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Saturday, 7 July 2012
Seawall
Adapted from : Wikipedia
A seawall (also written as sea wall) is a form of coastal defence constructed where the sea, and associated coastal processes, impact directly upon the landforms of the coast. The purpose of a seawall is to protect areas of human habitation, conservation and leisure activities from the action of tides and waves.[1] As a seawall is a static feature it will conflict with the dynamic nature of the coast and impede the exchange of sediment between land and sea.[2]
The coast is generally a high-energy, dynamic environment with spatial variations occurring over a wide range of temporal scales.[3]The shoreline is part of the coastal interface which is exposed to a wide range of erosional processes arising from fluvial, aoelian and terrestrial sources, meaning that a combination of denudational processes will work against a seawall.[4] Given the natural forces to which seawalls are constantly subjected, maintenance (and eventually replacement) is an ongoing requirement if they are to provide an effective long term solution.
The many types of seawall in use today reflect both the varying physical forces they are designed to withstand, and location specific aspects, such as: local climate, coastal position, wave regime, and value of landform. Seawalls are classified as a hard engineeringshore based structure used to provide protection and to lessen coastal erosion. However, a range of environmental problems and issues may arise from the construction of a seawall, including disrupting sediment movement and transport patterns, which are discussed in more detail below.[5] Combined with a high construction cost, this has led to an increasing use of other soft engineering coastal management options such as beach replenishment.
Seawalls may be constructed from a variety of materials, most commonly: reinforced concrete, boulders, steel, or gabions. Additional seawall construction materials may include: vinyl, wood, aluminium, fibreglass composite, and with large biodegrable sandbags made of jute and coir.[6] In the UK, sea wall also refers to an earthen bank used to create a polder, or a dike.
Advantages and Disadvantages
| Seawall type | Advantage | Disadvantage | Global example |
| Vertical |
|
| Vancouver Seawall |
| Curved |
|
| Torcross UK andSeagrove Bay UK. |
| Mound |
|
| Central Waterfront, Seattle |
( Short video on how a Seawall looks like)
Seawall in Singapore : http://wildshores.blogspot.com/2011/10/construction-at-changi-east-seawalls.html
Soft engineering Methods and Hard engineering Methods
In this Earth, about 60% of it’s population lives along coasts. But, erosion may occur along the coast and causes the land to retreat inland and affect the building along the coast. Thus, there is a need to protect them. Coastal protection measures is divided into two groups, the hard engineering and the soft engineering.
Hard engineering means the building of structures that could prevent erosion, such as Seawalls, Breakwaters, Groynes, and Gabions. In other hand, the soft engineering is a cheaper option than hard engineering and it applies knowledge of natural processes to protect the coast. Examples are Stablising coastal dunes, Planting mangroves, Beach nourishment, and by Encouraging the growth of coral reefs.
Breakwaters
Breakwaters or seawalls are man-made structures built from granite and concrete, lining the coasts. Breakwaters were usually built to protect sandy beaches and reclaimed shores from strong waves and erosion. Such a habitat is rather similar to natural rocky habitats. But artificial environments like breakwaters, with steeply sloping or vertical seawalls, tend to have less biodiversity.
Many of Singapore's shorelines have been heavily modified. One can find breakwaters in places such as the East Coast Park, Changi Beach, West Coast, and the Southern Islands (including Semakau Landfill, St John's Island, and Sentosa Island).
(A video on Breakwater in other countries)
More Info About Breakwaters in Singapore .
Coastal Protection:
BREAKWATERS
Location:
East Coast Park, Siloso Beach
http://www.geographicasia.com/coasts/ecp1.html:
Two new breakwaters have been built at Siloso beach, on the
southwest shore of Sentosa island. They will serve to protect the beach there,
as erosion has been accelerated by the wash from the high-speed ferries plying
between the nearby World Trade Centre and the Riau islands of Indonesia. At
almost a kilometre in length, Siloso beach is the longest of three artificial
beaches built at a cost of $20 million in 1991. The new breakwaters cost more
than $1 million. They are each eighty metres long and are placed about a
hundred metres offshore.
Breakwaters are only needed at Siloso Beach and along the
East Coast Park because elsewhere in
Singapore, longshore drift is negligible.
How:
The breakwaters may be small structures, made of granites
and placed one to three hundred feet offshore in relatively shallow water,
designed to protect a gently sloping beach
When oncoming waves hit these breakwaters, their erosive
power is concentrated on these
structures some distance away from the coast. In this way,
there is an area of slack water behind
the breakwaters, which thus will reduce erosion.
Limitations:
When the breakwaters deflect the incoming waves before they
reach the shore, these
waves that are deflected to other places (exposed areas of
the coast) causing erosion.
Breakwaters are unable to provide complete protection for
the whole coast and therefore
unprotected areas will prone to erosion.
Check this out for the amzaing history about Breakwaters in Singapore ----> http://thelongnwindingroad.wordpress.com/tag/breakwater/
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