Seawall
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A seawall (or sea wall) is a form of
Seawall designs factor in local climate, coastal position, wave regime (determined by
Seawalls are constructed from various materials, most commonly
Types
A seawall works by reflecting incident wave energy back into the sea, thus reducing the energy available to cause erosion.
Different designs of man-made
The appropriate seawall design relies on location-specific aspects, including surrounding erosion processes.[12] There are three main types of seawalls: vertical, curved, stepped, and mounds (see table below).
Type | Illustration | Advantages | Disadvantages | Example |
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Vertical | Vertical seawalls are built in particularly exposed situations. These reflect wave energy. Under storm conditions a non-breaking In some cases, piles are placed in front of the wall to lessen wave energy slightly. | |||
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Curved | Curved or stepped 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. | |||
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Mound | Mound type seawalls, using 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.[16]
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Natural barriers
A report published by the
Trade-offs
A cost-benefit approach is an effective way to determine whether a seawall is appropriate and whether the benefits are worth the expense. Besides controlling erosion, consideration must be given to the effects of hardening a shoreline on natural
Advantages | Disadvantages |
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Generally, seawalls can be a successful way to control coastal erosion, but only if they are constructed well and out of materials that can withstand the force of ongoing wave energy. Some understanding is needed of the coastal processes and
Issues
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.[21] The most recent analyses of long, good-quality tide gauge records (corrected for GIA and when possible for other vertical land motions by the Global Positioning System, GPS) indicate a mean rate of sea level rise of 1.6–1.8 mm/yr over the twentieth century.[22] The Intergovernmental Panel on Climate Change (IPCC) (1997)[23] 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)[24] who calculated similar statistics including a rise of between +16-19.3 cm throughout 1900–1988. Superstorm Sandy of 2012 is an example of the devastating effects rising sea levels can cause when mixed with a perfect storm. Superstorm Sandy sent a storm surge of 4–5 m onto New Jersey's and New York's barrier island and urban shorelines, estimated at $70 billion in damage.[25] This problem could be overcome by further modeling and determining the extension of height and reinforcement of current seawalls which needs to occur for safety to be ensured in both situations. Sea level rise also will cause a higher risk of flooding and taller tsunamis.[citation needed]
Hydrostatic water pressure
Seawalls, like all
Extreme events
Extreme events also pose a problem as it is not easy for people to predict or imagine the strength of
Ecosystem impacts
The addition of seawalls near marine ecosystems can lead to increased shadowing effects in the waters surrounding the seawall. Shadowing reduces the light and visibility within the water, which may disrupt the distribution as well as foraging capabilities of certain species.
Other issues
Some further issues include a lack of long-term trend data of seawall effects due to a relatively short duration of data records; modeling limitations and comparisons of different projects and their effects being invalid or unequal due to different beach types; materials; currents; and environments.[28] Lack of maintenance is also a major issue with seawalls. In 2013, more than 5,000 feet (1,500 m) of seawall was found to be crumbling in Punta Gorda, Florida. Residents of the area pay hundreds of dollars each year for a seawall repair program. The problem is that most of the seawalls are over a half-century old and are being destroyed by only heavy downpours. If not kept in check, seawalls lose effectiveness and become expensive to repair.[29]
History and examples
Seawall construction has existed since ancient times. In the first century BCE, Romans built a seawall or breakwater at Caesarea Maritima creating an artificial harbor (Sebastos Harbor). The construction used Pozzolana concrete which hardens in contact with seawater. Barges were constructed and filled with the concrete. They were floated into position and sunk. The resulting harbor/breakwater/seawall is still in existence today – more than 2000 years later.[30]
The oldest known coastal defense is believed to be a 100-meter row of boulders in the
More recently, seawalls were constructed in 1623 in Canvey Island, UK, when great floods of the Thames estuary occurred, prompting the construction of protection for further events in this flood-prone area.[32] Since then, seawall design has become more complex and intricate in response to an improvement in materials, technology, and an understanding of how coastal processes operate. This section will outline some key case studies of seawalls in chronological order and describe how they have performed in response to tsunamis or ongoing natural processes and how effective they were in these situations. Analyzing the successes and shortcomings of seawalls during severe natural events allows their weaknesses to be exposed, and areas become visible for future improvement.[citation needed]
Canada
The Vancouver Seawall is a stone seawall constructed around the perimeter of Stanley Park in Vancouver, British Columbia. The seawall was constructed initially as waves created by ships passing through the First Narrows eroding the area between Prospect Point and Brockton Point. Construction of the seawall began in 1917, and since then this pathway has become one of the most used features of the park by both locals and tourists and now extends 22 km in total.[33] The construction of the seawall also provided employment for relief workers during the Great Depression and seamen from HMCS Discovery on Deadman's Island who were facing punishment detail in the 1950s (Steele, 1985).[34]
Overall, the Vancouver Seawall is a prime example of how seawalls can simultaneously provide shoreline protection and a source of recreation which enhances human enjoyment of the coastal environment. It also illustrates that although shoreline erosion is a natural process, human activities, interactions with the coast, and poorly planned shoreline development projects can accelerate natural erosion rates.[citation needed]
India
On December 26, 2004, towering waves of the
The barrier was initially completed in 1735 and over the years, the French continued to fortify the wall, piling huge boulders along its 1.25 mi (2 km) coastline to stop erosion from the waves pounding the harbor. At its highest, the barrier running along the water's edge reaches about 27 ft (8.2 m) above sea level. The boulders, some weighing up to a ton, are weathered black and brown. The seawall is inspected every year and whenever gaps appear or the stones sink into the sand, the government adds more boulders to keep it strong.[36]
The Union Territory of Pondicherry recorded around 600 deaths from the huge tsunami waves that struck India's coast after the mammoth underwater earthquake (which measured 9.0 on the moment magnitude scale) off Indonesia, but most of those killed were fishermen who lived in villages beyond the artificial barrier which reinforces the effectiveness of seawalls.[citation needed]
Japan
At least 43 percent of Japan's 29,751 km (18,486 mi)
The risks of dependence on seawalls were most evident in
The failure of the world's largest seawall, which cost $1.5 billion to construct, shows that building stronger seawalls to protect larger areas would have been even less cost-effective. In the case of the ongoing crisis at the nuclear power plants, higher and stronger seawalls should have been built if power plants were to be built at that site. Fundamentally, the devastation in coastal areas and a final death toll predicted to exceed 10,000 could push Japan to redesign its seawalls or consider more effective alternative methods of coastal protection for extreme events. Such hardened coastlines can also provide a false sense of security to property owners and local residents as evident in this situation.[39]
Seawalls along the Japanese coast have also been criticized for cutting settlements off from the sea, making beaches unusable, presenting an eyesore, disturbing wildlife, and being unnecessary.[40]
United States
After 2012's Hurricane Sandy, New York City Mayor Bill de Blasio invested $3,000,000,000 in a hurricane restoration fund, with part of the money dedicated to building new seawalls and protection from future hurricanes.[41] A New York Harbor Storm-Surge Barrier has been proposed, but not voted on or funded by Congress or the State of New York.[citation needed]
In Florida, tiger dams are used to protect homes near the coast.[42][43]
See also
General:
- Coastal management – Preventing flooding and erosion of shorelines
- Hard engineering – Construction of hydraulic structures to reduce coastal erosion
Related types of walls:
- Accropode – Concrete breakwater element
- Breakwater (structure) – Coastal defense structure
- Dike (construction)– Ridge or wall to hold back water
- Levee – Ridge or wall to hold back water
- Retaining wall – Artificial wall used for supporting soil between two different elevations
Specific walls:
- Alaskan Way Seawall – Seawall in Seattle, Washington
- Galveston Seawall – structure in Galveston, Galveston County, Texas
- Georgetown Seawall– 280-mile wall in Guyana
- Gold Coast Seawall
- Saemangeum Seawall – World's longest man-made dyke
- Sea Bright–Monmouth Beach Seawall – Seawall in New Jersey
- The Embarcadero (San Francisco)– Waterfront and roadway along San Francisco Bay
- Walls of Constantinople#Sea Walls – City walls of Constantinople (modern Istanbul, Turkey) (Constantinople seawalls)
References
- ^ Kamphuis, W J. (2010) Introduction to Coastal Engineering and Management. World Scientific Publishing Co Ltd. Singapore.
- S2CID 153826622
- ^ Kraus, N & McDougal. (1996) The Effects of Seawalls on the Beach: Part I: An Updated Literature Review in Journal of Coastal Research. Vol. 12, No. 3.
- ^ Clarke, J R. 1994. Integrated Management of Coastal Zones. Fao Corporate Document Repository, USA.
- ^ Hsiung AR, Tan WT, Loke LHL, Firth LB and others (2020) Little evidence that lowering the pH of concrete supports greater biodiversity on tropical and temperate seawalls. Mar Ecol Prog Ser 656:193-205
- ^ Kajendra, R. (2011)
- ^ Masselink, G and Hughes, M J. (2003) Introduction to Coastal Processes and Geomorphology. Oxford University Press. New York. Ch 11.
- ^ NOAA. (2007) Shoreline Management: Alternatives to Hardening the Shore. Retrieved online 15 April 2011 from: http://coastalmanagement.noaa.gov/shoreline.html
- S2CID 209492205.
- ^ "India builds tsunami barrier". News 24. January 14, 2005. Retrieved March 29, 2011.
- ^ "Design of a tsunami barrier to The North of Penang Island". Universiti Teknologi Malaysia Institutional Repository. 25 November 2010. Archived from the original on 12 November 2017. Retrieved March 29, 2011.
- ^ a b GeoResources. (2001) Coastal management. Retrieved online 18 April 2011 from: "GeoResources - Geography website". Archived from the original on 2012-08-01. Retrieved 2011-04-30.
- ISBN 0-12-161856-0.
- ISBN 0-8493-2891-8. Archived from the original(PDF) on 2007-07-22.
- ISBN 0-8493-8425-7.
... the reflected wave energy interacted with the incoming waves to produce standing waves known as clapotis, which promote erosion at the toe of the wall.
- S2CID 154733601.
- ^ [1] Archived 2011-07-16 at the Wayback Machine Satellite imagery and modelling show how forests cushion the impact of tsunamis
- ^ "Tsunami Barriers". Science NetLinks. Retrieved March 30, 2011.
- ^ Short, A. (1999) Handbook of Beach and Shoreface Morphodynamics. John Wiley and Sons Ltd. Ch 7.
- ^ MEDUS. (2011) Marine Engineering Division of University of Salerno. Retrieved online 10 April 2011 from: http://www.diciv.unisa.it/docenti/dentale/medus_.php Archived 2011-07-22 at the Wayback Machine (MEDUS)
- ^ Allan, J C, Kirk, R M, Hemmingsen, M & Hart, D. (1999) Coastal Processes in Southern Pegasus Bay: A Review – A Report to Woodward-Clyde New Zealand Ltd. and the Christchurch City Council. Land and Water Studies Ltd. Christchurch.
- ^ Intergovernmental Panel on Climate Change. 2007. IPCC Fourth Assessment Report: Climate Change 2007. Retrieved Online 15 April 2011 from: www.ipcc.ch/publications_and_data/publications_and_data_reports
- ^ Hannah, J. (1990) "The Analysis of Mean Sea Level Data from New Zealand for the Period 1899–1988" in The Journal of Geophysical Research, 95, No. 88.
- ^ Link test, "Sea-Level Rise Implications for Coastal Protection from Southern Mediterranean to the USA Atlantic Coast." EGU General Assembly Conference Abstracts. Vol. 15. 2013.
- S2CID 218959238.
- S2CID 220518548.
- ^ Christchurch City Council. (2009) Study of the Effects of Sea Level Rise for Christchurch. Tonkin + Taylor, Christchurch.
- ^ [1] Archived 2014-02-26 at the Wayback Machine, "More failing Seawalls in Punta Gorda Isles – NBC-2.com WBBH News for Fort Myers, Cape Coral & Naples, Florida." NBC-2.com. Nbc, 21 Oct. 2013. Web. 21 Feb. 2014.
- ^ Does anyone have a reference for this? The closest thing I could find is: "Ancient Roman concrete mixture seawall". Popular Mechanics.
- ISSN 0190-8286. Retrieved 2023-05-03.
- ^ Council of Europe. (1999) European code of conduct for coastal zones, Council of Europe, Strasbourg.
- ^ Belyea, R (21 January 1992). The Stanley Park Technical Report. Vancouver: Stanley Park Task Force, prepared by Belyea, Sorensen & Associates. P 15.
- ^ Steele, Richard M. (1985). The Stanley Park Explorer. Vancouver: Whitecap Books. pp. 23–24.
- ^ writer, CHRIS TOMLINSON, Associated Press. "Historic town in eastern India saved from destruction by sea wall built by French". New Bedford Standard-Times. Retrieved 2023-10-04.
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: CS1 maint: multiple names: authors list (link) - ISBN 0-7277-3042-8..
- ^ "The World Factbook". CIA.gov. 13 February 2024.
- ^ Norimitsu Onishi (March 13, 2011). "Japan's Seawalls Didn't Provide Security from tsunami". The Star. Archived from the original on October 24, 2012.
- ^ a b Msubi (2011) Seawalls are no Match for Japan Tsunami. Retrieved online 8 April 2011 from: "great-east-japan-earthquake-of-2011/sea-walls-were-no-match-for-this-tsunami". nippon-sekai.com (Archived copy ed.). Archived from the original on 2012-03-08. Retrieved 2011-04-30.
- ^ Craft, Lucy (11 March 2014). "In Tsunami's Wake, Fierce Debate Over Japan's 'Great Wall'". NPR.
- ^ "Why big hurricanes weaken before they hit America's coast". The Economist. 7 January 2017. Retrieved 2017-01-20.
- ^ Edlund, Ashley (23 November 2022). "'An enormous effort:': Daytona Beach Shores residents seek permanent fix to damaged seawall". Yahoo. Retrieved 25 November 2022.
- ^ Barreto, Jessica (23 November 2022). "'It's been a losing battle' : Seawall collapses in South Ponte Vedra as coast reels from storms". Yahoo. Retrieved 25 November 2022.
External links
- Channel Coastal Observatory – Seawalls Archived 2018-12-14 at the Wayback Machine
- Seawalls and defences on the Isle of Wight Archived 2021-10-09 at the Wayback Machine
- MEDUS (Maritime Engineering Division University Salerno) Archived 2011-07-22 at the Wayback Machine
- "Japan may rethink seawalls after tsunami", New York Times, March 14, 2011
- General overview of residential and small commercial steel seawall construction