Numerical analysis of the hydrogeologic controls in a layered coastal aquifer system, Oahu, Hawaii, USA |
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Authors: | Delwyn S. Oki William R. Souza Edward L. Bolke Glenn R. Bauer |
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Affiliation: | (1) U.S. Geological Survey, 677 Ala Moana Blvd., Suite 415, Honolulu, Hawaii 96813, USA Fax: +1 808 522 8298 e-mail: dsoki@usgs.gov, US;(2) U.S. Geological Survey, 10615 S.E. Cherry Blossom Drive, Portland, Oregon 97216, USA, US;(3) Hawaii State Commission on Water Resource Management, 1151 Punchbowl Street, Honolulu, Hawaii 96813, USA, US |
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Abstract: | The coastal aquifer system of southern Oahu, Hawaii, USA, consists of highly permeable volcanic aquifers overlain by weathered volcanic rocks and interbedded marine and terrestrial sediments of both high and low permeability. The weathered volcanic rocks and sediments are collectively known as caprock, because they impede the free discharge of groundwater from the underlying volcanic aquifers. A cross-sectional groundwater flow and transport model was used to evaluate the hydrogeologic controls on the regional flow system in southwestern Oahu. Controls considered were: (a) overall caprock hydraulic conductivity; and (b) stratigraphic variations of hydraulic conductivity in the caprock. Within the caprock, variations in hydraulic conductivity, caused by stratigraphy or discontinuities of the stratigraphic units, are a major control on the direction of groundwater flow and the distribution of water levels and salinity. Results of cross-sectional modeling confirm the general groundwater flow pattern that would be expected in a layered coastal system. Groundwater flow is: (a) predominantly upward in the low-permeability sedimentary units; and (b) predominantly horizontal in the high-permeability sedimentary units. Received, October 1996 Revised, August 1997 Accepted, September 1997 |
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Keywords: | USA Hawaii numerical modeling salt-water/fresh-water relations groundwater flow |
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