3)
On December 26, 2004, towering waves of the 2004 Indian Ocean earthquake tsunami crashed against India's south-eastern coastline killing thousands. However, the former French colonial enclave of Pondicherry escaped unscathed. This was primarily due to French engineers who had constructed (and maintained) a massive stone seawall during the time when the city was a French colony. This 300-year-old seawall effectively kept Pondicherry's historic centre dry even though tsunami waves drove water 24 feet above the normal high-tide mark.

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 mile (2 km) coastline to stop erosion from the waves pounding the harbour. At its highest, the barrier running along the water's edge reaches about 27 feet above sea level. The boulders, some weighing up to a ton, are weathered black and brown. The sea wall is inspected every year and whenever gaps appear or the stones sink into the sand, the government adds more boulders to keep it strong (Allsop, 2002).[24]

The Union Territory of Pondicherry recorded some 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.

Example of advantage of sand nourishment at Gold Coast 
   In May 2009 a significant east coast low storm hit the Gold Coast region. The maximum wind gust recorded was 117 km/h from the south east on 20 May 2009. The minimum pressure reading was 1008.3 hecto Pascal on 21 May 2009. Figures 1 and 2 demonstrate the benefits of sand nourishment at Main Beach and Narrowneck in maintaining a healthy beach during severe storms. Previous beach nourishment campaigns assisted in minimising damage to shoreward properties and protected ecological communities on the dunes. 

Disadvantages: 

 

The coral reefs around the main islands of the Seychelles that were almost completely destroyed by consistently high sea temperatures in during the El Niño of 1998, are showing slow but definite signs of new growth. The El Niño of 1998 has caused up to 95% of corals to bleach and die. In some areas, seaweed and algae overgrowth is also threatening to overtake the reefs entirely.

 

However now, half of the sites that were surveyed are now recovering very well, and by 2014 had similar coral cover to pre-bleaching levels (based on surveys in 1994). Sadly, the other half of the monitoring sites are not showing much sign of recovery at all, with continuing dominance of macroalgae and very little coral.

 

Seychellois Sylvanna Antha who is in charge of marine research and surveillance at the islands’ Marine Parks Authority has also been closely monitoring the corals and is of the same view as the international experts that indeed there is recovery of the Seychelles corals. “All the variety of corals are recovering but what we have observed is that some species grows faster than others,” Antha told SNA. “What we have also seen is that the new corals are proving to be more resistant when it comes to higher, they can better adapt to temperature that is higher than 31 degrees for a longer period of time.” According to Antha, the growth of the corals is also bringing back some fish species that had disappeared from the islands’ coral reefs like the butterfly fish.

 

A coral reef rescue project on Cousin Island, started in 2010 by Nature Seychelles, financially supported by the United States Agency for International Development (USAID) uses a method called ‘reef gardening’ – taking bits of healthy corals from donor sites and raising them in underwater nurseries until they grow to required size, when they are ‘planted’ in degraded sites. The project has so far proved itself to be a success, but there are three other sites around Cousin that have shown signs of natural recovery as well, a huge relief to the researchers given the high levels of mortality and degradation seen in the first ten years.

 

In short, although some Seychelles reefs remain heavily degraded from the 1998 bleaching event, we are finding cause for optimism that many reefs have the ability to recover from these major bleaching events, and reducing local sources of stress to these reefs should offer them the best chance of continuing to bounce back from any future bleaching events. 

 

An article published in Think Progress, researchers have postulated that government protection of herbivorous coral grazers such as parrotfish and sea urchins is the key to protecting the coral reefs of the Caribbean from becoming overgrown with seaweed. Coral grazers such as parrotfish spend up to 90 percent of their day eating algae off coral. The report states that overfishing has contributed to steep declines in Caribbean parrotfish populations over the last several decades, as has pollution and local tourism. The study found that some of the healthiest coral reefs were those that have taken steps to protect parrotfish.

 

Graham agrees that herbivorous fish are vital to control algal growth and give corals a better chance of recruiting and growing. He says that at one of the monitoring sites around Cousin Island, the macroalgae cover has been reduced, presumably by the abundant protected herbivorous fish in the reserve, and coral recruits are beginning to take hold on the reef. “Carefully managed herbivore fisheries can be enough to maintain this important ecosystem function,” he said, adding that species such as rabbitfish (Siganus sutor) were fast-growing enough to sustain some fishing and still maintain high enough numbers. It’s this type of natural recovery that Seychelles should be striving for in terms of the reefs bouncing back on larger scales, says Graham.

 

Minimising local impacts in the form of sedimentation, nutrient input and regulating fishing pressure will all be important for this. In terms of giving the reefs that are still dominated by macroalgae a helping hand, active removal of macroalgae in large patches may be a useful way to kick start natural regeneration.  

3.

Mangroves in Kannur, India.

A red mangrove, Rhizophora mangle.

beautiful view

Bundar, Thatta, Pakistan

- The boulders must be large, strong and resistant to erosion. Granite and basalt are often used. Small or weak rocks would not be able to withstand the impact from the waves and would quickly be eroded.

 

Absorb the energy of waves.

Allows the build up of a beach.

Can be very cheap.

Effective for many years.

Disadvantages:

Visually unattractive.

Can make the beach inaccesible

Infograph by Khee Hean and Boon Khiam:

https://magic.piktochart.com/output/14710987-coastal-protection

Infograph by NIcholas and Chun Wei: