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Hanawi Stream near Nahiku, Maui, Hawaii.


Recent hydrologic conditions, West Hawaii : Water levels

Data collected by the U. S. Geological Survey in cooperation with the State of Hawaii Commission on Water Resource Management. Data after September 30, 2009 are provisional and subject to revision.

Water levels in observation wellsFresh groundwater in West Hawaii is found in two main forms: (1) as a lens-shaped body of freshwater, called a freshwater lens, floating on denser, underlying saltwater within permeable lava flows near the coast, and (2) as water impounded to high levels within the inland part of the aquifer with lower overall permeability (high-level groundwater). Freshwater in the highly permeable lava flows near the coast exists in only the upper part of the aquifer, and in only a small fraction of the total thickness of the aquifer. Fresh groundwater flows from the inland area to coastal discharge areas. Because the volcanic rocks are highly permeable and crop out offshore, freshwater can readily discharge to the ocean, groundwater levels are relatively low (generally less than 10 ft above sea level and commonly less than 5 ft above sea level), and saltwater can readily enter the aquifer. In areas near the coast where saltwater mixes thoroughly with seaward-flowing freshwater, a freshwater lens may not form and brackish water may exist immediately below the water table.

Within the high-level groundwater area, which occurs at distances greater than about 2 to 5 miles inland from the coast, low-permeability rocks compartmentalize the more permeable rocks, resulting in groundwater being impounded to high altitudes. Because of this compartmentalization of the aquifer, water levels can change by hundreds of feet over horizontal distances of less than a mile. The source of freshwater in the high water-level area is groundwater recharge from (1) infiltration of rainfall and fog drip and (2) irrigation water. Fresh groundwater in the high water-level area that is not withdrawn from wells flows to downgradient areas where water levels are lower and where a freshwater lens may exist.

Currently, the USGS measures water levels about six times per year in one well in West Hawaii, Kawaihae W-3 (well 6147-01). The Kawaihae W-3 well is located in the Waimea aquifer system. The well was drilled for the State of Hawaii in 1963 and water-level measurements have been made on a regular basis (about every two to three months) since 1975. In 2006, long-term water-level monitoring in four other USGS wells in West Hawaii was discontinued. These wells are: Kealakekua (well 3155-01), Kiholo (well 4953-01), Waikoloa MLR 1 (well 5846-01), and Hapuna Beach Park (well 5948-01).

In 1991, the State of Hawaii Commission on Water Resource Management started a groundwater monitoring program that involves occasional water-level measurements at 40 private and public wells in West Hawaii. A 2003 study by the State of Hawaii summarized the results of this program through 2002. Occasional measurements continue to be made at a number of these wells.


Additional information about groundwater in West Hawaii can be found in:

Geohydrology and numerical simulation of the groundwater flow system of Kona, island of Hawaii: U.S. Geological Survey Water Resources Investigations Report 99–4073, 70 p. by Oki, D.S., 1999.

Water levels for selected wells

Water-level records for Kawaihae H-3, Waikoloa MLR1, Hapuna Beach Park, and Kiholo wells and the monthly ocean level at Kawaihae Harbor, 1984 to the present.


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