Water security in Pacific Atolls requires a new approach, researchers say

Hydrology experts at Flinders University are calling for an urgent investigation into the operation of Borefields, which access fresh groundwater to the Pacific Islands, including Kiliberty, where sea level rise is already at risk for local water supply.

“These atoll islands have fresh groundwater that is the most threatened of the planet and rely on some of the most remote communities,” says Professor Adrian Werner of Flinders University.

Modeling a specialized form of fresh groundwater extraction, characterized by horizontal wells, reduces the risk of excessive use of aquifer reserves and may provide low-salt drinking water.

Also known as infiltration gallery or skimming wells, these wells play an important role in extracting fresh groundwater into the atoll island. They are usually made up of horizontal or slightly inclined slot pipes surrounded by gravel packs and connected to extraction wells or sumps.

These penetration galleries minimize the risk of saltwater invasion under thin underground freshwater lenses, while skimming fresh groundwater from shallow depths. Usually the thickness is 3-21 meters. The design, construction and operation of these galleries must be accurate to avoid pulling seawater into the island’s water supply.

Such galleries are currently operating on several atoll islands, with Flinders researchers focusing on nine small islands in the Pacific Ocean, including Kiritimati Atoll and Bonriki Island in Kiribati, Rifka Island in Tonga and the Cocos Islands.

These systems provide important freshwater supplies, but lack information on the optimal layout, pipe characteristics and pump speed of the infiltration gallery. There is also limited data on performance, particularly salinity and salinity levels of these galleries on small atoll islands.

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

We also performed modeling to assess how atoll penetration gallery will be affected by future sea level rise.

This comprehensive study, published in the Journal of Hydrology, collected extensive data on the hydraulic properties of the Atoll Island aquifer and analyzed the design of infiltration gallery across the region.

Invaluable insights were gathered from penetration gallery operators during Flinders University’s participation in the Pacific Ground Gallery Knowledge Exchange (PGGKE) workshop held at Kiritimati Atoll (Kiribati) in November 2023.

This study also incorporates computer modeling simulations and physics laboratory experiments conducted at Flinders University’s Sand Tank Laboratory, providing a deeper understanding of the performance of the penetration gallery.

The results of this study are published as a science and technology report for the United Nations Development Programme (UNDP), which provides important guidance for Pacific’s sustainable groundwater management.

“While many studies have looked at horizontal wells in other contexts, certain conditions on small islands, particularly atolls, put unique requirements in penetration galleries,” says Professor Werner.

Dr. Jazayeri says the research team continues to focus on solutions to protect freshwater resources and uses a wide range of research technologies to meet the demands of isolated Pacific communities.

“We believe that expanding the use of infiltration gallery systems in other coastal aquifers will significantly contribute to the management of important coastal freshwater resources in both Australia and the world,” says Dr. Jazayari.

Professor Werner believes the findings have a wider application in many countries.

“The insights gained from applying the penetration gallery to Pacific atolls provide a wider range of uses within continental aquifers, particularly by mixing with seawater to mitigate seawater intrusion, allowing for capture of the fresh groundwater discharges of lost submarine submarines,” he says.

“All of this contributes to the global groundwater management strategy.”