Simulation Methods

As with any other physical process we try to estimate, in a numerical simulation simplifications must be made.  In the case of infiltration, Darcy's law would ideally be used in the mathematical model, however it is difficult to know important parameters such as the hydraulic conductivity and moisture content of soil across an entire watershed.  Therefore for simpler deterministic models like the rational method and HEC-1/HMS estimates are made by empirical methods such as the rational runoff coefficient or the curve number.