As stated in the Preface, and emphasized repeatedly, the objective of this book is to present and discuss the underlying fundamentals, as well as the actual construction, of groundwater flow and solute transport models. Such models can predict the future behavior, e.g., in the form of water levels and solute concentrations, in specified subsurface domains. The relevant domains of interest here are aquifers and the unsaturated zone. So far, we have been focussing only on conceptual and mathematical models. We have repeatedly emphasized, and we shall do so again in Chap. 11, that optimal management decisions should not be made unless we use models to predict the consequences of implementing the proposed decision alternatives. By analyzing these consequences, or forecasts, we can make sure that constraints are not violated, and that the optimal decision alternative is, indeed, selected. Such forecasts can be made by solving the mathematical models that
the behavior in the domain of interest, in response to the implementation of various proposed alternative decisions. Unfortunately, although analytical solutions are preferable, they are seldom possible for problems of practical interest, because of the irregular boundaries of the problem domain, the heterogeneity of the domain, with respect to its physical parameters, and, sometimes, the nonlinearity of the equations. Instead, computer-based numerical methods are used in practice for solving (or ‘running’) these models.