2-PHASE FLOW INFILTRATION EQUATIONS ACCOUNTING FOR AIR ENTRAPMENT EFFECTS

Water infiltration into the unsaturated zone is potentially affected b y air compression ahead of the wetting front. Analytical infiltration equations accounting for air compression, air counterflow, and flow hy steresis in a porous medium were derived on the basis of the Green and Ampt [1911] assumptions. Air compression ahead of the wetting front w as predicted using the perfect gas law. The capillary pressure at the wetting front was found to vary between the dynamic water-bubbling val ue 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 th e Philip [1957a, b, c, d] equations. The equation parameters are physi cally meaningful and can be readily obtained from field measurements o f the natural saturated hydraulic conductivity and soil water retentio n or pressure infiltrometer data. Experimental testing showed that the equations are reasonably accurate.