Windara shellfish reef construction

South Australia was once home to native oyster reefs along 1,500 km of its coastline. Over-harvesting in the 1800s resulted in the collapse of these reefs, removing a vital ecosystem and its many associated benefits. Restoration of these reefs is a key component of The Nature Conservancy's oceans program. In 2018 construction of Windara Reef, a 20-hectare reef in Gulf St Vincent commenced, which to date is the largest restoration of shellfish reefs in Australia. Restoration at this scale has been made possible through funding under the Australian Government's National Stronger Regions Fund program, philanthropic donations and state and local government funding. The long-term aim of this project is to improve fish stock and enhance recreational fishing opportunities. Reef design was based on several factors; stability, geotechnical conditions, currents, constructability, cost and suitability for oyster colonisation. Final design included the construction of 144 individual reefs of varying lengths with the whole system constructed from 10,005t of dolomitic limestone rock. Post construction, the reefs were seeded with oyster spat grown on recycled oyster shell. To achieve the precise reef specifications prescribed under the Contract, Maritime Constructions engineered and fabricated a bespoke rock deployment system. This involved a 55m Barge and custom built hydraulically operated rock deployment chute which incorporated fully adjustable fall pipes and formwork type box, which was lowered to the seafloor prior to rock placement. The system was able to accommodate variations in; reef dimensions, tidal movements, currents, barge draft, rock descent and rock dimensions. The tracking ability of the fall pipes over the cake tin coupled with GPS positioning to within 1m accuracy allowed for precise and efficient rock placement in the x and y plane whilst the telescopic function of the fall pipes ensured minimal rock wastage and height control (z).