Modeling Infiltration During Soil Seal Formation: Effects of Seal Non-Uniformity in Depth and Soil Heterogeneity in Space

Abstract

The impact of raindrops on the soil surface disturbs the soil upper layer and causes changes in its properties. The result is the sealing of the soil to water infiltration. A dynamic model is developed, that describes soil sealing in terms of the increase of the soil bulk density, being maximal at the soil surface and decreasing exponentially with depth. The formulation of the relationships between the soil bulk density and its hydraulic parameters allows the determination of the hydraulic functions at every point within the disturbed layer and at every moment during seal formation. It is, thus, possible to solve the flow equations not only for the undisturbed soil but also within the seal domain. Once calibrated, the predictive ability of the dynamic model was found to be rather good on basis of verification with extensive experimental results. Therefore, it can be used now to evaluate the effects of various variables affecting flow processes, like soil and rainfall properties, initial conditions, or chemical conditions of the soil-water system, on infiltration and runoff generation. The dynamic model is used to compare the effects of accounting for the nonuniformity with depth of the seal layer and the areal heterogeneity of the soil hydraulic properties under soil surface sealing conditions on infiltration are studied. The depth dependent properties of the non-uniform 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).