Extraordinary defender against the rising seas of Bangladesh

Located on the southern coast of Bangladesh, the island is becoming increasingly marine, pushing back both land and sea life. Many of the people who have settled here have left their sacks and those who could not go have retreated because the island they have considered their home for many generations is changing. By 2050, approximately 13 million people will be displaced by climate change. Even so, there is a glimmer of hope amidst the waves, just off the coast of Katubadia Island. Out of the water, oyster rocks glow in the sun. These oyster rocks are a wonderful habitat for marine life and a potential source of livelihood for the locals. Chaudhry hopes that these oyster rocks will protect Katubdia Island from rising sea levels.

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The idea of ​​oyster rocks on Katubadia Island first came to mind in 2012 when Chaudhry Shah Nawaz was a research associate at the Institute of Marine Life at the University of Chittagong. The logic is simple: oyster cliffs can calm sea waves before they reach shore as a defense against coastal erosion. This theory was first worked on in the Netherlands and had positive results in the US state of Louisiana. Researchers at Vijnining University are now working with Chaudhry and his colleagues to improve the condition of Katubdia Island. The problem with all this work is that Bangladesh, the Netherlands, and in fact Louisiana, are thousands of miles apart and have very different ecological contexts.

Katubadia Island is one of the most difficult of all problems due to its rapidly shrinking coastline. By 2050, one in seven Bangladeshis will be homeless due to climate change. We are facing more terrible waves due to global warming and hot water. Traditional structural interventions, such as concrete embankments or dykes, have been a common method of protecting the coast. According to Raza-ul-Karim Chaudhry, executive director of the Bangladesh NGO Coast, 60 percent of the country’s coastline is protected by embankments. But some say that defenses made of oysters can be more effective than defenses made of concrete.

Oysters

Environmental engineering, or eco-engineering, involves designing sustainable ecosystems with both natural and human value. They adapt to the environment by clumping on submerged surfaces and working together to form rock structures. Their role in filtering and retaining nutrients in the water, providing spawning and shelter for fish, and thus increasing biodiversity, is well recognized. Oyster rocks are home to other animals as well as improve water quality and help grow seagrass. But Shah Nawaz Chaudhry and his associates were interested in the role of their natural embankments in the Netherlands. Oyster cliffs can protect the coast from the constant onslaught of strong waves, although this is not the only benefit.

Petra Dankers, a senior consultant for morphology and eco-engineering at the University of Wageningen, who is researching the Katubadia Island project, said: The rocks give you wider shores and (consequently) calm water. Such a flow is the hallmark of a building with a view of nature. And instead of seeing it as a blow, it becomes part of the plan. “It’s a dynamic process, it’s not a solid structure,” says Ad Small, a professor of shellfish culture at Wageningen University. And it’s a new understanding of how to use natural forces to achieve our goals. ”

It is important to understand the natural structures that preserve the Kutubdia because, unlike many oyster rock projects around the world (for example in the Gulf of Mexico), it was not a restoration of declining rock. It was to introduce new rocks as engineering structures. Shah Nawaz Chaudhry in his initial survey in this regard found that fortunately this region offered many ideal conditions for oyster rocks. The salt content and oxygen content of the water were also adequate. The water had all the traces of aquatic life and oysters could be raised here.

The next thing they had to do was see if there were oyster eggs in the waters of the Bay of Bengal. “It wasn’t like you put something in the water and hoped it would work positively,” says Ad Small. He says there was also a sea level where marine life and oyster eggs were found. He says this meant that the eggs floating in the oyster water could settle here and they could not move from here despite the strong sea waves.

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In fact, on the island of Katubdia, oysters were growing naturally around a large number of cement rocks. Research shows that concrete structures are a good alternative to the natural growth of oysters. Therefore, Chaudhry and his associates needed more concrete to make oyster rocks. “We wanted to use things that were locally available and cheap,” he says. This structure was also custom made, ie round pillars that the locals used to make their toilets. They could not be immediately available but they could stand during the harsh monsoon season.

Knowledge as an expert

But while oysters can grow abundantly on concrete in some situations, they are very special about other features of their habitat. “Oysters have a special preference for breeding. They cannot be exposed to wind or sun for more than 20% of the time,” says Chaudhry. Chaudhry says the best people to help find the right place for the artificial rock were the local coastal community, who were already in tune with the rhythm of the waves. The knowledge of the local islanders about Costura (a local word for oysters) proved invaluable to him and his research colleagues before a 300kg concrete ring-shaped structure was thrown into the water at an experimental site in 2014.