Need for new freshwater solutions in Pacific Islands

The Pacific is one of the world’s most disaster-prone regions, facing intensifying cyclones, droughts, and rising tides — and now, a growing threat to its freshwater supplies.

Hydrology experts at Flinders University are calling for an urgent investigation into how bore fields extract fresh groundwater in the region. The new study, published in the Journal of Hydrology, warns that current methods may not withstand the pressures of a changing climate, putting long-term water security at risk for vulnerable island communities.

“These atoll islands have the most threatened fresh groundwater on earth and are relied upon by some of the most remote communities,” says co-author Professor Adrian Werner.

Infiltration galleries

Many Pacific islands extract fresh water from the ground by installing horizontal or inclined perforated pipes connected to an extraction well and pump. Known as “infiltration galleries”, these systems skim fresh groundwater from shallow depths while minimising the risk of saltwater intrusion beneath thin subterranean freshwater lenses, which typically range 3 to 21 metres in thickness. The design, construction and operation needs to be precise to avoid drawing seawater into the island’s water supply.

The authors of the paper say: “Despite their long-term use, the design of infiltration galleries is documented mainly in industry reports, and as such, published guidance on their construction lags current practice by some 30 years.”

A recent workshop involving gallery operators from across the Pacific was held in Kiritimati Atoll (Kiribati) to draw together new insights into the design, operation and performance of infiltration galleries

While infiltration galleries provide vital water supplies across several atoll islands—ranging from Kiritimati Atoll and Bonriki Island in Kiribati to Lifuka Island in Tonga and the Cocos Islands—information is lacking about the optimal layout of infiltration galleries, pipe characteristics and pumping rates.

“There are some islands in the Pacific that actually record the salinities going up at high tide and down at low tide,” explains Werner. “That’s how narrow the margins are for operating these things. If you put the horizontal well in too deep and you’re too close to the saltwater, you’re going to pull up saltwater. If you put it in too shallow at low tide, it’s going to be dry, and you can’t take any water out.”

Learning from locals

In response to these challenges, a dedicated research team from the National Centre for Groundwater Research and Training (NCGRT) at Flinders University – led by Werner and Dr Amir Jazayeri – was commissioned by the Pacific Community (SPC), to address these research gaps and evaluate the performance of infiltration galleries across Pacific islands.

“People are overcoming various tricky situations with their own innovations and a lot of that isn’t making its way into international literature, so we wanted to get that information and put it into one place,” says Werner. 

Back at Flinders University, the team integrated advanced computer modelling simulations with physical laboratory experiments at the Sand Tank Laboratory to deepen understanding of how infiltration galleries perform under varying conditions, such as fluctuating tidal forces and changes in salinity.

Beyond the Pacific

“The insights gained from applying infiltration galleries to Pacific atolls offer opportunities for more widespread applications within continental aquifers, especially to capture submarine fresh groundwater discharge that is otherwise lost through mixing with seawater and to mitigate seawater intrusion,” says Werner.  

This research emphasises the potential for Pacific innovations to revolutionise water management on a global scale. With climate change driving ever-changing, extreme conditions, refining these techniques could prove essential in protecting coastal aquifers and securing sustainable freshwater supplies for the future.

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