Towards Pore-Scale Analysis of Preferential Flow and Chemical Transport

Luxmoore, R. J.; Ferrand, Lin A.

doi:10.1007/978-3-642-77947-3_5

Cited by 27 publications

(22 citation statements)

References 29 publications

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“…[1990] provides a useful conceptual framework for relating the unsaturated zone response to our catchment hydrologic response, and it connotes a dependence of the hydrologic response on the temporal development of unsaturated zone processes and subsurface flow paths (e.g., connect-disconnect hypothesis [Luxmoore and Ferrand, 1993]). Here pressure heads greater than -0.05 m correspond to Luxmoore's macroporosity, and from the plot irrigation response characteristics we reason that in the near-zero pressure head range, soil-water contents greater than ---0.35 m3/m 3 will persist only as long as there is an applied flux across the ground surface.…”

Section: Soil-water Retention Properties and Macroporesmentioning

confidence: 99%

Unsaturated zone processes and the hydrologic response of a steep, unchanneled catchment

Torres¹,

Dietrich²,

Montgomery³

et al. 1998

Water Resources Research

241

275

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Abstract. As part of a larger, collaborative study, we conducted field experiments to investigate how rainfall signals propagate through an unsaturated soil profile, leading to a rapid pore pressure response and slope instability. We sprinkler-irrigated an entire, unchanneled headwater basin in the steep, humid Oregon Coast Range, and we drove the system to quasi steady state as indicated by tensiometers, piezometers, and discharge. During initial wetting some of the deeper tensiometers responded before the arrival of an advancing head gradient front. With continued irrigation most tensiometers attained nearzero pressure heads before most piezometers responded fully, and a stable unsaturated flow field preceded the development of a stable saturated flow field. Steady discharge occurred after the last piezometer reached steady state. With the onset of steady discharge the unsaturated zone, saturated zone, and discharge became delicately linked, and a spike increase in rain intensity led to a response in the saturated zone and discharge much faster than could have happened through advection alone. We propose that the rain spike produced a slight pressure wave that traveled relatively rapidly through the unsaturated zone, where it caused a large change in hydraulic conductivity and the rapid effusion of stored soil water. An important control on the hydrologic response of this catchment lies with the soil-water retention curve. In general, below pressure heads of about -0.05 m, soil-water contents change slightly with changes in pressure head, but above -0.05 rn the soil-water content is highly variable. Minor rainstorms upon a wet soil can produce slight changes in pressure head and corresponding large ch•nges in soil-water content, giving rise to the passage of pressure waves in response to increased rain intensity and a relatively rapid response in the unsaturated zone. This rapid unsaturated zone response led to a rapid rise in the saturated zone, and it may be the underlying mechanism enabling short bursts of rain to cause slope instability.

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Section: Soil-water Retention Properties and Macroporesmentioning

confidence: 99%

Unsaturated zone processes and the hydrologic response of a steep, unchanneled catchment

Torres¹,

Dietrich²,

Montgomery³

et al. 1998

Water Resources Research

241

275

View full text Add to dashboard Cite

show abstract

“…As the macropore flow and nodes become conditioned by increasing moisture content, either during an extended storm or over a rainy season, they are able to interconnect via switching functions at the node, thus providing a backbone that allows the preferential flow system to expand. Earlier work by Luxmoore and Ferrand (1993) proposed the concept of percolation theory to simulate a similar 'switching mechanism' for preferential flow at the pore scale.…”

Section: Introductionmentioning

confidence: 99%

How do disconnected macropores in sloping soils facilitate preferential flow?

Nieber

Sidle

2010

Hydrological Processes

110

118

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Abstract:Runoff from hillslopes is generated by processes such as infiltration-excess and saturation overland flow, subsurface stormflow and subsurface return flow. Preferential flow through macropores can affect any one of these runoff generation processes. Field studies at the Hitachi Ohta Experimental Watershed in Japan have noted that self-organization processes may manifest the connectivity of such subsurface flow paths, particularly via macropores, from hillslopes to stream channels. It is well established from soil physics principles that the connectivity of macropore networks depends on soil wetness and this has been shown experimentally at Hitachi Ohta where subsurface flow and streamflow respond to thresholds of wetness. Numerical solutions to the three-dimensional Richards equation are derived for a sloping soil block containing a population of disconnected macropores of various sizes, shapes and orientations. Solutions for the case of steady water flux applied to the surface of the soil block are evaluated to determine the conditions where the disconnected macropores become active in the flow process. Results show that subsurface flow is directed through the preferential flow network in the saturated portion of the soil but bypasses the macropores in the drier regions. The preferential flow network expands as the degree of saturation increases. The expanding network of active macropores leads to less resistance to overall flow in the domain and access to increased volumes of the flow domain. Although the individual macropores are disconnected, it is argued that large localized hydraulic gradients can potentially lead to preferred zones of subsurface erosion. In addition to the importance of these findings related to stormflow generation in catchments, they add support to the concept of self-organization of subsurface flow systems in soils.

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“…[2] Because of the variably saturated and heterogeneous nature of the subsurface environment, the interplay between resident water and infiltrating water in the vadose zone is very complex [Luxmoore and Ferrand, 1993;Hendrickx and Flury, 2001;Berkowitz et al, 2004]. For instance, the distribution of air and water at the pore scale mediates the effective pore water velocity field, thus controlling the pathways and rates of advective transport.…”

Section: Introductionmentioning

confidence: 99%

“…On the basis of temporal evolution of chemical concentrations in outflows, a number of studies have demonstrated that old water can be a significant component of vadose zone outflows Sklash et al, 1986;Luxmoore and Ferrand, 1993;Turton et al, 1995;Collins et al, 2000]. Moreover, it has been demonstrated that the capillary fringe and the region immediately below the water table may significantly affect the evolution of fluid flow and chemical transport between the vadose and groundwater zones [Silliman et al, 2002;Berkowitz et al, 2004].…”

Section: Introductionmentioning

confidence: 99%

“…Some approaches also consider network models [Luxmoore and Ferrand, 1993]. More recent development of the continuous time random walk approach has been shown to capture solute transport and long tailing behavior of solutes through partially saturated porous media [Cortis and Berkowitz, 2004] more effectively than models assuming Fickian dispersion.…”

Section: Introductionmentioning

confidence: 99%

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Simulation of the interplay between resident and infiltrating water in partially saturated porous media

Gouet-Kaplan

Tartakovsky

Berkowitz

2009

Water Resources Research

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[1] The interplay between resident water already in the subsurface environment (''old water'') and infiltrating water (''new water'') is examined. A smoothed particle hydrodynamics technique is used to simulate the interplay between old water and new water in a porous medium over a cycle of drainage of old water and infiltration of new water. The effect of varying the average pore size is investigated via the Bond number. Four parameters (maximal mixing amount, minimal average size of old water pockets, mixing value for which the number of old water pockets decreases, and amount of old water remaining in the system for long times) are found to be independent of the average pore size. However, the rate of change is always higher for larger pores. In particular, some old water remains in the system within stable water pockets even after infiltrating new water reaches steady state.Citation: Gouet-Kaplan, M., A. Tartakovsky, and B. Berkowitz (2009), Simulation of the interplay between resident and infiltrating water in partially saturated porous media, Water Resour. Res., 45, W05416,

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Towards Pore-Scale Analysis of Preferential Flow and Chemical Transport

Cited by 27 publications

References 29 publications

Unsaturated zone processes and the hydrologic response of a steep, unchanneled catchment

Unsaturated zone processes and the hydrologic response of a steep, unchanneled catchment

How do disconnected macropores in sloping soils facilitate preferential flow?

Simulation of the interplay between resident and infiltrating water in partially saturated porous media

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