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

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.