Hydrogeology Journal

, Volume 13, Issue 2, pp 436–450

Three-dimensional variable-density flow simulation of a coastal aquifer in southern Oahu, Hawaii, USA

Report

Abstract

Three-dimensional modeling of groundwater flow and solute transport in the Pearl Harbor aquifer, southern Oahu, Hawaii, shows that the readjustment of the freshwater–saltwater transition zone takes a long time following changes in pumping, irrigation, or recharge in the aquifer system. It takes about 50 years for the transition zone to move 90% of the distance to its new steady position. Further, the Ghyben–Herzberg estimate of the freshwater/saltwater interface depth occurred between the 10 and 50% simulated seawater concentration contours in a complex manner during 100 years of the pumping history of the aquifer. Thus, it is not a good predictor of the depth of potable water. Pre-development recharge was used to simulate the 1880 freshwater-lens configuration. Historical pumpage and recharge distributions were used and the resulting freshwater-lens size and position were simulated through 1980. Simulations show that the transition zone moved upward and landward during the period simulated.

Previous groundwater flow models for Oahu have been limited to areal models that simulate a sharp interface between freshwater and saltwater or solute-transport models that simulate a vertical aquifer section. The present model is based on the US Geological Survey’s three-dimensional solute transport (3D SUTRA) computer code. Using several new tools for pre- and post-processing of model input and results have allowed easy model construction and unprecedented visualization of the freshwater lens and underlying transition zone in Hawaii’s most developed aquifer.

Keywords

Groundwater development Groundwater management Hawaii Numerical modeling Salt-water/fresh-water relations 

Résumé

La modélisation tridimensionnelle de l’écoulement et du transport dans la partie sud de l’aquifère Oahu-Hawai montre que le temps de réajustement de la zone de transition entre l’eau douce et l’eau salée est assez long et dépend de la variation des pompages et des irrigations, ainsi que de la recharge du système aquifère. Il sont nécessaires 50 ans pour que la zone de transition parcoure 90% de la distance qui la sépare de sa nouvelle position. La profondeur du biseau estimée par le schéma Ghyben–Herzberg se trouve entre les contours de 10 et 50% de la concentration de l’eau salée. Ce résultat a été obtenu après la simulation de l’histoire du pompage de l’aquifère pendant une période de 100 ans. Donc le schéma Ghyben–Herzberg conduit aux valeurs erronées de la profondeur de l’eau potable. La valeur de la recharge d’avant l’exploitation de l’aquifère a été utilisée pour simuler la configuration des lentilles d’eau douce en 1880. En utilisant l’histoire du pompage et la distribution de la recharge ont on a simulé les dimensions et le positions des lentilles d’eau douce jusqu› en 1980. Les simulation montrent que le mouvement de la zone de transition est ascendant et vers le continent.

Les modèles antérieurs de la zone d’Oahu ont été des modèles locaux qui ont simulé une interface nette eau douce-eau salée ou des modèles de transport bidimensionnels, dans une coupe verticale. Le modèle actuel est basé sur le code 3D-SUTRA, réalisé par le Service Géologique des États-Unis. L› utilisation des différents techniques de traitement des données a permis une construction facile du modèle, ainsi qu› une visualisation sans précédent des lentilles d’eau douces et de la zone de transition sous-jacente dans le plus grand aquifère du Hawai.

Resumen

La modelación tridimensional del flujo de agua subterránea y del transporte de solutos en el acuífero de Pearl Harbor, en la parte sur de Oahu, Hawaii, muestra que el reajuste de la zona de transición agua dulce–agua salada, toma un largo tiempo a partir de cambios en el bombeo, irrigación o recarga en el sistema acuífero. Le toma alrededor de 50 años, a la zona de transición, moverse el 90% de la distancia hacia su nueva posición estacionaria. Además, el estimativo de Ghyben–Herzberg, sobre la profundidad de la interfase agua dulce–agua salada, se encuentra entre el 10 y el 50% en los contornos simulados de concentración de agua salada, de una manera compleja, durante 100 años de la historia de bombeo del acuífero. Por tanto, no es este un buen predictor de la profundidad del agua potable. Se utilizó una recarga pre – desarrollo, para simular la configuración del lente de agua dulce en 1880. Fueron utilizadas las distribuciones históricas del bombeo y de la recarga y se simularon el tamaño y posición resultantes del lente de agua dulce hasta 1980. Esas simulaciones muestran que la zona de transición se movió tierra adentro y hacia arriba, durante el periodo que se simuló.

Los anteriores modelos de flujo para agua subterránea en Oahu, han sido limitados a modelos areales, que simulan una interfase abrupta entre agua dulce y agua salada, o bien han sido modelos de transporte de solutos que simulan una sección vertical del acuífero. El modelo presente está basado en el programa de computador del US Geological Survey (3D SUTRA), para transporte de solutos en tres dimensiones. Mediante el uso de varias herramientas nuevas para pre – procesamiento y post – procesamiento de las entradas y resultados del modelo, se ha permitido una construcción fácil del mismo y una visualización sin precedentes del lente de agua dulce y de la zona de transición subyacente en el acuífero más desarrollado de Hawaii.

Supplementary material

readme.doc (30 kb)
Instructions for viewing the Electronic Supplementary Material readme.doc
east.swf (5 mb)
Flash File Format PearlHarbor east.swf (5.2 MB)
west.swf (3.1 mb)
Flash File Format PearlHarbor west.swf (3.2 MB)
grid.wrl (441 kb)
grid.wrl (450 KB)
1880.wrl (648 kb)
1880.wrl (660 KB)
1980.wrl (631 kb)
1980.wrl (640 KB)

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Copyright information

© Springer-Verlag 2005

Authors and Affiliations

  1. 1.US Geological SurveyHonoluluUSA
  2. 2.US Geological SurveyRestonUSA

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