Development of a spreadsheet-based model for transient groundwater modelling

Understanding and modelling the passage of groundwater is important for a wide range of environmental and earth science disciplines. The science of groundwater modelling is mature, and advanced modelling algorithms are routinely implemented, for example via the widely used MODFLOW software. However, for the non-specialist scientist or student, the fundamentals of such software can be difficult to comprehend, whilst the algorithms are arguably too complex to be easily applied for many applications which require integration of a groundwater model with climate, surface-water, soil or ecological data. In this context, a spreadsheet-based groundwater model (A2016), capable of solving transient groundwater behaviour in multiple spatial dimensions, was developed. Inter-comparison tests investigating nine transient groundwater scenarios were performed between MODFLOW, A2016 and the Time-dependent Groundwater Modeling using Spreadsheet Simulation (TGMSS) model. Results demonstrated that A2016 is directly comparable to MODFLOW, with identical hydraulic heads in all model experiments. TGMSS was not able to accurately simulate hydraulic heads for any of the model experiments. A groundwater-lake interaction scenario was identified for which MODFLOW will produce unrealistic results, due to the way conductance beneath lakes is determined. Applying a specified saturated thickness approximation for the region beneath the lake resulted in improved lake-groundwater interactions. A2016 is potentially useful for educational purposes and as a tool for groundwater experiments by non-specialists, as it is modular in nature and incorporates MODFLOW terminology and techniques.