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This study investigated the contributions of the wetting liquid and electrical double layers (EDLs) to the bulk electrical conductivity (σ) of sand–clay mixtures. The conductivity is small at small water content due to few conductive pathways and low ionic mobility. The fully expanded state of the EDLs provided the largest σ in distilled water but not in salt solutions. At small water content, σ increases following a logarithmic function, but changes linearly at large water content after reaching a transitional large value. This conductivity increases with increasing electrical conductivity of the wetting solution (σw) exponentially at small water content, but linearly at large water content. Existing bulk electrical conductivity models described the measured σ values well and resulted in stable values of the electrical formation factor (F) and dimensionless parameter. Due to considerable leach cations in the clay, the cations in the bulk solution exerted negligible influence on the surface conductivity (σs). Although F is independent of σw, the confounding effect of shrink–swell in the samples with changing σw shows an apparent dependency of F on σw The surface mobility of the counterions decreased nonlinearly with increasing water‐filled porosity (ϕ), and also with increasing σw The cementation exponent (m) decreased monotonically from −4.4 at ϕ = 0.22 to −94.1 at ϕ = 0.93 in the samples wetted with distilled water. With increasing σw, m also increased. The value of m for three samples wetted with salt solutions of σw = 0.878, 1.273, and 1.572 S m−1 ranged from 2.1 to 2.5 at ϕ = 0.22 and 4.1 to 5.3 at ϕ = 0.93.

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Fingered flow rapidly moves water and pollutants from the root tensiometers in Hele-Shaw cells to observe pressure zone to the groundwater through a limited fraction of the unsaturated heads in the induction zone. Of those, only the latter zone, limiting the possibilities for decay and adsorption. The onset had enough observation points in the induction zone to of wetting front instability and the characteristics of the flow pattern under nonponding infiltration have received limited attention. We study lateral flow toward the fingers in an induction aim to theoretically and experimentally advance our understanding zone below a fine-over-coarse interface. Geiger and of pre-fingered flow, and contrast fingered flow under ponding and Durnford (2000) performed similar measurements in nonponding conditions. We developed a Green-Ampt based expres-12.7-mm diameter columns. sion for the pressure head in a developing induction zone (from which As indicated above, detailed lateral pressure head disfingers protrude) for the time before fingers developed. A uniform, tributions in the induction zone have only been observed nonponding water flux was applied to the surface of two-dimensional in ponded fine-over-coarse profiles. We therefore perglass bead porous media with a dry region above a capillary fringe. formed nonponding infiltration experiments with two-Microtensiometers recorded pressure heads in the induction zone. dimensional glass bead porous media. We studied all The pressure head data confirmed both the theoretical early-time stages of finger development and compared finger bepre-finger model, and a model developed earlier for late-time lateral flow toward fully developed fingers. The physically more realistic havior with earlier ponded infiltration experiments (Cho constant flux boundary condition of our experiments gave larger finger and de Rooij, 2002). Flow inside the fingers was theoretispacings and travel times, compared to the frequently used set-up cally treated by Selker et al. (1992b), while de Rooij with ponding infiltration into a fine-over-coarse porous medium.