While there are many effective groundwater modelling methods available, engineers often fall back on just a few while ignoring those which could offer deeper insight and greater efficiency.
The default approach for many has become finite element and finite difference methods. Finite element and finite difference methods are powerful tools capableof simulating very complex, conceptualisations of the groundwater system. However, while they may be the right tool for many groundwater inquiries, the predictive power of a groundwater model depends on its ability to correctly identify the dominant controlling factors and their influences, not upon its completeness or complexity.
This means there are many other frequently overlooked mathematical tools in the toolbox which could be more appropriate for identifying the controlling factors and understanding their influence on the system.
One of the most comprehensive and easy to use of these is Analytical Element Modelling (AEM). While it’s a relative newcomer to numerical modelling it has applications in various fields, including groundwater hydrology, heat conduction analysis, contaminant transport, seepage problems, periodic waves, and deformation by force.
AEM is a meshless numerical modelling method that relies on the well-worn mathematical principle of superposition. The method allows for extremely flexible internal and external boundary conditions and this, combined with the absence of a mesh (or grid), ensures accurate representation of hydrologic features across the entire domain. This is a very practical advantages over other methods allowing for quick and easy adjustments in model construction, enabling expansion or refinement without altering boundary conditions or redesigning the computational mesh or grid. This adaptability is crucial for stepwise modelling approaches, where simpler models can guide initial project phases and gradually evolve into more complex representations as more data and insights become available. It is a very intuitive and fast modelling method for creating and testing assumptions. As such AEMit is very well suited to identifying the controlling factors and understanding their influence on the system. In short, it can offer more insight in less time than other numerical methods.
AEM is a tried and tested methodology which has been applied in hydrogeology since the late 1970’s. It was pioneered by Otto Strack when he was tasked with modelling the environmental impact of the Tennessee-Tombigbee Waterway for the U.S. Army Corps of Engineers. Since then, numerous researchers have continued to add to the body of AEM knowledge, although these were generally limited to steady state and 2D flow problems. However, beginning in 1999,
breakthrough developments in AEM were made by Dr Charles Fitts, who solved many of the mathematical challenges that hindered AEM development for decades, including developing methods for aquifer zonation, anisotropy, multipleaquifer layers, sub-domains, heterogeneity, and fully transient simulations. Dr. Fitts’ contribution to AEM resulted in the development of AnAqSim (Analytic Aquifer Simulator), a groundwater modelling application, in 2011.
Due to its flexibility and speed AEM is increasing in popularity, not only in hydrogeology applications but in simulating other physical processes. Typical applications in hydrogeology include regional scale modelling of groundwater flow regimes, wellhead protection assessments, mining impact assessments, construction dewatering planning, in-situ groundwater remediation designs, slurry wall designs, open loop geothermal designs, saltwater intrusion studies, and aquifer storage and recovery planning.
There are many tools available that allow us to simulate and assess how a groundwater flow regime behaves and forecast both natural and man-made changes to that regime. As professionals we should consider all the tools available to us, from data driven models to closed-form equations to numerical methods and choose the best tool for the job. AEM is one of those tools which might have been buried deep in the toolbox and, until now, overlooked. It makes sense to consider AEM as an option that offers quick development models, rapid testing/iteration of design concepts and, ultimately, better-informed decision making on many projects.