Coasts
The sea wall that grows itself
Along the Merrow estuary, reefs built from old oyster shells are holding back the tide better than the concrete did.
Three years ago, volunteers laid six hundred mesh bags of oyster shell along the eastern bank of the Merrow estuary, where the old concrete wall had cracked and the marsh behind it was washing away. The shells came from the restaurants on the waterfront, which used to throw them away. Baby oysters settled on them within a season. Now the bags have vanished under a living reef that rises a few centimetres every year, by itself. Behind the reef, the marsh has stopped shrinking. In two places it has grown back. “Concrete is the strongest it will ever be on the day you pour it,” said Ana Brightwater, the engineer who designed the project. “A reef gets stronger every year it is alive.” The council is now pricing a reef for the western bank. It would cost a fifth of a new wall.
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