Seawalls are constructed out of materials such as reinforced concrete and granite. They are constructed in front of the coastal area and serve the function of slowing down direct wave erosion of a beach cliff.
A wave striking a seawall is forced abruptly upward, such that the swash comes down more steeply and with greater force, eroding the sand in front of the seawall. Instead of protecting the beach, bigger waves would now approach closer to shore, accelerating the rates of erosion and removal of the beach. When the water in front of the beach becomes sufficiently deep, the beach would then be completely removed and the waves may undermine the barrier. Seawalls can be found in areas such as the coastal areas of Seletar facing the Straits of Johor. Seawalls over here are built low due to the calm and sheltered waters.Revetments are a form of seawall consisting of large angular boulders that are used to protect the seaward end of the East Coast Reclamation Scheme in various phases. They have also been constructed at the fringe of the reclaimed islands at the southern zones of Singapore. Gaps have been placed in the revetments to facilitate the creation of beaches, especially in the sheltered areas.
Breakwaters are built offshore and parallel to the shore to promote deposition in the protected area behind the barrier and erosion on the downdrift sides. They trap sand moving along the beach and cause erosion further down the beach. Without continuous supply, beaches that are starved of sand would then be eroded away.
Marine erosion has been removing much sand from the 1.3km long Siloso Beach and the worst affected is the middle section of the beach. Four islets, acting like breakwaters have been erected about 100m from the shore to ameliorate the force of the waves before they hit the beach. Breakwaters are also erected in the Pasir Panjang Wharf Complex to protect the coast against squalls and waves reaching 1.2m high during the southwest monsoon season between June and September.Mangroves serve as a natural buffer zone between the sea waves and coastline. The muddy, waterlogged soils are capable of absorbing much of the energy between from strong winds, waves and storms. The authorities such as National Parks Board (NParks) have been stepping up efforts to manage and conserve mangrove areas. NParks designed a set-up of mud-filled bags, rocks, mangrove seedlings and poles to replace lost mangrove seedlings and prevent repeated episodes of erosion at the 1.65 stretch of coastline at Pulau Tekong.
Coral reefs are also effective in protecting coastal areas but are increasingly threatened by activities such as sedimentation brought about by reclamation works and dredging of shipping channels, which are smothering the corals to death. Corals in the deeper waters are the greatest victims as the silt block out much of the sunlight and food.
Coral reefs in Singapore
There are about 54 square km of coral reefs in Singapore, with most of them concentrated in and around Sentosa. Coral reefs are able to buffer the shorelines from waves, currents and storms, absorbing about 90% of the energy produced by wind generated waves.With reference to:
- Hyndman, D. (2006) Natural Hazards and Disasters
- Chong, M. (2001) Aspects of Physical Geography
- http://reefwalk.blogspot.com/2006/02/tribute-to-singapores-coral-reefs-part.html
