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John F. Mink

Publications and source records attributed to John F. Mink.

4 recordsLinked to original sources
USGS1982

Water resources of southeastern Oahu, Hawaii

Southeastern Oahu comprises the eastern end of the Koolau Range and is divided into two roughly equal parts by the crest of the range. The northside of the crest is commonly called the windward side and the southside, the leeward. Precipitous cliffs aproned by a gently sloping landscape are the main topographic features on the windward side. The leeward side is a gentle lava-flow slope incised by steep narrow valleys. The main Koolau fissure zone, including the caldera, lies on the windward side. The leeward side includes minor rift zones that are perpendicular to and intersect the main fissure zone. Dikes in the main fissure zone strike from nearly east-west in the eastern end to about N. 55? W. in the western part. Dikes in the minor rift zones strike from north-south to slightly northeasterly. Water use is about 18 Mgal/d (million gallons per day) of which only 4 Mgal/d is obtained locally from ground-water sources. About a third of the 14 Mgal/d deficit is imported from sources northwest of the study area on the windward side and the remainder from sources in the Honolulu and Pearl Harbor areas on the leeward side. The 4 Mgal/d being developed represents only about 3 percent of the area's rainfall compared to a development-rainfall ratio of 20 percent for the rest of the island. Streams are short and flashy. Perennial streamflow to the sea occurs only in Maunawili Valley and in the Waimanalo area. Mean annual discharge is estimated at 20 Mgal/d in the windward side and at 15 Mgal/d on the leeward side. Low flow, expressed as the flow that is equaled or exceeded 90 percent of the time, is 5 Mgal/d windward of the crest and zero leeward of it. Most fresh ground water occurs in lava flows of the Koolau Volcanics. It is impounded by dikes in the rift zones and floats on saline ground water as lenses outside the rift zones. Small but important bodies of freshwater are perched in volcanic rocks of the Honolulu Group in Maunawili Valley. Fresh ground water occurs in near-shore calcareous sands that overlie a clay horizon in the Waimanalo area. Deeply buried talus and alluvium also carry fresh ground water in the Waimanalo area. Wells tapping saline ground water in fresh lava flows of the Honolulu Group provide water for a sea-life park in the Makapuu area. The same aquifer is tapped by wells for disposal of the saline waste water. The current development scheme in the windward side that utilizes only the free-flow equilibrium discharge of dike-impounded water is inefficient and does not cope with the annual weather cycle. The flow available for development under this scheme is greatest in the rainy winter months when demand is the lowest and least in the summer months when demand is the highest. A more optimal scheme would be to change this natural flow pattern by depleting storage by pumping to increase flow in the high-demand summer months and allowing the depleted storage to recover naturally in the low-demand winter months. Depleting storage would lower water levels which would provide more room for infiltration and provide less opportunity for evapotranspiration. The basal-water reservoir in the leeward side is isolated hydrologically from abutting reservoirs outside the area and can and should be fully exploited. The existing development of the basal-water reservoir is small compared to the natural ground-water flow and that part not being developed is wasting to the sea. Because the area is hydrologically isolated, development will not be detrimental to or reduce the ground-water supply outside the area.

Open-File Report↗
USGS1981

Evaluation of major dike-impounded ground-water reservoirs, Island of Oahu, with a section on flow hydraulics in dike tunnels in Hawaii

Ground-water reservoirs impounded by volcanic dikes receive a substantial part of the total recharge to ground water on the island of Oahu because they generally underlie the rainiest areas. They accumulate the infiltration from rainfall, store it temporarily, and steadily leak it to abutting basal reservoirs or to streams cutting into them. The dike reservoirs have high hydraulic heads and are mostly isolated from saline water. The most important and productive of the dike-impounded reservoirs occur in an area of about 135 square miles in the main fissure zone of the Koolau volcano where the top of the dike-impounded water reaches an altitude of at least 1,000 feet. Water is impounded and stored both above and below sea level. The water stored above sea level in the area of about 135 square miles has been roughly estimated at 560 billion gallons by using a mean water level of 400 feet and a mean specific yield of 0.05. In comparison, the water stored above sea level in reservoirs with a mean water level of 300 feet and mean specific yield of 0.03 underlying a dike-intruded area of about 53 square miles in the Waianae Range has been roughly estimated at 100 billion gallons. Storage below sea level is indeterminable, owing to uncertainties in the ability of the rock to store water resulting from increasing dike density and decreasing porosity. Total leakage from storage in the WaLanae Range has not been estimated because underflow is difficult to determine. Much of the surface leakage, about 4 Mgal/d in the upper parts of Waianae, Makaha, and Lualualei Valleys, has been diverted by tunnels. Hence, supplies available, other than surface leakage, cannot be estimated from the discharge end of the hydrologic cycle. Infiltration in the Waianae Range to dike-intruded reservoirs in the upper part of the valleys on the west (leeward) side has been estimated at about 20 Mgal/d, and on the east (windward) side, at about 10 Mgal/d. The available supply has been estimated at about 15 Mgal/d from the infiltration on the leeward side, of which about 4 Mgal/d is now being developed. No estimate has been made for the available supply on the windward side. Dike-intruded reservoirs at shallow depths west (lee side) of the crest are in upper Makaha, Waianae, and Lualualei Valleys. They are at moderate depths in upper Haleanu and in lower Kaukonahua Gulches on the east (windward) side. Flow hydraulics in dike tunnels is also discussed.

Hawaii↗