Description of water and air movement during infiltration

An approximate analytical solution for the problem of one-dimensional infiltration into a homogeneous porous medium is presented. The solution is made possible by assuming that capillary pressure can be partially neglected. Two equations involving two unknowns, water saturation and total velocity, are derived and then solved in a step-wise fashion to yield the saturation profile and the total velocity at any time. Infiltration quantities are obtained by integration of the area under the saturation profile. Analytical concepts and procedures relevant to the determination of the evolving saturation profile are discussed in some detail. Particular attention is given to the nature and behavior of the fractional flow function. The occurrence of air counterflow during infiltration is also discussed.