Seawall
[3] Combined with a high construction cost, this has led to increasing use of other soft engineering coastal management options such as beach replenishment.
Other possible construction materials include vinyl, wood, aluminum, fiberglass composite, and biodegradable sandbags made of jute and coir.
A report published by the United Nations Environment Programme (UNEP) suggests that the tsunami of 26 December 2004 caused less damage in the areas where natural barriers were present, such as mangroves, coral reefs or coastal vegetation.
A Japanese study of this tsunami in Sri Lanka used satellite imagery modelling to establish the parameters of coastal resistance as a function of different types of trees.
[citation needed] 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.
Seawalls can be very helpful; they can offer a more long-term solution than soft engineering options, additionally providing recreation opportunities and protection from extreme events as well as everyday erosion.
[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.
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.
An extreme event can dissipate hundreds of times more energy than everyday waves, and calculating structures that will stand the force of coastal storms is difficult and, often the outcome can become unaffordable.
Tel Hreiz was discovered in 1960 by divers searching for shipwrecks, but the row of boulders was not found until storms cleared a sand cover in 2012.
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.
[36] 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).
[citation needed] On December 26, 2004, towering waves of the 2004 Indian Ocean earthquake tsunami crashed against India's south-eastern coastline killing thousands.
This 300-year-old seawall effectively kept Pondicherry's historic center dry even though tsunami waves drove water 24 ft (7.3 m) above the normal high-tide mark.
[38] 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.
[39] 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] At least 43 percent of Japan's 29,751 km (18,486 mi)[40] coastline is lined with concrete seawalls or other structures designed to protect the country against high waves, typhoons, or even tsunamis.
Arguably, the additional defense provided by the seawalls presented an extra margin of time for citizens to evacuate and also stopped some of the full force of energy which would have caused the wave to climb higher in the backs of coastal valleys.
[42] 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.
