Seawater intrusion

Fresh groundwater stored in coastal aquifers constitutes an important resource for urban, agricultural (irrigation) and industrial activities.

On Australia’s coastal fringe, continuing population expansion allied with significant reductions in rainfall have led to an increasing dependency on coastal groundwater resources.

Excessive extraction of groundwater in coastal settings can lead to salinisation of the aquifers through the encroachment of seawater. Seawater (or saltwater) intrusion (SWI) is a major environmental threat and management challenge, particularly in areas where there is a history of over-exploitation of coastal aquifers. Seawater intrusion can have major impacts on water quality in aquifers, rivers and estuaries, and can impact significantly on floodplain and wetland ecosystems.

In Australia, the relatively short history of groundwater exploitation along the coast means that seawater intrusion has thus far only been noted in a few hotspots. While excessive groundwater abstraction is the principle cause of SWI in Australian coastal areas, reduced rainfall and low recharge to coastal freshwater aquifers can also lead to encroachment of seawater.

Importantly, there are increasing concerns about the longer term impacts of climate change as sea levels rise and seawater inundation of low-lying coastal landscapes is predicted. While in some cases, the damage caused by seawater intrusion can be reversed; in many cases, seawater ingress can cause significant irreversible damage.