Derivation of an equation of infiltration

Abstract

Since the publication of the article of Green and Ampt (1911) the two constants appearing in their ‘equation of infiltration’ have been considered to be empirical constants. In fact, they can be deduced simply from the soil characteristics, and they have a very precise physical meaning. However, the assumption of an abrupt front separating a saturated zone from the zone at the initial water content can lead to prediction errors of the order of 10–70%. Derived formulas display explicitly the functional dependence of the effective (or flowing) capillary head and of the viscous correction factor as a function of the initial water content. These formulas are both simple and accurate and of practical value to the hydrologist.