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Groundwater on Tropical Pacific Islands —Understanding a Vital Resource
Released: 5/1/2009 8:00:00 AM

Contact Information:
U.S. Department of the Interior, U.S. Geological Survey
Office of Communication
119 National Center
Reston, VA 20192
Gordon  Tribble 1-click interview
Phone: 808-587-2405

Precious drinking water in Hawai‘i and the Pacific region is particularly vulnerable to environmental stresses imposed by rapidly growing populations, increasing economic development, and global climate change.

To an outside observer, tropical islands seem idyllic. Closer scrutiny reveals that their generally small size makes freshwater resources susceptible to many threats. Groundwater is the main source of drinking water on many islands, and for quite a few islands, it is the only reliable source of water throughout the year. Faced with a growing demand for this valuable resource, and the potential negative effects on its availability and quality from changes in global climate, increasingly sophisticated management approaches will be needed to ensure a dependable supply of freshwater for the residents of these islands.

The newly published U.S. Geological Survey (USGS) 35-page report, Groundwater on Tropical Pacific Islands - Understanding a Vital Resource, by Gordon Tribble, is available free online. Paper copies are available from the contact listed above. Intended for a non-technical audience, the report includes easy-to-understand diagrams, copious color photos and illustrations, and a glossary of terms.

According to the report’s author, Gordon Tribble, “USGS reports are internationally recognized for their technical accuracy and thoroughness, but are generally written for the scientific community. Because of their complexity, important information in these reports about water resources can be misunderstood or overlooked. The purpose of this report is to summarize existing groundwater information about Hawai‘i and other Pacific islands so that it can be understood by policy makers, planners, landowners, and the general public. Increased understanding by all stakeholders helps to ensure that informed decisions are made about the management of groundwater.”

This report describes some of the factors that influence the availability of groundwater on tropical Pacific islands, such as recharge, aquifer properties, patterns of flow, salinity distribution, and the effects of pumping. Some examples of USGS studies in Hawai‘i and other Pacific islands are used to illustrate these concepts and their relevance to the management of groundwater resources.

As the demand for freshwater grows, new monitoring and research efforts will be needed to (1) characterize the extent and sustainability of groundwater resources on different tropical Pacific islands, (2) better understand linkages between groundwater discharge and freshwater and nearshore ecosystems, and (3) prepare for the effects of climate change, which will likely include the loss of habitable land and reduced areas for the accumulation of groundwater as a result of rising sea levels.

Underground water or “groundwater” is the primary source of water on many tropical Pacific islands. Contained in porous, regionally extensive geologic formations or “aquifers,” fresh groundwater on these islands floats on and is surrounded by more dense saltwater from the ocean. The potential for an aquifer to provide a reliable source of good-quality water depends on the amount of recharge that occurs from rainfall, the physical properties of the aquifer, and how the water is pumped or removed from the ground. Because of their relatively small size and oceanic setting, groundwater resources on tropical Pacific islands are vulnerable to over-pumping and saltwater intrusion, especially during droughts caused by climatic variations such as El Niño events. This vulnerability is made worse because the effects of groundwater pumping are initially difficult to perceive.

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