Pacific island nations face most critical freshwater supply problems in the world. “Skimming wells,” or long horizontal pumping systems, are providing help for the problem.
An international team from The Australian National University, Ecowise Environmental, the Government of the Republic of Kiribati, the French agency CIRAD and the Pacific Islands Applied Geoscience Commission has been studying the impacts of natural and human-induced changes on ground water in the central Pacific nation of Kiribati since 1996.
Very limited land areas and extremely permeable coral soils in atolls reduce surface runoff to insignificant amounts and decrease the potential for surface storages of water. This means thin lenses of fresh ground water floating over seawater are the major source of reliable freshwater for people in many atolls. The team found that both the quantity and salinity of atoll ground water is extremely vulnerable to frequent ENSO-related droughts. Droughts can last as long as four years, and occur with a frequency of one significant drought, coupled to La Niña events, every six to seven years. In long droughts, domestic water wells often are too salty too drink, and some communities have to rely on large ground water lenses or on coconuts.
Population growth due to natural increases, inward migration and urbanization mean that fresh ground water sources are reaching their limit of sustainable supply in urban South Tarawa in Kiribati. Ground water can become salty due to over-pumping or inappropriate methods of pumping. Long, horizontal infiltration pumping galleries or “skimming wells,” placed just beneath the ground water table (the top layer of soil and rock that is saturated with water) provide the best method of skimming off lower-salinity ground water. The study team tested the impact of infiltration galleries on lowering the watertable and on salinity. The researchers also used the results to examine how the permeability of the coral sands varied across islands and found that surface contaminants could reach shallow fresh ground water within an hour of being split on the soil surface.
The team proposed a number of strategies to help increase the resilience of small island communities to water-related climate and human changes. These included providing a sound institutional basis for the management of water and sanitation; improving community participation in water and related land planning and management; increasing the capacity of villagers and local agencies to manage water and sanitation under variable climates; improving knowledge of available water resources and demand for them; improving water conservation and demand management and reducing leakages; increasing the use of rainwater by households and communities; protecting ground water source areas from contamination; improving sanitation systems to minimize water use and ground water pollution; and ensuring that water aid programs are long-term partnerships that foster local engagement and ownership of solutions.