Stochastic analysis of simulated vadose zone solute transport in a vertical cross section of heterogeneous soil during nonsteady water flow

1991 ◽  
Vol 27 (3) ◽  
pp. 267-283 ◽  
Author(s):  
David Russo
Keyword(s):  
Solute Transport ◽  
Water Flow ◽  
Cross Section ◽  
Vadose Zone ◽  
Stochastic Analysis ◽  
Vertical Cross Section ◽  
Heterogeneous Soil

Vadose Zone, Part I : Characterization and Flow Processes

2003 ◽  
Author(s):  
Yoram Rubin
Keyword(s):  
Porous Media ◽  
Water Flow ◽  
Governing Equation ◽  
Vadose Zone ◽  
Stochastic Analysis ◽  
Transport Processes ◽  
Richards Equation ◽  
Saturated Porous Media ◽  
Flow And Transport ◽  
Flow Processes

Many of the principles guiding stochastic analysis of flow and transport processes in the vadose zone are those which we also employ in the saturated zone, and which we have explored in earlier chapters. However, there are important considerations and simplifications to be made, given the nature of the flow and of the governing equations, which we explore here and in chapter 12. The governing equation for water flow in variably saturated porous media at the smallest scale where Darcy’s law is applicable (i.e., no need for upscaling of parameters) is Richards’ equation (cf. Yeh, 1998)

scholarly journals Comparison between field measurements and numerical simulation of steady-state solute transport in a heterogeneous soil profile

1997 ◽  
Vol 1 (4) ◽  
pp. 853-871 ◽  
Author(s):  
J. Vanderborght ◽  
D. Jacques ◽  
D. Mallants ◽  
P.-H. Tseng ◽  
J. Feyen
Keyword(s):  
Solute Transport ◽  
Water Flow ◽  
Random Fields ◽  
Hydraulic Properties ◽  
Soil Hydraulic Properties ◽  
Field Scale ◽  
Flow Heterogeneity ◽  
Heterogeneous Soil ◽  
Soil Hydraulic ◽  
Second Procedure

Abstract. Abstract: Field-scale solute dispersion is determined by water flow heterogeneity which results from spatial variability of soil hydraulic properties and soil moisture state. Measured variabilities of soil hydraulic properties are highly sensitive to the experimental method. Field-scale dispersion derived from leaching experiments in a macroporous loam soil was compared with field-scale dispersion obtained with numerical simulations in heterogeneous random fields. Four types of random fields of hydraulic properties having statistical properties derived from four different types of laboratory measurements were considered. Based on this comparison, the measurement method depicting heterogeneities of hydraulic properties most relevant to field-scale solute transport was identified. For unsaturated flow, the variability of the hydraulic conductivity characteristic measured on a small soil volume was the most relevant parameter. For saturated flow, simulated dispersion underestimated the measured dispersion and it was concluded that heterogeneity of macroscopic hydraulic properties could not represent solute flow heterogeneity under these flow conditions. Field-scale averaged solute concentrations depend both on the detection method and the averaging procedure. Flux-averaged concentrations (relevant to practical applications) differ from volume-averaged or resident concentrations (easy to measure), especially when water flow is more heterogeneous. Simulated flux and resident concentrations were subsequently used to test two simple one-dimensional transport models in predicting flux concentrations when they are calibrated on resident concentrations. In the first procedure, solute transport in a heterogeneous soil is represented by a 1-D convection dispersion process. The second procedure was based on the relation between flux and resident concentrations for a stochastic convective process. Better predictions of flux concentrations were obtained using the second procedure, especially when water flow and solute transport are very heterogeneous.

Emerging Measurement Techniques for Vadose Zone Characterization

1999 ◽  
Author(s):  
Jan W. Hopmans ◽  
Jan M. H. Hendrickx
Keyword(s):  
Solute Transport ◽  
Water Flow ◽  
Vadose Zone ◽  
Measurement Techniques ◽  
Soil Physics ◽  
Flow And Transport ◽  
Regional Project ◽  
The Difference ◽  
Magnetic Resonance Imaging Mri ◽  
Western Regional

Variables and parameters required to characterize soil water flow and solute transport are often measured at different spatial scales from those for which they are needed. This poses a problem since results from field and laboratory measurements at one spatial scale are not necessarily valid for application at another. Herein lies a challenge that vadose zone hydrologists are faced with. For example, vadose zone studies can include flow at the groundwater-unsaturated zone as well as at the soil surface-atmosphere interface at either one specific location or representing an entire field or landscape unit. Therefore, vadose zone measurements should include techniques that can monitor at large depths and that characterize landsurface processes. On the other end of the space spectrum, microscopic laboratory measurement techniques are needed to better understand fundamental flow and transport mechanisms through observations of pore-scale geometry and fluid flow. The Vadose Zone Hydrology (VZH) Conference made very clear that there is an immediate need for such microscopic information at fluid-fluid and solid-fluid interfaces, as well as for methodologies that yield information at the field/landscape scale. The need for improved instrumentation was discussed at the ASA-sponsored symposium on “Future Directions in Soil Physics” by Hendrickx (1994) and Hopmans (1994). Soil physicists participating in the 1994-1999 Western Regional Research Project W-188 (1994) focused on “improved characterization and quantification of flow and transport processes in soils,” and prioritized the need for development and evaluation of new instrumentation and methods of data anlysis to further improve characterization of water and solute transport. The regional project documents the critical need for quantification of water flow and solute transport in heterogeneous, spatially variable field soils, specifically to address preferential and accelerated contaminant transport. Cassel and Nielsen (1994) describe the contributions in computed tomography (CT) using x-rays or magnetic resonance imaging (MRI) as “an awakening,” and they envision these methodologies to become an integral part of vadose zone research programs. The difference in size between measurement and application scales poses a dilemma for the vadose zone hydrologist.

scholarly journals Interplay between Fingering Instabilities and Initial Soil Moisture in Solute Transport through the Vadose Zone

Water ◽  
2020 ◽  
Vol 12 (3) ◽  
pp. 917
Author(s):  
Luis Cueto-Felgueroso ◽  
María José Suarez-Navarro ◽  
Xiaojing Fu ◽  
Ruben Juanes
Keyword(s):  
Spatial Distribution ◽  
Solute Transport ◽  
Soil Water ◽  
Water Flow ◽  
Vadose Zone ◽  
Preferential Flow ◽  
Solute Diffusion ◽  
Wetting Front ◽  
Initial Soil ◽  
The Impact

Modeling water flow and solute transport in the vadose zone is essential to understanding the fate of soil pollutants and their travel times towards groundwater bodies. It also helps design better irrigation strategies to control solute concentrations and fluxes in semiarid and arid regions. Heterogeneity, soil texture and wetting front instabilities determine the flow patterns and solute transport mechanisms in dry soils. When water is already present in the soil, the flow of an infiltration pulse depends on the spatial distribution of soil water and on its mobility. We present numerical simulations of passive solute transport during unstable infiltration of water into sandy soils that are prone to wetting front instability. We study the impact of the initial soil state, in terms of spatial distribution of water content, on the infiltration of a solute-rich water pulse. We generate random fields of initial moisture content with spatial structure, through multigaussian fields with prescribed correlation lengths. We characterize the patterns of water flow and solute transport, as well as the mass fluxes through the soil column. Our results indicate a strong interplay between preferential flow and channeling due to fingering and the spatial distribution of soil water at the beginning of infiltration. Fingering and initial water saturation fields have a strong effect on solute diffusion and dilution into the ambient water during infiltration, suggesting an effective separation between mobile and inmobile transport domains that are controlled by the preferential flow paths due to fingering.

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