A user's approach to assess numerical codes for saturated and unsaturated seepage conditions

Numerical models are useful tools to evaluate problems and design remedial measures relative to groundwater seepage. They provide information for decision-making and guidance for collecting new data. Most users do not know in detail how the numerical code works. However, they must be sure that it gives reliable predictions for the problem under study. The major questions relative to the computer calculations are as follows: Can the results of the code be trusted? Under which conditions and to what extent are its predictions uncertain? This paper describes an approach that can be followed by model users to evaluate the results of a groundwater numerical code. This approach is relatively general, although each code is unique and may require specific controls. It begins with simple problems and progressively moves towards more complex problems: from steady-state to unsteady-state conditions, from one- to three-dimensional problems, and from saturated to saturated-unsaturated conditions. This approach is illustrated with a commercial code that passed the successive tests.