete/stone
• —> built parallel to coasts

+
—-> protect coastlines against wave attack by absorbing wave energy

-

• —> costly to build and maintain
• —> constant repairs
• —> absorb only some wave energy and reflect incoming waves
• —> achieve initial success
• —> powerful backwash washes away beach materials beneath seawall
• —> erosion of waves undermines the base
• —> seawall collapses

WHERE

• —> Drakes islands in England
• —> seawall collapses due to erosion occurring at its base

Question 6

Gabions

Answer 6

WHAT

• —> wire cages filled with crushed rocks
• —> built along the shore/behind a beach

+

• —> weakens wave energy
• —> absorb wave energy better than seawalls
• —> gaps btw rocks allow water to filter through
• —> successful defences against high energy waves

-

• —> unsightly
• —> costly as need to maintain regularly
• —> easily corroded by seawater
• —> damaged by excessive trampling/vandalism

WHERE

• —> East Coast Park, Singapore
• —> gabions were removed as they were vandalised

Question 7

Breakwaters

Answer 7

WHAT
—-> built either parallel to coasts/ with one end attached to the coast

+

• —> help to break the force of incoming waves
• —> when constructed offshore, breakwaters create a zone of calm water
• —> materials deposited and build up in this zone of calm water to form beaches

-

• —> aesthetically unappealing
• —> costly to build
• —> protect the coasts unevenly
• —> materials deposited in the zone behind the breakwater are protected
• —> those in the zones far away from breakwater are subjected to wave action and erosion

WHERE

• —> Portland Harbour England
• —> resulted in erosion and flooding problems
• —> affected properties, beaches and communication infrastructure

Question 8

Groynes

Answer 8

WHAT
—-> low walls constructed at right angles to the shore

+

• —> retain sentiments that might otherwise be removed due to longshore drift
• —> These structures absorb/reduce the energy of waves
• —> cause materials to deposit on the updrift side of the groyne facing the longshore drift
• —> help sustain and extend beach areas

-

• —> expensive to built/maintain
• —> unsightly
• —> no new materials deposited at the downdrift side which is not protected by the groyne
• —> longshore drift will erode away unprotected part of beach
• —> Hence, tips of groynes are sometimes angled at about 10 degrees

WHERE

• —> New Jersey, USA
• —> sentiments eroded on the downdrift side of groyne
• —> groyne eventually demolished

Question 9

Tetrapods

Answer 9

WHAT

• —> 4 pronged concrete structures
• —> stacked offshore in an interlocking position

+

• —> dissipate wave energy
• —> allow water to pass around them rather than hit against them
• —> no powerful backwash generated, reducing the possibility of tetrapods being damaged by waves
• —> offers immediate protection

-

• —> aesthetically unappealing
• —> expensive to build
• —> dangerous to swimmers, surfers and boats

WHERE

• —> Cresent City, California
• —> defend against coastal erosions and reduce the impact of tsunamis, which occurred 31 times btw 1933 and 2008