Oyster reef restoration project

Prior to European settlement, naturally occurring oysters reefs were widely found around Australia and within Sydney Harbour. Indeed, diaries of early settlers suggest that oyster reefs were so abundant that they were described as a shipping hazard. However, since the 1880s these reefs have largely disappeared due to over-exploitation (for consumption and cement production), pollution, increased estuarine siltation and the introduction of a parasitic mudworm. Government regulations were introduced in Queensland, NSW and SA in the 1850s and 1860s but came too late to preserve the natural oyster reefs.

A novel technique has been proposed to encourage oyster reef restoration and reduce intertidal riverbank erosion. This innovation uses seeded oyster shells in coconut fibre bags. Deliberately utilising only organic materials, the fibres will naturally decay in time with the intention of leaving a new, intact oyster reef structure behind.

To support this unique form of eco-engineering, our research program has focused on improving the design and function of oyster bags using our state-of-the-art facilities. In 2015, we initially undertook preliminary two-dimensional physical modelling of oyster bags to better understand their expected behaviour when exposed to wave attack. As the study was not site specific, test situations were developed based on typical wind and boat waves that the oyster bags may be exposed to. These preliminary investigations identified threshold wave heights for initiation of oyster bag rocking and displacement. The tests also demonstrated that wave driven foreshore erosion processes are expected to be attenuated immediately landward of oyster bag structures.

In 2016, the research was extended by combining oyster bags with sand filled geotextile containers of the same size. These tests showed that the stability of a structure composed of oyster bags under wave attack could be increased by replacing some oyster bags with sand filled geotextile containers. The results of these tests are available via the thesis link below.

WRL is continuing its research on oyster bags with a view to developing a comprehensive engineering guideline for their use. Watch this space for further news…