Fresh groundwater stored in Australian coastal aquifers is an important resource for humans and the natural environment. Many Australian coastal aquifers are vulnerable to seawater intrusion (SWI)—the landward encroachment of sea water into coastal aquifers—which can significantly degrade water quality and reduce freshwater availability. The increasing demands for fresh water in coastal areas and the anticipated impacts of climate change (such as sea-level rise and variations in rainfall recharge) may result in increases in the incidence and severity of SWI. Comprehensive investigations of SWI are relatively uncommon and the extent of monitoring and investigations specific to SWI are highly variable across the nation. In response to the threat posed by SWI, Geoscience Australia and the National Centre for Groundwater Research and Training, in collaboration with state and territory water agencies, undertook a national-scale assessment of the vulnerability of coastal aquifers to SWI. This assessment identified the coastal groundwater resources that are most vulnerable to SWI, including future consequences of over-extraction, sea-level rise, and recharge–discharge variations associated with climate change. The study focused on assessing the vulnerability of coastal aquifers to the landward migration of the freshwater–saltwater interface, rather than surface waterbodies.

This report was compiled and written to summarise the four-year (2008 to 2012) 'Sustainable management of coastal groundwater resources' project. This project was funded by the National Water Commission's (NWC) Raising National Water Standards Program. Geoscience Australia was a key project partner, and worked closely with collaborators from Ecoseal, Arche Consulting, GHD, Kempsey Shire Council and the NSW Department of Primary Industries (Office of Water). The summary report was published under the National Water Commission's 'Waterlines' series. This executive summary document is supported by related publications that deal with the following topics: 1. hydrogeology, monitoring and hydrochemistry; 2. development of a groundwater flow and transport model for the Macleay Sands Aquifer; 3. mapping and risk assessment of groundwater-dependent ecosystems (GDEs); 4. development and application of early warning indicators to assess the condition of groundwater resources; and 5. socioeconomic assessment and cost-benefit analysis, The key project objective was to develop an integrated approach for managing the availability and quality of coastal groundwater resources so that coastal aquifers do not become overallocated, depleted or degraded as a consequence of increasing demand from rapidly expanding urban centres such as South West Rocks. The second objective was to combine groundwater and seawater intrusion modelling tools, assessment of groundwater dependent ecosystems (GDEs), and a framework for applying indicators and cost–benefit analysis to support the long-term management of coastal sand aquifers. These methodologies can then be applied to similar coastal sand dune aquifers along the North Coast of New South Wales and help ensure that any new groundwater sources are developed sustainably, with minimal impact on GDEs such as coastal dune vegetation communities. The study will help improve management of groundwater resources in coastal dune aquifers in the Mid North Coast region and, potentially, other coastal communities reliant on coastal dune systems for water supplies.