Dependence of anisotropy on saturation in a stratified sand

Stephens, Daniel B.; Heermann, Stephen

doi:10.1029/wr024i005p00770

Cited by 61 publications

(40 citation statements)

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“…Small-scale layering in sands, even with modest size differences (gradation changes), has been shown to cause significant horizontal spreading at both the laboratory and field scale (Stephens and Heermann 1988;McCord et al 1991). This small-scale layering is the primary cause of anisotropic behavior, a phenomenon that has also been shown to be dependent on moisture conditions.…”

Section: Previous Data Analysis and Modelingmentioning

confidence: 99%

Vadose Zone Transport Field Study: Status Report

Gee¹,

Ward²

2001

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SummaryStudies were initiated at the Hanford Site to evaluate the process controlling the transport of fluids in the vadose zone and to develop a reliable database for testing vadose-zone transport models. These models are needed to evaluate contaminant migration through the vadose zone to underlying groundwater at Hanford. A study site that had previously been extensively characterized using geophysical monitoring techniques was selected in the 200 E Area. Techniques used previously included neutron probe for water content, spectral gamma logging for radionuclide tracers, and gamma scattering for wet bulk density. Building on the characterization efforts of the past 20 years, the site was instrumented to facilitate the comparison of nine vadose-zone characterization methods: advanced tensiometers, neutron probe, electrical resistance tomography (ERT), high-resolution resistivity (HRR), electromagnetic induction imaging (EMI), cross-borehole radar (XBR), and cross-borehole seismic (XBS). Soil coring was used to obtain soil samples for analyzing ionic and isotopic tracers.Laboratory-scale experiments with hypersaline fluids in Hanford sediments suggest that fluid properties may influence transport behavior, to the extent of finger formation, through an interaction between fluid and hydraulic properties. Yet, the importance of these mechanisms to field-scale transport is largely unknown, thereby limiting the accuracy of contaminant-transport predictions. To assess the importance of these interactions in field-scale solute transport, tank leaks were simulated by performing a series of injections with dilute fluids in late spring and early summer of FY 2000 and with hypersaline fluids (36 wt% sodium thiosulfate) during the spring of 2001. In both tests, a suite of isotopic and ionic tracers was included in the injected fluids. The test in FY 2000 consisted of injecting to ground a series of five 3875 L (1000 gal) pulses of water and tracers, weekly, for five weeks. The FY 2001 test, which was designed partly to evaluate the effects of fluid properties and transport processes, involved the injection of 19,000 L (5000 gal) of hypersaline fluid over the course of 5 weeks. This was followed by 11,400 L (3000 gal) of solute-free water applied in a 2-week period. In FY 2000, infiltration and redistribution were monitored using the nine characterization methods over the course of the injections and for 2 months after the last injection. In FY 2001, all methods except EMI were used to monitor the infiltration and redistribution of the 30,000 L (7925 gal) plume over the course of 3 months.Thus far, field-measured distributions of soil water content have been analyzed using threedimensional spatial-moment analysis. Results clearly show that the subsurface distributions of both the dilute and hypersaline fluids are controlled by an interaction between small-scale horizontal stratification and fluid properties. The centers of mass for the two plumes were similar in the lateral and transverse directions, but were significantly d...

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Section: Previous Data Analysis and Modelingmentioning

confidence: 99%

Vadose Zone Transport Field Study: Status Report

Gee¹,

Ward²

2001

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“…Few studies have investigated the effective properties for partially saturated media. Theoretical work [e.g., Mualem , 1984; Yeh et al , 1985a, 1985b; Mantoglou and Gelhar , 1987; Green and Freyberg , 1995], numerical simulations [e.g., Yeh , 1989; Desbarats , 1998; Wildenschild and Jensen , 1999b; Bagtzoglou et al , 1994; Polmann et al , 1991; Ababou , 1988] and experimental studies [e.g., Stephens and Heermann , 1988; Yeh and Harvey , 1990; McCord et al , 1991; Wildenschild and Jensen , 1999a] of unsaturated flow indicate that the effective hydraulic conductivity ( K ) tensor for stratified sediments can exhibit moisture or tension‐dependent anisotropy. That is, the anisotropy (ratio of K parallel bedding to K perpendicular to bedding) increases with increasing tension.…”

Section: Introductionmentioning

confidence: 99%

Upscaled flow and transport properties for heterogeneous unsaturated media

Khaleel

Yeh

Lü

2002

Water Resources Research

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[1] To represent a heterogeneous unsaturated medium by its homogeneous equivalent, stochastic theory-based analytical formulas and numerical Monte Carlo simulations are used to obtain upscaled (effective) flow and transport properties. The Monte Carlo experiments simulate steady state flow and transient transport of nonreactive solute in two-dimensional heterogeneous media. Constitutive relations for unsaturated media at the mesh-size scale are based on the van Genuchten-Mualem relationships. A unit-mean-gradient approach is used to derive upscaled properties for flow parallel and perpendicular to bedding. Upscaled moisture retention and unsaturated conductivities (K ) and longitudinal dispersivities are obtained by simulating steady gravity drainage conditions for a series of applied infiltration rates, characteristic of relatively dry conditions in coarse-textured sediments. Macrodispersivities are calculated on the basis of spatial moments of the ensemble-mean plume. Results show that the calculated effective unsaturated K based on the analytical formulas compare well with those based on Monte Carlo simulations. The macroscopic anisotropy (ratio of K parallel to bedding to K perpendicular to bedding) increases with increasing tension, although the increase is rather mild. The longitudinal macrodispersivity for the equivalent homogeneous medium also increases with increasing tension. A comparison of numerical results with stochastic solutions suggests that the computed dispersivities are of the same order of magnitude at low tensions. At higher tensions the dispersivity estimates deviate significantly. Nonetheless, both numerical and analytical results show that the longitudinal dispersivities for flow parallel to bedding are higher than those for flow perpendicular to bedding. In addition, our results suggest that the Fickian regime is reached much earlier for cases with flow perpendicular to bedding than for those with flow parallel to bedding.

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“…I n the past two decades , numerous studies have investigated the effects of flow and solute transport in variably saturated media. Theoretical work (e.g., Yeh and Gelhar, 1983; Mualem, 1984; Yeh et al, 1985a, 1985b, 1985c; Mantoglou and Gelhar, 1987; Green and Freyberg, 1995), numerical simulations (e.g., Yeh, 1989; Desbarats, 1998; Wildenschild and Jensen, 1999b; Bagtzoglou et al, 1994; Polmann et al, 1991; Ababou, 1988; Ababou et al, 1991; Khaleel et al, 2002), and experimental studies (e.g., Stephens and Heerman, 1988; Yeh and Harvey, 1990; McCord et al, 1991; Wildenschild and Jensen, 1999a) indicate that if stratified sediments are regarded as an equivalent homogeneous medium, the effective hydraulic conductivity ( K ) tensor for the equivalent medium can exhibit moisture‐ or tension‐dependent anisotropy. That is, the anisotropy (ratio of K parallel to bedding to K perpendicular to bedding) increases with decreasing saturation (increasing tension).…”

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confidence: 99%

Infiltration in Unsaturated Layered Fluvial Deposits at Rio Bravo: Macroscopic Anisotropy and Heterogeneous Transport

Glass

Brainard

Yeh

2005

Vadose Zone Journal

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An infiltration and dye transport experiment was conducted to visualize flow and transport processes in a heterogeneous, layered, sandy‐gravelly fluvial deposit adjacent to Rio Bravo Boulevard in Albuquerque, NM. Water containing red dye followed by blue‐green dye was ponded in a small horizontal zone (about 0.5 by 0.5 m) above a vertical outcrop (about 4 by 2.5 m). The red dye lagged behind the wetting front due to slight adsorption, thus allowing both the wetting front and dye fronts to be observed in time at the outcrop face. After infiltration, vertical slices were excavated to the midpoint of the infiltrometer, exposing the wetting front and dye distribution in a quasi three‐dimensional manner. At small scale, wetting front advancement was influenced by the multitude of local capillary barriers within the deposit. However, at the scale of the experiment, the wetting front appeared smooth with significant lateral spreading, twice that in the vertical, indicating a strong anisotropy due to the pronounced horizontal layering. The dye fronts exhibited appreciably more irregularity than the wetting front, as well as the influence of preferential flow features (a fracture) that moved the dye directly to the front, bypassing the fresh water between. To illustrate the ability of equivalent homogeneous media models to capture the behavior of the wetting front, we performed numerical simulations using equivalent homogeneous media with isotropic, anisotropic, and moisture‐dependent anisotropic properties. Those containing anisotropy matched the experimental data best.

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Dependence of anisotropy on saturation in a stratified sand

Cited by 61 publications

References 10 publications

Vadose Zone Transport Field Study: Status Report

Vadose Zone Transport Field Study: Status Report

Upscaled flow and transport properties for heterogeneous unsaturated media

Infiltration in Unsaturated Layered Fluvial Deposits at Rio Bravo: Macroscopic Anisotropy and Heterogeneous Transport

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