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Simulating seawater intrusion in a complex coastal karst aquifer using an improved variable-density flow and solute transport–conduit flow process model

  • Zhongyuan Xu
  • Bill X. Hu
  • Zexuan XuEmail author
  • Xiujie Wu
Paper
  • 46 Downloads

Abstract

VDFST-CFP (variable-density flow and solute transport–conduit flow process) is a density-dependent discrete-continuum numerical model for simulating seawater intrusion in a dual-permeability coastal karst aquifer. A previous study (Xu and Hu 2017) simulates variable-density flow only in a single conduit, and studies the parameter sensitivities only in the horizontal case (2D domain as horizontal section) by the VDFST-CFP model. This paper focuses on the density-dependent vertical case (2D domain as vertical section) with two major improvements: 1) when implementing double-conduit networks in the domain, simulated intruded plumes in the porous medium are extended in the double-conduit scenario, compared to the single-conduit system; 2) by quantifying micro-textures on the conduit wall by the Goudar-Sonnad equation and considering macro-structures as local head loss. Sensitivity analysis shows that medium hydraulic conductivity, conduit diameter and effective porosity are important parameters for simulating seawater intrusion in the discrete-continuum system. On the other hand, rougher micro-structures and additional macro-structure components on the conduit wall would reduce the distance of seawater intrusion to the conduit system, but, rarely affect salinity distribution in the matrix. Compared to the equivalent mean roughness height, the new method (with more detailed description of structure) simulates seawater intrusion slightly landward in the conduit system. The macro-structure measured by local head loss is more reasonable but needs further study on conduit flow. Xu and Hu (2017) Development of a discrete-continuum VDFST-CFP numerical model for simulating seawater intrusion to a coastal karst aquifer with a conduit system. Water Resources Research: 53, 688-711.

Keywords

Karst Numerical modeling Seawater intrusion VDFST-CFP 

Simulation de l’intrusion saline dans un aquifère côtier karstique complexe en utilisant un modèle amélioré d’écoulement dans les conduits et de transport de solutés à densité variable

Résumé

VDFST-CFP (écoulement dans les conduits et transport de solutés à densité variable) est un modèle numérique discret-continu permettant de simuler l’intrusion saline dans un aquifère côtier karstique à double perméabilité. Une étude antérieure (Xu and Hu 2017) simule l’écoulement à densité variable dans un conduit unique et évalue la sensibilité des paramètres pour une configuration horizontale (2D selon une section horizontale) avec le modèle VDFST-CFP. Cet article se focalise sur le cas de l’écoulement à densité variable dans le plan vertical (domaine 2D selon une section verticale) avec deux améliorations majeures: 1) en introduisant un réseau de double conduit dans le domaine, les panaches d’intrusion simulés dans le milieu poreux sont plus étendus dans le scénario du double conduit, en comparaison du système à conduit unique ; 2) en quantifiant les micro-textures sur les parois du conduit par l’équation Goudar-Sonnad et en considérant les macro-structures tel que les pertes de charges hydrauliques locales. L’analyse de sensibilité montre que la conductivité hydraulique moyenne, le diamètre du conduit et la porosité efficace sont les paramètres importants pour la simulation de l’intrusion saline dans le système discret-continu. De plus, des micro-structures plus rugueuses et des macro-structures additionnelles sur les parois du conduit réduisent la distance de l’intrusion dans le système de conduit, mais n’impactent que très peu la répartition de la salinité dans la matrice. En comparaison avec la valeur de la rugosité moyenne équivalente, cette nouvelle méthode (incluant une description plus détaillée de la rugosité) simule l’intrusion saline légèrement plus à l’intérieur des terres au sein du système de conduit. La macro-structure mesurée par les pertes de charge hydrauliques locales semble plus adéquate mais nécessite des études additionnelles sur les écoulements dans les conduits. Xu Z. and Hu B.X. (2017) Development of a discrete-continuum VDFST-CFP numerical model for simulating seawater intrusion to a coastal karst aquifer with a conduit system. (Développement d’un modèle numérique discret-continu VDFST-CFP pour simuler l’intrusion saline dans un aquifère côtier karstique avec un système de conduit.) Water Resources Research: 53, 688-711.

Simulación de la intrusión de agua de mar en un complejo acuífero kárstico costero utilizando un modelo mejorado de procesos de flujo en conducto con flujo de densidad variable y transporte de solutos

Resumen

El VDFST-CFP (procesos de flujo en conductos – flujos de densidad variable y transporte de soluto) es un modelo numérico de continuo - discreto dependiente de la densidad para simular la intrusión de agua de mar en un acuífero kártico costero de doble permeabilidad. El estudio anterior (Xu y Hu, 2017) simula el flujo de densidad variable en un solo conducto y estudia la sensibilidad de los parámetros solo en el caso horizontal (dominio 2D como sección horizontal) mediante el modelo VDFST-CFP. Este documento se enfoca en el caso vertical dependiente de la densidad (dominio 2D como sección vertical) con dos mejoras principales: 1) cuando se implementan redes de doble conducto en el dominio, las plumas de la intrusión simulada en el medio poroso se extienden en el escenario de doble conducto, en comparación con el sistema de un solo conducto; 2) cuantificando las micro texturas en la pared del conducto mediante la ecuación de Goudar-Sonnad y considerando las macroestructuras como pérdida de carga hidráulica local. El análisis de sensibilidad muestra que la conductividad hidráulica media, el diámetro del conducto y la porosidad efectiva son parámetros importantes para simular la intrusión de agua de mar en el sistema continuo - discreto. Por otro lado, las microestructuras más rugosas y los componentes de macroestructura adicionales en la pared del conducto reducirían la distancia de la intrusión de agua de mar al sistema de conducto, pero rara vez afectarán la distribución de salinidad en la matriz. En comparación con la altura de rugosidad media equivalente, el nuevo método (con una descripción más detallada de la rugosidad) simula la intrusión de agua de mar ligeramente hacia el interior del sistema de conductos. La macroestructura medida por la pérdida de carga local es más razonable, pero necesita más estudios sobre el flujo del conducto. Xu Z. y Hu B.X. (2017) Development of a discrete-continuum VDFST-CFP numerical model for simulating seawater intrusion to a coastal karst aquifer with a conduit system (Desarrollo de un modelo numérico continuo discreto VDFST-CFP para simular la intrusión de agua de mar en un acuífero kárstico costero con un sistema de conductos). Water Resources Research: 53, 688-711.

采用改进的变密度流及溶质运移-管道流过程模型模拟复杂沿海岩溶含水层的海水入侵

摘要

VDFST-CFP(变密度流及溶质运移-管道流过程)是一个基于密度的离散-连续数值模型,用来于模拟双渗透系统的沿海岩溶含水层的海水入侵。先前的研究(Xu和Hu,2017年)用变密度流及溶质运移-管道流过程模型只模拟了单管道的情况,并且只研究了在水平面的情况下(二维域作为水平剖面)的参数灵敏度问题。本文着重研究垂直情况(二维域作为垂直剖面)下的变密度流体并做了两方面的改进:1),使用双管道系统并与单管道系统相比,结果显示双管道情形下孔隙介质中海水入侵面分布更广;2)通过Goudar-Sonnad方程量化管道壁上的微纹理,并通过局部水头损失的方法考虑宏观结构的作用。灵敏度分析显示,介质水力传导率、管道直径及有效孔隙度是模拟离散-连续系统中海水入侵的重要参数。另一方面,管道壁上较粗糙的微观结构以及额外的宏观结构成分会减少海水在岩溶管到中的入侵距离,但是,很少能影响非岩溶管道区域的盐度分布。与等量平均粗糙度相比,新的模型(具有更详细的宏观结构描述)模拟出海水在岩溶管到中向陆地的入侵距离更远。由局部水头损失测量的宏观结构更合理,但需要对管道流进行进一步的研究。Xu和Hu B.X. (2017)。Development of a discrete-continuum VDFST-CFP numerical model for simulating seawater intrusion to a coastal karst aquifer with a conduit system. (模拟具有管道系统的沿海岩溶含水层海水入侵的离散-连续变量-密度流及溶质运移-管道流过程数值模型的开发。) Water Resources Research (水资源研究):53, 688-711

Simulação de intrusão de água do mar em um aquífero cárstico costeiro complexo usando um fluxo de densidade variável e transporte de soluto melhorados - modelo de processo de fluxo de conduto

Resumo

O FDVTS-PFC (fluxo de densidade variável e de transporte de soluto - processo de fluxo de conduto) é um modelo numérico contínuo-discreto dependente da densidade para simular a intrusão de água do mar em um aquífero cárstico costeiro de dupla permeabilidade. O estudo anterior (Xu e Hu, 2017) simula o fluxo de densidade variável apenas em um único conduto e estuda as sensibilidades do parâmetro apenas no caso horizontal (domínio 2D como seção horizontal) pelo modelo FDVTS-PFC. Este artigo foca o caso na densidade-dependente vertical (domínio 2D como seção vertical) com duas grandes melhorias: 1) ao implementar redes de condutos duplos no domínio, plumas intrusivas simuladas no meio poroso são estendidas no cenário de duplo-conduto, em comparação com o sistema de conduto-único; 2) pela quantificação de micro-texturas na parede do conduto pela equação de Goudar-Sonnad e considerando macroestruturas como perda de carga local. A análise de sensibilidade mostra que a condutividade hidráulica média, o diâmetro do conduto e a porosidade efetiva são parâmetros importantes para simular a intrusão da água do mar no sistema contínuo-discreto. Por outro lado, microestruturas mais rugosas e componentes macroestruturais adicionais na parede do conduto reduziriam a distância da intrusão da água do mar ao sistema de condutos, mas, raramente, afetam a distribuição da salinidade na matriz. Em comparação com a altura média equivalente de rugosidade, o novo método (com uma descrição mais detalhada da rugosidade) simula a intrusão da água do mar ligeiramente para o interior do sistema de condutos. A macro-estrutura medida pela perda de carga local é mais razoável, mas precisa de um estudo mais aprofundado sobre o fluxo do conduto. Xu Z. e Hu B.X. (2017) Development of a discrete-continuum VDFST-CFP numerical model for simulating seawater intrusion to a coastal karst aquifer with a conduit system (Desenvolvimento de um modelo numérico contínuo-discreto FDVTS-PFC para simulação de intrusão de água do mar em um aquífero cárstico costeiro com um sistema de conduto.) Water Resources Research: 53, 688-711.

Notes

Acknowledgements

The authors would like to thank Dr. Ming Ye, Dr. Stephen Kish and Dr. Yang Wang at Florida State University for providing useful insights and comments during the development of the conceptual model and numerical modeling. This project is partially funded by the National Natural Science Foundation of China (grant number 41530316) and partially by Osmond Tanner Endowment.

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Copyright information

© Springer-Verlag GmbH Germany, part of Springer Nature 2019

Authors and Affiliations

  • Zhongyuan Xu
    • 1
    • 2
  • Bill X. Hu
    • 3
    • 4
  • Zexuan Xu
    • 5
    Email author
  • Xiujie Wu
    • 2
  1. 1.College of Earth, Ocean, and EnvironmentUniversity of DelawareNewarkUSA
  2. 2.College of Environment & Civil EngineeringChengdu University of TechnologyChengduChina
  3. 3.School of Water Resources and EnvironmentChina University of Geosciences (Beijing)BeijingPeople’s Republic of China
  4. 4.Institute of Groundwater and Earth SciencesThe Jinan UniversityGuangzhouPeople’s Republic of China
  5. 5.Climate and Ecosystem Sciences DivisionLawrence Berkeley National LaboratoryBerkeleyUSA

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