Two‐phase flow infiltration equations accounting for air entrapment effects

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Abstract
Water infiltration into the unsaturated zone is potentially affected by air compression ahead of the wetting front. Analytical infiltration equations accounting for air compression, air counterflow, and flow hysteresis in a porous medium were derived on the basis of the Green and Ampt [1911] assumptions. Air compression ahead of the wetting front was predicted using the perfect gas law. The capillary pressure at the wetting front was found to vary between the dynamic water‐bubbling value and the dynamic air‐bubbling value of the material. These equations, accounting also for the effects of macropores near the soil surface, turned out to be simpler than the traditional Kostiakov [1932] and the Philip [1957a, b, c, d] equations. The equation parameters are physically meaningful and can be readily obtained from field measurements of the natural saturated hydraulic conductivity and soil water retention or pressure infiltrometer data. Experimental testing showed that the equations are reasonably accurate.