Improving water security for Great Palm Island – a preliminary study towards implementation of desalination plant. Hemerson Tonin, Craig Steinberg, Richard Brinkman and Elizabeth (Libby) Evans-Illidge Australian Institute of Marine Science, Townsville, Australia Great Palm Island (Bwgcolman), located approximately 60km north of Townsville in the central Great Barrier Reef, is home to a community of 5000 people. In 20015, the water storage dams supplying the island’s largely indigenous community fell to critically low levels due to a succession of ‘failed’ wet seasons with below average rainfall. The emergency response proposed in December 2015 was the implementation of a desalination plant on the site, with the need to build infrustructure and discharge brine into the GBR World Heritage Area. To support the emergency approval s process, we performed a preliminary study with regard to the design of the discharge pipeline and the diffuser system. This design was infomed by numerical hydrodynamic modelling of the near-field and far-field plume distribution to predict the spatial and temporal extent of the hypersaline influence with regard to relevant water quality guidelines. This assessment has required studies of the diffuser system (head numbers, height above the seabed, different angles, etc), distances from the shore and sensitive receptors, and dilution rates in scales from centimetres up to hundreds of meters. The study focused on two possible locations, and the results are supporting a broader environmental approvals process with the Great Barrier Reef Marine Park Authority (GBRMPA). Extensive stakeholder engagement has occurred throughout, including with local indigenous community, relevant state and federal agencies and the Palm Island council. .