Reducing groundwater vulnerability in Carbonate Island countries in the Pacific

Many small island countries in the Pacific rely on shallow, fresh groundwater lenses in highly permeable coral sand and karst limestone aquifers, underlain and surrounded by seawater, as their main freshwater source. The delicate balance in small islands, between groundwater recharge and discharge into and mixing with seawater, as well as extraction of groundwater by communities, is threatened regularly by climate variability, storm surges, overpumping, as well as by pollution from land uses and waste disposal. In low islands, predicted sea-level rises resulting from climate change are a further major threat. Together, the hydrogeology of fresh groundwater lenses and these natural climatic and anthropogenic threats make small coral island groundwater some of the most vulnerable systems in the world. This linkage between natural and human pressures means that small coral island groundwater systems are exemplars of the GRAPHIC approach to sustainable groundwater management. In this chapter, a simple steady- state approximation is used to provide insight into the key climatic, hydrogeological, physiographic, and management factors that influence the quantity of, and saline intrusion into freshwater lenses. Examples of the dynamic nature of freshwater lenses as they respond to these drivers are given. Natural and human- related threats to freshwater lenses are discussed. Strategies and policies processes to ensure groundwater sustainability and reduce its vulnerability in small islands are presented and suggested improvements to donor and aid programs in water are also advanced. It is argued that because of the extreme vulnerability of small island groundwater systems, management strategies and policy must be based on the very best technical information and using regional networks as exemplified by GRAPHIC.