Artificial Oyster Reefs for Erosion Reduction

Dutch and Bangladesh Researchers Used a Concrete Structure Measuring 50 Metres Long and Approximately 70 Centimetres High to Imitate a Fully-grown Oyster Reef toPrevent Coastal Erosion and Grow Fast Enough in Height to Keep Pace with Sea Level Rise

Additionally oyster reefs increases the biodiversity, providing shelter and substrate for fish and crab, creating a source of food for the local human population

These are two main outcomes of a two year Dutch pilot on the Kutubdia Island, Bangladesh. The pilot was part of the Ecological Engineering for Coastal Protection and Food Production (Ecobas) project that concluded in December 2014.

Imitation reef of concrete

Dutch and Bangladesh researchers used a concrete structure measuring 50 metres long and approximately 70 centimetres high to imitate a fully-grown oyster reef.

"This proved to be the best, technologically and financially. The oysters attached themselves to the hollow concrete structures, which also form a habitat for crabs and fish", says professor Tom Ysebaert of Dutch marine ecology research institute Imares. Ysebaert investigated the socio-economic possibilities of the artificial oyster reef.

Well growing oysters
After one year there were large numbers of oysters, while the wave-dampening effects resulted in sediment being deposited behind the reef. "The oysters showed good growth. After one year we already had oysters measuring four centimetres", reveals Ysebaert.

According to calculations with models, the oyster reef could grow in height by about two centimetres per year. This will allow it to keep pace with the rising sea level.

Protection against tropical storm

But when a genuine tropical storm hits, an oyster reef is not enough. "'We expect that the mangrove forest will survive better and spread faster if there is an oyster reef present. In order to protect the coast, a strip of mature mangroves measuring at least 250 to 500 metres wide is needed", explains Ysebaert.

Self-reparing coastal defence

Not every sea floor location along the coast is suited for mangroves and oyster reefs. Ysebaert: "This method can be applied at a great many locations. It's impossibly expensive to construct concrete dikes everywhere, and the earthen dikes alone are often too vulnerable. This form of eco-engineering is sustainable, durable and relatively inexpensive. In the long term, it provides a self-repairing coastal defence system of oyster reefs and mangrove forests."

Participants in the Ecobas-project were engineering firm Royal HaskoningDHV, University of Chittagong and research institutes Imares (Institute for Marine Resources & Ecosystem Studies), LEI (Agricultural Economics Research Institute) of Wageningen University.

Source: Dutch Water Sector

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