the phenomena, as well as the spatial and temporal trends of hydrologic parameters and stresses, and historical rainfall, flow rate, water level and solute concentration records.
For surface hydrology the most widely used simulation models can be grouped into the following classes (De Vries and Hromadka, 1992), according to the types of hydrologic problems they are intended to deal with:
single event rainfall – runoff models;
continuous – stream flow models, accounting in time for precipitation and water movement through the catchment;
With regard to groundwater hydrology, the two kinds of models most commonly used for solving flow and transport equations are based on finite difference or finite element techniques. The choice between a finite difference and a finite element model depends on the problem to be solved and on user preference. Anderson et al. (1992) provided an exhaustive and still topical literature review on this subject.
Model data requirements vary considerably. In many design studies of surface hydrology, rainfall distribution and volumes are applied to catchments, for which runoff response is characterized by synthetic unit hydrograph and generalized loss-rate functions. For physically based distributed-parameter models, a great deal of data is required for calibration purposes. In groundwater hydrology, knowledge of spatial and temporal characteristics of the aquifers, distribution of piezometric heads, recharge and discharge rates and mass concentrations, along with flow-path information, play a crucial role in testing and validating predictive simulations.