http://en.wikipedia.org/wiki/Seawall
http://tinglefactor.typepad.com/.a/6a0120a4f9a8ff970b01348632fedd970c-pi
http://www.georesources.co.uk/seawall.gif
http://www.dnr.state.oh.us/Portals/7/pubs/fs_gifs/stfs16fig1.gif
2011-06-28
URL of used website
Conclusion
In conclusion,
we have learnt different kinds of seawalls and their different purposes. (E.g curved seawalls, vertical seawalls and mound type seawalls)
we have analyzed the effectiveness and the ineffectiveness of different kinds of seawalls. (E.g a strong defence/costly, can be used for sightseeing/eyesore)
we have thought up problems that seawalls face. (E.g extreme events like tsunami, storm and rise in sea level)
we have found some examples of seawalls. (E.g Vancouver Seawall,Canada & Seagrove Bay,UK)
Even though seawalls are useful for our daily lives as they provide denfence and safety, seawalls still have some insurmountable problems such like extreme events and rise in sea level. Thus, we should choose correct seawalls to be built in appropriate places to exert seawalls' optimum efficiency and to make the best result.
2011-06-27
Seawall in Qingdao,China
This picture of seawall was taken in Qingdao, China.
This seawall is a curved seawall. We can see that the seawall is curved built at the upper part. From my observation, it was built in concrete and steel.
This design of seawall enable waves to break to dissipate wave energy and to repel the waves back in to the sea. It can also prevent the wave over-topping the wall and provide additional protection for the toe of the wall.
2011-06-26
Problems that seawalls face - 3 -
Other Limitations
Some further limitations include:
*lack of long term trend data of seawall effects due to a relatively short duration of data records
*modelling limitations
*comparisons of different projects and their effects being invalid or unequal due to different beach types;materials; currents; and environments (Christchurch City Council, 2009).
Problems that seawalls face - 2 -
Extreme Events
Extreme events also pose a problem as it is not easy for people to predict or imagine the strength of hurricane or storm induced waves compared to normal, expected wave patterns.
An extreme event can dissipate hundreds of times more energy than everyday waves, and calculating structures which will stand the force of coastal storms is difficult and, often the outcome can become unaffordable.
For example, Omaha Beach seawall in New Zealand was designed to prevent erosion from everyday waves only, and when a storm in 1976 carved out 10m behind the existing seawall the whole structure was destroyed (GeoResources, 2001).
Problems that seawalls face - 1 -
Sea Level Rise
Sea level rise creates an issue for seawalls worldwide as it raises both the mean normal water level and the height of waves during extreme weather events, which the current seawall heights may be unable to cope with (Allan et al. 1999).
The International Panel on Climate Change (IPCC) (1997) suggested that sea level rise over the next 50 – 100 years will accelerate with a projected increase in global mean sea level of +18 cm by 2050 AD.
This data is reinforced by Hannah (1990) who calculated similar statistics including a rise of between +16-19.3 cm throughout 1900–1988.
This problem could be overcome by further modelling and determining the extension of height and reinforcement of current seawalls which needs to occur for safety to be ensured in both situations.
Effectiveness and Ineffectiveness in overall
Effectiveness:
- Long term solution in comparison to soft beach nourishment.
-Effectively minimizes loss of life in extreme events and damage to property caused by erosion.
-Can exist longer in high energy environments in comparison to ‘soft’ engineering methods.
-Can be used for recreation and sightseeing.
-Forms a hard and strong coastal defence.
Ineffectiveness:
-Very expensive to construct.
-Can cause beaches to dissipate rendering them useless for beach goers.
-Scars the very landscape that they are trying to save and provides an ‘eyesore.’
-Reflected energy of waves leading to scour at base.
-Can disrupt natural shoreline processes and destroy shoreline habitats such as wetlands and
intertidal beaches.
-Altered sediment transport processes can disrupt sand movement that can lead to increased erosion down drift from the structure.
Effectiveness and Ineffectiveness in three kinds of seawalls
Vertical seawalls
Effectiveness:
-The first implemented, most easily designed and constructed type of seawall.
-Vertical sea walls deflect wave energy away from the coast.
-Loose rubble can absorb wave energy.
Ineffectiveness:
-These are partial to a lot of expensive damage in a short period of time.
-Vertical design can be undercut by high-wave energy environments over a long period of time.
Curved seawalls
Effectiveness:
-Concave structure introduces a dissipative element.
-The curve can prevent waves from overtopping the wall and provides extra protection for the toe of the wall
-Curved seawalls aim to re-direct most of the incident energy, resulting in low reflected waves and much reduced turbulence.
Ineffectiveness:
-More complex engineering and design process.
-The deflected waves can scour material at the base of the wall causing them to become undermined.
Mound-type structures
Effectiveness:
-Current designs use porous designs of rock, concrete armour.
-Slope and loose material ensure maximum dissipation of wave energy.
-Lower cost option.
Ineffectiveness:
-Less durable.
-Shorter life expectancy.
-Cannot withstand or protect from high-energy conditions effectively.
Different Kinds of Seawalls
Vertical seawalls are built in particularly exposed situations. These reflect wave energy and, under storm conditions, standing waves (clapotis) will develop. In some cases piles are placed in front of the wall to lessen wave energy slightly.
This kind of seawalls is rarely used now, another kind of seawalls called Curved seawalls are used instead.
Eg.Vancouver Seawall
Curved seawalls are designed to enable waves to break to dissipate wave energy and to repel waves back to the sea. The curve can also prevent the wave overtopping the wall and provides additional protection for the toe of the wall.
Eg.Torcross UK and Seagrove Bay UK.
Mound-type structures (revertments, riprap) are used in less demanding settings where lower energy erosional processes operate. The least exposed sites involve the lowest-cost bulkheads and revetments of sand bags or geotextiles. These serve to armour the shore and minimise erosion and may be either watertight or porous, which allows water to filter through after the wave energy has been dissipated.
Eg.Central Waterfront, Seattle
Description of Seawalls (Research from internet)
Seawalls
A seawall 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.
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.
Given the natural forces that seawalls are constantly subjected to, 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 reflects 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 engineering shore based structure used to provide protection and to lessen coastal erosion.
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. In the UK, sea wall also refers to an earthen bank used to create a polder, or a dike.
Adapt and edit from Wikipedia
Description of Seawalls (point-form from textbook)
Seawalls
*To protect coasts from erosion
*Built in front of a cliff or along the coast
*usually made of concrete
*it absorb the energy of the waves
*and therefore protects the coast against strong waves (especially during storms)
Picture: Seawalls in Labrador Park, Picture website
Brief Intro
This is a brief introduction to our blog.
During this June-Holiday, our group of three, Tsai Meng-Hsiu, Liu Jingyan, and me, Zhang Xueyang, did some research on seawall which is a kind of coastal protection.
Due to the fact that we were all overseas, we did not go to Labrador Park to check the seawalls in Singapore. However, one of our group members, Tsai MengHsiu, took some pictures of seawalls in Qingdao, China.
With the help of these pictures and internet research, we will show you what seawalls are, and both the effectiveness and the ineffectiveness of seawalls.
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