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AkvaGIS is a novel, free and open source module included in the FREEWAT plugin for QGIS that supplies a standardized and easy-to-use workflow for the storage, management, visualization and analysis of hydrochemical and hydrogeological data. The main application is devised to simplify the characterization of groundwater bodies for the purpose of building rigorous and data-based environmental conceptual models (as required in Europe by the Water Framework Directive). For data-based groundwater management, AkvaGIS can be used to prepare input files for most groundwater flow numerical models in all of the available formats in QGIS. AkvaGIS is applied in the Walloon Region (Belgium) to demonstrate its functionalities. The results support a better understanding of the hydrochemical relationship among aquifers in the region and can be used as a baseline for the development of new analyses, e.g., further delineation of nitrate vulnerable zones and management of the monitoring network to control chemical spatial and temporal evolution. AkvaGIS can be expanded and adapted for further environmental applications as the FREEWAT community grows. © 2018 The Authors

Within a natural system, it is common to find different physical and chemical processes in different parts of the domain. The spatial distribution of these processes may also vary in time. Examples include: groundwater flow problems where a part of the domain becomes unsaturated, and solute transport problems that have nonzero concentrations in only a part of the domain. When numerically modeling such systems with codes not designed for this task, this problem can be dealt with by solving trivial equations in all the domain (eg, solving transport over all the domain, even where it is known that no solute is present) or by solving overly general equations (eg, formulating an unsaturated flow problem even there where it is saturated), usually more expensive to solve. However, a more elegant and efficient approach is to adapt the mathematical model in space and time to the characteristics of the system. We present here a design to accomplish this feat. Specifically, our design is of a group of classes that will operate within Proost, an object oriented framework for numerically solving partial differential equations (PDE0s) for hydrogeological problems, with (for now) the finite element method. Both the solution variables of these PDE’s and the coefficients that appear in them are scalar, vector or tensor fields. In addition to the PDE’s these fields can be related by local or constitutive laws. For example, groundwater flow is represented mathematically by the flow equation (a PDE), while the relative permeability that appears in it is a local equation.In the abstraction underlying this design, we distinguish four types of equations that need solving. First, equations that have no relation to the system state, for example the intrinsic permeability of the porous medium as a function of space. These can be calculated straightforwardly. Second, the PDE themselves. They need to be solved with a numerical method, and often also a linearization method such as Newton or Pic