UNDERSTANDING GROUNDWATER MODELING: A SPREADSHEET APPROACH

Groundwater modeling is an essential skill all hydrogeology students should be exposed to in their education. Courses in groundwater modeling typically start with an introduction to the differential equations that govern groundwater systems and their numerical solution. The student writes relatively simple computer programs to set up a grid and solve the groundwater flow equation for the head at each element. The student advances to using standard programs (such as MODFLOW) that have been refined over the years by modeling experts to solve more complicated problems. Typically, the biggest hurdle in the learning process is when a student has to write a program. A programming course is rarely required in geoscience curricula, leaving most students at a disadvantage. Additionally, the programming language (FORTRAN) that many of the accepted groundwater codes (e.g., MODFLOW) are written in and that many groundwater modelers use when teaching modeling is no longer offered at many universities. There is also the problem of compiler availability and cost for institutions and students. The need to learn a computer programming language as part of a groundwater modeling course may not be necessary. A different method, using a computer spreadsheet program such as Microsoft Excel, is suggested as a better alternative. Excel can be used to solve iterative problems on the spreadsheet (it is like a built in Gauss-Seidel iterative solver) while simultaneously charting the results. The incorporation of wells, different boundary conditions, and spatially varying hydraulic conductivity and infiltration are easily incorporated and understood. Reasonably complicated confined or unconfined single layer models can be quickly constructed. For those insistent on students learning basic programming, the built-in Excel macro language (Visual Basic for Applications) can be used to write programs just as any other programming language while benefiting from stream-lined input, output, and graphing. The obvious advantages are that students get a better understanding of groundwater flow equations and how they are used by modeling programs, Excel is widely available to students, and students can quickly progress through the “programming” stage, allowing more time to use with the more established programs.