FROM WASTE TO WALLS: Building climate-resilient embankments from locally sourced discarded oyster shells

FROM WASTE TO WALLS: Building climate-resilient embankments from locally sourced discarded oyster shells
November 14, 2018 3:06 pm Blog

Take a walk around coastal Sierra Leone, and you might find your feet trample more than just soil. Here, on the Western coast of Africa, piles of discarded oyster shells litter the streets and yards of rural villages. These sharp, pointy byproducts of the oyster industry have only taken up space and posed health risks —until now.

Oysters are bivalves—a family which includes more than 15,000 species of clams, oysters, mussels and scallops whose shells are divided into left and right.

 

For many households in coastal Sierra Leone, the sale of oyster meat constitutes a significant source of income, often in poor rural areas. Women are the primary harvesters of this important protein source, receiving occasional support from their children and husbands. Although the shells are valued elsewhere for their use in ceramics and other crafts, the lack of processing opportunities in Sierra Leone means they are usually discarded in waste piles. Their sharp edges can cause physical injury or create a breeding habitat for disease-causing bacteria and mosquitoes.

Pile of abandoned oyster shells
Pile of abandoned oyster shells

But empty oyster shells are no longer just waste products in some coastal villages. Residents in the southern communities of Kortimoh and Momayah are now giving the strong, calcium-rich shells a new purpose: protecting against the impacts of climate change.

The need for improved coastal infrastructure was underscored in the findings of a Climate Change Vulnerability Assessment conducted by the West Africa Biodiversity and Climate Change (WA BiCC) program. Exploring low-cost and locally available materials was key to designing infrastructure that was affordable and replicable.

After conducting field assessments and holding consultations with locals in Kortimoh and Momaya, WA BiCC designed an embankment concept that would increase resilience to climate change by reducing erosion, buffering sea level rise and storm surges, and catalyzing mangrove rehabilitation and growth. Of the locally available materials considered, only oyster shells served two important functions at once: preventing flooding by allowing water to flow freely through them, and strengthening the shoreline when mixed with sand or soil. The inspiration for this design can be found in some key ecological functions of the oyster, in its habitat; the presence of oyster shells creates a hard bottom which stabilizes sediments and also prevents shoreline erosion by currents and waves.

Oyster shells used for embankment construction
Oyster shells used for embankment construction

The structure is now set to protect over 5,200 people from two communities in coastal Sierra Leone. Community members were trained on how to construct the embankments in order to replicate the structure in similarly vulnerable communities.

And the cherry on top: nobody has to eat less oysters.

Happy kids in a pose near the embankment
Happy kids in a pose near the embankment