Hydrology experts at Flinders University are calling for urgent investigations into the operation of bore-fields that access fresh groundwater on Pacific islands, including Kiribati, where rising sea levels are already putting local water supplies at risk.

“These atoll islands have the most threatened fresh groundwater on Earth, and are relied upon by some of the most remote communities,” says Flinders University’s Professor Adrian Werner.

Modeling of a specialized form of fresh groundwater extraction, featuring horizontal wells, has the potential to reduce the risk of aquifer reserves being overused, and to provide drinking water of lower salinity.

Such wells, also known as infiltration galleries or skimming wells, play a crucial role in extracting fresh groundwater on atoll islands. They typically comprise horizontal or slightly inclined slotted pipes, surrounded by a gravel pack and connected to an extraction well or sump.

These infiltration galleries skim fresh groundwater from shallow depths while minimizing the risk of saltwater intrusion beneath thin subterranean freshwater lenses, which typically range from 3 to 21 meters in thickness. The design, construction and operation of these galleries need to be precise to avoid drawing seawater into the island’s water supply.

Such galleries are currently in operation across several atoll islands, and Flinders researchers have focused on nine small islands in the Pacific Ocean, including Kiritimati Atoll and Bonriki Island in Kiribati, Lifuka Island in Tonga, and the Cocos Islands.

While these systems provide crucial freshwater supplies, information is lacking about the optimal layout of infiltration galleries, pipe characteristics and pumping rates. There is also limited data on the performance of these galleries—specifically pumping rates and salinity levels—on small atoll islands.

A research team from the National Center for Groundwater Research and Training (NCGRT) at Flinders University, led by Professor Werner and Dr. Amir Jazayeri, was commissioned by the Pacific Community (SPC), under the management of Peter Sinclair, to address these research gaps and evaluate the performance of infiltration galleries across Pacific islands.

They also performed modeling to assess how infiltration galleries on atolls will be affected by rising sea levels in the future.

This comprehensive study, published in the Journal of Hydrology, involved collecting extensive data on the hydraulic properties of atoll island aquifers and analyzing the design of infiltration galleries across the region.

Valuable insights were gathered from infiltration gallery operators during Flinders University’s participation in the Pacific Groundwater Gallery Knowledge Exchange (PGGKE) workshop, held on Kiritimati Atoll (Kiribati) in November 2023.

The research also incorporated computer modeling simulations and physical laboratory experiments conducted at Flinders University’s Sand Tank Laboratory, to gain a deeper understanding of infiltration gallery performance.

The findings of this study have been published as a United Nations Development Program (UNDP) scientific technical report, providing critical guidance for sustainable groundwater management in the Pacific.

“While many studies have examined horizontal wells in other contexts, the specific conditions of small islands, especially atolls, places unique demands on infiltration galleries,” says Professor Werner.

Dr. Jazayeri says the research team continues to focus on solutions to protect freshwater resources and serve the demands of isolated communities across the Pacific, using a wide range of research techniques.

“We believe that expanding the use of infiltration gallery systems in other coastal aquifers can significantly contribute to managing crucial coastal freshwater resources, both in Australia and globally,” says Dr. Jazayeri.

Professor Werner is confident the findings will have wider applications across many countries.

“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,” he says.

“This all contributes to global groundwater management strategies.”