Search

Sorptivity is a parameter of primary importance in the study of unsaturated flow in soils. This hydraulic parameter is required to model water infiltration into vertical soil profiles. Sorptivity can be directly estimated from the soil hydraulic functions (water retention and hydraulic conductivity curves), using the integral formulation of . However, calculating sorptivity in this manner requires the prior determination of the soil hydraulic diffusivity and its numerical integration between initial and final saturation degrees, which may be difficult in some situations (e.g., coarse soil with diffusivity functions that are quasi-infinite close to saturation). In this paper, we present a procedure to compute sorptivity using a scaling parameter, cp, that corresponds to the sorptivity of a unit soil (i.e., unit values for all parameters and zero residual water content) that is utterly dry at the initial state and saturated at the final state. The cp parameter was computed numerically and analytically for five hydraulic models: Delta (i.e., Green and Ampt), Brooks and Corey, van Genuchten-Mualem, van Genuchten-Burdine, and Kosugi. Based on the results, we proposed brand new analytical expressions for some of the models and validated previous formulations for the other models. We also tabulated the output values so that they can easily be used to determine the actual sorptivity value for any case. At the same time, our numerical results showed that the relation between cp and the hydraulic shape parameters strongly depends on the chosen model. These results highlight the need for careful selection of the proper model for the description of the water retention and hydraulic conductivity functions when estimating sorptivity.

Understanding linkages between heterogeneous soil structures and non-uniform flow is fundamental for interpreting infiltration processes and improving hydrological simulations. Here, we utilized ground-penetrating radar (GPR) as a non-invasive technique to investigate those linkages and to complement current traditional methods that are labor-intensive, invasive, and non-repeatable. We combined time-lapse GPR surveys with different types of infiltration experiments to create three-dimensional (3D) diagrams of the wetting dynamics. We carried out the GPR surveys and validated them with in situ observations, independent measurements and field excavations at two experimental sites. Those sites were selected to represent different mechanisms that generate non-uniform flow: (1) preferential water infiltration initiated by tree trunk and root systems; and (2) lateral subsurface flow due to soil layering. Results revealed links between different types of soil heterogeneity and non-uniform flow. The first experimental site provided evidence of root-induced preferential flow paths along coarse roots, emphasizing the important role of coarse roots in facilitating preferential water movement through the subsurface. The second experimental site showed that water infiltrated through the restrictive layer mainly following the plant root system. The presented approach offers a non-invasive, repeatable and accurate way to detect non-uniform flow.

Soil water repellency can substantially alter hydrologic processes, particularly the ability of soils to infiltrate water. Water repellency often changes through time, making it difficult to simulate infiltration behaviors of water-repellent soils using standard models. Here, we propose a simple rate-based correction term that starts with a value of zero at the beginning of the infiltration process (t = 0) and asymptotically approaches 1 as time increases, thus simulating decreasing soil water repellency through time. The correction term can be used with any infiltration model. For this study, we selected a simple two-term infiltration equation and then, using two data sets of infiltration measurements conducted in soils with varying water repellency, compared model error with versus without the added term. The correction substantially reduced model error, particularly in more repellent soils. At the same time, the rate constant parameter introduced in the new model may be useful to better understand dynamics of soil water repellency and to provide more consistent interpretations of hydraulic properties in water-repellent soils.

This introduction to the special section Nonuniform Flow across Vadose Zone Scales is a brief summary of this special section's diverse contributions covering nonuniform flow across a wide range of scales, processes, and applications. We summarize the 17 articles constituting this special section and hope that those contributions are positive steps toward a new, generalizable, and comprehensive paradigm to modeling flow and transport in porous media.

This introduction to the special section Nonuniform Flow across Vadose Zone Scales is a brief summary of this special section's diverse contributions covering nonuniform flow across a wide range of scales, processes, and applications. We summarize the 17 articles constituting this special section and hope that those contributions are positive steps toward a new, generalizable, and comprehensive paradigm to modeling flow and transport in porous media.