Summary appraisals of the Nation's ground-water resources; Hawaii region

Abstract

The water resources of the Hawaii Region, taken as a whole, are far greater than foreseeable future demands on them, but this is not so for the individual islands. Each and every island is independent with respect to water supply, and the occurrence and availability of water vary widely from island to island. The groundwater resources offer better prospects for supplying additional water needs in the future than the surface-water resources. Most of the surface supplies that are easy to develop have been fully utilized where needed, and conduits and reservoirs necessary to develop new or additional supplies would generally require large and perhaps prohibitive outlays of capital. In 1975, ground water supplied 46 percent, and surface water 54 percent of the water needs but, in the years ahead, these percentages will likely be reversed as more groundwater development takes place. Total water use, in 1975, averaged about 1,775 million gallons per day, ofwhich about 810 million gallons per day was ground water. The total water use is divided into public supply, 11 percent; self-supplied industrial use, 23 percent; and agricultural, 66 percent. Rainfall is the principal source of groundwater recharge. Local mean annual rainfall ranges from less than 20 inches to more than 300 inches, with the annual average rainfall on the large islands exposed to the trade winds being slightly more than 73 inches and that on the small islands situated in the rain shadow of the larger islands being less than 26 inches. Groundwater recharge has been estimated at about 2,400 billion gallons per year (6.5 billion gallons per day) or roughly 30 percent of the rainfall. Most fresh ground water in the region is stored below sea level in porous lava flows, much of it as basal-water lenses floating on saline ground water, as distinguished from dike-impounded water in the interior of the islands. The basal-water lens is maintained by recharge, which, if reduced, leads to thinning of the lens and subsequent encroachment of seawater. Seawater is the biggest pollutant of freshwater, and many of the groundwater problems are, in some way, associated with the encroachment of saline water induced by development. The major problem areas include the entire island of Oahu, south Kohala-Kona coast on the island of Hawaii, Lahaina District in Maui, and the Koloa and Kekaha-Mana areas in Kauai.

Groundwater depletion in the United States (1900−2008)

“…Over 1,184 wells, tunnels, and shafts had been constructed, with over 800 of the structures still in use, by the year 1985 (Nichols and others, 1996). Drainage into water-supply tunnels has caused substantial reductions of volumes of dike-impounded groundwater in storage, and the construction of eight tunnels in Oahu caused a depletion of about 0.1 km 3 on the windward side of the island (Takasaki, 1978).…”

Groundwater availability in the Lahaina District, west Maui, Hawai'i

“…6;Yamanaga and Huxel, 1970, fig. 7;Takasaki, 1978). The boundary used in this report was drawn considering water-level data from wells that were not available to previous investigators ( fig.…”

Textural and compositional evidence for the evolution of pedogenic calcite and dolomite in a weathering profile on the Kohala Peninsula, Hawai’i

“…This is in sharp contrast to the eastern side and summit of Hawai'i island, where trade-wind driven orographic precipitation can exceed 400 cmly (Giambelluca and Schroeder 1998). The present-day water table on Hawai'i is near sea level, well below the elevation of our soils, because of the high permeability of the volcanic strata that make up the island (Stearns and MacDonald 1946;Takasaki 1978). Because the island is experiencing long term subsidence (Ludwig et al 1991;Moore and Clague 1992) and eustatic sea level is at its highest for at least the last 250 k.y.…”