About 1,000 million gallons of water per day moves toward or into ground-water bodies of Kilauea Volcano from the lavas of Mauna Loa Volcano. This movement continues only to the northern boundaries of the east and southwest rift zones of Kilauea, where a substantial quantity of ground water is deflected downslope to other ground-water bodies or to the ocean. In the western part of Kilauea, the Kaoiki fault system, which parallels the southwest rift zone, may be the main barrier to ground-water movement. The diversion of the ground water is manifested in the western part of Kilauea by the presence of large springs at the shore end of the Kaoiki fault system, and in the eastern part by the apparently large flow of unheated basal ground water north of the east rift zone. Thus, recharge to ground water in the rift zones of Kilauea and to the areas to the south of the rift zones may be largely by local rainfall. Recharge from rainfall for all of Kilauea sources. Four possible sources are (1) cold meteoric water, (2) cold seawater, (3) hydrothermal fluids of meteoric origin, and (4) hydrothermally modified seawater. The chloride-ion to magnesium-ion ratio of ground water indicates whether the water has been geothermally modified. A ratio greater than 15 to 1 generally denotes geothermally modified ground water.

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.

No abstract

No abstract

Introduction 1 Purpose and scope 2 Evolution of the concept for the development of dike-impounded water Geologic sketch 4 Volcanic activity 4 Rift-zone structures 4 Marginal dike zone defined 6 Attitude of dikes 7 Dikes and their effects on storage and movement of ground water 7 Geologic framework of dike-impounded reservoirs 7 Factors controlling recharge and discharge of dike-impounded water 9 Dikes in the Koolau Range 11 Rift zones 11 Data base 11 Attitude and density of dikes 11 Strike or trend 11 Dip 13 Thickness 13 Density 14 Dike-impounded water in the Koolau Range 14 The reservoir 14 Development 19 Dike-impounded water in selected subzones 19 The northern end subzone 19 Dikes 19 Dike-impounded reservoirs 19 Past and potential development 27 Waiahole-Kaluanui subzone 27 Dikes 27 Dike-impounded reservoirs 29 Past and potential development 35 Kaneohe subzone 38 Dikes 38 Dike-impounded reservoirs 40 Past and potential development 42 The southeastern end subzone 48 Dikes 48 Dike-impounded reservoirs 48 Past and potential development 52 Maunawili Valley 52 Waimanalo area 55 Leeward area 56 Summary of dike-impounded water in the subzones of the Koolau Range 56 Contents III Dikes in the Waianae Range 60 Rift zones 60 Data base 60 Attitude and density of dikes 60 Dike-impounded water in the Waianae Range 63 The reservoir 63 Development 65 Potential development 65 Flow hydraulics in dike tunnels, by John F. Mink 67 Turbulent flow 68 Determination of volume of storage 70 Applications of the free-flow equations in Hawaii 71 Flow decay and storage at Waihee and Kahana tunnels 72 Summary 74 References 75 Metric conversion factors 77 IV Contents 17. Logs showing position and orientation of the dikes and flow measurements in the Uwau and Kahana tunnels 34 18. Duration curves of daily flows for windward stream, Kahana (sta. 2965) and leeward stream, North Fork Kaukonahua (sta. 2000) 39 19. Relative altitudes of base-flow measuring points in streams in Waiahole and Hakipuu areas 40 20. Map of Kaneohe subzone, showing dikes, dike-intruded rocks in dike complex and marginal dike zone, and location of tunnels, wells, and gaging stations 41 21. Sketch showing probable directions of groundwater movement between parallel dikes above an altitude of 600 feet in the area between Luluku and Kaalaea Streams 43 22. Duration curves of daily flows for windward stream, Kamooalii (sta. 2739) and leeward stream, North Halawa (sta. 2260) 44 23. Section showing zones of discharge in the Kaneohe subzone 45 24. Graph relating pumping rate versus drawdown for selected wells in the marginal dike zone and the dike complex of the Kaneohe subzone 47 25. Map of the southeastern end subzone, showing dikes, dike-intruded rocks in dike complex, marginal dike zone, minor rift zone and location of tunnels, wells, and gaging stations 49 26. Map of Palolo-Waialae District, showing frequency and distribution of dikes and sills 50 27. Hydrograph showing water levels in test holes 2046-01,-02, and 2047-02 51 28. Hydrograph showing water levels during drilling...