Wetting Front Instability in Homogeneous Sandy Soils under Continuous Infiltration

Selker, John S.; Steenhuis, T. S.; Parlange, Jean‐Yves

doi:10.2136/sssaj1992.03615995005600050003x

Cited by 116 publications

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“…Since these experiments have been performed from initially dry and random close-packed glass beads, S 0 = 0 and S s = , where is the porosity, representing the maximum amount of water that can be contained within the pore spaces. Equation (11) has shown good agreement with experimental results obtained from sand [2,10,33].…”

Section: Model Discussionsupporting

confidence: 77%

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Kinetics of gravity-driven water channels under steady rainfall

et al. 2014

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We investigate the formation of fingered flow in dry granular media under simulated rainfall using a quasi-twodimensional experimental setup composed of a random close packing of monodisperse glass beads.Using controlled experiments, we analyze the finger instabilities that develop from the wetting front as a function of fundamental granular (particle size) and fluid properties (rainfall, viscosity). These finger instabilities act as precursors for water channels, which serve as outlets for water drainage. We look into the characteristics of the homogeneous wetting front and channel size as well as estimate relevant time scales involved in the instability formation and the velocity of the channel fingertip. We compare our experimental results with that of the wellknown prediction developed by Parlange and Hill [D. E. Hill and J. Y. Parlange, Soil Sci. Soc. Am. Proc. 36, 697 (1972)]. This model is based on linear stability analysis of the growth of perturbations arising at the interface between two immiscible fluids. Results show that, in terms of morphology, experiments agree with the proposed model. However, in terms of kinetics we nevertheless account for another term that describes the homogenization of the wetting front. This result shows that the manner we introduce the fluid to a porous medium can also influence the formation of finger instabilities. The results also help us to calculate the ideal flow rate needed for homogeneous distribution of water in the soil and minimization of runoff, given the grain size, fluid density, and fluid viscosity. This could have applications in optimizing use of irrigation water. We investigate the formation of fingered flow in dry granular media under simulated rainfall using a quasitwo-dimensional experimental setup composed of a random close packing of monodisperse glass beads. Disciplines Physical Sciences and Mathematics | PhysicsUsing controlled experiments, we analyze the finger instabilities that develop from the wetting front as a function of fundamental granular (particle size) and fluid properties (rainfall, viscosity). These finger instabilities act as precursors for water channels, which serve as outlets for water drainage. We look into the characteristics of the homogeneous wetting front and channel size as well as estimate relevant time scales involved in the instability formation and the velocity of the channel fingertip. We compare our experimental results with that of the well-known prediction developed by Parlange and Hill [D. E. Hill and J. Y. Parlange, Soil Sci. Soc. Am. Proc. 36, 697 (1972)]. This model is based on linear stability analysis of the growth of perturbations arising at the interface between two immiscible fluids. Results show that, in terms of morphology, experiments agree with the proposed model. However, in terms of kinetics we nevertheless account for another term that describes the homogenization of the wetting front. This result shows that the manner we introduce the fluid to a porous medium can also influence the formation...

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Section: Model Discussionsupporting

confidence: 77%

“…The geometry of the setup certainly influences channel size [33,34]. The experiment is designed as such not just for reproducibility, but also so that we can observe larger as well as multiple channels.…”

Section: Methodsmentioning

confidence: 99%

Kinetics of gravity-driven water channels under steady rainfall

et al. 2014

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“…Within the domain of reactive flow in unsaturated soils three main types of interfering instabilities occur: (i) reaction instabilities due to initial heterogeneities in the hydraulic properties with dissolution of wormholes and karst phenomena [1,[96][97][98][99][100][101][102][103][104][105], (ii) flow instabilities with moisture content fingering during the infiltration of a moisture front [106][107][108][109][110][111][112][113][114][115][116] and (iii) density instabilities due to local differences of solution densities [117][118][119][120][121][122][123][124]. However, the scope of this paper is not to investigate instability phenomena, but to propose a new approach that relates changes in mineral volumes and hydraulic properties.…”

Section: General Model Discussionmentioning

confidence: 99%

Effect of mineral reactions on the hydraulic properties of unsaturated soils: Model development and application

Wissmeier

Barry

2009

Advances in Water Resources

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This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. ACCEPTED MANUSCRIPT AbsThe selective radius shift model was used to relate changes in mineral volume due to precipitation/dissolution reactions to changes in hydraulic properties affecting flow in porous media. The model accounts for (i) precipitation/dissolution taking place only in the water-filled part of the pore space and further that (ii) the amount of mineral precipitation/dissolution within a pore depends on the local pore volume. The pore bundle concept was used to connect pore-scale changes to macroscopic soil hydraulic properties. Precipitation/dissolution induces changes in the pore radii of water-filled pores and, consequently, in the effective porosity. In a time step of the numerical model, mineral reactions lead to a discontinuous pore-size distribution because only the water-filled pores are affected. The pore-size distribution is converted back to a soil moisture characteristic function to which a new water retention curve is fitted under physically plausible constraints. The model equations were derived for the commonly used van Genuchten/Mualem hydraulic properties. Together with a mixed-form solution of Richards' equation for aqueous phase flow, the model was implemented into the geochemical modelling framework PHREEQC, thereby making available PHREEQC's comprehensive geochemical reactions. Example applications include kinetic halite dissolution and calcite precipitation as a consequence of cation exchange. These applications showed marked changes in the soil's hydraulic properties due to mineral precipitation/dissolution and the dependency of these changes on water contents. The simulations also revealed the strong influence of the degree of saturation on the development of the saturated hydraulic conductivity through its quadratic dependency on the van Genuchten parameter . Furthermore, it was shown that the unsaturated hydraulic conductivity at fixed reduced water content can even r tract increase du ing precipitation due to changes in the pore-size distribution.

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“…Even under the condition of a continuous supply of water from the surface, finger flow can be observed by limiting the water flux with alternating layers of overlaying finer material having a lower saturated hydraulic conductivity than the medium and the ponding water [Tabuchi, 1961;Hill and Parlange, 1972;Glass et al, 1989;Baker and Hillel, 1988;Cho and de Rooij, 1999] or by applying a water flux that is lower than the saturated hydraulic conductivity into a uniform medium [Selker et al, 1992a;Yao and Hendrickx, 1996;Kawamoto and Miyazaki, 1999]. However, the occurrence of finger flow is limited to dry granular materials of relatively large [Diment and Watson, 1985] and relatively uniform particle sizes .…”

Section: Introductionmentioning

confidence: 99%

Unexpected water content profiles under flux‐limited one‐dimensional downward infiltration in initially dry granular media

Shiozawa

Fujimaki

2004

Water Resources Research

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[1] Distinct water-content profiles, having saturated q-bumps at and immediately behind wetting fronts, were observed in narrow columns (9 mm ID) of homogeneous air-dried glass beads under downward one-dimensional infiltration with applied water fluxes at lower than the saturated hydraulic conductivity. The infiltrating water content profiles and the position of the wetting front as a function of time were also calculated based on Richards' equation using an independently measured hydraulic conductivity function K(q), and water retention characteristic q(h), of the drainage process, and by applying a pressure boundary condition, h we , which is almost atmospheric pressure, at the moving wetting front. The good agreement between the calculated profiles and the observed confirms that the dynamic water entry pressure h we (where q(h we ) is the saturated water content), does exist for air-dried glass beads, although it is in contradiction to the modern theory of unsaturated water flow in porous media. This physical property of dry media creates an upward negative pressure profile behind the wetting front that would inevitably produce finger flow if the column diameter were larger. At the wetting front, the water content and pressure should be completely discontinuous at the level of pore size, and hence Darcy's equation cannot be applied across the interface between the air-dried and saturated media.

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Wetting Front Instability in Homogeneous Sandy Soils under Continuous Infiltration

Cited by 116 publications

References 0 publications

Kinetics of gravity-driven water channels under steady rainfall

Kinetics of gravity-driven water channels under steady rainfall

Effect of mineral reactions on the hydraulic properties of unsaturated soils: Model development and application

Unexpected water content profiles under flux‐limited one‐dimensional downward infiltration in initially dry granular media

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