Soil seal formation and its effect on infiltration: Uniform versus nonuniform seal approximation

Abstract

Two different approaches to the solution of the problem of flow through the dynamic stage of seal formation as well as through soil with a fully developed seal are studied. The first approach considers the disturbed seal layer and the undisturbed soil underneath as a continuous nonuniform soil profile. The second replaces the nonuniform seal by a uniform equivalent layer, thereby generating a homogeneous two-layer flow system. The depth-dependent properties of the nonuniform seal are expressed in terms of the exponential model of Mualem and Assouline [1989]. The dynamics of seal formation are modeled according to Assouline and Mualem [1997]. During the first rainfall on an undisturbed soil profile, when the seal layer is formed, the application of the first or the second approach has only a minor effect on the calculated infiltration curves. However, there is a significant difference between the two solutions regarding the dynamic changes of the water content in the soil surface and, consequently, within the seal layer. During subsequent rainfalls on a sealed soil profile, when the seal layer is completely developed, the differences between the two ways of accounting for the seal layer become evident, and their effects on the infiltration curve are much more significant. Representing the seal as an equivalent uniform layer increases the ponding time and the infiltration rates at the early stage of the process. The amplitude of these effects is increased when the rainfall rate is higher and the seal layer is thicker. An important result is that the relationship between infiltration rate and cumulative infiltration is unique in the case of a completely developed seal and when the seal is considered as a nonuniform layer. However, this relationship is not unique during seal formation, independent of the approach applied to represent the seal layer.