A Two‐Phase Numerical Model for Prediction of Infiltration: Applications to a Semi‐Infinite Soil Column

Abstract

A numerical algorithm for prediction of infiltration and water content profiles evolution in a soil column is presented. The algorithm is derived from the two‐phase flow theory for water and air. However, the governing equations reduce to the usual one‐phase flow equations by setting a parameter to a zero value. The model can shift back and forth from the one‐phase to the two‐phase mode within the course of a simulation as demanded by the situation. The need for the two‐phase approach is demonstrated for a couple of illustrative situations both with a semi‐infinite lower boundary condition, that is, for a case when the two‐phase approach might appear a priori least needed. It is shown that it is indeed needed even for a semi‐infinite soil column when mobile air cannot be confined. Rather amazingly the two‐phase computer runs cost less than the corresponding one‐phase runs. It is shown that the two‐phase algorithm is naturally more stable than the one‐phase algorithm when the water contents are high in a portion of the column. Thus the two‐phase approach is not only more realistic, but it is even less expensive whenever it is needed.