Abstract
The combined effect of salinity and temperature on density-driven convection was evaluated in this study for a large (28 km2) cooling canal system (CCS) at a thermoelectric power plant in south Florida, USA. A two-dimensional cross-section model was used to evaluate the effects of hydraulic heterogeneities, cooling canal salinity, heat transport, and cooling canal geometry on aquifer salinization and movement of the freshwater/saltwater interface. Four different hydraulic conductivity configurations, with values ranging over several orders of magnitude, were evaluated with the model. For all of the conditions evaluated, aquifer salinization was initiated by the formation of dense, hypersaline fingers that descended downward to the bottom of the 30-m thick aquifer. Saline fingers reached the aquifer bottom in times ranging from a few days to approximately 5 years for the lowest hydraulic conductivity case. Aquifer salinization continued after saline fingers reached the aquifer bottom and coalesced by lateral movement away from the site. Model results showed that aquifer salinization was most sensitive to aquifer heterogeneity, but was also sensitive to CCS salinity, temperature, and configuration.
Résumé
L’effet combiné de la salinité et la température sur la convection due à la densité a été évalué dans cette étude pour un large (28 km2) canal du système de refroidissement (CCS) d’une centrale hydroélectrique de production d’énergie du sud de la Floride, Etats-Unis. Une coupe transversale en deux dimensions a été utilisée pour évaluer les effets des hétérogénéités hydrauliques, de la salinité du canal de refroidissement, du transport de chaleur et de la géométrie du canal sur la salinisation d’un aquifère et les mouvements à l’interface eau douce-eau salée. Quatre configurations de conductivité hydraulique, avec des valeurs variant de plusieurs ordres de grandeur, ont été évaluées avec un modèle. Pour toutes les conditions évaluées, la salinisation de l’aquifère a commencé par la formation de doigts de forte densité et salinité descendant vers le fond de l’aquifère de 30 m d’épaisseur. Les doigts salés ont atteint le fond de l’aquifère après un temps variant de quelques jours à 5 ans environ dans le cas des plus faibles conductivités hydrauliques. La salinisation de l’aquifère a continué après que les doigts salés aient atteint le fond de l’aquifère et aient fusionnés par des mouvements latéraux en dehors du site. Les résultats du modèle montrent que la salinisation de l’aquifère a été très sensible à l’hétérogénéité de l’aquifère et également à la salinité, température et configuration du CCS.
Resumen
En este estudio se evaluó el efecto combinado de la salinidad y la temperatura sobre la convección forzada por la densidad del sistema del canal de enfriamiento (CCS) de un área (28 km2), en una planta de energía termoeléctrica en el sur de Florida, EEUU. Se usó un modelo bidimensional de sección transversal para evaluar los efectos de las heterogeneidades hidráulicas, la salinidad del canal de enfriamiento, el transporte de calor, y la geometría del canal de enfriamiento sobre la salinización de un acuífero y movimiento de la interfase agua dulce - agua salada. Con el modelo se evaluaron cuatro configuraciones diferentes de conductividad hidráulica, con valores que abarcaron varios órdenes de magnitud. Para todas las condiciones evaluadas, la salinización del acuífero se inició con la formación de densas interdigitaciones que descienden la base del acuífero de 30 m de espesor. Las interdigitaciones salinas alcanzaron la base del acuífero en tiempos que fluctuaron desde unos pocos días y 5 años aproximadamente para el caso de la menor conductividad hidráulica. La salinización del acuífero continúa después que la digitazación alcanza en la base del acuífero y es coalescente fuera del sitio por movimientos laterales. Los resultados del modelo mostraron que la salinización del acuífero era más sensitiva a la heterogeneidad del acuífero, pero que también era sensitiva a la salinidad, temperatura y configuración del CCS.
摘要
本研究针对美国佛罗里达南部某热电厂的大型冷却管道系统(ccs)估算了盐度和温度对于密度驱动的对流的耦合影响。在某二维剖面上估算水力非均质、冷却管道的盐度和形状、及热传递对含水层盐化和淡水-咸水界面运动的影响。应用该模型评估了四种不同渗透系数结构 (渗透系数相差几个量级) 。所有条件下, 含水层盐化皆由30m厚含水层中的稠密、超咸、向底部下降的指进触发。咸指进体抵达含水层底所需时间为自几天至渗透系数最低时的约5年。其后盐化继续发生, 并因离开该场地的侧向运动而发生合并。模拟结果显示, 含水层盐化对含水层非均质性最为敏感, 但对CCS盐度、温度和结构亦然。
Resumo
Neste estudo foi avaliado o efeito combinado da salinidade e da temperatura na convecção provocada pela densidade para um grande (28 km2) sistema de canais de arrefecimento (SCA) numa central termoeléctrica no sul da Flórida, EUA. Utilizou-se um modelo bidimensional de secção transversal para avaliar os efeitos das heterogeneidades hidráulicas, da salinidade do canal de refrigeração, do transporte de calor e da geometria do canal de refrigeração na salinização do aquífero e na deslocação da interface de água doce-água salgada. Com base no modelo, foram avaliadas quatro configurações de condutividade hidráulica diferentes, com os valores a variar entre várias ordens de grandeza. Para todas as condições avaliadas, a salinização do aquífero iniciou-se através de formas semelhantes a “dedos” de sal densos e hipersalinos, que desceram à base do aquífero, com 30 m de espessura. Esses “dedos” de sal atingiram a base do aquífero em tempos que variavam de alguns dias a sensivelmente 5 anos, para o caso da condutividade hidráulica mais baixa. A salinização do aquífero continuou, através de coalescência, por movimento lateral, após os “dedos” terem atingido a base do aquífero. Os resultados dos modelos mostraram que a salinização do aquífero foi mais sensível à heterogeneidade do mesmo, mas foi também sensível à salinidade, temperatura e configuração do SCA.
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Acknowledgments
The authors would like to thank J. D. Decker (US Geological Survey), R. Renken (US Geological Survey), and V. Walsh (Miami-Dade Water and Sewer Department) for reviewing an earlier version of the manuscript. Reviewers for Hydrogeology Journal (E. Abarca, W. E. Sanford, and two anonymous reviewers) provided excellent suggestions that greatly improved the manuscript.
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Hughes, J.D., Langevin, C.D. & Brakefield-Goswami, L. Effect of hypersaline cooling canals on aquifer salinization. Hydrogeol J 18, 25–38 (2010). https://doi.org/10.1007/s10040-009-0502-7
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DOI: https://doi.org/10.1007/s10040-009-0502-7