Generic workflow of groundwater flow simulations in geologically complicated domains with millions of unstructured grids

Abstract

Numerical groundwater flow simulation involves manual and tedious pre-processing and post-processing procedures. Hence, this study developed a systematic and efficient workflow to alleviate model buildup and data-processing burdens, allowing researchers to focus on the application aspects of simulation results. This highly automatic workflow allows researchers to execute three-dimensional groundwater flow simulations in sites with complex hydrogeological conditions. Processes in the workflow are formed as a trilogy: building a hydrogeological conceptual model, generating a site-specific unstructured mesh and specifying simulation conditions, and executing the simulation and post-processing results. The workflow feasibility has been demonstrated by simulating the three-component (water, brine, and air) fluid flow in Huayu Islet, the only andesitic island of the basaltic Penghu archipelago, using TOUGH3 (Transport of Unsaturated Groundwater and Heat version 3) and its EOS7 (Equation of State #7) fluid module. Our self-developed mesh generator can produce a locally refined unstructured mesh with millions of grid cells that can capture the essential geological features of Huayu. It was found that, of the three scenarios considered, only the one using a fine mesh coupled with a two-phase Dirichlet boundary condition at the top surface could obtain a physically meaningful bowl-shaped fresh water and brine interface and reasonable transport pathway characteristics. In summary, the developed workflow serves as a practical methodology to authentically characterize the hydrogeologic mechanisms of a site with complicated geology.