coasts 3 Flashcards
1
Q
what are the coastal protection measures?
A
SOFT
- —> Beach nourishment
- —> Planting vegetations & stablising dunes
- —> Encouraging coral growth
HARD
- —> Seawalls
- —> Gabions
- —> Breakwaters
- —> Groynes
2
Q
Beach nourishment
A
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
3
Q
Planting vegetation & stabilizing dunes
A
- —> 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
4
Q
Encouraging coral reef growth
A
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
5
Q
Seawalls
A
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
6
Q
Gabions
A
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
7
Q
Breakwaters
A
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
8
Q
Groynes
A
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
9
Q
Tetrapods
A
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
