UH researchers discover large fresh water supply on Hawaiʻi Island

This unprecedented find on the Big Island could change the way we understand the geology of the Hawaiian islands and the state’s fresh water supply.

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Donald Thomas, geochemist and director of UH Hilo Center for the Study of Active Volcanoes

In March 2013, researchers from the University of Hawaiʻi at Mānoa and UH Hilo began drilling at 64-hundred feet above sea level, between the mountains of Mauna Loa and Mauna Kea in the saddle region of the Big Island of Hawaiʻi.

UH Mānoa professor Donald Thomas is leading the effort, called the Humuʻula Saddle Hydrologic Study Project.

What they discovered seven months later may radically change conventional wisdom regarding the state’s most valuable resource: fresh water.

“The conventional model that we worked with for years and years is that we have a relatively thin basal fresh water lens, is what we call it,” said UH Professor Donald Thomas, the director of the (UH Hilo) Center for the Study of Active Volcanoes. “A layer of fresh water saturated rock that rises very slowly as we move inland.”

According to that conventional model developed decades ago, the research team should have had to drill for 5,900 feet to 500 feet above sea level, before reaching the Big Island’s fresh water supply.

“We found something just completely different,” said Thomas. “The stable water table in the saddle is not 500 feet above sea level. It’s more like 4,500 feet above sea level. So we are almost ten times higher than we could have expected when we started out on the project.”

Geologists have long thought that only a small fraction of rainwater is stored in the islands because the geological makeup of Hawaiʻi is volcanic and porous.

“With our findings here, it looks as though the islands really act as huge containers,” said Thomas.

The impact could be far-reaching for residents, ranchers and farmers in drought stricken areas across the island chain and on Oʻahu, where fresh water may be scarce one day after supporting the majority of the state’s population for decades.

Right now, only one thing is certain.

“What we really need to do is go back and look again, using modern geophysical methods, to really define the ground water systems within all of the islands,” said Thomas.

The next step for the Humuʻula Saddle Hydrologic Study Project is a second drill site six miles from the first, to measure the extent of the groundwater discovered. If that test well proves successful, it will also provide strong support for high level water beneath a large tract of Department of Hawaiian Home Lands property on the eastern side of the Humuʻula Saddle where their lessees have long needed a reliable source of water for ranching operations.

The United States Army is funding the project in hopes of finding water for its Pōhakuloa Training Area, where the first drill site is located. Currently, the Army spends $1.5 million each year trucking fresh water to the training camp for use by troops and support staff.

“It’s been, as far as I am concerned, an outstanding partnership,” said Thomas. “We are able to develop scientific information that I think is really of fundamental importance to Hawaiʻi and at the same time, we have a practical outcome.”

As UH-led work continues in the area, ripples of excitement are spreading through the community. This unprecedented find on the Big Island could change the way we understand the geology of the Hawaiian islands and the state’s fresh water supply.

“I really believe the university should really try to become involved in to try and really improve the quality of life and preserve the quality of life that we have here in Hawaiʻi,” said Thomas.

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