A Comparison of Physically-Based Infiltration Equations

Three infiltration equations, each derived in some manner from a consideration of the physics of flow through porous media, are compared quantitatively over the whole time range from zero to infinity. Compared with the Green and Ampt equation, the two-term Philip equation is never more than 15.1 percent higher, while the equation arising out of Philip's linearization analysis is never less than 9.2 percent lower. For practical purposes, these discrepancies may frequently be ignored. Because of its mathematical simplicity and adaptability, the two-term Philip equation, however, would be the preferred choice.