Hydrogeology Journal

, Volume 18, Issue 1, pp 73–93 | Cite as

Current challenges using models to forecast seawater intrusion: lessons from the Eastern Shore of Virginia, USA

Paper

Abstract

A three-dimensional model of the aquifer system of the Eastern Shore of Virginia, USA was calibrated to reproduce historical water levels and forecast the potential for saltwater intrusion. Future scenarios were simulated with two pumping schemes to predict potential areas of saltwater intrusion. Simulations suggest that only a few wells would be threatened with detectable salinity increases before 2050. The objective was to examine whether salinity increases can be accurately forecast for individual wells with such a model, and to address what the challenges are in making such model forecasts given current (2009) simulation capabilities. The analysis suggests that even with current computer capabilities, accurate simulations of concentrations within a regional-scale (many km) transition zone are computationally prohibitive. The relative paucity of data that is typical for such regions relative to what is needed for accurate transport simulations suggests that even with an infinitely powerful computer, accurate forecasting for a single well would still be elusive. Useful approaches may include local-grid refinement near wells and geophysical surveys, but it is important to keep expectations for simulated forecasts at wells in line with chloride concentration and other data that can be obtained at that local scale.

Keywords

Numerical modeling Salt-water/fresh-water relations USA 

Défis actuels de l’utilisation des modèles pour prédire l’intrusion d’eau de mer: Des leçons de la côte est de la Virginie, USA

Résumé

Un modèle tridimensionnel du système aquifère de la côte est de la Virginie, USA, a été calé pour reproduire les historiques des niveaux d’eau et pour prédire les risques d’intrusion d’eau de mer. Des scénarios futurs ont été simulés pour deux systèmes de pompage, en vue de prédire les zones où l’intrusion d’eau de mer est possible. Ces simulations laissent à penser que seuls quelques puits seraient menacés par des hausses détectables de salinité avant 2050. L’objectif était d’évaluer si les augmentations de salinité pouvaient être précisément prédites pour des puits particuliers avec un tel modèle, et d’aborder les défis que poserait la réalisation de tels modèles de prédiction compte tenu des capacités de simulation actuelles (2009). L’analyse montre que, même avec les moyens de calculs actuels, des simulations précises de concentration à l’intérieur d’une zone de transition à l’échelle régionale (plusieurs kilomètres) sont prohibitives d’un point de vue calculatoire. Au vu du manque relatif de données, caractéristique de telles régions, au regard des besoins pour des simulations du transport précises, il apparaît que même avec un ordinateur de puissance illimitée, une prévision précise pour un puits unique restera hors d’atteinte. Une discrétisation fine du maillage à proximité des puits et une prospection géophysique peuvent être utiles, mais il convient que les attentes en termes de prévisions simulées soient conformes aux concentrations en chlore et aux autres données qui peuvent être obtenues cette échelle locale.

Desafíos actuales del uso de los modelos para pronosticar la intrusión de agua de mar: lecciones de la costa Este de Virginia, EEUU

Resumen

Un modelo tridimensional de un sistema acuífero de la costa Este de Virginia, EEUU fue calibrado para reproducir los niveles de agua históricos y pronosticar las áreas potenciales de intrusión de agua salada. Los escenarios futuros fueron simulados con dos esquemas de bombeo para predecir las áreas potenciales de intrusión de agua salada. Las simulaciones sugieren que solamente unos pocos pozos podrían estar amenazados con incrementos de salinidad detectables antes del 2050. El objetivo fue examinar si el incremento de salinidad puede ser pronosticado con precisión para pozos individuales con tal modelo, y especificar cuales son los desafíos al modelar tales pronósticos dada la actual (2009) capacidad de simulación. El análisis sugiere que aún con las actuales capacidades computacionales, simulaciones precisas de concentraciones dentro de la zona de transición a una escala regional (muchos km) son computacionalmente prohibitivas. La relativa escasez de datos que es típica para tales regiones en relación con lo que es necesario para precisas simulaciones de transporte sugiere que, aún con una infinitamente poderosa computadora, pronósticos para un pozo simple sería aún elusivo. Enfoques útiles pueden incluir un refinamiento de la red local cerca de los pozos y relevamientos geofísicos, pero es importante mantener las expectativas para pronósticos simulados en los pozos en línea con concentraciones de cloruro y otros datos que pueden ser obtenidos a escala local.

利用模型预测海水入侵面临的挑战: 以美国弗吉尼亚东部滨海为例

摘要

通过校正美国弗吉尼亚州东部滨海的含水层系统的三维模型来重现历史水位以及预测海水入侵的发展趋势。此外, 利用两个抽水计划模拟未来的假定来预测海水入侵的可能区域。模拟表明2050年前, 根据能检测的盐度增加, 仅有少数井将会受到威胁。此研究的目标就是, 利用这个模型检测对于单个井能否准确预测盐度的增加以及阐述建立预测当前 (2009) 给定的模拟条件下模型的挑战性。分析表明即使在目前的计算机水平条件下, 区域尺度 (km) 变换带内的浓度的准确模拟是不可能的。对于准确的运移模拟十分必要的区域的典型的但相对少的数据表明即使是有强大能力的计算机, 但对于单个井的准确预测仍然是非常难的。有用的方法可能包括井附近的局部网格细化和地球物理调查, 但是使模拟预测结果与氯化物的浓度以及区域尺度上能获得的其他数据一致是非常重要的。

Desafios actuais no uso de modelos de previsão da intrusão marinha: lições da Costa Leste (Eastern Shore) da Virgínia, EUA

Resumo

Um modelo tri-dimensional do sistema aquífero da Costa Leste (Eastern Shore) da Virgínia, EUA, foi calibrado para reproduzir níveis de água históricos e para prever o potencial de intrusão marinha. Cenários futuros foram simulados com dois esquemas de bombagem, para prever áreas potenciais de intrusão marinha. As simulações sugerem que apenas alguns furos seriam afectados por aumentos detectáveis de salinidade antes de 2050. O objectivo era analisar se os aumentos de salinidade podem ser previstos com precisão para cada captação, individualmente e com este modelo, e abordar os desafios se põem em fazer tais previsões com as actuais (2009) potencialidades de modelação. A análise sugere que, mesmo com as capacidades actuais de computação, simulações precisas de concentrações a uma escala regional (muitos km) para as zonas de transição, são computacionalmente proibitivas. A típica relativa escassez de dados quando comparada com as necessidades requeridas pelas simulações dos modelos de transporte, sugere que, mesmo com um computador infinitamente poderoso, previsões precisas, para cada captação, seriam possivelmente enganadoras. Abordagens úteis incluem refinamentos nas redes locais, perto das captações, e a utilização de dados de prospecção geofísica, mas é importante manter as expectativas para as simulações nas captações, em linha com as concentrações de cloretos e com outros dados disponíveis à escala local.

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Copyright information

© US Government 2009

Authors and Affiliations

  1. 1.US Geological SurveyRestonUSA
  2. 2.US Geological SurveyRichmondUSA

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