Groundwater models are computer implementations of a set of mathematical descriptions of the physical, chemical, and/or biological processes governing the flow of water (sometimes in
conjunction with other fluids) and the transport of chemical constituents and biota in the subsurface. They are used by groundwater specialists as a tool in analyzing and understanding the complexities of a
groundwater system, and for computing the response of such a system to natural, and proposed or historic man-induced changes.
The development of an operational model of a specific groundwater system is often called "model application" or "model construction." To obtain an acceptable and
defensible representation of the hydrogeologic system involved, model application should follow a step-wise protocol, such as described in ASTM Standard D-5447 (Standard Guide for Application of a Ground Water Flow
Model to a Site Specific Problem). The construction of an operational model of a groundwater system consist of four major stages (see Figure):
- formulation of objectives and conceptualization of the groundwater system
- code selection and model construction
- prediction and uncertainty analysis
Each stage consists of various steps. Often, results from a particular step are used as feedback for previous steps, resulting in a rather iterative procedure.
Level of complexity, detail, and effort in modeling should be commensurate with project objectives. Modeling is one of the tools in the ground water
professional's toolbox, albeit a very powerful one. It should not replace detailed site investigation and professional judgement.