Steady state lateral water flow through unsaturated soil layers

Warrick, A. W.; Hinnell, A. C.; Ferré, T. P. A.; Knight, J. H.

doi:10.1029/2007wr006784

Cited by 8 publications

(5 citation statements)

References 13 publications

(18 reference statements)

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“…Funneled flow can often be interpreted as diffuse flow within a heterogeneous medium. If the conductive zone carrying the flow contains a statistically representative collection of pores to meet representative elementary volume (REV) criteria (Bear, 1972, p. 19), then the flow can be modeled as STVF (Warrick, Hinnell, Ferré, & Knight, 2008). Doing so of course requires knowledge of the hydraulic properties with adequate spatial resolution.…”

Section: Funneled Preferential Flowmentioning

confidence: 99%

The processes of preferential flow in the unsaturated zone

Nimmo

2021

Soil Science Soc of Amer J

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Preferential flow, a major influence in unsaturated soil and rock almost everywhere, occurs by multiple phenomenologically distinct hydraulic processes. For the mode known as funneled flow, concentrated in particularly conductive portions of the medium, the surface-tension/viscous-flow processes of traditional unsaturated flow theory predominate. Fingered flow, through conductive paths of higher water content than surrounding material, requires amendments to traditional theory concerning instabilities and dynamic flow-regime boundaries. Macropore flow, the most recognized preferential flow mode, poses unanswered questions and major difficulties in practice. Accumulated evidence shows that water flows preferentially mostly through macropores that are (a) only partially filled with water, and (b) surrounded by matrix material that is drier, sometimes much drier, than saturation. With partial filling, geometric characteristics such as aperture have much less influence than was previously thought, and the intra-macropore configuration of the flowing water phase, about which little is conclusively known, is then a dominant controlling influence. With unsaturated surroundings, macropore/matrix exchange interactions control, for given input and medium, the initiating circumstances, conveyed flux, and duration of macropore flow. The multiple processes in play during such interactions have different sensitivities to the matrix water state and different directions of influence. The net influence of matrix water content on macropore flow is thus highly complex and a major research need. Additional high-priority topics are: flowpath connectivity, for watersheds as well as small scales; intra-macropore processes, to discern their importance and possible means of quantification; and the identification of measurable soil and rock properties that can be utilized predictively. 1 INTRODUCTION Flow through preferred pathways, bypassing most of the subsurface medium, travels generally faster and with greater fluxes than other types of flow in the unsaturated zone. Preferential flow is often associated with obvious flowpaths such as biopores and fractures but occurs also in sandy soils devoid of Abbreviations: REV, representative elementary volume; STVF, surface-tension viscous flow.

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Section: Funneled Preferential Flowmentioning

confidence: 99%

The processes of preferential flow in the unsaturated zone

Nimmo

2021

Soil Science Soc of Amer J

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“…This assumption is common in development of unsaturated models in multi-layer or exponentially varying K s systems (e.g. Srivastava and Yeh, 1991;Warrick and Knight, 2003;Warrick et al, 2008). Across the sides of the domain in both unsaturated and saturated zones, no-flow conditions in the x-direction are imposed (Figure 1a) as…”

Section: Mathematical Formulationmentioning

confidence: 99%

The exponential decline in saturated hydraulic conductivity with depth: a novel method for exploring its effect on water flow paths and transit time distribution

Ameli

McDonnell

Bishop

2016

Hydrological Processes

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Abstract:The strong vertical gradient in soil and subsoil saturated hydraulic conductivity is characteristic feature of the hydrology of catchments. Despite the potential importance of these strong gradients, they have proven difficult to model using robust physically based schemes. This has hampered the testing of hypotheses about the implications of such vertical gradients for subsurface flow paths, residence times and transit time distribution. Here we present a general semi-analytical solution for the simulation of 2D steady-state saturated-unsaturated flow in hillslopes with saturated hydraulic conductivity that declines exponentially with depth. The grid-free solution satisfies mass balance exactly over the entire saturated and unsaturated zones. The new method provides continuous solutions for head, flow and velocity in both saturated and unsaturated zones without any interpolation process as is common in discrete numerical schemes. This solution efficiently generates flow pathlines and transit time distributions in hillslopes with the assumption of depth-varying saturated hydraulic conductivity. The model outputs reveal the pronounced effect that changing the strength of the exponential decline in saturated hydraulic conductivity has on the flow pathlines, residence time and transit time distribution. This new steady-state model may be useful to others for posing hypotheses about how different depth functions for hydraulic conductivity influence catchment hydrological response.

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“… This work adds to recent literature on capillary barriers (e.g., Qian et al, 2010; Zhang et al, 2009) and lateral flow in the vadose zone (e.g., Warrick et al, 2008) through further discussing both the mechanisms causing nonvertical fluxes in layered, unsaturated media and the potential to take advantage of natural heterogeneity similar to capillary barriers to both induce horizontal components to water fluxes and divert vertical flow. This work provides a documented caution that the horizontal components of induced water flux in the vadose zone are likely to be difficult to establish except under very specific field conditions and require substantial time to effectively displace pore water in fine‐grained sediments over distances greater than a few meters. As such, this work both suggests limitations on application of this approach to inducing flow and identifies the mechanisms limiting its application (low unsaturated hydraulic conductivities, limitations on the magnitude of the hydraulic gradient that can be imposed, and the challenge of more complex heterogeneities). This work provides an additional potential application of new strategies being investigated to withdraw water from the vadose zone.…”

Section: Discussionmentioning

confidence: 66%

Potential for Establishing Nonvertical Flow within the Vadose Zone

Silliman

Fisker

Pescatore

2011

Vadose Zone Journal

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Laboratory experiments and numerical studies are used to study the potential to induce water flux in the vadose zone, which is characterized by significant horizontal components of the water velocity. Specifically, a question is addressed as to whether water can be injected or withdrawn from lenses or layers of fine sediments (bordered by coarse sediments), thus establishing flow in those portions of the vadose zone commonly associated with higher moisture contents and a higher mass of dissolved contaminants. Laboratory experiments provided the base‐line proof of concept of the ability to induce horizontal components to flow in unsaturated sediments through use of suction‐cup lysimeters, but were limited to ideal media and short distance scales (<0.5 m). A numerical model was used in combination with published moisture retention and relative permeability parameters for a variety of sediment types to study conditions under which such horizontal flow components might be induced over substantially greater distances (e.g., 10 m). While these numerical results support arguments that flow induction is theoretically possible, induced flow will generally result in slow transport velocities such that application will likely be limited either to short flow distances (e.g., less than a meter) or long‐term (>50 years) time scales, and only with thorough knowledge of subsurface heterogeneity. Implications of this work beyond the present study may include continuing discussions of constructed capillary barriers and development of improved technologies for removal of water from the vadose zone.

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Steady state lateral water flow through unsaturated soil layers

Cited by 8 publications

References 13 publications

The processes of preferential flow in the unsaturated zone

The processes of preferential flow in the unsaturated zone

The exponential decline in saturated hydraulic conductivity with depth: a novel method for exploring its effect on water flow paths and transit time distribution

Potential for Establishing Nonvertical Flow within the Vadose Zone

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